الفهرس 
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Abstract
The course of the trigeminal nerve is divided into five segments: brainstem, cisternal, Meckels’s cave and cavernous sinus, skull base and extracranial segments.
The purpose of this study was to determine the efficacy of Magnetic Resonance Imaging in assessment of different lesions involving the course of the trigeminal nerve.
Brain stem lesions include demyelinating disease, neoplasm, vascular lesions and infection. It should always be kept in mind that any pathologic processes involving the upper spinal cord may lead to trigeminal neuropathy by affecting the dorsally located trigeminal tracts.
The lesions affecting the cisternal part of the trigeminal nerve include vascular causes as neurovascular compression is now accepted as being the commonest cause of trigeminal neuralgia, and neoplastic causes as meningioma, lipoma, schwannoma and metastatic disease or inflammatory.
For Meckel’s cave and cavernous sinus, most pathologic processes affecting the cisternal segment may also affect the cavernous segment.
Trigeminal neuropathy arising from the Meckel’s cave and cavernous sinus was due to neoplasms like schwannoma, parasellar meningiomas, clival chordoma, osteocartilaginous tumors, invasive pituitary adenomas, plasmacytoma, lymphoma and metastatic disease as well as central skull base lesion and aggressive bacterial or fungal infections and inflammatory non-infectious conditions like sarcoidois, Wegener’s granulomatosis and periarteritis nodosa also vascular lesions like carotid aneurysms and perineural spread.
Peripheral segment can be affected by perineural spread of head and neck malignancies, Primary tumors of the peripheral branches, trauma and neural compression at the bony foramina due to fibro-osseous conditions such as fibrous dysplasia and Paget’s disease.
Magnetic Resonance Imaging is valuable in detection of all lesions and demonstration of the full extent of the pathologic processes.
The contrast enhanced images are helpful in differentiating cerebellopontine angle masses from epidermoid cysts which typically shows no enhancement. Also contrast injection is essential for diagnosis of metastatic lesions as well as the leptomeningeal extent in the case of neurosarcoidosis.
We propose a scheme for using MRI scan in diagnosis of trigeminal neuropathy. This scheme will provide a standardized framework for the differential diagnosis of trigeminal nerve disorders by using different MRI sequences.
MRI scan protocol:
Collectively, we can conclude that MR imaging is the modality of choice for delineation of the full anatomic course of the trigeminal nerve. The lack of accurate clinical localization of the lesion necessitates comprehensive imaging in patients with trigeminal neuropathy that should include imaging of the whole brain together with the skull base. The enhanced images are of great value in the differential diagnosis of most of the lesions.