Imaging Sinonasal Disease: The Radiologist′s Arsenal
Plain Film Radiographs
Computed tomography (CT) has replaced plain film radio-graphs as the primary modality in evaluating sinonasal disease. Functional endoscopic sinonasal surgery (FESS) has supplanted external procedures like the Caldwell-Luc and maxillary antrostomy for the treatment of sinusitis. This has required much better and precise anatomic delineation, which is not provided by plain film radiographs. Overlapping structures on plain film radiographs limit evaluation of the ostiomeatal complex, as well as the individual paranasal sinuses. There is also insufficient detail regarding the osseous framework of the sinonasal cavity. There are a few limited applications for radiographs. They are sometimes obtained in intensive care unit settings when sinusitis is suspected or needs to be excluded and the patient is too sick to come to the radiology department for CT imaging. However, the increasing availability of portable CT units has resulted in progressive decrease in the use of radio-graphs for this purpose.
As FESS has replaced external surgical procedures for treating sinusitis, CT imaging has become necessary to provide the surgeon with precise anatomic information as seen by the endoscopist. Surgery is directed toward removing blockages to mucociliary clearance at the ostiomeatal complex. For the surgeon performing FESS, coronal CT is ideal as it simulates the appearance of the sinonasal cavity from an endoscopic view ( Fig. 3.1A–D ).
Direct coronal thin section imaging (1 to 3 mm) is frequently obtained through the paranasal sinuses.7 Using the newer helical CT scanners, high quality axial reformatted images may be created from these coronal images. Alternatively, direct axial CT imaging may be performed with subsequent creation of coronal reformatted images. The recent literature suggests the use of low-dose CTs to decrease radiation exposure to the lenses.8–13 Many computer software programs allow instant three plane reconstructions (coronal and sagittal reconstructions from axial images). Intravenous contrast material is usually not necessary for imaging sinonasal inflammatory disease. Should CT imaging show findings such as bone destruction or an extension of disease outside the sinonasal cavity concerning for a more aggressive process like a neoplasm or invasive sinusitis, magnetic resonance imaging (MRI) should be obtained with and without intravenous contrast (gadolinium) administration, which is a more sensitive study.7,14,15 If the patient has a contraindication to MRI (i.e., pacemaker) and an enhanced study is indicated, then contrast-enhanced CT is the appropriate alternative study.