Spinal Cord Ependymoma

Introduction

Spinal cord ependymomas are the most common intramedullary tumor in adults and the second most common tumor in children after astrocytomas.

Ependymomas typically present within the fourth decade of life and affect men more often than women. A higher incidence of these tumors occurs in patients with neurofibromatosis type II.

The presenting symptoms are often insidious and nonspecific, with the majority of patients being symptomatic for an average of 3 years before diagnosis. The most common presenting symptoms are back or neck pain (67%), sensory deficits (52%), motor weakness (46%), and bladder or bowel dysfunction (15%).

Ependymomas tend to arise centrally from the cord and to displace the surrounding neural tissue as they grow, resulting in relatively symmetric cord expansion. Mass effect on the spinothalamic tracts is thought to explain the higher proportion of patients who initially present with predominantly sensory symptoms. In general, motor symptoms are present with larger lesions.

The majority of spinal cord ependymomas occur in the cervical cord (32%) and conus medullaris and cauda equina (26.8%), followed by the cervicothoracic cord (16.3%), thoracic cord (16.3%), and thoracolumbar cord (5.1%) ( Fig. 33.1 ). Histologically, the tumors can be divided into several subtypes: papillary, clear cell, tancytic, melanocytic, and myxopapillary. The cellular subtype was removed from the WHO 2016 Classification. The myxopapillary subtype accounts for 13% to 35% of spinal cord ependymomas and typically involves the filum terminale or conus medullaris. Myxopapillary ependymomas are unique in that they can be intradural and extramedullary or be completely extradural, which is thought to be secondary to heterotopic ependymal cell rests or vestigial remnants of the distal neural tube.

Under the World Health Organization (WHO) classification system, myxopapillary tumors are categorized as grade I lesions, whereas most other subtypes are grade II lesions. An anaplastic variant is a rare, more aggressive form of the tumor and is classified as a grade III lesion.

On gross pathology, spinal cord ependymomas are soft tan- or gray-colored masses, which are usually well circumscribed with a discrete plane between the tumor and normal spinal cord. Histologically, the tumors are composed of small monomorphic cells with round or oval nuclei and rare mitoses. True rosettes are diagnostic of ependymomas but are seen less frequently than pseudorosettes, which can be present in both ependymomas and astrocytomas. Tumor cells surrounding a central ependymal canal type of lumen characterize a true rosette, whereas in a pseudorosette, the cells and their fibrillary processes surround a vascular structure ( Fig. 33.2 ).