Plain radiographs do not approach the sensitivity and specificity of CT but are useful in some cases. Plain films are often ordered in cases of facial trauma, especially isolated nasal trauma. The films can be complementary to the physical examination.
Plain radiographs of the sinuses are still useful in certain circumstances. Plain sinus radiographs are reasonably accurate in assessing the maxillary and frontal sinuses in cases of acute sinusitis. Complete opacification or an air-fluid level in one of these sinuses usually indicates acute sinusitis. However, the relatively low sensitivity and specificity of plain films, especially in evaluating the ethmoid sinuses, have limited their usefulness.
Computed tomography has become an invaluable diagnostic tool for evaluating chronic nasal and sinus problems and has essentially supplanted the use of plain sinus films. CT of the sinuses allows unparalleled imaging of the complicated anatomy of the nose and paranasal sinuses. It has also increased understanding of the pathophysiology of sinusitis. CT scanning can show areas of mild mucosal thickening in the sinuses (indicating chronic sinusitis), complete opacification (seen in acute sinusitis, polyps, or sinus tumors), bone erosion, or abscess formation in adjacent critical structures such as the orbit or brain (Fig. 19-6). CT can show whether the ostiomeatal complex (the "bottleneck" of normal sinus drainage) is patent or obstructed and shows the myriad nasal and sinus normal variants, some of which predispose to sinonasal pathology.
Computed tomography of the sinuses should be ordered when the diagnosis of chronic sinusitis is suspected, medical treatment of sinusitis has failed and surgery is being contemplated, a complication of sinusitis is suspected, or a nasal or sinus mass is suspected. CT is not required as a confirmatory test in the treatment of uncomplicated acute sinusitis except in certain circumstances. The scan is helpful, however, in cases of recurrent acute sinusitis or when the diagnosis is not certain. Obtaining a scan during a patient's presumed infection allows the diagnosis to be confirmed or ruled out. Although some abnormalities require further treatment occasionally, the scan identifies abnormalities or variations of normal anatomy that require no intervention. Mucus retention cysts, for example, are seen in up to 20% of the population. Unless they are large or infection is suspected (the patient complains of pain in the vicinity of the cyst), no treatment is required.
Magnetic resonance imaging is not particularly helpful in evaluating sinusitis and has two main limitations in evaluating inflammatory sinus conditions. First, MRI often tends to be too sensitive, showing mucosal thickening that is clinically insignificant. Second, MRI fails to show bony anatomy, which is critical in diagnosis and surgical planning in chronic sinusitis. MRI is useful in evaluating suspected sinonasal tumors and fungal infections of the sinuses. The limitations of MRI and its relatively high cost compared with CT do not justify its routine use in evaluating chronic sinusitis. When incidental sinusitis is noted on an MR image and the degree of sinusitis is severe, is asymmetric, or the patient is symptomatic, treatment (and sometimes ENT referral) is indicated.
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