The Paranasal Sinuses

Tumors of the nasal cavity and paranasal sinuses are the most challenging lesions to stage. The cosmetic

Figure 3-4. Enhanced axial CT through thoracic inlet. (1) Thickened esophagus related to squamous cancer. (2) Necrotic lymph node in the left tracheo-esophageal groove.

Figure 3-5. Corongal FDG-PET image of torso. (1) Activity related to unsuspected lymph node metastasis. (2) Activity related to glottic squamous cancer.

and functional impact of these tumors is immediately apparent. They rarely present at an early stage. There are few, if any, discriminating imaging features among the various subtypes of tumors in this region. The challenge is to accurately predict the tissue compartments that have been violated without overestimating the boundaries of the tumor. Unlike the neck, this region requires multiplanar imaging. Radiographs and tomographic radiographs no longer have a role in this work-up. The coronal view is the single most important imaging plane (Figure 3-10) for the orbital margin and for the cribriform plate for high naso-ethmoidal lesions.34 Prior to MRI, high resolution CT was used to evaluate these thin osseous barriers. Any distortion of the bone texture raised the suspicion of involvement of the adjacent soft-tissue space. With the advent of MRI, not only is the coronal plane easier to acquire but also the soft tissue within any compartment is directly evaluated,35 not inferred from bony change. MRI is probably the single best baseline-imaging exam for paranasal neoplasms.36 Certain vagaries of physics disturb tissue signal at these bone tissue air interfaces, but this is less problematic when tumor or fluid replaces the air of the sinus cavity. The critical determination of whether or not an orbit should be exenterated demands the application of both modalities (CT and MRI). These complementary modali ties each provide vital but incomplete information. Nowhere else than the skull-base margin is perineural extension more problematic.37 Some very small and very peripheral lesions track deep into the skull base foramina (Figure 3-11) while other larger, more centrally located masses grow in a simple centrifugal manner. The interpretation must be made with a high index of suspicion while the oncologist must have a great deal of confidence in the interpretation. A brain imaging protocol is often applied but is inadequate in its standard form. A standard neck imaging protocol will not provide adequate spatial resolution at the skull base. A well-designed CT or MR imaging protocol with appropriate plane, range and section thickness is necessary for accurate diagnosis. Coronal, axial and sometimes sagittal views track the deep margin to best advantage. The cavernous sinus is the most difficult compartment to confidently pronounce clear of disease with imaging. The vascular channels intermixed with fat are alternately bright and dark on MR imaging and inhomogeneously bright on CT. Tumor extension within the cavernous sinus can actually be identified on non-contrast images (Figure 3-12). Contrast images are necessary, however, to exclude disease

Figure 3-6. Axial T1-weighted MR image through maxilla in a patient with squamous cancer of the soft palate. (1) Neurotropic extension to the left pterygopalatine fossa (PPF). (2) Normal appearance of right PPF. (3) Vidian canals, diseased on the left.

beyond the cavernous sinus, within the basal cisterns (Figure 3-13). Axial views are familiar to most observers and easily outline the deep posterolateral extracranial extension to the masticator and para-

Figure 3-7. A, Enhanced axial CT through lower neck. (1) Left common carotid artery (CCA). (2) Recurrent squamous cancer surrounding the CCA. (3) Normal right CCA. (4) Normal right internal jugular vein. B, Nonselective cervical catheter angiogram. (1) Proximal left CCA. (2) Extrinsic compromise of distal left CCA. (3) Normal caliber proximal left internal carotid artery.

pharyngeal spaces. The lateral retropharyngeal lymph node station can also be cleared in this view. Extra-paranasal extension into the clinically suspected buccal and pre-maxillary spaces is confirmed in this plane as well. Involvement of the palate must be determined to allow appropriate preoperative consultation with the maxillofacial prosthodontist.

Epithelial tumors of the hard palate are best staged by cross-sectional imaging protocols that evaluate deep extension such as a paranasal sinus protocol. The larger lesions are staged for the deep margin that is neither visible nor palpable. Both advanced and apparently early/small lesions are at risk for central neurotropic extension to and through the foramina at the skull base (Figure 3-14). Distant perineural extension is more typical of the minor salivary histologies but can be seen in squamous neoplasms, particularly those with desmoplastic features. MRI has the distinct advantage over CT by revealing abnormal perineural enhancement before evidence of widening of the corresponding fissure or foramen. These images help determine the extent and appropriateness of skull base resection and portal planning for radiation therapy in anticipation of a positive margin.

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