Trigeminal perineural spread of head and neck tumors.

Perineural tumor spread (PNS) of head and neck malignancies is a well-known form of metastatic disease in which a lesion can migrate away from the primary site along the endoneurium or perineurium. MR imaging is considered the primary method for evaluating patients with symptoms related to the trigeminal nerve in most clinical settings. Both CT and MR imaging can detect perineural spread, but MRI is the modality of choice because of its capability to detect direct signs (nerve enlargement and enhancement) and indirect signs (neuropathic muscular atrophy, obliteration of fat planes). In addition, MRI is more sensitive because of its superior soft-tissue contrast, its multiplanar capability and decreased artifacts from dental hardware. Fat suppression images after contrast injection are mandatory to better detect nerve enhancement. CT is useful in detecting foraminal enlargement or more destructive bone patterns. Nerve function can be perserved until later in the course of the disease: patients with perineural spread demonstrated at radiologic or pathologic examination may have normal or nonspecific nerve function at clinical examination (patients are misdiagnosed with Bell's palsy or trigeminal neuralgia). Hence MRI assessment of perineural tumor location and extension is important.