Rhinosinusitis is a commonly encountered disease. Imaging is not typically required in acute uncomplicated rhinosinusitis; however, it is integral in the evaluation of patients who present with prolonged or atypical symptoms or when acute intracranial complications or alternate diagnoses are suspected. Knowledge of the paranasal sinus anatomy is important to understand patterns of sinonasal opacification. Bacterial, viral, and fungal pathogens are responsible culprits and, with duration of symptoms, serve to categorize infectious sinonasal disease. Several systemic inflammatory and vasculitic processes have a predilection for the sinonasal region. Imaging, along with laboratory and histopathologic analysis, assist in arriving at these diagnoses.
Key points
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Rhinosinusitis is a commonly encountered condition. Although often treated clinically, a thorough understanding of the role of diagnostic imaging is crucial to diagnosing alternative causes and complications. CT and MRI are often complementary in the evaluation of sinonasal infectious and inflammatory processes.
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Rhinosinusitis exists on a spectrum ranging from acute to chronic defined by symptoms, disease duration, and sometimes radiologic findings. Treatment implications, complications, and prognosis will vary along this spectrum.
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Fungal rhinosinusitis is classified into invasive and noninvasive subtypes affecting different patient populations. The acute invasive subtype has high morbidity and is suspected in the setting of rapidly progressive symptoms and certain complications such as vascular and cranial nerve compromise.
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Various inflammatory conditions can manifest as rhinosinusitis both clinically and radiographically and should be considered as differential diagnoses in the appropriate clinical context.
| CT | Computed tomography |
| MR | Magnetic Resonance |
| MRI | Magnetic resonance imaging |
| OMC | Ostiomeatal complex |
| OMU | Ostiomeatal unit |
| CSF | Cerebral spinal fluid |
| DWI | diffusion weighted imaging |
| FLAIR | Fluid attenuation inversion recovery |
| IgG4-RD | IgG4 related disease |
| GPA | Granulomatosis with polyangiitis |
| ANCA | Antineutrophil cytoplasmic antibodies |
| CST | cavernous sinus thrombosis |
Introduction
Rhinosinusitis affects approximately 12% of adults in the United States per year. As one of the most common conditions encountered by clinicians, a large proportion of ambulatory office and emergency room visits and a similarly large proportion of adult antibiotic prescriptions are attributed to sinonasal disease each year. Perhaps more important than the direct health care costs of diagnosing and treating sinusitis is the significant impact on quality of life experienced by those affected, which can contribute to the indirect costs of the disease from lost productivity and days away from work. ,
Sinusitis is defined as a symptomatic inflammatory process of the paranasal sinuses. As inflammation of the sinuses is generally accompanied by inflammation of the nasal mucosa, the term rhinosinusitis is preferred. Rhinosinusitis can be classified by the duration of symptoms and further subclassified by the cause of disease and responsible pathogen. The diagnosis and treatment of uncomplicated sinusitis—where inflammation is confined to the sinonasal spaces—does not usually require imaging and can be made by (duration of) symptoms and physical examination findings. ,
Imaging can assist clinicians in surgical planning, reaching a correct diagnosis when an alternative process is suspected, and evaluating for rare but serious complications. In addition to neoplastic processes that may affect the sinonasal region, some systemic and inflammatory processes have a predilection for the nasal cavity and paranasal sinuses. Although these cases can present with nonspecific symptoms mimicking rhinosinusitis, they will occasionally have more onerous signs leading the clinician to pursue imaging to confirm their suspicion of an alternate cause. ,
This article discusses the role of diagnostic radiology, the imaging features, and differential diagnoses of infectious and inflammatory sinonasal diseases. Neoplastic processes are covered in another article in this issue.
Role of imaging
Imaging evaluation of patients presenting with uncomplicated rhinosinusitis may not be indicated if clinical diagnostic criteria are met. Acute uncomplicated rhinosinusitis is medically managed with antibiotic therapy. The clinical scenario in combination with imaging recommendation guidelines can be used to direct the appropriate imaging modality (or modalities) on a patient-specific basis when sinonasal symptoms are present and an alternative diagnosis or complications of sinonasal inflammatory disease are suspected.
Computed tomography (CT) is the modality of choice in the evaluation of inflammatory disease given its wide availability and ability to provide high spatial resolution for evaluating the fine osseous and anatomic detail of the paranasal sinuses. CT images are usually acquired with thin-slice technique in the axial plane with coronal and sagittal reformations provided for interpretation. Images are reviewed in both osseous and soft tissue algorithms. Iodinated contrast is generally not necessary unless there is concern for a complicated extrasinus process. High-resolution CT is also the modality of choice in preoperative planning for endoscopic sinus surgeries.
MRI offers improved soft tissue contrast resolution and affords accurate delineation of suspected extrasinus soft tissue and intracranial complications and allows for sensitive characterization of soft tissue masses. MRI is infrequently used in the diagnosis of rhinosinusitis unless complications are suspected. The field of view for standard multiplanar multisequence MRI technique of the paranasal sinuses should include the orbits, skull base, and adjacent intracranial structures. Multiplanar fat-suppressed T1-weighted images acquired after the administration of intravenous gadolinium are used to evaluate the extent of an extrasinus process and enhancement patterns of soft tissue masses. High-resolution MRI also allows for detailed evaluation of small anatomic structures such as the skull base foramina, cranial nerves, and vessels.
MRI and CT imaging are often complementary in the complete characterization of sinonasal processes, in particular when atypical or complicated processes are suspected. With the increasing availability of cross-sectional imaging modalities providing superior anatomic detail of the paranasal sinuses and sinonasal pathologies, radiography has become relatively obsolete with its lower sensitivity and specificity in detection of disease.
Relevant anatomy
A detailed review of paranasal sinus anatomy and physiology is outside of the scope of this article, and the reader is directed to Richard D. Beegle and colleagues’ article, “ Normal and Variant Sinonasal Anatomy ,” in this issue. However, a discussion of paranasal sinus disease would not be complete without a brief review of mucociliary clearance physiology and sinus drainage pathways.
The sinonasal cavity is lined by ciliated pseudostratified columnar epithelium with mucinous and serous glands that aid in directing secretions through the drainage pathways. Mucociliary clearance is an important defense mechanism against inhaled pathogens. The cilia act in a concerted fashion to direct secretions through the sinus ostium (sometimes in an antidependent manner), to the nasal cavity, where they then travel to the nasopharynx and are eventually swallowed.
The frontal recess is an anatomically variable portion of the frontal sinus outflow tract that drains the frontal sinuses ( Fig 1 A). Depending on the attachment point of the uncinate process to either the anterior skull base medial to the frontal recess or to the lamina papyracea and agger nasi cell, the frontal recess may drain into either the ethmoid infundibulum or the middle meatus, respectively. , Rhinosinusitis may occur when the frontal recess is obstructed ( Fig. 1 B, C).
The ostiomeatal complex (OMC) or ostiomeatal unit (OMU) is the common drainage pathway of the frontal and maxillary sinuses and the anterior ethmoid air cells. The maxillary infundibulum, hiatus semilunaris, middle meatus, and frontal recess comprise the OMC ( Fig. 2 A). Anatomic variants may result in narrowing of the OMC with the potential to contribute to obstruction. , Pneumatization of the middle turbinate (concha bullosa) or a paradoxic curvature of the middle turbinate may distort the uncinate process and narrow the infundibulum , ( Fig. 2 B). Other variants such as infraorbital or uncinate air cells, prominent ethmoid bulla, and nasal septal deviation may also alter the OMC. , An OMC pattern of obstruction will be seen on imaging as opacification of the anterior ethmoid air cells and frontal and maxillary sinuses ( Fig. 2 C and D).
The basal lamella, the coronal attachment the middle turbinate, separates the anterior and the posterior ethmoid air cells. , The anterior ethmoid air cells drain through the OMC and the middle meatus. The posterior ethmoid air cells drain via the superior or supreme meati, and with the sphenoid sinus, into the sphenoethmoidal recesses to the nasal cavity. ,
Rhinosinusitis arises when there is retention of mucous secretions due to apposition of mucous membranes and resultant unproductive mucociliary clearance with obstruction of outflow. This condition can lead to superimposed bacterial infection due to an increase in oxygen tension in the local environment. The frontal recess, the infundibulum, the middle meatus, and the sphenoethmoidal recess are anatomic “tight spots” where obstruction may occur. A list of common pathogens responsible for rhinosinusitis can be found in Table 1 .
| Viral | Acute Bacteria | Chronic Bacteria | Allergic Fungal | Invasive Fungal | Chronic Invasive Fungal |
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The nasal cycle refers to physiologic congestion and subsequent decongestion of unilateral nasal mucosa occurring in a reciprocal pattern where congestion of one side is accompanied by decongestion on the other. On imaging, mucosal thickening of approximately 2 to 3 mm is seen in the nasal cavity and anterior ethmoid air cells with accompanying hyperemia and swelling of the ipsilateral turbinates. , , It is important to recognize this process and its imaging features as a normal physiologic phenomenon that should not be confused with a pathologic source of nasal obstruction.
As CT is often obtained for surgical planning, the radiologist should be familiar with (and report) anatomic variations that may have implications for surgical misadventure. Variants that affect critical structures that place the patient at risk for cerebrospinal fluid leaks or for major arterial, orbital, optic nerve, or nasolacrimal duct injuries must be described. ,
Infectious and inflammatory processes
Rhinosinusitis
Rhinosinusitis is considered acute if characteristic symptoms are present for less than 4 weeks in duration and chronic if symptoms are present for greater than 12 weeks. Subacute sinusitis occurs in the time frame between 4 and 12 weeks. Bacterial, viral, and fungal pathogens may be responsible culprits and can also serve as further classification criteria (see Fig. 17 , Table 1 ). Uncomplicated rhinosinusitis refers to inflammation confined to the paranasal sinuses without extension into adjacent structures such as the intracranial vault, orbits, or adjacent soft tissues. ,
Acute Rhinosinusitis
Imaging is generally not necessary in patients who meet the clinical criteria for acute rhinosinusitis unless an alternative diagnosis or intracranial, orbital, or other extrasinus soft tissue complications of sinusitis are suspected. Acute rhinosinusitis is diagnosed clinically in patients who present with cardinal symptoms of the disease; patients with acute rhinosinusitis may experience up to 4 weeks of purulent nasal drainage in combination with nasal obstruction and/or facial pain, pressure, or fullness. A distinction between bacterial and viral causes may be made based on clinical improvement (presumed viral origin) or failure to improve (presumed bacterial origin) within a 10-day period. This distinction helps to guide appropriate use of antibiotic therapy. ,
CT findings of acute rhinosinusitis are relatively nonspecific and include mucosal thickening, air fluid levels, and bubbly or aerated opacification ( Fig. 3 ). The imaging findings should be taken in the context of clinical symptoms to arrive at the correct diagnosis. An odontogenic source of sinusitis occurs in approximately 20% of cases and can be suspected radiographically in the presence of adjacent dental caries, periapical lucency, and/or focal osseous dehiscence between the affected tooth and sinus , ( Fig. 4 ).
Chronic Rhinosinusitis
Chronic rhinosinusitis is a commonly diagnosed otolaryngologic disease occurring after 12 weeks duration of sinonasal symptoms and usually resulting from repeated episodes of acute or subacute sinusitis. A Task Force on Rhinosinusitis published a consensus report in 1997 to standardize clinical diagnostic criteria of this process requiring either 2 major or 1 major and 2 minor criteria for diagnosis. Major criteria include facial pain, congestion, obstruction, nasal discharge, purulence, and olfactory disturbances. Minor criteria include headache, fever, fatigue, cough, ear pain, halitosis, and dental pain.
CT is the most used imaging modality for the diagnosis of chronic rhinosinusitis, although as in the case of its acute counterpart, imaging features are not specific for the disease and must be interpreted in the appropriate clinical context. For example, mucosal thickening has been shown to be present in greater than 90% of patients with a viral upper respiratory illness.
Repeated episodes of inflammation may result in mucosal hypertrophy and retention cysts in the affected sinus with these findings often visualized on CT ( Fig. 5 ). Mucosal thickening of up to 3 mm may be seen in normal individuals. , Sinonasal polyps and bony changes including hyperostosis and sclerosis of the sinus walls can also be seen and may be used to confirm a chronic process because these signs generally are not present in the true acute setting. , Hyperdense sinus opacification may represent inspissated mucus or proteinaceous debris, calcification, or an atypical fungal process. Calcifications related to chronic rhinosinusitis generally show a peripheral pattern, whereas calcifications located centrally suggest fungal disease.
