Imaging

Imaging studies are an essential component in the diagnosis, staging, and follow-up of sinonasal malignancies. Computed tomography (CT) scans give a good initial overview of the tumor's location with excellent bone detail (Figure 11-3). Because the paranasal sinuses and nasal cavity are mucosal-lined bony chambers, CT is helpful in determining whether a tumor remains confined within these natural boundaries or has eroded through the surrounding bone. CT provides details of the extent of local bone invasion, and is particularly useful in assessing the lamina papyracea, orbital floor, fovea eth-moidalis, cribriform plate, pterygoid plates, hard palate, and skull base.9 The signal of the tumor is of soft-tissue density and may be either homogeneous or heterogeneous if focal areas of necrosis or hemorrhage exist. Intravenous contrast causes tumor enhancement, although inflamed mucosa may enhance similarly. Radiodensities within a mass may

Figure 11-3. A and B, Axial and coronal CT scans accurately demonstrate the extent of bone destruction from a left-sided maxillary sinus tumor.

have particular characteristics suggestive of tumoral mineral deposition, residual destroyed bone from tumor invasion, or chronic fungal sinusitis.10

In comparison to CT, magnetic resonance imaging (MRI) allows a better distinction of tumor from adjacent soft tissue (Figure 11-4). MRI is particularly useful for determining invasion of the orbital contents, dura, brain, and cavernous sinus.9 MRI may also be better for assessing carotid artery invasion, and newer techniques such as MR angiography per mit intraluminal carotid assessment without the associated risks of conventional angiography. Inflamed mucosa, retained secretions, and benign polyps generally have a high signal on T2-weighted images. In contrast, tumors which are more cellular, with less

Figure 11-4. A and B, A saggital and coronal MRI scan with gadolinium contrast shows a large ethmoid malignancy completely filling both ethmoid sinuses and the right nasal cavity, with extensive intracranial extension.

Figure 11-4. A and B, A saggital and coronal MRI scan with gadolinium contrast shows a large ethmoid malignancy completely filling both ethmoid sinuses and the right nasal cavity, with extensive intracranial extension.

amounts of extracellular water, exhibit an intermediate signal on T2-weighted images.11 The exceptions to this characteristic are some schwannomas, minor salivary gland tumors, and a subgroup of inverted papillomas. Benign tumors extending intracranially tend to be more heterogeneous on MRI than malignant tumors.12 With gadolinium injection on T1-weighted images, tumors enhance less intensely than inflamed mucosa, while secretions do not enhance. Mucoceles may be distinguished from tumors by peripheral enhancement.13 CT and MRI therefore complement one another in the assessment of sinonasal tumors. CT provides excellent bone detail, while MRI offers better soft tissue imaging.

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