Intradural Extramedullary Nonconus Nonfilum Spinal Ependymomas: Report of a Rare Variant and Newer Insights into Their Histogenesis with Proposal of a Classification Scheme and a Management Algorithm Based on a Review of Literature

Background Ependymomas are common intramedullary spinal tumors but there are scattered reports of this tumor presenting with exophytic growth patterns masquerading as intradural extramedullary (IDEM) tumors. Such IDEM ependymomas are seldom suspected preoperatively and it is only during surgery that their existence is revealed. Little is known of such rare growth patterns of an otherwise common intramedullary spinal cord tumor, their characteristics, and their management considerations. Methods We present a case of an exophytic dorsal ependymoma with a stalk like attachment to the spinal cord and the surgical management in a 24-year old woman. An extensive literature search was carried out on all prominent databases to find out similar cases reported earlier. We excluded filum/conus ependymoma, purely extradural spinal ependymoma as well as the extraspinal ependymomas. Details of each case reported before were obtained and tabulated. Results IDEM ependymomas have been reported in 54 patients so far, including the present case. Four patterns of growth emerged from the literature review: intramedullary ependymoma with exophytic component (group I, n = 9), exophytic IDEM ependymoma without intramedullary component (group II, n = 6), IDEM ependymoma arising from nerve roots (group III, n = 7), and pure IDEM ependymoma (group IV, n = 32). Except in group I, IDEM ependymoma affects females more frequently, without any specific age predilection. Thoracic spinal cord/canal is the most common location across all groups. Multifocal disease, craniospinal dissemination, and recurrences tend to be maximum in group IV. Conclusions IDEM ependymomas are more common in thoracic segment of the cord and broadly divisible into 4 subgroups. We suggest a subpial origin of group II IDEM ependymomas. We also advocate proliferation index estimation in grade II ependymomas to enable formulation of an optimal management plan.