CC
A 20-year-old male is referred for evaluation of a swelling on his right mandible.
Odontogenic keratocyst
Odontogenic keratocysts (OKCs) show a slight predilection for males and are predominantly found in individuals of Northern European descent. The peak incidence is seen between 11 and 40 years of age. Patients with larger lesions may present with pain secondary to infection of the cystic cavity. Smaller lesions are usually asymptomatic and are frequently diagnosed during routine radiographic examination.
The World Health Organization (WHO) defines OKCs as an odontogenic cyst characterized by a thin, regular lining of parakeratinized stratified squamous epithelium with palisading hyperchromatic basal cells. From 2005 to 2017, the WHO recommended use of the term keratocystic odontogenic tumor rather than odontogenic keratocyst based on the suspected neoplastic nature of the lesion, including its propensity for recurrence and common genetic chromosomal abnormality of the PTCH gene on chromosome 9q22.3-q31. However, in 2017, the WHO changed the classification back to OKC. The WHO determined that there was insufficient evidence to justify classification as a neoplasm because not all OKCs possess PTCH mutations, and the mutation is also found in other types of cysts, including dentigerous cysts.
HPI
The patient complains of a 2-month history of progressive, nonpainful swelling of his right posterior mandible. (Approximately 80% of OKCs occur in the mandible, most often in the posterior body and ramus region. OKCs account for ∼10%–20% of all oral cystic lesions.) The patient denies any history of pain in his right lower jaw, fever, purulence, or trismus. He does not report any neurosensory changes (which are generally not seen with OKCs).
MHX/PDHX/medications/allergies/SH/FH
Noncontributory. There is no family history of similar presentations.
Nevoid basal cell carcinoma syndrome (NBCCS), also known as Gorlin syndrome, is an autosomal dominant inherited condition with features that can include multiple basal cell carcinomas of the skin, multiple OKCs, intracranial calcifications, and rib and vertebral anomalies. Up to 5% of OKC cases occur as part of NBCCS. Many other anomalies have been reported with this syndrome ( Box 1.1 ). The prevalence of NBCCS is estimated to be 1 in 31,000 to 1 in 164,000 persons.
Diagnosis: The diagnosis of BCNS can be established based on:
- 1.
One major criterion and genetic confirmation
- 2.
Two major criteria
- 3.
One major criterion and two minor criteria
Major criteria
- 1.
BCCs before age 20 years or multiple BCCs
- 2.
OKCs before age 20 years
- 3.
Palmar or plantar pitting
- 4.
Lamellar calcification of the falx cerebri
- 5.
Medulloblastoma (desmoplastic variant)
- 6.
First-degree relative with BCNS
Minor criteria
- 1.
Rib anomalies
- 2.
Macrocephaly
- 3.
Cleft lip or palate
- 4.
Ovarian or cardiac fibroma
- 5.
Lymphomesenteric cysts
- 6.
Ocular abnormalities (i.e., strabismus, hypertelorism congenital cataracts, glaucoma, coloboma)
- 7.
Other specific skeletal malformations and radiological changes (i.e., vertebral anomalies, kyphoscoliosis, short fourth metacarpals, postaxial polydactyly)
Prevalence: 1 in 31,000–164,000
Incidence: 1 in 18,976 births
Genetic test: In 50%–70% of patients with a clinical diagnosis of BCNS, an underlying PTCH1 mutation is found, and ±4% of patients have an underlying SUFU mutation. In case of high clinical suspicion, postzygotic mosaicism can be ascertained by finding an identical mutation in at least two BCCs.
Genetics: An autosomal dominant inheritance with 50% chance of passing on the mutated gene to offspring
In 20%–40% of patients, the disorder is caused by a de novo mutation.
Examination
Maxillofacial. The patient has slight lower right facial swelling isolated to the lateral border of the mandible and not involving the area below the inferior border. The mass is hard, nonfluctuant, and nontender to palpation. (Large cysts may rupture and leak keratin into the surrounding tissue, provoking an intense inflammatory reaction that causes pain and swelling.) There are no facial or trigeminal nerve deficits. (Paresthesia of the inferior alveolar nerve would be more indicative of a malignant process.) The intercanthal distance is 33 mm (normal), and there is no evidence of frontal bossing. His occipitofrontal circumference is normal (an intercanthal distance [the distance between the two medial canthi of the palpebral fissures] of greater than 36 mm is indicative of hypertelorism, and an occipitofrontal circumference greater than 55 cm is indicative of frontal bossing; both can be seen with NBCCS).
Neck. There are no palpable masses and no cervical or submandibular lymphadenopathy. Positive lymph nodes would be indicative of an infectious or a neoplastic process. A careful neck examination is paramount in the evaluation of any head and neck pathology.
Intraoral. Occlusion is stable and reproducible. The right mandibular third molar appears to be distoangularly impacted. (OKCs do not typically alter the occlusion.) The interincisal opening is within normal limits. There is buccal expansion of the right mandible, extending from the right mandibular first molar area posteriorly toward the ascending ramus. Resorption of bone may include the cortex at the inferior border of the mandible, but this is observed at a slower rate than in intermedullary bone, which is less dense. For this reason, OKCs characteristically extend anteroposteriorly rather than buccolingually. This pattern of expansion into less dense bone explains why maxillary OKCs show more buccal than palatal expansion and often expand into the maxillary sinus. There is no palpable thrill or audible bruit, both of which are seen with arteriovenous malformations (AVMs). The oral mucosa is normal in appearance with no signs of acute inflammatory processes.
Thorax-abdomen-extremity. The patient has no findings suggestive of NBCCS (e.g., pectus excavatum, rib abnormalities, palmar or plantar pitting, skin lesions; see Box 1.1 ).
Imaging
A panoramic radiograph is the initial screening examination of choice for patients presenting for evaluation of intraosseous mandibular pathology (10%–20% of OKCs are incidental radiographic findings). This provides an excellent overview of the bony architecture of the maxilla, mandible, and associated structures. Computed tomography (CT) scans can be obtained when large lesions are found. CT scans are valuable in that they provide additional information, such as the proximity of adjacent structures (e.g., the mandibular canal), the integrity of cortical plates, and the presence of perforations into adjacent soft tissues. CT scans provide accurate assessment of the size of the lesion and can demonstrate additional anatomic details (or lesions) that do not appear on panoramic radiographs.
A cone-beam computed tomography (CBCT) scan is appropriate for the evaluation of this lesion. Given its higher resolution, lower radiation dose (∼20% of the radiation of a conventional [helical] CT), and lower cost, a CBCT can replace helical CT for evaluation and follow up of such a lesion. The CBCT scan can also be used to create a stereolithic model of the area of interest.
It has been demonstrated that T2-weighted magnetic resonance imaging (MRI) can detect OKCs in 85% of new cases with a readily recognizable pattern. Several studies have found that MRI signal intensity can be useful in distinguishing OKCs from ameloblastomas. However, the use of MRI for management of suspected OKCs is not routine and is mainly used as a complementary technique to CT in select cases to better visualize soft tissue involvement and internal cystic features.
In this patient, the panoramic radiograph reveals a large, well-demarcated, multilocular radiolucent lesion with a corticated margin and with possible displacement of the right mandibular third molar ( Fig. 1.1 ). There are also several carious teeth and a retained root tip of the right mandibular second bicuspid (tooth #29). (In a patient with a radiolucent lesion of the mandible presumed to be an odontogenic cystic lesion, a multilocular appearance is associated with a 12-fold increased risk for the diagnosis of OKC; however, the majority of OKCs present as unilocular lesions [∼70%].)
Labs
No laboratory tests are indicated unless dictated by the medical history.
Fine-needle aspiration (FNA) is a relatively noninvasive technique used in diagnosis of many masses but has not been used often for oral or jaw lesions because of diversity of lesion types and heterogeneity of cell populations. However, FNA biopsy and cytokeratin-10 immunocytochemical staining have been shown to differentiate OKCs from dentigerous and other nonkeratinizing cysts. A study of FNA use in diagnosis of 72 oral and jaw cysts and neoplasms reported a 91.6% diagnostic accuracy rate for FNA with 1 false-positive and 6 false-negative cases. Despite their availability, these techniques are not routinely ordered because of difficulty accessing and aspirating lesions and limited experience.
Differential diagnosis
The differential diagnosis of multilocular radiolucent lesions can be divided into lesions of cystic pathogenesis, neoplastic (benign or malignant) lesions, and vascular anomalies (least common). The differential diagnosis of multilocular radiolucent lesions is presented in Box 1.2 and can be further narrowed by the clinical presentation. Special consideration should be given to radiolucent lesions with poorly defined or ragged borders, which have a separate differential.
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Ameloblastoma —The most frequent location is the posterior mandible, and the tumor’s most common radiographic appearance is that of a multilocular radiolucent lesion. This is the most frequently diagnosed odontogenic tumor.
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Keratocystic odontogenic tumor (KCOT) —This lesion cannot be differentiated on clinical and radiographic grounds from an ameloblastoma. KCOTs generally do not cause resorption of adjacent teeth. The orthokeratin variant is usually associated with an impacted tooth.
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Dentigerous cyst —Large dentigerous cysts can have a multilocular appearance on radiographs, given the existence of bone trabeculae within the radiolucency. However, they are histologically a unilocular lesion. There is a strong association with impacted mandibular third molars. Painless bony expansion and resorption of adjacent teeth are uncommon but can occur.
- •
Ameloblastic fibroma —The posterior mandible is also the most common site for this lesion. It is predominantly seen in the younger population, and most lesions are diagnosed within the first 2 decades of life. Large tumors can cause bony expansion. The lesion can manifest as a unilocular or multilocular radiolucent lesion that is often associated with an impacted tooth. Ameloblastic fibro-odontomas are mixed radiopaque–radiolucent lesions.
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Central giant cell tumor —Approximately 70% of these lesions occur in the mandible, most commonly in the anterior region. The tumor’s radiographic appearance can be unilocular or multilocular. These lesions can contain large vascular spaces that can lead to substantial intraoperative bleeding. The aneurysmal bone cyst has been suggested to be a variant of the central giant cell tumor. The majority of these lesions are discovered before the age of 30 years.
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Odontogenic myxoma —Although myxomas are seen in all age groups, the majority are discovered in patients who are 20 to 40 years of age. The posterior mandible is the most common location, and the tumor’s radiographic appearance can be unilocular or multilocular. At times, the radiolucent defect may contain thin, wispy trabeculae of residual bone, given its “cobweb” or “soap bubble” trabecular pattern.
- •
Aneurysmal bone cyst —Lacking a true epithelial lining, these cysts most commonly occur in the long bones or the vertebral column. They rarely occur in the jaws, but when they do, it is mostly in young adults. They can present as a unilocular or multilocular radiolucent lesion with marked cortical expansion that usually displaces but does not resorb teeth.
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Traumatic bone cyst —This lesion lacks a true epithelial lining and frequently involves the mandibular molar and premolar region in young adults. These cysts can cause expansion and usually show a well-defined unilocular, scalloping radiolucency between the roots without resorption. The lesion always exists above the inferior alveolar canal.
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Calcifying epithelial odontogenic tumor (CEOT) —This is an uncommon tumor. The majority are found in the posterior mandible, mostly in patients aged 30 to 50 years. A multilocular radiolucent defect is seen more often than a unilocular radiolucency. Although the tumor may be entirely radiolucent, calcified structures of varying sizes and density are usually seen within the defect. CEOTs can also be associated with an impacted tooth.
- •
Lateral periodontal cyst (botryoid odontogenic cyst) —This is usually found in older individuals (fifth to seventh decades of life). The botryoid variant often shows a multilocular appearance. It is most commonly seen in the premolar canine areas.
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Calcifying odontogenic cyst —Most commonly found in the incisor canine region, this cyst is usually diagnosed in patients in the mid-30s. Although the unilocular presentation is most common, multilocular lesions have been reported. Radiopaque structures are usually present in approximately one-third to one-half of the lesions.
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Intraosseous mucoepidermoid carcinoma —This is the most common salivary gland tumor arising centrally within the jaws. Most commonly found in the mandible of middle-aged adults, the tumors can appear radiographically as unilocular or multilocular radiolucent lesions. Association with an impacted tooth has been reported.
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Hyperparathyroidism (brown tumor) —Parathyroid hormone (PTH) is normally produced by the parathyroid gland in response to decreased serum calcium levels. In primary hyperparathyroidism, uncontrolled production of PTH is caused by hyperplasia or carcinoma of the parathyroid glands. Secondary hyperparathyroidism develops in conditions of low serum calcium levels (e.g., renal disease), resulting in a feedback increase in PTH. Patients with hyperparathyroidism usually present with a classic triad of signs and symptoms, described as “stones, bones, and abdominal groans.” Patients with primary hyperparathyroidism have a marked tendency to develop renal calculi (“stones”). “Bones” refers to the variety of osseous changes that are seen, including the brown tumor of hyperparathyroidism. These lesions can appear as unilocular or multilocular radiolucent lesions, most commonly affecting the mandible, clavicle, ribs, and pelvis. “Abdominal groans” refers to the tendency of these patients to develop duodenal ulcers and associated pain. When dealing with any giant cell lesions, the clinician must rule out the brown tumor of hyperparathyroidism by evaluating the patient’s serum calcium level. (It is elevated in those with hyperparathyroidism.) Patients with brown tumor also have elevated levels of PTH (which is confirmed by radioimmunoassay of the circulating parathyroid levels).
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Cherubism —In this rare developmental inherited condition, painless bilateral expansion of the posterior mandible produces cherublike facies (plump-cheeked little angels depicted in Renaissance paintings). In addition, involvement of the orbital rims and floor produces the classic “eyes upturned toward heaven.” Radiographically, the lesions are usually bilateral multilocular radiolucent lesions. Although rare, unilateral involvement has been reported.
- •
Intrabony vascular malformations —Arteriovenous malformations are most often detected in patients between 10 and 20 years of age and are more commonly found in the mandible. Mobility of teeth, bleeding from the gingival sulks, an audible bruit, or a palpable thrill should alert the clinician. The radiographic appearance is variable, but the malformation most commonly presents as a multilocular radiolucent lesion. The loculations may be small, giving the honeycomb appearance that produces a “soap bubble” radiographic appearance. Aspiration of all undiagnosed intrabony lesions is warranted to rule out the presence of this lesion because fatal hemorrhage can occur after an incisional biopsy.
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