eRadiograph Volume 7: Imaging of Oral Cavity | Page 197

neurofibromas. Schwanomas usually arise from the 5th trigeminal nerve. This may occur as a isolated or part of NF2. Schwannomas are typically of T2 signal hyperintensity and enhance homogeneously with I.V contrast. As schwannomas grow larger they may demonstrate areas of cystic degeneration, thus may demonstrate heterogeneous enhancement. Plexiform neurofibroma is a common manifestation of NF 1. These represent multiple fascicles of a nerve in the form of a network. On T2WI these appear as a target - with a hypo intensity in the centre and peripheral hyperintensity. They have a 7-13% life time risk of turning malignant. Neoplasms of the mandible may present in the masticator space as evidenced by lytic destruction of the mandible with or without associated soft tissue or as a permeative erosion(moth eaten appearance). These may be due to osteogenic sarcoma, Ewings sarcoma, chondrosarcoma, lymphoma or metastases. Other pathologic processes which may resemble mandibular neoplasms are osteomyelitis or osteonecrosis. Osteomyelitis usually has associated soft tissue abscess or associated sequestrum. Osteonecrosis occurs due to radiation and presents as progressive sclerosis of mandible. Endothelial Malformations Endothelial malformations are divided into 2 groups based on endothelial turnover, normal endothelial turnover are classified as vascular malformation and those with a high cell turnover as vascular tumors. Vascular malformation grow in size proportion to body size as there is normal endothelial turnover, vascular tumors grow disproportionate to body size as they have a higher endothelial cell turn over. Another form of classification of vascular malformations is to classify them into high flow and low flow lesions. Malformations with arterial components are considered high flow lesions. Those without arterial components are considered low flow lesions. 197 Masticator Space MALIGNANCY FROM NEIGHBOURING SPACES The nasopharynx is separated from the masticator space just below the skull base by the thin parapharyngeal space. Nasopharyngeal carcinomas can extend across to the masticator space after breaching the pharyngiobasilar fascia. Involvement of the masticator space implies potential perineural spread via the mandibular nerve to the foramen of ovale. MRI is the modality of choice to evaluate for perineural spread. Spread commonly occurs centripetally, extending intracranially from the primary tumor. Imaging findings include enhancement and/ or enlargement of the involved nerve, foraminal enlargement or erosion, loss of normal fat at the extracranial openings of the neural foramina and denervation atrophy of the involved muscle.