Coauthor(s): Ali Nawaz Khan, mbbs, frcs, frcp, frcr, lrcp



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Sinusitis

Author: Rochita V Ramanan, MD, Consultant in charge, Department of Radiology, The Apollo Heart Centre, Chennai, India
Coauthor(s): Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia; Durre Sabih, MBBS, MSc, Visiting Faculty, Department of Nuclear Medicine, Pakistan Institute Applied Sciences and Nishtar Medical College, Director, Multan Institute of Nuclear Medicine and Radiotherapy
Contributor Information and Disclosures

Updated: Feb 20, 2007

Introduction

Background

Sinusitis is an inflammation of the mucosal lining of the paranasal sinuses. As the mucosa of the sinuses is continuous with that of the nose, rhinosinusitis is a more suitable term.

Functional endoscopic sinus surgery (FESS) has revolutionized the treatment of sinusitis in recent years. The therapeutic benefits of FESS have helped a large number of patients with chronic sinus disease.

Obstruction of the draining pathways of the sinuses is now thought to be the main cause of sinusitis. Examples of these pathways include the ostia of the maxillary sinuses and the hiatus semilunaris, where the anterior group of paranasal sinuses drains. Clearance of this obstruction is the aim of endoscopic surgery.

Imaging has also progressed with FESS, and CT scanning can now demonstrate the sinus anatomy and patterns of sinusitis in exquisite detail before surgery.

Pathophysiology

Sinusitis is an inflammation of the mucosal lining of the paranasal sinuses usually related to viral, bacterial or fungal infections. Allergic sinusitis is also common. Inflammatory response to allergens results in edema and thickening of the mucous membrane. Usually the margins of the edematous mucosa have a scalloped appearance, but in severe cases, mucous may completely fill a sinus, making it difficult to distinguish an allergic process from infectious sinusitis. Characteristically, all of the paranasal sinuses are affected and the adjacent nasal turbinates are swollen. Air-fluid levels and bone erosion are not features of uncomplicated allergic sinusitis; however, swollen mucosa in a poorly draining sinus is more susceptible to secondary bacterial infection.

The sinuses are lined by respiratory epithelium. The mucosal coat lining the sinuses can be subdivided into a superficial viscous layer and a deeper serous layer. Mucous secreted by the sinus mucosa traps bacteria. The mucous is naturally extruded through the normal ostia and expectorated or swallowed. The cilia expel the sinus secretions towards the natural ostia by beating in the serous layer.

Normal sinus function is maintained as long as the ostia remain patent and the cilia function normal. Another ingredient of normal function is the quality of the mucous secreted.

The most important factor in the pathogenesis of sinus disease is ostial obstruction, which leads to hypo-oxygenation, which in turn results in poor ciliary function and secretion of suboptimal quality of the mucous. Ciliary dysfunction leads to retention of the mucous within the sinuses.

Several other factors that can lead to impaired ciliary function. Cold air is said to stun the ciliary epithelium, leading to impaired ciliary movement and retention of secretions in the sinus cavities. On the contrary, inhaling dry air desiccates the sinus mucous coat, leading to reduced secretions. Any mass lesion with the nasal air passages and sinuses, such as polyps, foreign bodies, tumors, and mucosal swelling from rhinitis, may block the ostia and predispose to retained secretions and subsequent infection. Drinking alcohol can also cause nasal and sinus mucosa to swell and cause impairment of mucous drainage. Kartagener syndrome is associated with immobile cilia and hence the retention of secretions and predisposition to sinus infection.

Sinusitis can be subdivided into acute, subacute, and chronic disease. Acute sinusitis is defined as disease lasting less than 1 month, subacute disease lasts 1-3 months, and chronic sinusitis lasts longer than 3 months and generally related to suboptimally treated acute or subacute disease. Acute and subacute sinusitis is treated medically, whereas chronic sinusitis may require surgical intervention.

Frequency

United States

Sinusitis is one of the most common diseases in the United States, affecting an estimated 15% of the population. The incidence of sinusitis has increased dramatically with the increasing incidence of asthma, allergies, and other upper respiratory tract infections. Each year, an estimated 50 million people in the United States have sinusitis, but the incidence of clinical frontal sinusitis specifically is lower.

CT scans depict sinus abnormalities in 31-45% of the asymptomatic pediatric population.

International

Acute sinusitis affects 3 in 1000 people in the United Kingdom. Chronic sinusitis affects 1 in 1000 people. Sinusitis is more common in winter than in summer. Rhinoviral infections are prevalent in autumn and spring. Coronaviral infection occurs mostly from December to March.

Mortality/Morbidity

Sinusitis does not cause any significant mortality by itself. However, complicated sinusitis may lead to morbidity and, in rare cases, mortality.

Complications of sinusitis include acute and chronic sequelae. The incidence of intracranial complications in all patients hospitalized with sinusitis has been reported as 3.7%. Sinusitis is implicated as a source of subdural abscess in 35-65% of cases.


  • Acute distant effects include toxic shock syndrome. Acute local effects can also occur. Acute orbital complications include the following: cellulitis, proptosis, chemosis, ophthalmoplegia, orbital cellulitis, subperiosteal abscess, and orbital abscess.

  • Other acute complications include intracranial sequelae such as meningitis; encephalitis; cavernous or sagittal sinus thrombosis; and extradural, subdural, or intracerebral abscesses. Bony complications include dental involvement and osteitis or osteomyelitis. Potts puffy tumor refers to swelling of the scalp, caused by an underlying osteitis of the skull or extradural abscess. A classical cause of such a swelling is complicated frontal sinusitis.

  • Chronic complications of sinusitis include mucocele and pyocele.

Race

No significant race preponderance exists.

Sex

Women have more episodes of infective sinusitis than men because they tend to have more close contact with young children. The rate in women is 20.3%, compared with 11.5% in men.

Age

Sinusitis is more common in children and young adults, who are particularly susceptible to rhinovirus infections, than in others.

Anatomy

The paranasal sinuses are hollow cavities within the bones of the face and base of skull. The sinuses are lined by mucous membrane that is continuous with that of the nasal cavity. In addition, the sinuses are all paired.

The frontal sinuses are posterior to the superciliary arch between the outer and inner tables of the frontal bone. The ethmoidal sinuses consist of thin-walled cavities in the ethmoid labyrinth. They vary in number and size from 3 large to 18 small sinuses. Their openings into the nasal cavity are highly variable.

The 2 sphenoid sinuses are sited posterior to the upper part of the nasal cavity contained within the body of the sphenoid bone. The posterior ethmoid and sphenoid sinuses are in close relation to the optic nerve and the nerve may even be enclosed within the sphenoid sinus at times. The 2 maxillary sinuses are pyramidal cavities in the bodies of the maxillae. Their ostia are positioned nearer the roof than the floor.

The anatomy of the sinuses on CT scans is described under CT Scan.

Presentation

Clinical findings may include the following: (1) pain over cheek and radiating to frontal region or teeth, increasing with straining or bending down; (2) redness of nose, cheeks, or eyelids; (3) tenderness to pressure over the floor of the frontal sinus immediately above the inner canthus; (4) referred pain to the vertex, temple, or occiput; (5) postnasal discharge; (6) a blocked nose; (7) persistent coughing or pharyngeal irritation; (8) facial pain; and (9) hyposmia.

Preferred Examination

Radiography

Plain radiography is generally obsolete, but exceptions include its use in confirming air-fluid levels in acute sinusitis and evaluating size and integrity of the paranasal sinuses. Radiographs may still provide a useful adjunct to diagnosis in parts of the world, where sophisticated imaging is not yet available.

Whether the Waters view is sufficient for evaluating suspected acute bacterial sinusitis is debated. In general, Waters, Caldwell, and lateral views are obtained.

Magnetic resonance imaging

MRI is generally reserved for the evaluation of any complications of local sinus infections, particularly suspected intracranial extension.

T1-weighted images and fat-suppressed T2-weighted images effectively depict the paranasal sinuses and adjacent facial compartments. Fat-suppressed gadolinium-enhanced T1-weighted images are helpful for assessing extension to the skull base and intracranial cavity. MRI is useful in differentiating sinusitis from neoplasia and in imaging patients with dental fillings that cause artifacts on CT scans and patients who cannot lie prone because of kyphoscoliosis.

MRI clearly depicts tumor from surrounding inflammatory tissue and secretions within the sinuses. Typically, edema of inflamed tissue and retained secretions have low intensity on T1-weighted images and high intensity on T2-weighted images because of their increased water content. However, because of the often chronic nature of these secretions at diagnosis, a certain amount of free water will have been absorbed, and a variable pattern of intensity may be seen. On the contrary, 95% of sinus tumors are highly cellular with decreased water content, resulting in low-to-intermediate signal intensity on both T1- and T2-weighted imaging.

Gadolinium enhancement provides additional information. Most sinus tumors show diffuse enhancement, whereas inflamed mucosa enhances more intensely and peripherally. Perineural spread to tumor can also be shown on MRI; this is most important in the context of adenoid cystic carcinoma. The correlation of MRI and histologic findings at surgery is as high as 94% with improvement to 98% with gadolinium enhancement.

Some of the advantages of MRI are now being eroded by modern multisection CT with its capability for instant axial and coronal reformatting, which avoids dental artifact. In fact, MRI may now be limited by dental amalgams.

Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with troublemoving

orstraightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.



CT scanning

CT is the examination of choice in the evaluation of sinusitis, particularly chronic sinus disease providing excellent detail of sinus anatomy. However, CT is usually not useful in acute sinusitis, as diagnosis is primarily based on clinical findings. Good anatomic definition is desirable before surgical intervention.

CT scans are more sensitive than plain radiography for depicting sinus pathology, especially in the sphenoid and ethmoid sinuses. However, CT findings can also be nonspecific and many centers do not use it routinely in the diagnosis of acute sinusitis.

Coronal CT imaging is the preferred initial procedure. Bone-window views provide excellent resolution and a good definition of the complete osteomeatal complex and other anatomic details that play a role in sinusitis. In addition, the coronal view is best correlated with findings from sinus surgery.

In general, nonenhanced CT scans suffice in cases of uncomplicated sinusitis. Multisection CT seems to have the potential to replace primary coronal CT of the paranasal sinuses without any loss of image quality, and it may even improve the overall diagnostic value. However, the doses of radiation may still have to be reduced.

Limitations of Techniques

On plain radiographs, other bony structures overlap the sinuses, and the rate of false-negative results is high. The posterior ethmoids are poorly visualized. The osteomeatal complex cannot be adequately assessed.

The superiority of CT over other methods of imaging the sinuses can be summarized as follows: First, coronal CT is ideal for evaluating sinusitis because the anatomy and pathology visualized in a plane almost identical to that seen by the endoscopist, and this imaging plane displays the osteomeatal unit. Second, the bony walls of the sinuses are better demonstrated with CT in the high-resolution mode than with other modalities. Third, CT provides an excellent anatomic display of soft tissue attenuation. This depiction includes fluid levels and polypoid masses within the normally air-filled cavities of the sinuses, nasal cavity, and postnasal space. Most important, disease extending beyond the bony perimeters of the sinuses into the adjacent soft tissue of the orbit, brain, and infratemporal fossa can be imaged.

These applications of CT have disappointed in only one way. Although it provides an excellent anatomic display, CT generally does not help in predicting the histologic nature of the pathologic process.

A major milestone in radiology occurred with the introduction of MRI. This modality provides greater soft-tissue contrast, tissue differentiation, and marginal lesion definition than those achieved with other studies. However, the bony margins of the sinuses are imaged as a plane of absent signal intensity on MRIs. Moreover, the signal intensity from the high fat content of bone narrow, as in the basisphenoid and petrous apices and around the frontal sinuses, can be confusing, particularly because fluid retained in the sinuses has signal intensity similar to that of the high water content.

On CT scans, it is difficult or impossible to differentiate tumor tissue from retained fluid in sinuses, where the drainage of a sinus is blocked by obstruction from the tumor. Extension of disease into the cranial cavity is shown well on MRIs, and the ability to image in any plane is a considerable advantage.

Differential Diagnoses

Other Problems to Be Considered

Wegener granulomatosis: This involves angiitis associated with focal necrosis and granulomatous reaction, which initially affects the respiratory tract but which may progress to involve other organs.

Ataxia-telangiectasia: This autosomal recessive disorder is associated with recurrent sinusitis, pulmonary infections, bronchiectasis, pulmonary fibrosis, tracheomegaly, diminished lymphoid tissue, and cerebral and cerebellar atrophy.

Cystic fibrosis: This autosomal recessive disorder associated with respiratory, GI, cardiovascular and sinus abnormalities, among others.

Immotile cilia syndrome: This autosomal recessive disorder is associated with recurrent chest infections and/or pulmonary consolidation, sinusitis, bronchiectasis, and Kartagener syndrome.

Kartagener syndrome: This autosomal recessive disease is associated with sinusitis, situs inversus, recurrent respiratory infections, and bronchiectasis, among other abnormalities.

Nasal polyposis: Hyperallergic patients may have innumerable polyps filling the nasal cavity and obstructing the paranasal sinuses, giving a characteristic imaging appearance. This disease is closely associated with asthma.

Wiskott-Aldrich syndrome: This X-linked, recessive, immune deficiency disease is associated with recurrent respiratory tract infections and/or pneumonia, sinusitis, and mastoiditis.

Yellow-nail syndrome: The mode of inheritance is not known. This syndrome is associated with recurrent pleural effusions, pericardial effusions, chylothorax, bronchiectasis, and sinusitis.

Young syndrome: The mode of inheritance is unknown. The syndrome is associated with azoospermia secondary to epididymal obstruction and recurrent respiratory infections and sinusitis.



Sinusitis: Imaging

Author: Rochita V Ramanan, MD, Consultant in charge, Department of Radiology, The Apollo Heart Centre, Chennai, India
Coauthor(s): Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR, LRCP, Chairman of Medical Imaging, Professor of Radiology, NGHA, King Fahad National Guard Hospital, King Abdulaziz Medical City, Riyadh, Saudi Arabia; Durre Sabih, MBBS, MSc, Visiting Faculty, Department of Nuclear Medicine, Pakistan Institute Applied Sciences and Nishtar Medical College, Director, Multan Institute of Nuclear Medicine and Radiotherapy

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.



Intervention

Sinus puncture may be undertaken with the patient under local anesthetic to aspirate a small amount of fluid from the sinuses. The fluid is then cultured to determine what type of bacteria is causing sinusitis. Sinus puncture is performed only if a reasonable diagnosis cannot be made by using noninvasive techniques.



Medicolegal Pitfalls

  • Invasive forms of sinusitis and malignancy must be differentiated.

  • Infection of the ethmoid air-cells when associated with bone erosion should be regarded as an ears, nose, and throat emergency because of the risk of spreading infection to the intracranial structures and orbit.

  • Sinus infection in an immunocompromised patient needs aggressive emergency treatment.

 

Multimedia

air-fluid level (arrow) in the maxillary sinus su...

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Media file 1: Air-fluid level (arrow) in the maxillary sinus suggests sinusitis.

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air-fluid level (arrow) in the maxillary sinus su...

Air-fluid level (arrow) in the maxillary sinus suggests sinusitis.

accessory ostia in the medial walls of both maxil...

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Media file 2: Accessory ostia in the medial walls of both maxillary sinuses with left maxillary sinusitis.

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accessory ostia in the medial walls of both maxil...

Accessory ostia in the medial walls of both maxillary sinuses with left maxillary sinusitis.

deviated nasal septum on a coronal high-resolutio...

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Media file 3: Deviated nasal septum on a coronal high-resolution CT scan.

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deviated nasal septum on a coronal high-resolutio...

Deviated nasal septum on a coronal high-resolution CT scan.

bilateral ethmoid sinusitis on an mri.

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Media file 4: Bilateral ethmoid sinusitis on an MRI.

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bilateral ethmoid sinusitis on an mri.

Bilateral ethmoid sinusitis on an MRI.

concha bullosa of the right middle turbinate.

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Media file 5: Concha bullosa of the right middle turbinate.

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concha bullosa of the right middle turbinate.

Concha bullosa of the right middle turbinate.

ethmoid sinusitis with intracranial extension and...

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Media file 6: Ethmoid sinusitis with intracranial extension and also extension into the left orbit.

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ethmoid sinusitis with intracranial extension and...

Ethmoid sinusitis with intracranial extension and also extension into the left orbit.

paradoxical curves of both middle turbinates caus...

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Media file 7: Paradoxical curves of both middle turbinates cause narrowing of the osteomeatal units.

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paradoxical curves of both middle turbinates caus...

Paradoxical curves of both middle turbinates cause narrowing of the osteomeatal units.

sinonasal polyposis. soft tissues completely fill...

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Media file 8: Sinonasal polyposis. Soft tissues completely fill the maxillary and ethmoid sinuses and extend into the nasal cavities.

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sinonasal polyposis. soft tissues completely fill...

Sinonasal polyposis. Soft tissues completely fill the maxillary and ethmoid sinuses and extend into the nasal cavities.

ct scan obtained after functional endoscopic sinu...

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Media file 9: CT scan obtained after functional endoscopic sinus surgery (FESS) shows surgical defects in both nasal cavities in the form of excision of the entire right osteomeatal unit and the left uncinate process with residual left ethmoid and maxillary sinusitis.

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ct scan obtained after functional endoscopic sinu...

CT scan obtained after functional endoscopic sinus surgery (FESS) shows surgical defects in both nasal cavities in the form of excision of the entire right osteomeatal unit and the left uncinate process with residual left ethmoid and maxillary sinusitis.

polypoid mucosal thickening in the right maxillar...

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Media file 10: Polypoid mucosal thickening in the right maxillary sinus with a mucous retention cyst in the left on a Waters view.

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polypoid mucosal thickening in the right maxillar...

Polypoid mucosal thickening in the right maxillary sinus with a mucous retention cyst in the left on a Waters view.

right-sided sphenoethmoidal pattern of sinusitis.

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Media file 11: Right-sided sphenoethmoidal pattern of sinusitis.

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right-sided sphenoethmoidal pattern of sinusitis.

Right-sided sphenoethmoidal pattern of sinusitis.

mucous retention cysts along the floor of the rig...

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Media file 12: Mucous retention cysts along the floor of the right and the anterior wall of the left maxillary sinuses.

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mucous retention cysts along the floor of the rig...

Mucous retention cysts along the floor of the right and the anterior wall of the left maxillary sinuses.

mucosal thickening in the left anterior ethmoid a...

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Media file 13: Mucosal thickening in the left anterior ethmoid and maxillary sinuses and in the region of the infundibulum. This indicates an osteomeatal pattern of sinusitis.

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mucosal thickening in the left anterior ethmoid a...

Mucosal thickening in the left anterior ethmoid and maxillary sinuses and in the region of the infundibulum. This indicates an osteomeatal pattern of sinusitis.

frontal mucocele. expansion of the left frontal ...

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Media file 14: Frontal mucocele. Expansion of the left frontal sinus indicated by low-attenuating soft tissues with thinning of the walls but no erosion.

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frontal mucocele. expansion of the left frontal ...

Frontal mucocele. Expansion of the left frontal sinus indicated by low-attenuating soft tissues with thinning of the walls but no erosion.

fungal sinusitis. soft tissues occupy the right m...

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Media file 15: Fungal sinusitis. Soft tissues occupy the right maxillary and ethmoid sinuses with central hyperattenuating areas typical of fungal sinusitis. Medial walls of the affected sinuses are eroded.

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fungal sinusitis. soft tissues occupy the right m...

Fungal sinusitis. Soft tissues occupy the right maxillary and ethmoid sinuses with central hyperattenuating areas typical of fungal sinusitis. Medial walls of the affected sinuses are eroded.

mri shows intraorbital extension of ethmoid sinus...

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Media file 16: MRI shows intraorbital extension of ethmoid sinusitis on the right side.

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mri shows intraorbital extension of ethmoid sinus...

MRI shows intraorbital extension of ethmoid sinusitis on the right side.

axial mri in the same patient as in image 16 show...

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Media file 17: Axial MRI in the same patient as in Image 16 shows right intraorbital extension of sinusitis with medial displacement of medial rectus muscle.

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axial mri in the same patient as in image 16 show...

Axial MRI in the same patient as in Image 16 shows right intraorbital extension of sinusitis with medial displacement of medial rectus muscle.

expansion of the left anterior ethmoid sinuses wi...

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Media file 18: Expansion of the left anterior ethmoid sinuses with thinned bit intact bony walls; these findings suggest a mucocele.

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expansion of the left anterior ethmoid sinuses wi...

Expansion of the left anterior ethmoid sinuses with thinned bit intact bony walls; these findings suggest a mucocele.

http://img.medscape.com/pi/emed/ckb/radiology/336139-382802-384649-1374951tn.jpg

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