Radiography
Findings
Examination in the erect position is desirable to reveal fluid levels, which may be present. The following projections allow a good all round assessment of the paranasal sinuses:
- Occipitomental or Waters view: This view shows the maxillary antra clearly. The frontal sinus is projected obliquely. The ethmoid air cells are obscured, but a few may be seen along the medial walls of the orbit and within the nose. The sphenoid sinus is seen through the open mouth.
- Occipitofrontal of Caldwell view: The frontal sinuses are well seen. The floors of the maxillary sinuses are visible. The floor of the sella turcica, the crista galli, the nasal septum and the middle and inferior nasal turbinate can be seen. The anterior ethmoid air cells are also seen. However, the sphenoid sinus is obscured.
- Lateral view: The sphenoid sinus and frontal sinus are visualized. The rest of the sinuses are superimposed. The nasopharyngeal soft tissue and the adenoids are also well visualized.
- A modified basilar view (a submental vertex view) may be a useful adjunct when dealing with sphenoid sinus disease.
An orthopantomographic view is not a standard view and requires different equipment. This provides a panoramic view of the floors of the maxillary sinuses and the upper and lower alveoli.
Fluid levels are the most common finding in acute bacterial sinusitis and are not generally seen in other forms of sinusitis. Mucosal thickening represented by parallel soft tissue opacity along the bony walls of the sinuses may be seen. Mucous retention cysts are represented by soft tissue opacity with a surface convex towards the cavity of the sinus, along any of the walls.
Hypertrophy of the turbinates may be seen. The nasal cavities may be filled in with soft tissues; this finding is suggestive of polyps. Total opacification of a sinus may also be seen. If the sinus is more opaque than its pair or the ipsilateral orbit, it is thought to be totally filled in with soft tissues or fluid.
Degree of Confidence
With the advent of CT, the role of conventional radiography has taken second place and presently has a limited role in the management of sinusitis. There are wide intraobserver differences in the interpretation of plain radiographs, and the rate of false-negative results is high.
Possible findings in acute sinusitis include mucosal thickening, air-fluid levels, and complete opacification of the involved sinus. The role of imaging in acute sinusitis is controversial, and many regard acute sinusitis a clinical diagnosis. Mucosal thickening is seen in more than 90% of patients with sinusitis, but this finding is highly nonspecific. Air-fluid levels and complete opacification are more specific for sinusitis, but they are seen in only 60% of sinusitis cases.
Air-fluid levels generally indicate bacterial sinusitis, and its presence is helpful in excluding other forms of sinusitis.
In infants aged 3 years or younger, conventional sinus radiographs usually contribute little because of the sinus opacification secondary to normal nonpneumatized sinuses. Conventional radiographs allow poor visualization of ethmoid air cells. If used at all, conventional radiographs should be reserved for patients with persistent symptoms despite appropriate therapy. A single occipitomental (Waters view) suffices in this situation.
Aalokken and associates evaluated plain radiography in a prospective investigation of patients with clinically suspected acute sinusitis by using standard CT as the criterion standard. They recruited 47 consecutive patients, who underwent conventional radiography and standard-dose CT on the same day. The sensitivity and specificity of the plain radiography were calculated. The specificity was high, but the sensitivity was low except for imaging of the maxillary sinus (sensitivity, 80%). Therefore, for maxillary sinusitis, plain radiography was reasonably accurate. A negative finding in the other sinuses was not reliable. The authors concluded that the sensitivity of plain radiography for detecting sinus opacifications was unacceptably low for the ethmoid, frontal, and sphenoid sinuses. The specificity was high.
Garcia and associates evaluated radiography and CT for the examination of the paranasal sinuses in 91 pediatric patients with chronic upper respiratory tract symptoms for at least 3 months.
When sinus radiographs were compared with CT scans, radiographs could not depict minimal disease. For clinically significant sinusitis, sinus radiographs depicted disease in 20% of frontal sinuses, 0% of sphenoidal sinuses, and 54% of ethmoidal sinuses. With the minimal criteria of 40-50% opacification or fluid-level filling of the maxillary antrum, radiographs depicted disease in 75%.
The sensitivity and specificity of a Waters view to confirm clinically significant chronic sinusitis without specifying the sites and severity were acceptable at 76% and 81%, respectively. The authors concluded that a single Waters view is an acceptable part of the initial evaluation of pediatric chronic sinusitis; however, they found a limited CT scan a better alternative.
False Positives/Negatives
Findings on CT should be interpreted in conjunction with clinical and endoscopic findings because of high rates of false-positive findings. As many as 40% of asymptomatic adults have abnormalities on sinus CT scans, as do more than 80% of those with minor upper respiratory tract infections.
The differentiation of infection, tumor, polyp, and allergic mucosal thickening may be difficult, and all of these conditions can lead to a false-positive diagnosis. Sinus mucosal thickening or opacification may also occur in hematologic disorders, fibrous dysplasia, Wegener granulomatosis, and Paget disease.
Computed Tomography
Findings
Anatomy
CT evaluation of paranasal sinuses for sinusitis should include an assessment of the pattern of disease, the extent of disease, the probable mechanical cause, and the relevant anatomic details required for planning surgery.
To evaluate the pattern of sinusitis, one must understand the drainage of various sinuses. The anatomy of drainage revolves around the osteomeatal unit which is not a single morphological structure but a combination of the following structures: (1) middle turbinate, (2) ethmoid bulla, (3) uncinate process, (4) maxillary infundibulum, (5) hiatus semilunaris (ie, space beneath the middle turbinate), and (6) maxillary os.
The hiatus semilunaris is a space between the uncinate process anteroinferiorly and the ethmoid bulla posterosuperiorly. The anterior group of ethmoid air cells drains into the anterior aspect of the hiatus semilunaris through the frontonasal duct. The middle group drains into the hiatus semilunaris on or above the ethmoidal bulla. The frontal sinus drains through the frontonasal duct or through the anterior ethmoidal cells into the hiatus semilunaris. The maxillary infundibulum drains into the posterior part of the hiatus semilunaris. The frontal, maxillary, anterior, and middle ethmoidal sinuses all drain into the hiatus semilunaris of the middle meatus. Any mechanical block in this region causes inflammation of the above mentioned sinuses. This is called the osteomeatal pattern or middle meatus syndrome.
The sphenoid sinus drains posterior to the superior turbinate into the sphenoethmoid recess through the sphenoid ostium. The posterior ethmoid air cells also drain through the superior meatus into the sphenoethmoid recess. An obstruction in this region gives rise to the sphenoethmoid pattern of sinusitis.
Normal variants
Concha bullosa is an aerated middle turbinate that could compress the uncinate process and obstruct the middle meatus and the infundibulum (see Image 5). It is present in 35% of the population. The degree of pneumatization may vary from side to side. Usually, 1 cell and, occasionally, 2 or 3 cells are seen.
The Haller cell, or infraorbital cell, extends inferior to the ethmoid bulla and lateral to the maxillary sinus roof and interposes itself between the lamina papyracea and the uncinate process. A large Haller cell may obstruct the middle meatus. It is usually located in the anterior ethmoid, but it may extend all the way from anterior to posterior. It is seen in 10% of the population, in whom it is unilateral in 5.4% and bilateral in 4.5%.
The middle turbinates may have a paradoxical curve, causing narrowing of the middle meatus. A deviated nasal septum or a septal spur may cause compression of the middle turbinates and resultant narrowing of the middle meatus. A large ethmoid bulla can protrude into the middle meatus and cause it to become narrowed.
Pathology
Polypoid mucosal thickening may be seen in the affected sinuses. Polypoid soft-tissue masses may be seen to extend from the sinuses into the nasal cavities. The osteomeatal complexes may be obstructed by concha bullosa, enlarged bulla ethmoidalis, a long infundibulum or mucocele. A bony erosion may suggest the presence of a mucocele. An air-fluid level within the sinuses may be seen. Hyperattenuating soft tissue surrounded by hypoattenuating mucoperiosteum in the sinuses is suggestive of fungal infection, although it can also be seen with inspissated secretions and old polyps. Bony erosion is well demonstrated on CT scans.
The following are the patterns of sinus inflammation on CT scans: (1) polyps; (2) fungal sinusitis; (3) mucocele; (4) sinusitis, which can occur as sinonasal polyposis or in an infundibular, osteomeatal unit, sphenoethmoidal recess, or sporadic or unclassifiable pattern; and (5) granulomatous sinusitis, which can be infectious (eg, due to tuberculosis, actinomycosis, rhinoscleroma, or leprosy) or noninfectious (eg, Wegener granulomatosis, sarcoid).
With fungal sinusitis, the maxillary and ethmoid sinuses are most commonly involved. Allergic fungal sinusitis can involve complete opacification of multiple paranasal sinuses, unilateral or bilateral; sinus expansion and erosion of a wall of the involved sinus; or high-attenuating areas scattered amid mucosal thickening on nonenhanced scans. These areas are due to inspissated secretions or heavy metals such as iron, manganese, and calcium.
Acute invasive fungal sinusitis can involve aggressive bone erosion with extension of disease into the adjacent soft tissues. Intrasinus high-attenuating areas may not be present in acute invasive fungal sinusitis. This condition may be associated with orbital, intracranial, and cheek soft-tissue invasion.
Sinus mycetoma may cause a focal area of increased attenuation that is usually centered within a diseased sinus.
Findings of acute sinusitis include an air-fluid level, mucosal thickening, and complete opacification of the sinus. Blood in the sinus due to recent trauma may mimic an air-fluid level in the sinus, but it is easily distinguished by density measurements.
In chronic sinusitis, the ethmoid sinus is commonly involved. Findings include mucosal thickening, complete opacification, bone remodeling and thickening due to osteitis, and polyposis.
Mucoceles often occur in patients with chronic pansinusitis and nasal polyposis. The pathogenesis involves accumulation of mucoid secretions behind an obstructed paranasal sinus ostium with expansion of the sinus cavity and thinning of the sinus walls. The frontal sinuses account for about 60% of cases, ethmoid 30%, maxillary 10%; the sphenoid sinus is only rarely involved. Frontal sinus mucoceles may present with decreased visual acuity, visual field defect, proptosis, and intractable headaches.
Conventional radiography shows a soft tissue density mass causing sinus cavity expansion, sometimes with bony erosion. Macroscopic calcification may be seen in 5% of cases, especially where there is superimposed fungal infection. Full assessment requires CT or MRI.
CT techniques and indications
CT techniques include thin-section, high-resolution, and coronal scanning for the evaluation of inflammatory sinonasal disease. Plain coronal scans are typically acquired with 2- to 3-mm sections and a high-frequency algorithm. Scans are obtained from the frontal sinus to the sphenoid sinus. Axial scans are not routinely necessary.
Administration of antibiotics or antihistaminics may be required to permit scanning when patient has minimal symptoms. Having the patient blow his or her nose before scanning is useful for clearing mucus, and a prone position to drain fluid away from osteomeatal unit.
Degree of Confidence
The criterion standard imaging modality in the diagnosis of sinusitis is CT, which provides more detailed information about the anatomy and abnormalities of the sinuses than does plain radiography. The osteomeatal units are brilliantly shown on CT scans, which provide greater definition of the pathology than do other images, especially within the sphenoid and ethmoid sinuses. CT also provides the relationship of the sinuses to the orbit and the brain. This is an invaluable piece of information in any patient with rhinosinusitis that is severe enough to produce complications.
The primary role of CT is to aid in the diagnosis and management of recurrent and chronic sinusitis and to define the anatomy of the sinuses prior to surgery.
A nonenhanced coronal CT viewed in a bone window provides excellent resolution and good definition of the complete osteomeatal complex and other soft-tissue abnormalities seen in sinusitis. The coronal view is best correlated with findings from sinus surgery. Contrast-enhanced CT may be required in cases of acute sinusitis complicated by periorbital cellulitis or abscess.
False Positives/Negatives
CT findings should not be interpreted in isolation, and scans should always be read in conjunction with clinical and endoscopic findings because of high rates of false-positive results. Up to 40% of asymptomatic adults have abnormalities on sinus CT scans, as do more than 80% of those with minor upper respiratory tract infections.
Dhong and associates evaluated the accuracy of diagnosing sinus fungus balls with CT and compared their results with operative findings. The sensitivity of CT evaluation was 62%, and the specificity was 99%. The false-positive and false-negative rates were 22% and 2%, respectively. The authors concluded that, to diagnose fungus ball, a high index of suspicion is necessary and pathologic confirmation is mandatory.
In immunocompromised patients with invasive sinusitis, CT findings may be negative in the early stages. In advanced cases, differentiating this condition from malignancy may be difficult on the basis of imaging alone. Thus, the clinician cannot rely solely on CT imaging and must maintain a high index of suspicion when evaluating immunocompromised patients to establish a prompt diagnosis. Early nasal endoscopy with biopsy and the initiation of appropriate therapy are necessary to improve the patient's prognosis.
Magnetic Resonance Imaging
Findings
CT remains the criterion standard modality in diagnosing sinusitis, but MRI is indicated with clinically suspected complications, especially in patients with intracranial complications and an extension of infection or in those with suspected superior sagittal venous thrombosis. Both diagnostic methods have improved the care and outcomes of patients who have sinusitis with complications.
T1-weighted and fat-saturated T2-weighted coronal sequences are routinely performed. Axial T1- and T2-weighted and fat-saturated T2-weighted sagittal sequences may also be performed.
Fluid is hypointense on T1-weighted images and hyperintense on T2-weighted images. Mucosal swelling may be confused with fluid on T2-weighted MRIs; however, on T1-weighted MRIs, it stands out as soft tissue thickening against the fluid. Tumor tissue appears hypointense, as compared with mucosal swelling on T2-weighted images. Mucocele is hyperintense with both T1- and T2-weighted sequences because of its protein content. The signal intensity on MR depends on the age and degree of inspissation of the secretions. Older mucoceles will lose their T2 signal, then their T1 signal.
Degree of Confidence
MRI improves the differentiation of soft tissue, but it does not help in evaluating bones. MRI clearly depicts tumor from surrounding inflammatory tissue and secretions in the sinuses (see Findings, above). CT relies on the high contrast between air, soft tissue, and bone in evaluating the paranasal sinuses. Membrane, polyps, and mucous have similar attenuation, but the polypoid appearance helps in distinguishing the inflammatory polyps. On T2-weighted MRIs, the edematous membrane and mucous are distinctly hyperintense, whereas nasal polyps have more intermediate signal intensity. MRI cannot define bony anatomy as well as CT does.
Other disadvantages of MRI include a high rate of false-positive findings and its higher cost. MRIs take considerably longer to acquire than CT scans, and they may be difficult to obtain in patients who are claustrophobic.
False Positives/Negatives
The false-positive rate with MRI is high. Abnormal sinus MRI findings are common among otherwise healthy adults, among children attending school, and among totally asymptomatic children. Incidental MRI findings should be interpreted as normal and do not indicate a need for treatment in children imaged for purposes other than the evaluation of sinus disease.
Ultrasonography
Findings
In general, ultrasonography has not been thought to be useful in the diagnosis of sinusitis. However, several published works (Vento, 1999; Hilbert, 2001) have shown it to be more accurate than MRI or plain radiography in the diagnosis of maxillary sinusitis. When used in combination with radiography, sonograms can depict 86% of infections.
Degree of Confidence
A-mode ultrasonography has been a reliable tool in the diagnosis of acute maxillary sinusitis. However, controversy still exists regarding the reliability of A-mode ultrasonography in detecting fluid retention or mucosal swelling in patients with chronic polypous rhinosinusitis or in transantrally operated-on maxillary sinuses.
Ultrasonography has several limitations in the diagnosis of sinusitis. Ultrasonography can result in a positive diagnosis in the presence of antral fluid, but sonograms do not define the cause of the fluid. Sonograms cannot provide information about bony detail, and the diagnosis of frontal, ethmoidal, and sphenoidal sinusitis is difficult.
False Positives/Negatives
Sonographic findings cannot be used to differentiate sinus disease from bacterial, viral, fungal, and allergic causes, as with most cross-sectional imaging.
Nuclear Imaging
Findings
Javer and associates compared scintigraphy with indium Indium-111, gallium-67, and technetium-99m to differentiate acute infection from chronic inflammation involving bone (osteitis) and/or mucosa. This information was then used to guide management. Nuclear scintigraphy results were compared with CT and surgical findings.
111 In was the best isotope for identifying pus or acute disease in the sinuses, whereas67 Ga was good for identifying both chronic mucosal disease and acute disease.99m Tc was sensitive for identifying bony remodeling and therefore not useful if the patient had undergone previous sinus surgery. The authors concluded that scintigraphy should not be considered a first-line diagnostic test. Instead, nuclear scintigraphy is useful in cases in which CT results are nondifferentiating.
Goshen and associates performed bone and gallium scans of the sinus regions in 32 patients presenting with frontal sinusitis. Bone scans classified according to99 Tc methylene diphosphonate (MDP) distribution patterns indicated active and resolving sinusitis, as well as surgery-related bone trauma. However, the intensity of gallium uptake was well correlated with the final outcome. This uptake was useful for differentiating between active and resolving sinusitis, with more specifically than that of the corresponding bone scans. Thus, combined studies may have a role in the diagnosis and management of frontal sinusitis.
Degree of Confidence
Radionuclide studies cannot be regarded as the primary modality in the imaging of sinusitis, but they have a place when cross-sectional imaging cannot differentiate between infection and other causes of mucosal disease. Gallium and labeled WBCs are both nonspecific agents and may be taken up in infections, inflammations, and tumors.
False Positives/Negatives
Roccatello and associates described facial uptake of111 In-labeled granulocytes in cases of Wegener granulomatosis mimicking sinusitis.
Angiography
Findings
Non-inflammatory lesions in the sphenoid sinus are common. Therefore, thorough preoperative evaluation is imperative. The location and character of these lesions can be defined by means of nasal endoscopy and CT, and no other investigations may be necessary. In some patients, MRI may help further define the nature and extent of a lesion.
Angiography should be considered if a vascular lesion is suspected. The clinical and imaging findings should all be taken into consideration when the surgical approach is planned (Martin, 2002). Mycotic aneurysms, cerebral infarction, brain abscess, and intracranial venous thrombosis are rare but well-known complications of sinusitis. Sphenoid sinusitis may invade adjacent intracranial vessels, and angiography may be required.
Degree of Confidence
Angiography is an invasive procedure, though it remains the criterion standard for depicting blood-vessel pathology. Most vascular evaluations can now be performed by using magnetic resonance angiography (MRA) or CT angiography (CTA). However, angiography may still be necessary for planning surgery and radiologic interventions, such as embolization of pseudoaneurysms.
False Positives/Negatives
Angiography provides little if any information regarding sinusitis itself. Although vascular invasion from extension of the sinus inflammatory process or venous thrombosis can be diagnosed reliably with angiography, such pathology has many causes that cannot be differentiated with angiography.
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Further Reading
Keywords
rhinosinusitis, functional endoscopic sinus surgery, FESS
