Specific Imaging Findings

Perineural tumor spread (PNS) typically occurs with head and neck cancers and may be seen on CT; however, MRI is far more sensitive, especially with dedicated high-resolution images. Maxillary (V2) and mandibular (V3) divisions of the trigeminal nerve, along with the facial nerve, are most commonly involved. Typical findings are obliteration of the fat planes at skull base foramina, contrast enhancement and/or enlargement of a nerve. Replacement of the normal fluid in the Meckel's cave and cavernous sinus enlargement are frequent additional findings. Muscle denervation atrophy is an indirect sign of (V3) PNS with T2 hyperintensity and enhancement in the early, and volume loss and T1 hyperintensity in the late phase. CT may show obliteration of the fat planes, primarily the pterygopalatine fossa, and expansion of the skull base foramina. Detection of a suspicious cavernous sinus mass should prompt a search for PNS and a head and neck malignancy. False positive enhancement occurs with other conditions that disrupt the blood–nerve barrier, primarily inflammation and edema, which are commonly present following surgery and radiotherapy. In addition to inflammatory and infectious processes, such as sarcoidosis, PNS rarely occurs with intracranial neoplasms, such as meningioma.

Pertinent Clinical Information

PNS is a common and a potentially devastating complication of head and neck malignancies; it may be the only evidence of the disease. As it is initially clinically silent in about a half of patients, imaging plays a crucial role in its detection and delineation. Undiagnosed, the cancer slowly progresses and eventually results in symptoms, usually facial weakness or numbness, sometimes 10 or more years after the initial cancer treatment. Facial pain and/ or paresthesias may also occur. Imaging evidence of PNS worsens prognosis; however, surgery followed by radiation results in a high cure rate (approximately 80%). In symptomatic patients aggressive treatment results in a cure rate of less than 50%.