INTRA DURAL EXTRA MEDULLARY ( IDEM ) SPINAL TUMORS

Intradural extramedullay means lesions inside the dura but outside the spinal cord. It is commonly mentioned as IDEM lesions. Common IDEM tumors are Schwannoma, neurofibroma and meningioma.They present with features of nerve root and cord compression.So the pain and weakness are the common symptoms. MRI of the spine with contrast is the investigation of choice. Dumbbell shaped lesion traversing the neural foramen suggests a nerve sheath tumor. Follwing neurosurgeons made a significant contribution in the understanding of these tumors: W.Gowers, Victor Horsley reported surgical removal of such tumor in 1888, Elsberg published a paper in 1925 and Harvey Cushing in 1938. Most of these tumors can be excised & Gross total macroscopic resection makes them amenable to surgical cure. Nerve sheath tumors are Schwannomas and neurofibromas. Schwannomas arise from the Schwann cells and according to their bundling pattern are grouped as Antoni A or Antoni B types, They constitute about 85 percent of nerve sheath tumors. About 15 percent of the nerve sheath tumors are Neurofibromas which consist of fibrous cell bundles admixed with nerve fibres. In common conversationboth Schwannomas and neurofibroma are commonly referred as neurofibromas. Neurofibromas are mostly benign tumors and are capsulated. They are mainly intradural arising from the nerve route and often extend through the nerve route through the spinal neural foramen giving it dumbbell shape. Second most common IDEM tumor is meningioma which arises from the arachnoidal cap cells. Spinal meningiomas fave the broad dural base and show homogeneous contrast enhancement on MRI contrast. Psammomatous type of meningioma is more common in spine. Other uncommon type of IDEM lesions are arachnoid cyst, epidermoid, dermoid. The recommended operation for the IDEM is midline posterior approach in prone position. After laminectomy dura is opened in the midline and tumor can be appproache from the psterion approach.