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Sinus conditions are extremely prevalent worldwide. Patients present with a variety of symptoms that may be mistaken for a common cold or allergy and are often times vague. In the past, the diagnosis for the clinician was more difficult, but with research providing evidence based criteria and the utilization of tools such as the rigid endoscope and computed tomography (CT) imaging, patients can now breathe a little easier.

Although the term sinusitis is used most often, the correct terminology is rhinosinusitis (rhino is Greek for “of the nose”). Rhinosinusitis is defined as symptomatic inflammation of the paranasal sinuses and nasal cavity.8 The paranasal sinuses are air cavities in the cranial bones, especially those near the nose and connecting to it. There are four paranasal sinuses named for the bone in which they are located.4

• Maxillary (one sinus located in each cheek)
• Ethmoidal (approximately 6-12 small sinuses per side, located between the eyes)
• Frontal (one sinus per side, located in the forehead)
• Sphenoid (one sinus per side, located behind the ethmoid sinuses, near the middle of the skull)

Appropriateness Guidelines for CT of the Sinuses

The diagnostic tests used most often in the evaluation of sinus conditions are allergy and autoimmune testing, nasal endoscopy and radiographic imaging. Imaging is generally not necessary in the diagnosis of most sinus conditions. However, when patients do not respond to the prescribed course of treatment or symptoms persist, diagnostic imaging may be indicated. In 2007, the American Academy of Otolaryngology–Head and Neck Surgery Foundation (AAO-HNSF) drafted appropriateness guidelines for the diagnosis and treatment of adult sinusitis including the use of radiography and Computed Tomography (CT).8 The AAO-HNS panel made a recommendation against radiographic imaging for patients who meet diagnostic criteria for acute rhinosinusitis (see definition below), unless a complication or alternative diagnosis is suspected.

When imaging of the sinus is deemed appropriate, CT is the preferred diagnostic imaging technique used to aid in the diagnosis and management of difficult cases, or to define the anatomy of the sinuses prior to surgery. It is also used as a tool to establish the severity of disease and evaluate the response to treatment and surgery. CT can define the boney nasal anatomy much more precisely than plain radiographs and Magnetic Resonance (MR). Clinical correlation of history and patient anatomy with the CT findings is essential to patient management to avoid over diagnosis of sinusitis. 40 percent of asymptomatic patients have abnormalities on sinus scans, with that figure being 80 percent for patients with minor upper respiratory tract infections. CT, accompanied by surgical planning, leads to decreased complications and morbidity.1,2,8

The Basic Principals of CT Imaging

Coronal View of the Ethmoidal and Maxillary Sinuses Source: Wikipedia

Nasal Septal Deviation With Bone Spur Image courtesy of Xoran Technologies, Inc.

Thin section axial and coronal views are typical images acquired through CT of the sinus structures. With functional endoscopic sinus surgery now a more widespread technique, coronal view CT has become the preferred imaging plane as it correlates best with the surgical procedure. On a conventional scanner, coronal views are taken with the patient lying prone and the gantry angled perpendicular to the patient’s hard palate. Computer generated coronals views can be reconstructed from axial images if the patient cannot tolerate this position or if the scanner is upright. To further delineate anatomic structures, sagittal reconstructions may be helpful.1,2

The qualified technical staff must take care to properly position the patient so that the external auditory canal is aligned with the inferior orbital rim on the axial slices. Rotation of the patient’s head will distort the anatomy of the images and reconstructions. Except for complicated acute sinusitis, a noncontrast CT scan is usually sufficient. Bone window settings provide excellent resolution and a good definition of the complete osteomeatal complex and other anatomic structures. For soft tissue lesions, inflammatory processes, vascular structures and tumors, CT contrast is generally used. Medical and technical staff must ensure that patient doses are determined in keeping with the As Low As Reasonably Achievable (ALARA) concept. Knowledge of the variation in sinus anatomic structures, complicated disease processes and surgical implications is critical to the interpretation of the CT scans. The interpreting physician must use a systematic approach when evaluating the images to determine the presence of disease, anatomic structures and potential problem areas when surgery is indicated. All structures seen in the CT image should be evaluated, and any appropriate recommendations for incidental or abnormal findings documented.2

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