Imaging Disease Processes of the Paranasal Sinuses


Imaging Disease Processes of the Paranasal Sinuses

Inflammatory Disease/Sinusitis

Sinusitis is among the most common ailments in the United States, with over 30 million Americans affected by sinusitis each year.27 Over 15 million visits to family physicians each year are related to sinus inflammation. Most cases of acute sinusitis are related to an antecedent viral upper respiratory tract infection. There is resultant swelling that results in apposition of the mucosal surfaces within the paranasal sinuses leading to obstruction of the normal drainage pathways. Inadequate drainage of secretions results in bacterial overgrowth and sinus infection. Although literature suggests that use of CT in uncomplicated community-acquired bacterial sinusitis is not cost-effective,28 unenhanced coronal CT imaging may be obtained in patients with suspected acute sinusitis to assess mucosal disease and/or blockage of the drainage passageways that support this clinically suspected diagnosis ( Fig. 3.3A,B ).2931 Although the empiric antibiotic therapy or treatment according to clinical guidelines are considered the cost- effective pathways,28,32 the imaging still could be used for those patients refractory to medications and antibiotics. If imaging is contemplated to follow-up a patient treated for sinusitis, it is best to obtain imaging 4 to 6 weeks following therapy as the resolution of the radio-logical findings may lag behind the clinical response.

In patients being assessed with CT imaging for chronic sinusitis, it is important for the radiologist to report the areas of mucosal thickening within the paranasal sinuses as well as the drainage passageways of the ostiomeatal complex and sphenoethmoidal recess ( Fig. 3.4A,B ).33,34 The location of sinusitis is as important as the extent of disease in producing symptoms. An evaluation of the nasal cavity and osseous confines (medial orbital walls, cribriform plate, sphenoid sinus roof), and identification of anatomic variants is essential in the assessment of sinonasal pathology. The presence of air-fluid levels or bubbly mucoid material should be reported. Hyperdense sinus contents may reflect the presence of inspissated secretions and/or fungal elements, and is an important finding in diagnosing allergic fungal sinusitis ( Fig. 3.5A,B ). Hemorrhage usually in the setting of trauma or instrumentation is also hyperdense.

The value of magnetic resonance imaging (MRI) in delineating a tumor from sinus secretions. (A) Axial unenhanced T1-weighted MRI shows complete opacification of the left maxillary and sphenoid sinuses with central material that is hyperintense (bright) consistent with proteinaceous, inspissated secretions (asterisk). There is complete opacification of the left nasal cavity with hypointense tissue (T). (B) Corresponding enhanced fat-suppressed T1-weighted MRI shows persistent hyperintensity of the central material (asterisk) in the left maxillary and sphenoid sinuses. Note that this is not enhancement as these areas are hyperintense on the unenhanced T1-weighted image (A) corresponding to proteinaceous secretions. Note the enhancing mass, which represented squamous cell carcinoma in the left nasal cavity (T) (compare with unenhanced image A). Note how magnetic resonance nicely delineates the margins of the tumor (—).
Acute sinusitis in a patient with left facial pain and nasal congestion. Axial T2-weighted (A) and contrast-enhanced T1-weighted (B) magnetic resonance images show mucosal disease in the bilateral maxillary sinuses (*) and an air-fluid level in the left maxillary sinus.
Computed tomography imaging of chronic sinusitis prior to functional endoscopic sinonasal surgery. Coronal images, (B) is anterior to (A), show mucosal disease in the bilateral maxillary sinuses, opacification of the ethmoid air cells (E), and opacification of the frontal sinuses (F). The ostiomeatal complexes (OMC) are obstructed. Opacification of the nasal cavity (NC) represented numerous polyps.
Classic imaging appearance of allergic fungal sinusitis with polyposis. Coronal unenhanced computed tomography scan in soft tissue detail (A), and a bone algorithm (B) shows complete opacification of the bilateral maxillary sinuses, ethmoid air cells, and nasal cavity. Note the laminated appearance of the material in the sinuses with areas of hyperdensity (representing fungal elements and proteinaceous material) alternating with low density (inflammatory tissue and mucosal disease). Tissue opacifying the bilateral nasal cavity represents inflammation and numerous small polyps. Note the preservation of the osseous confines of the sinonasal cavity.
Cerebrospinal fluid leak and meningitis presenting ~10 days following functional endoscopic sinonasal surgery. Coronal (A) and axial (B) computed tomography scans show intracranial air (*) seen as hypodense or dark areas. There is a surgically created defect in the left ethmoid fovealis (^).

When evaluating patients with chronic sinusitis for potential FESS, it is important to evaluate certain anatomic landmarks on high quality, thin section unenhanced CT images. Direct coronal images may be obtained, or direct thin section axial images may be obtained and coronal reformations created from these. The medial orbital walls, the cribriform plate, and the roof and lateral walls of the sphenoid sinus should be evaluated for osseous deficiencies. An unrecognized defect in the lamina papyracea may result in orbital penetration and hematoma formation, whereas a dehiscence in the cribriform plate or sphenoid sinus could result in a cerebrospinal (CSF) leak ( Fig. 3.6A,B ), intracranial complications (meningitis, encephalocele) ( Fig. 3.7 ), or carotid artery complications (perforation, acute subarachnoid hemorrhage; pseudoaneurysm formation).3539 The radiologist and clinician must also assess for anatomic variants or secondary changes of the drainage passageways that may impact surgery. For instance, if the uncinate process and/or middle turbinate are opposed to the orbital floor ( Fig. 3.8A,B ) and the endoscopist is unaware, vigorous removal may result in orbital penetration ( Fig. 3.9 ).

Post-FESS scanning is not accurate in distinguishing inflammation, granulation, and fibrous tissue. The absence of disease on a postoperative study is reliable, but the converse is not true. False-positive studies are common. In cases of suspected complications following FESS, CT scan is the study of choice. Many of these complications are evident within 24 to 48 hours following instrumentation. CT is accurate in identifying orbital hematomas, optic nerve injury in the orbit, as well as other orbital injuries.36,39 A CSF leak due to inadvertent injury to the cribriform plate or overly vigorous removal of the attachment of the middle turbinate to the ethmoid fovealis may be immediately evident in the operating room, or may present days to weeks after surgery with rhinorrhea or symptoms of meningitis ( Fig. 3.6A,B ).35,40

Complications of acute sinusitis include periorbital cellulitis and abscess formation, meningitis, thrombophlebitis (including cavernous sinus thrombosis), subdural empyema, brain abscess, and perineural and perivascular spread of infection (especially in invasive fungal disease).4144 These acute intracranial complications are most accurately assessed with a combined brain and orbital MRI, including contrast-enhanced imaging ( Fig. 3.10A,B ). Contrast- enhanced CT is reliable in assessing orbital and periorbital infection as long as there is not concern for extension to the orbital apex or intracranial compartment (in which case MRI should be obtained).7,14,45

Postfunctional endoscopic sinus surgery meningoencephalocele. Coronal T2-weighted magnetic resonance image shows findings consistent with extensive bilateral functional endoscopic sinonasal surgery. A left frontal encephalocele is noted through a left cribriform plate defect (E).
(A,B) Atelectatic right maxillary sinus (silent sinus) identified in a patient prior to functional endoscopic sinonasal surgery for chronic sinusitis. Contiguous direct coronal computed tomography images showing the right ostiomeatal complex (uncinate process and middle turbinate) are apposed to the orbital wall. The cribriform plate (C) and lamina papyracea (L) are intact. The right ethmoid air cells are opacified.
Defect in the orbital floor following functional endoscopic sinonasal surgery. The asterisk shows a defect in the floor of the right orbit with herniation of orbital fat into the defect. The patient had intermittent diplopia.

Mucoceles may complicate chronic sinusitis, facial trauma, or sinus surgical instrumentation. Mucoceles develop from obstruction of sinus ostia or septated compartments of a sinus and represent mucoid secretions encased by mucus- secreting epithelium (sinus mucosa). In over 90% of cases, mucoceles occur in the frontal sinuses or the ethmoid air cells.4648 Signs and symptoms of mucoceles are related to a mass effect such as frontal swelling, headache, and orbital pain. Orbital extension may result in proptosis or diplopia.49 A secondary infection (mucopyocele) or a direct extension into the anterior cranial fossa is not infrequent.5054 Advances in endoscopic sinus surgery have led to simple drainage procedures, even for some seemingly very complicated mucoceles.

In the radiologic evaluation of mucoceles, CT best shows the osseous changes of the sinus walls, which may be expanded and thinned. With large mucoceles, the adjacent bones may have frank defects ( Fig. 3.11A ). MRI may better assess the interface of a mucocele with intraorbital and intracranial structures. Enhanced MRI is useful in distinguishing a mucocele, which demonstrates peripheral enhancement, from a neoplasm, which typically demonstrates solid enhancement ( Fig. 3.11B ).14,55 Mucoceles have a spectrum of signal characteristics on MRI depending on their protein content relative to free water.56,57

Intracerebral abscess (Pott′s puffy tumor) complicating frontal sinusitis. (A) Axial enhanced T1-weighted magnetic resonance image (MRI) shows a multiloculated intracerebral mass in the left frontal lobe (m). The mass has peripheral enhancement and a fluid-debris level (—). Note enhancement in the frontal sinus (*), dural enhancement (d), and an associated subperiosteal abscess overlying the frontal bone (a). (B) Axial diffusion-weighted MRI shows that the left frontal lobe intracerebral mass is high in signal intensity (bright; m), consistent with an infection/abscess.
Mucopyocele of the left frontal sinus. (A) Axial unenhanced computed tomography image in a bone algorithm shows an expansile lesion of the left frontal sinus (M), with remodeling and thinning of the anterior and posterior cortical tables (*). (B) Axial contrast-enhanced fat-suppressed T1-weighted MR image shows the mucopyocele (M) with no central solid enhancement. Thick circumferential mucosal enhancement is noted (*).

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Jul 2, 2020 | Posted by in OTOLARYNGOLOGY | Comments Off on Imaging Disease Processes of the Paranasal Sinuses
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