Perineural spread of skin carcinoma to the base of the skull: detection with FDG PET and CT fusion.

A 66-year-old man underwent 2-F-18 fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) for evaluation of new-onset left jaw pain approximately 5 years after the diagnosis of squamous cell carcinoma of the lower lip. His initial surgery included a Mohs excision. As a result of tumor invasion, he subsequently underwent resection of his left lower lip, chin, and cheek as well as segmental mandibulectomy. Reconstruction included a Synthes plate and platysmal mucocutaneous flap. One week before the FDG PET scan, he underwent contrast computed tomography (CT) of the neck, which revealed enhancement of the left medial pterygoid muscle and widening of the mandibular foramen of the ipsilateral mandible. PET showed FDG hypermetabolism in the floor of the mouth near the site of the mandibular resection. PET also showed hypermetabolism tracking in the lateral face to the skull base. Fusion of PET with CT demonstrated this hypermetabolism to follow the course of the mandibular division of the trigeminal nerve (V 3 ). Exploratory surgery and accompanying histopathology confirmed the suspected recurrence of squamous cell carcinoma within pterygoid musculature, as well as the imaging diagnosis of perineural spread along V 3 . A search of the medical literature reveals no prior report of large perineural spread diagnosed with FDG PET using PET/CT fusion.