Clinical Implication.
The net result of maxillary sinus pneumatization is the deficiency in bone height for implant placement, thus requiring augmentation for increased bone quantity for future implant placement. With proper grafting techniques to increase bone volume, this anatomic area may be restored to a more predictable biomechanical location for future implant placement. If grafting is not completed where bone quantity is not adequate, an increased morbidity may result with failure or migration of implants.
Ridge Width/Lingual Repositioning
The maxilla has an inherently thinner facial cortical plate in comparison to other areas of the mouth (e.g., mandible) because of rapid resorption after tooth loss. The loss of maxillary posterior teeth results in an initial decrease in bone width at the expense of the labial bony plate. This process occurs at a faster rate than in any other region of the oral cavity.3 The resorption phenomenon is accelerated by the loss of vascularization of the alveolar bone and existing fine trabecular bone type. However, because the initial residual ridge is inherently wide in the posterior maxilla, even with a 60% decrease in the width of the ridge, adequate-diameter root form implants usually can be placed. As further time passes, the ridge shifts toward the palate until the ridge is resorbed into a medially positioned narrower bone volume.4 The posterior maxilla continues to progressively remodel toward the midline as the bone resorption process continues.
Clinical Implications.
Because of the less than ideal width of bone, buccal-lingual implant placement may not be ideal. Studies have shown that it is possible to perform ridge augmentation to increase width at the time of sinus grafting, but there is an increased rate of morbidity and implant failure when compared to sinus grafting alone. Due to the more lingual position of the ridge, implants will be placed more lingual than is ideal. Prosthetically, this will often result in the buccal cusp of the final restoration being cantilevered facially to satisfy esthetic requirements at the expense of biomechanics in the moderate to severely atrophic ridges (Fig. 13.2).1 In some severe resorption cases, the posterior maxillary implants are more ideally restored in a crossbite occlusion.
Bone Density
The bone quality in the posterior maxilla is usually poorer than in any other intraoral region. Bone strength is directly related to its density, and the low-density bone of this region is often five to ten times weaker compared with bone found in the anterior mandible.5 The various bone densities directly influence the bone-implant contact (BIC) percent, which accounts for the transmission of forces to the bone. The posterior maxilla most commonly exhibits D4 bone (Misch classification), which has the greatest biomechanical elastic modulus difference when compared with titanium under load. D4 bone is characterized by fine trabeculae with very little cortical bone. Implants placed into D4 bone are most susceptible to bone loss and increased morbidity. As such, strategic surgery techniques (e.g., under-preparation, use of osteotomes) when placing implants in the posterior maxilla to increase BIC are suggested.
Clinical Implications.
Because the BIC is least in D4 bone, the stress patterns (i.e., from biomechanical force) in this bone type migrate farther toward the apex of the implant. As a result, bone loss is more pronounced and occurs more apically along the implant body, while in denser bone types (D1), one would see only crestal bone loss. As a result the lateral cortical BIC to stabilize the implant is often insufficient. To increase BIC and success with posterior maxilla implants, the surgical and prosthetic technique requires modification; under preparation of the surgical site, use of osteotomes, greater healing periods, and progressive bone loading during the prosthetic phase of treatment (Fig. 13.3).
Anatomic Location
Because of the anatomic location (posterior maxilla), adequate surgical access is often a difficult problem because of a lack of interocclusal space. With the length of the handpiece and surgical drill often exceeding 40 mm, the posterior maxilla is one of the most difficult areas to complete a successful osteotomy. The implant clinician is often unable to drill the osteotomy with the correct angulation (Fig. 13.4) because of the opposing occlusion.
Clinical Implications.
The implant surgeon is often confronted with lack of interocclusal space, increasing the difficulty in all aspects of the surgical procedure. Visibility is diminished in the posterior maxilla, especially when increased bleeding occurs. This area also becomes very uncomfortable for the patient, especially if there is a positive gag reflex.
The lack of space also presents an issue with utilizing surgical templates, especially those guided by cone beam computed tomography (CBCT), because minimal space is available to accommodate the surgical drill along with the surgical template. However, newer surgical templates have been fabricated with the buccal aspect of the drilling tubes removed (buccal access), which allows the implant clinician additional space to prepare the osteotomy.
Predisposition to Pathology
The paranasal sinuses, especially the maxillary sinus, have been shown to be very susceptible to various disease processes. Studies have shown that in approximately 46% percent of asymptomatic patients requiring augmentation in the maxillary sinus, some degree of pathology exists.6 The pathology can range from incipient membrane inflammation to fully opacified sinuses.
Clinical Implications.
The implant clinician must have a working knowledge of the maxillary sinus anatomy, anatomic variants, and associated pathology. It is imperative the patency of the maxillary ostium be determined prior to placement of an implant or bone graft into the maxillary sinus. To minimize postoperative morbidity, the clinician must understand the indications for otolaryngologist (ENT) referral and clearance prior to any procedures that would involve grafting procedures into the maxillary sinus.
Understanding Paranasal Sinus Anatomy and Physiology
To decrease the morbidity of treatment in the posterior maxilla, knowledge of the important structures of the area must be attained. The implant clinician should evaluate these structures to determine normal anatomy and verify any presence free of anatomic variants and pathology (Fig. 13.5).
Osteomeatal Complex
The osteomeatal unit is composed of the maxillary ostium, ethmoid infundibulum, anterior ethmoid cells, hiatus semilunaris, and the frontal recess, which encompasses the area of the middle meatus. This common channel allows for air flow and mucociliary drainage of the frontal, maxillary, and anterior ethmoid sinuses. Blockage in this area leads to impaired drainage of the maxillary, frontal, and ethmoid sinuses, which may result in rhinosinusitis and postoperative complications after implant or grafting procedures.
Clinical Implications.
Radiographic identification of the osteomeatal complex and related structures must be evaluated to prevent potential postoperative complications. Pathology or variations within the osteomeatal complex may lead to postoperative sinus graft morbidity or implant complications due to compromised mucociliary drainage (alteration of normal sinus physiology) of the maxillary sinus.
Maxillary Ostium
The main drainage avenue of the maxillary sinus is through the maxillary ostium. The primary ostium is located in the superior aspect of the sinus medial wall and drains its secretions via the ethmoid infundibulum through the hiatus semilunaris into the middle meatus of the nasal cavity. The infundibulum is approximately 5 to 10 mm long and drains via ciliary action in a superior and medial direction. The ostium diameter averages 2.4 mm in health; however, pathologic conditions may alter the size to vary from 1 to 17 mm.1
The maxillary ostium and infundibulum are part of the anterior ethmoid middle meatal complex, the region through which the frontal and maxillary sinuses drain, which is primarily responsible for mucociliary clearance of the sinuses to the nasopharynx. As a result, obstruction in one or more areas of the complex will usually result in rhinosinusitis or lead to morbidity of the graft or implant.
Clinical Implications.
Patency of the maxillary ostium is most crucial pre- and postoperatively during maxillary graft sinus surgery to prevent infection and morbidity of the graft. Evaluating the patency of the ostium via a CBCT is easily accomplished with evaluation of serial cross-sectional images. A prophylactic regimen including antibiotics and corticosteroids should always be utilized when grafting or during implant placement in the sinus proper to maintain patency of the ostium during the postoperative period.
Schneiderian Membrane
The epithelial lining of the maxillary sinus is a continuation of the nasal mucosa and is classified as a pseudostratified, ciliated columnar epithelium, also called respiratory epithelium. The epithelial lining of the maxillary sinus is much thinner and contains fewer blood vessels than the nasal epithelium. This accounts for the membrane’s pale color and bluish hue. Five primary cell types exist in this tissue: (1) ciliated columnar epithelial cells, (2) nonciliated columnar cells, (3) basal cells, (4) goblet cells, and (5) seromucinous cells. The ciliated cells contain approximately 50 to 200 cilia per cell. In a healthy maxillary sinus the cilia cells assist in clearing mucus from the sinus and into the nasopharynx. The nonciliated cells compose the apical aspect of the membrane, contain microvilli, and serve to increase surface area. These cells have been theorized to facilitate humidification and warming of inspired air. The basal cell’s function is similar to that of a stem cell that can differentiate as needed. The goblet cells in the maxillary sinus produce glycoproteins that are responsible for the viscosity and elasticity of the mucus produced. The maxillary sinus contains the highest concentration of goblet cells in comparison with the other paranasal sinuses. The maxillary sinus membrane also exhibits few elastic fibers attached to the bone7 (no tenacious attachment is usually present), which simplifies elevation of this tissue from the bone during grafting procedures. The thickness of the sinus mucosa in health varies, but is generally 0.3 to 0.8 mm.8 In smokers, it varies from very thin and almost nonexistent to very thick, with a squamous type of epithelium.
Radiographic Evaluation.
A CBCT scan of normal, healthy paranasal sinuses reveals a completely radiolucent (dark) maxillary sinus. Any radiopaque (whitish) area within the sinus cavity is abnormal, and a pathologic condition should be suspected. The normal sinus membrane is radiographically invisible, whereas any inflammation or thickening of this structure will be radiopaque. The density of the diseased tissue or fluid accumulation will be proportional to varying degrees of gray values.
Clinical Implications.
Maintaining the integrity of the sinus membrane is crucial in decreasing postoperative complications, including loss of graft material and the possibility of infection. Many factors may alter the physiology of the sinus mucosa such as viruses, bacteria, and foreign bodies (implants). Care should be taken to minimize membrane perforations during surgery. If perforations occur, appropriate repair treatment protocols should be adhered to (see Sinus Perforations).
Mucociliary Drainage
Normal mucociliary flow is crucial to maintaining the healthy physiology of the maxillary sinus. In a healthy sinus an adequate system of mucus production, clearance, and drainage is maintained. The key to normal sinus physiology is the proper function of the cilia, which is the main component of the mucociliary transport system. The cilia move contaminants toward the natural ostium and then to the nasopharynx. The cilia of the columnar epithelium beat toward the ostium at 15 cycles per minute, with a stiff stroke through the serous layer, reaching into the mucoid layer. They recover with a limp reverse stroke within the serous layer. This mechanism slowly propels the mucoid layer toward the ostium at a rate of 9 mm per minute and into the middle meatus of the nose.8
In health, mucoid fluid is transported toward the ostium of the maxillary sinus and drains into the nasal cavity, eliminating inhaled small particles and microorganisms. This mucociliary transport system is an active transport system that relies heavily on oxygen. The amount of oxygen absorbed from the blood is not adequate to maintain this drainage system; additional oxygen has to be absorbed from the air in the sinus. This is why the patency of the ostium is crucial in maintaining the normal transport system.
Various elements may decrease the number of cilia and slow their beating efficiency. Viral infections, pollution, allergic reactions, and certain medications may affect the cilia in this way.9 Genetic disorders (e.g., dyskinetic cilia syndrome) and factors such as longstanding dehydration, anticholinergic medications and antihistamines, cigarette smoke, and chemical toxins also can affect ciliary action (Fig. 13.6).
Clinical Implications.
An alteration in the sinus ostium patency or the quality of secretions can lead to disruption in ciliary action, which may result in rhinosinusitis.
For clearance to be maintained, adequate ventilation is necessary. Ventilation and drainage is dependent on the osteomeatal unit, which is the main sinus opening. Ciliary movements of ciliated epithelial cells dictate clearance of the maxillary sinus. It is important to maintain the patency of the maxillary ostium and the osteomeatal complex in the postoperative period.
The physiologic mucociliary transport system may be compromised by abnormalities in the cilia, which include a decrease in overall ciliary number and poor coordination of their movement. This altered physiology may result in an increased morbidity of implant placement or bone graft healing. Therefore, it is crucial that the mucociliary drainage mechanism be maintained throughout the postoperative treatment period. This is most likely accomplished with good surgical technique, evaluation and treatment of prior drainage issues, and strict adherence to the use of pharmacologic agents (e.g., antibiotics, corticosteroids).
Maxillary Sinus Flora
There is much debate on the bacterial flora of the maxillary sinus. Maxillary sinuses have been considered to be sterile in health; however, bacteria can colonize within the sinus without producing symptoms. In theory, the mechanism by which a sterile environment is maintained includes the mucociliary clearance system, immune system, and the production of nitric oxide within the sinus cavity. In recent endoscopic studies, normal sinuses were shown to be nonsterile, with 62.3% exhibiting bacterial colonization. The most common bacteria cultured were Streptococcus viridans, Staphylococcus epidermidis, and Streptococcus pneumonia.10 The culture findings for secretions in acute maxillary sinusitis yielded high numbers of leukocytes, S. pneumoniae, or Streptococcus pyogenes, with Haemophilus influenzae being recovered from the purulent exudates with lower numbers of staphylococci. Other reports have indicated the bacterial flora of the maxillary sinus consists of nonhemolytic and alpha-hemolytic streptococci, as well as Neisseria spp. Additional microorganisms identifiable in various quantities belong to staphylococci, Haemophilus spp, pneumococci, Mycoplasma spp, and Bacteroides spp. This is important to note because the sinus graft procedure often violates the sinus mucosa, and bacteria may contaminate the graft site leading to post-operative complications.1
Clinical Implications
Sterile technique.
The implant clinician must understand the importance of reducing the bacterial count and possible microorganisms that may initiate infections in the maxillary sinus. A strict aseptic technique should be adhered to during any surgical procedures that invade the maxillary sinus proper. This will minimize the possibility of bacterial colonization within the graft, which may lead to increased morbidity.
Antibiotic.
The type of bacteria inhabiting the sinus is very important because it dictates what antibiotic is prescribed preoperatively, postoperatively, and therapeutically in case of infection. The most common bacteria present in the sinus must be susceptible to the specific antibiotic to prevent infection and decrease the morbidity of the graft. The antibiotic selected should not be the clinician’s “favorite” but should be the most ideal antibiotic, which is specific for the involved bacteria. Ideally, Augmentin (875/125 mg) has been shown to be most effective in the maxillary sinus.
Blood Supply
The vascular supply in the maxillary sinus is a vital part of the healing and regeneration of bone after a sinus graft and healing of a dental implant. The blood supply to the maxillary sinus comes directly from the maxillary artery, which emanates from the external carotid artery. The maxillary artery supplies the bone surrounding the sinus cavity and also the sinus membrane. Branches of the maxillary artery, which most often include the posterior superior alveolar artery and infraorbital artery, form endosseous and extraosseous anastomoses that encompass the maxillary sinus. The formation of the endosseous and extraosseous anastomoses in the maxillary sinus is termed the double arterial arcade. Studies have shown vascularization of postgraft material to depend on the intra- and extraosseous anastamoses, along with the blood vessels of the Schnedierian membrane, which is supplied by the posterior superior alveolar artery and the infraorbital artery along the lateral wall.11
There exists different factors that alter the vascularization in this area. With increasing age the number and size of blood vessels in the maxilla decrease. As bone resorption increases, the cortical bone becomes thin, resulting in less vascularization. As the lateral wall becomes thinner, the blood supply to the lateral wall and lateral aspect of the bone graft comes primarily from the periosteum, resulting in a compromised vascularization to the region.
Extraosseous Anastomosis.
Extraosseous anastomosis is found in approximately 44% of the population and is usually in close approximation to the periosteum of the lateral wall. The extraosseous anastomosis is superior to the endosseous unit, which is approximately 15 to 20 mm from the dentate alveolar crest.
Complication prevention.
To minimize vascular trauma to the extraosseous anastomosis, surgical and anatomic considerations should be addressed. Ideally, vertical incisions should be made as short as possible to decrease the possibility of blood vessel damage. It is crucial to gain adequate access to the lateral aspect of the maxilla, and the periosteum should be reflected full thickness with great care. Haphazard reflection may lead to severing or damage to the anastomosis with resultant postoperative edema.
Treatment implication.
Severing of the extraosseous anastomosis may result in significant increased bleeding during the surgical procedure. This intraoperative complication may give rise to impaired visibility for the clinician along with increased surgery duration. Additionally, postoperative complications such as pain, edema, and ecchymosis may result from the severing of these blood vessels.
If trauma to these vessels occurs, direct pressure or the use of electrocautery may be used. However, electrocautery may potentially cause membrane damage or necrosis. If severe bleeding occurs, curved Kelly hemostats are used to clamp the bleeding vessel followed by ligature placement. A slowly resorbable suture with high tensile strength such as Vicryl is recommended.
Intraosseous Anastomosis.
The intraosseous anastomosis is found within the lateral wall of the sinus, which supplies the lateral wall and the sinus membrane. In an edentulous maxilla with posterior vertical bone loss, the endosseous anastamosis may be 5 to 10 mm from the edentulous ridge. The endosseous artery has been shown to be observed on CBCT scans in approximately one half of the patients requiring a sinus graft.12 However, anatomic cadaver studies have shown the prevalence to be 100%.13 In 82% of cases the most common anatomic location was observed between the canine and second premolar region.14 However, with a long-term edentulous patient with a thin lateral wall, the artery may be atrophied and almost nonexistent.
Complication prevention.
Surgical, radiographic, and anatomic considerations should be addressed to minimize trauma to these blood vessels. The CBCT radiographic identification is extremely important in identifying these blood vessels prior to surgery so preparation may be made. Radiographically, smaller anastomoses will not be seen if the pixel size (~1.0 mm) is less than one-half the size of the anastamosis vessel. Using a 0.3 or 0.4 CBCT pixel size for radiographic evaluation will most likely show the smaller anastomoses.15
Studies have shown that in 20% of lateral wall osteotomies, significant bleeding complications may occur.16 This is mainly due to the anastomosis being greater than 1.0 mm in diameter. It has been shown that vessels larger than 1.0 mm are more problematic and associated with significant bleeding, whereas smaller vessels (<1.0 mm) are usually insignificant and easily managed (Fig. 13.7).
Treatment implication.
In most cases, bleeding is a minor complication and of short duration; however, in some instances it may be significant and difficult to manage. To control bleeding, there are many possible treatments: (1) the patient should be repositioned into an upright position and pressure applied with a surgical sponge; (2) electrocautery may be used, although this may lead to membrane necrosis and perforation with possible migration of graft material; (3) a second window may be made proximal to the bleeding source to gain access to the bleeding vessel, especially if location cannot be obtained from the original window; and (4) cutting the bone and vessel with a high-speed diamond with no irrigation (which cauterizes the vessel). (See Bleeding Chapter)
Posterior Lateral Nasal Artery.
A posterior lateral nasal artery (branch of the sphenopalatine artery that also rises from the maxillary artery) supplies the medial aspect of the sinus cavity. The medial and posterior walls of the maxillary sinus mucosa receive their blood supply from the posterior lateral nasal artery.
Complication prevention.
During sinus graft surgery the clinician may be in close approximation to this artery when elevating the membrane off the medial wall. Care should be exercised to minimize trauma to this area because aggressive reflection of the membrane may result in trauma to the blood vessel or perforation into the nasal cavity.
Treatment implication.
Trauma to this artery may cause significant bleeding in the sinus proper and also within the nasal cavity. Because the medial sinus wall is very thin (usually one-half the thickness of the lateral wall), aggressive membrane reflection may result in trauma leading to bleeding issues (see Chapter 7).
Sphenopalatine/Infraorbital Arteries.
The sphenopalatine artery is also a branch of the maxillary artery and enters the nasal cavity through the sphenopalatine foramen, which is near the posterior portion of the superior meatus of the nose. As the sphenopalatine artery exits the foramen, it branches into the posterior lateral nasal artery and the posterior septal artery.17 Additionally, the infraorbital artery enters the maxillary sinus via the infraorbital fissure in the roof of the sinus and ascends cranially into the orbital cavity. Because of the anatomic locations of these blood vessels, it is rarely a concern with respect to sinus graft surgery.
Complication implications.
The sphenopalatine and infraorbital blood vessels are usually not problematic for bleeding complications during lateral-approach sinus elevation surgery because of their anatomic locations. However, incorrect incision locations and aggressive reflection may damage the blood vessels. If bleeding does occur, it is usually easily controlled with pressure and local hemostatic agents.
The Anatomic Significance of the Maxillary Sinus Walls
The maxillary sinus features six bony walls, each of which contain important anatomic structures that may cause complications during maxillary sinus graft surgery. The implant clinician should have a strong understanding and foundation of these structures in the preoperative assessment prior to surgical procedures (Fig. 13.8).
Anterior Wall
The anterior wall of the maxillary sinus consists of thin, compact bone extending from the orbital rim to just above the apex of the cuspid. With the loss of the canine, the anterior wall of the antrum may approximate the crest of the residual ridge. Within the anterior wall and approximately 6 to 7 mm below the orbital rim, with anatomic variants as far as 14 mm from the orbital rim, is the infraorbital foramen. The infraorbital nerve runs along the roof of the sinus and exits through the foramen. The infraorbital blood vessels and nerves lie directly on the superior wall of the sinus and within the sinus mucosa. The infraorbital nerve gives sensory innervation to the soft tissue from the lower border of the orbit to lateral of the nose to the upper lip (Fig. 13.9A).
Complication Implications
Sinus infection.
Tenderness to pressure over the infraorbital foramen or redness of the overlying skin may indicate inflammation of the sinus membrane from infection or trauma, which may contraindicate graft surgery until resolution.
Nerve impairment.
In patients exhibiting anatomic variants, neurosensory impairment may occur during retraction of this area leading to neurapraxia type injuries. The use of worn, sharp-edged retractors should be avoided when reflecting tissue superiorly in this area. Within the anterior wall of the sinus, the thinnest part is the canine fossa, which is directly above the canine tooth. The anterior wall of the maxillary sinus may also serve as surgical access during Caldwell-Luc procedures to treat a preexisting or post–sinus graft, pathologic condition.
Superior Wall
The superior wall of the maxillary sinus coincides with the thin inferior orbital floor. The orbital floor slants inferiorly in a mediolateral direction and is convex into the sinus cavity. A bony ridge is usually present in this wall that houses the infraorbital canal, which contains the infraorbital nerve and associated blood vessels. Dehiscence of the bony chamber may be present, resulting in direct contact between the infraorbital structures and the sinus mucosa (Fig. 13.9B).
Complication Implications
Infection.
Ocular symptoms may result from infections or tumors in the superior aspects of the sinus region and may include proptosis (bulging of the eye) and diplopia (double vision). When these problems occur, the patient is closely supervised and a medical consult is advised to decrease the risk of severe complications that may result from the spread of infection in a superior direction. Superior-spreading infections may lead to significant ocular problems or brain abscesses. As a result, when ocular or cerebral symptoms appear, aggressive therapy to decrease the spread of infection is indicated. Overpacking the maxillary sinus with bone graft material during a sinus graft may result in pressure against the superior wall if a sinus infection develops.
Posterior Wall
The posterior wall of the maxillary sinus corresponds to the pterygomaxillary region, which separates the antrum from the infratemporal fossa. The posterior wall usually has several vital structures in the region of the pterygomaxillary fossa, including the internal maxillary artery, pterygoid plexus, sphenopalatine ganglion, and greater palatine nerve. The posterior wall should always be identified on the radiograph. When a posterior wall is not present, a pathologic condition (including neoplasms) is to be suspected (Fig. 13.9C).
Complication Implications
Bleeding.
Common donor sites to obtain autogenous bone for sinus augmentation procedures include the tuberosity area. Special consideration should be taken on the posterior extent of the tuberosity removal. Aggressive tuberosity removal may lead to bleeding in the infratemporal fossa (pterygoid plexus), resulting in life-threatening situations.
Pterygoid implants.
It should be noted that pterygoid implants placed through the posterior sinus wall and into this region might approach vital structures, including the maxillary artery. A blind surgical technique to place a pterygoid implant through the posterior wall may have increased surgical risk. However, they are of benefit primarily when third or fourth molars are needed for prosthetic reconstruction or sinus grafts are contraindicated and available bone posterior to the antrum is present.
Medial Wall
The medial wall of the antrum coincides with the lateral wall of the nasal cavity and is the most complex of the various walls of the sinus. On the nasal aspect the lower section of the medial wall parallels the lower meatus and floor of the nasal fossa; the upper aspect corresponds to the middle meatus. The medial wall is usually vertical and smooth on the antral side. Located in the superior aspect of the medial wall is the maxillary or primary ostium (Fig. 13.9D).
Complication Implications
Verify patency.
The patency of the ostium must be ascertained prior to surgery to prevent postoperative complications. This is easily verified via coronal or cross-sectional images on CBCT surveys. Of utmost importance is the patency of the ostium, which must be maintained throughout the postoperative period. If ostium patency is compromised, increased morbidity of the graft will occur as the mucociliary action of the maxillary sinus will be compromised.
Accessory ostia.
Smaller, accessory or secondary ostia may be present that are usually located in the middle meatus posterior to the main ostium. These additional ostia are most likely the result of chronic sinus inflammation and mucous membrane breakdown. They are present in approximately 30% of patients, ranging from a fraction of a millimeter to 0.5 cm, and are commonly found within the membranous fontanelles of the lateral nasal wall.18 Fontanelles are usually classified either as anterior fontanelles (AFs) or posterior fontanelles (PFs) and are termed by their relation to the uncinate process. These weak areas in the sinus wall are sometimes used to create additional openings into the sinus for treatment of chronic sinus infections. Primary and secondary ostia may, on occasion, combine and form a large ostium within the infundibulum.
Lateral Wall
The lateral wall of the maxillary sinus forms the posterior maxilla and the zygomatic process. This wall varies greatly in thickness from several millimeters in dentate patients to less than 1 mm in an edentulous patient. A CBCT examination will reveal the osseous thickness of the lateral wall, which is crucial in defining the osteotomy location and preparation technique. Patients exhibiting increased parafunction forces will have thicker lateral walls (Fig. 13.9E).
Complication Implications
Varying thickness.
The lateral wall thickness of the maxilla has been noted to be extremely variable, with some cases being nonexistent. This will lead to an increased possibility of membrane perforation, even occurring on reflection. In contrast, the lateral wall may be very thick, which is usually seen with patients that exhibit parafunction and have just recently lost the posterior teeth. In these situations, lateral wall sinus grafting becomes very difficult because of the cortical thickness.
Bleeding.
The lateral wall houses the intraosseous anastamosis of the infraorbital and posterior superior alveolar artery, which may lead to a bleeding complication because this area is the site for osteotomy preparation of the lateral wall sinus graft procedure.
Inferior Wall
The inferior wall or floor of the maxillary sinus is in close relationship with the apices of the maxillary molars and premolars. The teeth usually are separated from the sinus mucosa by a thin layer of bone; however, on occasion, teeth may perforate the floor of the sinus and be in direct contact with the sinus lining. Studies have shown that the first molar has the most common dehiscent tooth root, occurring up to approximately 30% of the time.19 In dentate patients the floor is approximately at the level of the nasal floor. In the edentulous posterior maxilla the sinus floor is often 1 cm below the level of the nasal floor (Fig. 13.9F).
Complication Implications
Irregular floor.
Radiographically, the sinus inferior floor morphology is easily seen via 3-D imaging. The floor is rarely flat and smooth; the presence of irregularities and septa should be determined and their exact locations noted. Irregular floors are most often seen after teeth are extracted, leaving residual bony crests that increase risk of perforation because of the difficulty in membrane reflection. In some cases, the bony crests are not even seen on the CBCT evaluation.
Septa.
Complete or incomplete bony septa may exist on the floor in a vertical or horizontal plane. Approximately 30% of dentate maxillae have septa, with three fourths appearing in the premolar region. Complete septa separating the sinus into compartments are very rare, occurring in only 1.0% to 2.5% of maxillary sinuses.20 The presence of septa complicate lateral wall sinus graft procedures, which leads to an increased likelihood of membrane perforation.
Anatomic Variants
Numerous anatomic variants arise that may predispose a patient to postsurgical complications. When these conditions are noted, a pharmacologic discipline may be altered and/or implants may be placed after the sinus graft has matured, rather than predisposing them to an increased risk by inserting them at the same time as the sinus graft.
Nasal Septum Deviation
The nasal septum is a bony partition and cartilage within the nasal cavity. The cartilage is termed the quadrangular cartilage and the bones are comprised of the maxillary alveolar crest, vomer bone, and the perpendicular plate of the ethmoid. A deviated septum occurs when the cartilaginous ridge leans to the right or left, resulting in an obstruction of the nasal passages that separates the right and left nasal cavities. The nasal septum is the bone and cartilage in the nose that separates the nasal cavity into the two nostrils. Normally, the septum lies centrally, and thus the nasal passages are symmetrical.5 Studies have shown a prevalence of septal deviation in up to 70% of the population.21 A deviated septum may be diagnosed by evaluating the coronal or 3-D CBCT images (Fig. 13.10A).
Complication Implications
Ostium blockage.
When this bony structure is maligned or deviated, the patient may be at risk of postoperative complications. This bony variant in extremes may cause obstruction of the osteomeatal complex, which results in inflammation from air turbulence, causing increased mucosal drying and particle deposition. If deviation is significant, or if preoperative sinus pathology is present, an ENT consultation is recommended. It should be noted that the ipsilateral side usually will have normal clearance issues and less of a possibility of postoperative complications.
Concha Bullosa
The middle turbinate plays a significant role in the proper drainage system of the maxillary sinus. Normally, this bony structure is lined by nasal respiratory mucosa. A variation of the middle turbinate is a concha bullosa, which is a pneumatization (air bubble) within the middle turbinate. The most ideal CBCT image to diagnose a concha bullosa is a coronal image. This variant has been shown to be present in approximately 4% to 15% of the population (Fig. 13.10A–B).22
Complication Implications
Ostium blockage.
When a concha bullosa is present, the implant clinician should carefully confirm the patency of the maxillary ostium and any pathology in the maxillary sinus. A concha bullosa may decrease the size of the middle meatus, interfering with normal mucociliary flow out of the maxillary sinus. Normally, this variant does not require surgical correction unless patency issues are present for which ENT evaluation and correction are indicated. Usually, corrective surgery includes a turbinectomy, which is the turbinate being reduced in size by endoscopic nasal surgery.
Paradoxical Middle Turbinate
Another variant within the middle turbinate is a paradoxically curved middle turbinate, which presents as a concavity toward the septum (backwards), decreasing the size of the meatus. Normally, the convex side of the middle turbinate will be oriented towards the midline or septum. A paradoxical middle turbinate is most easily seen on a CBCT coronal image with a prevalence of approximately 26% (Fig. 13.10C).
Complication Implications
Ostium blockage.
When present, the implant clinician should carefully confirm the patency of the maxillary ostium and any pathology in the maxillary sinus. The paradoxical middle turbinate may place pressure on the uncinate process, leading to a non-patent maxillary sinus ostium. A paradoxical middle turbinate may decrease the size of the middle meatus, interfering with normal flow out of the maxillary sinus.
Uncinate Process Variants
A deflected uncinate process (either laterally or medially) can narrow the ethmoid infundibulum, which affects the patency of the osteomeatal complex. Perforations may also be present within the uncinate process, leading to communication between the nasal cavity and ethmoid infundibulum. In addition, the uncinate process may be pneumatized and is a common area for ENT intervention in the treatment of chronic rhinosinusitis.
Complication Implications
Ostium blockage.
A deflected uncinate process may lead to narrowing of the flow out of the ostium, causing patency issues. When present, the implant clinician should carefully confirm the patency of the maxillary ostium and any pathology in the maxillary sinus. A deflected uncinate process may decrease the size of the middle meatus, interfering with normal flow out of the maxillary sinus. This may lead to post-operative complications after implant or bone graft surgery in the maxillary sinus.
Haller Cells
Haller cells, also known as infraorbital ethmoidal air cells or maxilloethmoidal cells, are pneumatized ethmoidal air cells. They project from the orbital floor and arise most often from the anterior ethmoids in approximately 34% of the population.23 Hallers cells are most easily seen on coronal images.
Complication Implications
Increased incidence of rhinosinusitis.
In most cases, Haller cells are asymptomatic and generally are associated with an increased incidence of rhinosinusitis. They may become infected and potentially extend into the orbit. Additionally, Haller cells may compromise the patency of the maxillary sinus ostium and also have been associated with chronic polypoid disease, which both may compromise and predispose to postsurgical disease (Fig. 13.11).
Supplemental Ostia
A supplemental ostium or secondary ostia may occur between the maxillary sinus and the middle meatus, which is often found in the posterior fontanelles (PF). The prevalence of supplemental or accessory ostia is approximately 18% to 30%. On occasion, these secondary ostia may be encountered during the membrane elevation off of the medial wall of the antrum, prior to placement of the sinus graft.
Complication Implications
Recirculation.
Because these secondary openings are usually located posterior and inferior to the natural ostium, they may predispose the patient to rhinosinusitis by the recirculation of infected secretions from the primary meatus back into the sinus cavity. The presence of supplemental ostia may increase morbidity for maxillary sinus graft patients. When observed, a piece of collagen is placed over the site to prevent graft material from entering the nasal cavity.
Maxillary Hypoplasia
Hypoplasia of the maxillary sinus may be a direct result of trauma, infection, surgical intervention, or irradiation to the maxilla during the development of the maxillary bone. These conditions interrupt the maxillary growth center, which produces a smaller than normal maxilla. The negative pressure within the maxillary sinus resulting from chronic ostial obstruction impedes the pneumatization process of the sinus, resulting in hypoplasia. Usually, a malformed and positioned uncinate process is associated with this disorder, leading to chronic sinus drainage problems. Maxillary sinus hypoplasia has been reported in 1.73% to 10.4% of patients with sinus symptoms; however, it is sometimes asymptomatic.24
Complication Implications
Predisposition to disease.
Although patients with hypoplastic maxillary sinuses exhibit a greater incidence of sinus pathology and clearance issues, the impact on the placement of implants in this area is negligible. Because of the smaller size of the sinus, there is a greater volume of available bone, negating the need for augmentation procedures. Usually, implant placement may be completed well below the inferior border of the sinus (Fig. 13.12).
Inferior Turbinate and Meatus Pneumatization (Big-Nose Variant)
A rare anatomic variant, which has a significant impact on implant treatment planning, is an inferior meatus pneumatization, or big-nose variant. When the nasal cavity pneumatizes posteriorly, it will reside over the alveolar residual ridge. This condition is most likely seen on a CBCT panoramic image. The prevalence of this condition has been documented to be approximately 3%.
Complication Implications
Lack of bone for implant placement.
When the patient has this condition, the maxillary sinus is lateral to the edentulous ridge. When inadequate bone height is present below this structure, a sinus graft does not increase available bone height for an implant. If a clinician is unaware of this variant, the implant may inadvertently be placed into the nasal cavity above the residual ridge and has been shown to penetrate the inferior meatus and contact the inferior turbinate. A sinus graft is usually contraindicated with this patient condition because the sinus is lateral to the position of the implants. Instead, an onlay graft is required to increase bone height and width (Fig. 13.13).
Pathology
Pathologic conditions associated with the paranasal sinuses are common ailments and afflict more than 31 million people each year. Approximately 16 million people will seek medical assistance related to rhinosinusitis, yet it is one of the most commonly undiagnosed diseases in clinical practice. Potential infection in the region of the sinuses may result in severe complications such as chronic rhinosinusitis, orbital cellulitis, meningitis, osteomyelitis, and cavernous sinus thrombosis. In fact, paranasal sinus infections account for approximately 5% to 10% of all brain abscesses reported each year.25
A preexisting, pathologic, maxillary sinus condition is a contraindication for many procedures that alter the sinus floor before or in conjunction with sinus grafting and/or implant insertion. The risk of postoperative infection is elevated and may compromise the health of the implant and the patient. Pathologic conditions, either preoperative or postoperative, of a maxillary sinus should be evaluated, diagnosed, and treated if indicated.
Pathologic conditions of the maxillary sinus may be divided into five categories: (1) inflammation, (2) cystic conditions, (3) neoplasms, (4) fungal, and (5) antroliths/foreign bodies. Studies have shown approximately 45% of the asymptomatic population has a subclinical pathologic condition in the maxillary sinus. A study completed at the Misch International Implant Institute evaluated over 1000 consecutive prospective candidates for maxillary sinus augmentations. The results concluded 32.7% of asymptomatic patients had maxillary sinus pathologic conditions on CBCT scan evaluation. Because of this high incidence, it is highly recommended that a thorough radiographic evaluation be completed on all prospective sinus elevation patients (Fig. 13.22).
Inflammatory
Odontogenic Sinusitis (Periapical Mucositis)
Odontogenic rhinosinusitis occurs when the maxillary sinus membrane is violated by infection of teeth or pathologic lesions of the jaws. The intimate approximation of the roots of the maxillary posterior teeth to the floor of the sinus may result in inflammatory changes of the periodontium or surrounding alveolar bone. These changes may initiate the development of pathologic conditions in the maxillary sinus.
Etiology.
Odontogenic rhinosinusitis is caused by a periapical abscess, cyst, granuloma, or periodontal disease that results in an expansile lesion within the floor of the sinus. Other causes include sinus perforations during extractions and foreign bodies (e.g., gutta-percha, root tips, amalgam). Odontogenic rhinosinusitis is often polymicrobial, with anaerobic streptococci, Bacteroides spp, Proteus spp, and coliform bacilli being involved. Studies have reported that approximately 30% to 40% of chronic sinusitis cases may have some odontogenic origin when teeth are present in the posterior maxilla.26 Approximately 42% of the time, one or more roots of the maxillary first molar root will protrude into the sinus cavity along with 40% of second molars roots.27
Radiographic Appearance.
Periodontitis may produce generalized sinus mucosal hyperplasia, which is seen as a radiopaque band that follows the contours of the sinus floor. A localized periapical mucositis reveals a thickening of the mucous membrane adjacent to the offending tooth and, on occasion, a perforation through to the floor of the sinus. This radiographic appearance has been termed a halo effect (Fig. 13.14A).
Differential Diagnosis.
Odontogenic rhinosinusitis presents with a thickening of the mucous membrane adjacent to a diseased tooth exhibiting a radiographic radiopaque band. This condition may be confused with acute rhinosinusitis or mild mucosal thickening. However, in odontogenic rhinosinusitis, the patient has teeth in the posterior maxilla and will usually exhibit symptoms related to the teeth (e.g., pain from a posterior tooth or a recent extraction, exudate around the existing natural posterior teeth).
Treatment.
Before sinus augmentation or implant placement, the tooth or teeth involved should be treated periodontally or endodontically, or extracted. After intraoral soft tissue healing and resolution of the pathologic condition, the sinus graft procedure may be performed with minimal risk of postoperative complications. A CBCT scan should be taken approximately 12–16 weeks postoperatively to determine sinus status, including sinus ostium patency.
Acute Rhinosinusitis
The most common sinusitis in the maxillary sinus is a nonodontogenic pathologic condition resulting in inflammation and infection termed acute rhinosinusitis. The signs and symptoms of acute rhinosinusitis are rather nonspecific, making it difficult to differentiate from the common cold, influenza type of symptoms, and allergic rhinitis. Usually patients will present with symptoms such as purulent nasal discharge, facial pain and tenderness, nasal congestion, and possible fever. Acute maxillary rhinosinusitis results in 22 to 25 million patient visits to physicians in the United States each year, with a direct or indirect cost of 6 billion US dollars.25
Etiology.
Acute rhinosinusitis is an inflammatory process that extends from the nasal cavity after a viral upper respiratory infection. Microbiologic cultures have shown the most common pathogens causing acute rhinosinusitis to be Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. These pathogens include approximately 20% to 27% beta-lactamase–resistant bacteria. Staphylococcus aureus has also been cited with the microbiology of acute rhinosinusitis. However, this pathogen is usually seen only in nosocomial (hospital-induced) sinusitis and is unlikely to be seen in elective sinus graft patients.
The most important factor in the pathogenesis of acute rhinosinusitis is the patency of the ostium.28 Mucous production within the sinus is usually abnormal in quality or quantity, along with a compromised mucociliary transport. In an occluded sinus, an accumulation of inflammatory cells, bacteria, and mucus exists. Phagocytosis of the bacteria is impaired with immunoglobulin (Ig)-dependent activities decreased by the low concentration of IgA, IgG, and IgM found in infected secretions.
The oxygen tension inside the maxillary sinus has significant effects on pathologic conditions. When the oxygen tension in the sinus is altered, rhinosinusitis occurs. Growth of anaerobic and facultative organisms proliferate in this environment. Many factors may alter the normal oxygen tension within the sinuses. A direct correlation exists between the ostium size and the oxygen tension in the sinus. In patients with recurrent episodes of sinusitis, oxygen tension is often reduced, even when infection is not present. As a consequence, a history of recurrent acute rhinosinusitis is relevant to determine whether an implant may be at increased risk when inserted at the same time as the sinus graft.
Radiographic Appearance.
The radiographic hallmark in acute rhinosinusitis is the appearance of an air-fluid level. A line of demarcation will be present between the fluid and the air within the maxillary sinus. If the patient is supine (CBCT), the fluid will accumulate in the posterior area; if the patient is upright during the imaging, the fluid will be seen on the floor and be horizontal. Additional radiographic signs include smooth, thickened mucosa of the sinus, with possible opacification. In severe cases, the sinus may fill completely with supportive exudates, which gives the appearance of a completely opacified sinus. With these characteristics the terms pyocele and empyema have been applied (Fig. 13.15A–B).
Differential Diagnosis.
Radiographically, the appearance of an air-fluid level is present with acute rhinosinusitis. The differential diagnosis of acute rhinosinusitis and prolonged viral upper respiratory infection are very similar. However, a classic air-fluid level in the maxillary sinus will give rise to the confirmation of acute rhinosinusitis. Additionally, viral rhinosinusitis will usually improve within 7–10 days, whereas acute bacterial rhinosinusitis most likely will persist for longer than 10 days.29
Treatment.
Because acute rhinosinusitis is one of the most common health problems today, patients having sinus augmentation procedures should be well screened for a past history and current symptoms. Even though acute rhinosinusitis is a self-limiting disease, a symptomatic patient should be treated and cleared by the physician before grafting procedures. These patients are also more prone to postoperative rhinosinusitis. As a result, a more conservative approach is to complete the sinus graft and allow for several months of healing before the placement of the implant.
Chronic Rhinosinusitis
Chronic rhinosinusitis is a term used for a sinusitis that does not resolve in 6 weeks and also has recurrent episodes. It is the most common chronic disease in the United States, affecting approximately 37 million people. Symptoms of chronic sinusitis are associated with periodic episodes of purulent nasal discharge, nasal congestion, and facial pain.
Etiology.
As maxillary rhinosinusitis progresses from acute to chronic, anaerobic bacteria become the predominant pathogens. The microbiology of chronic rhinosinusitis is very difficult to determine because of the inability to achieve accurate cultures. Studies have shown that possible bacteria include Bacteroides spp, anaerobic gram-positive cocci, Fusobacterium spp, as well as aerobic organisms (Streptococci spp, Haemophilus spp, Staphylococcus spp).30 A recent Mayo Clinic study showed that in 96% of patients with chronic sinusitis, active fungal growth was also present.31
Radiographic Appearance.
Chronic rhinosinusitis may appear radiographically as thickened sinus mucosa, complete opacification of the antrum, and/or sclerotic changes in the sinus walls (which give the appearance of denser cortical bone in the lateral walls). Chronic rhinosinusitisis is usually diagnosed from coronal CBCT images.
Treatment.
Medical evaluation and clearance by a physician experienced in sinus pathology is highly recommended for patients with chronic maxillary rhinosinusitis before sinus grafting because significant bacterial resistance and fungal growth is highly probable. Fungal infections may be difficult to treat and control, and serious complications may result in postoperative sinus graft patients. It is imperative that chronic rhinosinusitis patients be cleared by an ENT because these types of patient may be contraindicated for sinus graft surgery (Fig. 13.15C).
Allergic Rhinosinusitis
Etiology.
Allergic rhinosinusitis is a local response within the sinus caused by an irritating allergen in the upper respiratory tract. This allergen may be a cause of acute or chronic rhinosinusitis. This category of sinusitis may be the most common form, with 15% to 56% of patients undergoing endoscopy for sinusitis showing evidence of allergy. This condition often leads to chronic sinusitis in 15% to 60% of patients.32 The sinus mucosa becomes irregular or lobulated, with resultant polyp formation.
Radiographic Appearance.
Polyp formation related to allergic rhinosinusitis is usually characterized by multiple, smooth, rounded, radiopaque shadows on the walls of the maxillary sinus. Most commonly, these polyps are located near the ostium and are easily observed on a CT or CBCT examination. In advanced cases, ostium occlusion, along with displacement or destruction of the sinus walls may be present, with a radiographic image of a completely opacified sinus.
Treatment.
Special attention must be given to these patients to ensure a patent ostium and lack of bacterial resistance. Close postoperative supervision is highly recommended. The polyp, if enlarged, may be removed before the sinus graft by an ENT. This may be performed through an anterior Caldwell-Luc approach or by an endoscopic procedure through the ostium.
Allergic rhinosinusitis patients often have a greater risk of complications related to an increase in allergen production. Because sinus grafting is an elective procedure, the time of year for the surgery may be altered to decrease the postoperative infection risk. For example, if hay fever or a grass allergy is related to the patient’s sinusitis, the sinus graft surgery should be performed in the season or seasons that have least risk to aggravate the sinus mucosa (i.e., winter or fall) (Fig. 13.16).
Cystic Lesions
Cystic lesions are a common occurrence in the maxillary sinus, and studies have reported a prevalence range of 2.6% to 20%.34 They may vary from microscopic lesions to large, destructive, expansile pathologic conditions, which include pseudocysts, retention cysts, primary mucoceles, and postoperative maxillary cysts.
Pseudocysts (Mucous Retention Cyst)
The most common cysts in the maxillary sinus are mucous retention cysts. After much controversy, in 1984, Gardner35 distinguished these cysts into two categories: (1) pseudocysts and (2) retention cysts. Pseudocysts are more common and are of much greater concern during sinus graft surgery, compared with retention cysts. Pseudocysts reoccur in approximately 30% of patients and are often unassociated with sinus symptoms. As a consequence, many physicians do not treat these lesions. However, when their size is larger than 10 mm in diameter, pseudocysts may occlude the maxillary ostium during a sinus graft procedure and increase the risk of postoperative infection.
Etiology.
A pseudocyst is caused by an accumulation of fluid beneath the periosteum of the sinus mucosa, which elevates the mucosa away from the floor of the sinus, giving rise to a dome-shaped lesion. Pseudocysts have also been termed mucosal cysts, serous cysts, and nonsecreting cysts. Damage to the capillary walls from bacterial toxins (e.g., diseased tooth) results in the loss of intravascular proteins and fluid. The accumulation of the exudate in the connective tissue forms areolar spaces that will coalesce into a single cavity that is lined by fibroblasts, not from epithelium. Thus, pseudocysts are not true cysts because they lack an epithelial lining. The cause of the fluid is bacterial toxins from the sinus mucosa or from odontogenic sources. Histologically, the pseudocyst appears as a smooth, light blue, translucuent structure filled with a thin, clear, yellowish fluid.35a
Radiographic Appearance.
Pseudocysts are depicted radiographically as smooth, homogenous, dome-shaped, round to ovoid, well-defined radiopacities. Pseudocysts do not have a corticated (radiopaque) marginal perimeter and are always located on the floor of the sinus cavity (Fig. 13.17A–B). In rare cases, the pseudocyst can completely opacify the sinus cavity.
Treatment.
Pseudocysts are usually not a contraindication for sinus graft surgery. If a large pseudocyst is present, the elevation of the membrane during a sinus graft may raise the cyst to occlude the ostium. In addition, on elevation or placement of the grafting material, the cyst may be perforated, allowing fluid within the cyst to contaminate the graft. Large cysts of this nature should be drained and allowed to heal before or in conjunction with sinus elevation surgery. Most often, an ENT physician should evaluate this condition before the sinus graft. If a pseudocyst is less than 8 mm, less concern is needed and the fluid may be drained in conjunction with sinus grafting, depending on the surgeon’s experience in the treatment of this condition. This should be accomplished with care to prevent membrane perforation. A strict recall evaluation of these previously infected areas following sinus graft surgery is in order because reoccurrence of a pseudocyst is common. Many studies have shown the successful placement of dental implants in conjunction with the presence of pseudocysts.35b-d In rare cases, the pseudocyst may present with clinical symptoms such as headache or pain that may require surgical intervention.
Retention Cysts
The second type of mucous retention cyst is termed a retention cyst. Retention cysts may be located on the sinus floor, near the ostium, or within antral polyps. Because they contain an epithelial lining, researchers consider them to be mucous secretory cysts and “true” cysts. Retention cysts are often microscopic in size.
Etiology.
Retention cysts result from partial blockage of seromucinous gland ducts located within the connective tissue underlying the sinus epithelium. As the secretions collect, they expand the duct, producing a cyst that is encompassed by respiratory or cuboidal epithelium. They may be caused by sinus infections, allergies, or odontogenic conditions.
Radiographic Appearance.
Retention cysts are usually very small and not seen clinically or radiographically. In rare instances, they may achieve adequate size to be seen in a CT image and may resemble the appearance of a small pseudocyst.
Treatment.
No treatment for retention cysts exists before or in conjunction with a sinus graft and/or implant insertion.
Primary Maxillary Sinus Mucocele
A primary mucocele is a cystic, expansile, destructive lesion that may include painful swelling of the cheek, displacement of teeth, nasal obstruction, and possible ocular symptoms.36
Etiology.
The primary mucocele arises from blockage of the maxillary ostium by fibrous connective tissue. Because of the compromised drainage, the mucosa expands and herniates through the antral walls. The primary mucocele is classified as a cyst because of the epithelial lining, which contains mucin. As the mucoid secretions increase, the protein content of the cyst results in the molality increasing, which attracts more fluid to the lesion. As the hydrostatic pressure increases, the mucocele becomes elevated, resulting in pressure necrosis and bony erosion.35a
Radiographic Appearance.
In the early stages, the primary mucocele involves the entire sinus and appears as an opacified sinus. As the cyst enlarges, the walls become thin and eventually perforate. In the late stages, destruction of one or more surrounding sinus walls is evident (Fig. 13.18).
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