Effectiveness of 18 F-FDG PET/CT in detecting cranial nerve pathology

Learning Objectives 1. Know the PET/CT manifestations of common lesions affecting the cranial nerves. 2. Recognize the secondary signs of cranial nerve disease such as muscle atrophy. 3. Become familiar with perineural spread of malignancy along the cranial nerves.

Conventional CT and MRI have been the imaging modalities of choice for detection and characterization of benign and malignant neoplasms affecting the cranial nerves including schwannomas, neurofibromas, metastases, lymphoma and adjacent meningiomas. Positron Emission Tomography / Computed Tomography (PET/CT) with 2-[fluorine 18]fluoro-2-deoxy-d-glucose (18F-FDG) can also be utilized to detect cranial nerve pathology, however, it is not commonly used due to its low spatial resolution as well as the unfamiliarity of PET/CT readers with the PET/CT manifestations of cranial nerve disease. Perineural spread of malignancy which represents rare contiguous metastatic extension of tumor along a cranial nerve and portends a poor prognosis is unique to head and neck tumors and may also be identified on PET/CT. We will demonstrate the effectiveness of 18F-FDG PET/CT in detecting neoplastic lesions affecting cranial nerves which can manifest as foci of increased or decreased 18F-FDG avidity along the expected cranial nerve pathway. We will also illustrate secondary signs of cranial nerve involvement including benign and aggressive osseous changes in the affected skull base foramina as well as denervation atrophy of the muscles supplied by the diseased cranial nerve.