Nasopharynx: clinical, pathologic, and radiologic assessment.

NPC represents 0.2% of malignant disease in the white population but is more common in southern China, among Chinese in East Asia and the United [figure: see text] States, and in North Africa, including Saudi Arabia. NPC in these ethnic groups tends to manifest at a younger age. Undifferentiated carcinoma is the most common histopathologic type and is associated with EBV. The tumor is optimally assessed with CT and MR imaging for staging; PET scanning provides optimal assessment of recurrent tumor or small lymph node metastases. The primary tumor in the nasopharynx may be small and infiltrating, causing no or only a small mass effect in the nasopharynx. In these cases, obliteration of fat planes and loss of muscle boundaries are important diagnostic findings, which are best evaluated with MR imaging including, Gd-DTPA with fat suppression. The size of the NPC varies from 1 to 2 cm to large tumors that extend to the oropharynx, PPS, nasal cavities, paranasal sinuses, and orbits. Skull base erosion is independent of the size of the nasopharyngeal tumor and ranges from slight erosion to extensive destruction. A concomitant finding is intracranial invasion, predominantly to the basal cisterns and cavernous sinuses associated with cranial nerve palsies. Intracranial invasion should be assessed with contrast MR imaging. Lymph node metastases in the neck are present in 90% of cases and are bilateral in 50% of cases. In a small percentage of cases, extension of lymph node metastases to the mediastinum and hilar areas are encountered. Distant metastases involve the lungs, skeleton, and liver, and occasionally the choroid. They are usually present at the initial presentation [figure: see text] and increase in frequency in advanced disease and in recurrent tumors. In addition, the metastatic lymph nodes in the neck reveal no specific imaging features that would allow differentiation from other lymph node metastases. They may be discrete, often multiple, and large and bulky displaying a variable degree of necrosis and enhancement following introduction of contrast material. Local recurrence manifests commonly within the first 2 to 3 years posttherapy and is optimally evaluated by MR imaging and PET scanning.