Perineural invasion of squamous cell carcinoma of the lip with occult involvement of the infra-orbital nerve detected by PET-CT and treated with MRI-based IMRT: a case report.

A 51 year old male with a history of right facial numbness developed progressive upper lip swelling for one year, but an MRI of the head was unremarkable. A wide local excision of the upper lip was performed and pathology revealed a 1.7 cm mass, poorly differentiated squamous cell carcinoma with perineural invasion. Surgical margins were free of tumor. Two months postoperatively, a hybrid PET-CT of the whole body was performed due to the persistent right facial numbness. The CT portion identified an equivocal lesion at the base of the right orbit correlating to the right infraorbital nerve. However, the PET-CT image revealed avid uptake in this location suggesting perineural invasion which was confirmed with biopsy of the right infraorbital nerve demonstrating carcinoma. Subsequently, the patient was treated with Intensity Modulation Radiation Therapy (IMRT) using MRI fusion for proper delineation of the right infraorbital nerve to its origin in the base of skull. This case exemplifies the superiority of hybrid PET-CT over CT or MRI alone in head and neck imaging which can lead to significant impact on management for patients with head and neck cancer.