Radiologic tests

A normal sinus x-ray series has a negative predictive value

of 90 to 100 percent, particularly for the frontal and maxillary sinuses; that is normal sinus film virtually rules out sinusitis.

The standard study is four-view sinus series

that includes:

• Waters view: in which the occiput is tipped down (patient's chin and tip of the nose are against

  the film surface) to facilitate viewing of the maxillary and frontal sinuses;

• Caldwell view: in which the forehead and tip of the nose are placed in contact with the film (this offers superior visualization of the frontal and ethmoid sinuses).

• Lateral view: in which the sphenoid sinus and the posterior frontal sinus wall are visualized; and

• Submentovertex view: in which the sphenoid sinuses and posterior ethmoid cells are visualized.

Opacification of the affected sinus without bone destruction is the typical finding. An air-fluid level may be seen if the films are taken with the patient in the upright position. Thickening of the mucosa is a less specific finding for acute sinusitis, but is a common sequela of acute sinusitis and is the most common feature of chronic sinusitis.

The positive predictive value of x-rays using opacification and air-fluid levels as end points is 80 to 100 percent, (that is if opacification or air-fluid levels are found, the diagnosis or sinusitis is correct between 80 and 100 percent of the time), but the sensitivity is low since only 60 percent of patients with acute sinusitis have opacification or air-fluid levels.

A very well done study, using the standard criteria of air-fluid level, sinus opacity or mucosal thickening (greater than 6 mm) to diagnose sinusitis, demonstrated that a single Waters view had a high level of agreement with the complete sinus series. In this study, 88 percent of patients with sinusitis had maxillary disease. A single occipitomental (Waters) view in children has an overall accuracy of 87 percent in diagnosing acute sinusitis. In those few situations where x-rays are indicated, utilizing a single Waters view is preferred over the four-view study.

Although CT scanning and MR imaging are more sensitive than plain films of the sinuses, they are also more expensive and may show trivial baseline variations that can mimic sinusitis.

Computed tomographic (CT) scanning of the sinuses has no place in the routine evaluation of acute sinusitis. Sinus CT scanning has a high sensitivity but a low specificity for demonstrating acute sinusitis. Forty percent of asymptomatic patients and 87 percent of patients with community-acquired colds have sinus abnormalities on sinus CT. Air-fluid levels are easily appreciated with both modalities. Limited sinus CT studies are useful in delineating the osteomeatal complex in anticipation of an otolaryngology consultation and functional endoscopic sinus surgery to evaluate and treat chronic sinus inflammation.

Sinus tap is rarely necessary for the diagnosis of sinusitis. Its use should be reserved for patients with recalcitrant infection or severe underlying disease (eg, AIDS, cancer, residence in the intensive care unit).