Contributed by Siobhan O’Connor, MD and Kate McFadden, MD
The patient is a 43 year old morbidly obese man with chronic back pain, progressively increasing in severity and unresponsive to medical management. A magnetic resonance scan performed at an outside institution revealed a spinal mass at the L4-L5 vertebral level. The patient was referred to UPMC and underwent a laminectomy of the L4 and L5 vertebrae, and upper portion of the sacrum. Intraoperatively, the lesion was described as a "huge sausage-shaped mass approximately 3.5 cm to 4 cm long with all of the nerve roots peripherally draped over the mass." The mass was arising from the filum terminale and the surface appeared to be well-encapsulated. Complete resection of the tumor was achieved. The post-operative diagnosis was recorded as "intradural spinal cord tumor (ependymoma) L4, L5, S1."
The specimen consisted of an oblong portion of firm tissue measuring 4.0 x 2.0 x 1.8 cm, tan/pink and hemorrhagic with a vaguely lobulated, irregular external surface. On cut section, the surface was smooth, solid, tan/pink and hemorrhagic (Images 1 and 2).
At low power, lighter pink areas and darker blue areas are apparent (Image 3). At higher power, the blue areas consist of uniform round to oval cells arranged in nests and lobules separated by fibrovascular septae (Images 4 and 5). The centrally-located nuclei demonstrate stippled chromatin (Image 6). Some fields show extensive hyalinization (Image 7). Higher power examination of the pink areas reveals large ganglion cells with abundant eosinophilic cytoplasm and eccentric vesicular nuclei (Images 8, 9, and 10). Each nucleus demonstrates a single prominent nucleolus. The ganglion cells are arranged in small clusters and scattered singly. In addition, areas composed of both the small blue cells and the ganglion cells are present, with some cells showing features transitional between the two (Image 11).
Immunohistochemical stains for neuron specific enolase (Images 12 and 13) and synaptophysin (Images 14 and 15) are strongly positive in both types of cells. Neurofilament is positive in the ganglion cells and some small cells (Image 16). Glial fibrillary acidic protein (Image 17) and pankeratin (Image 18) immunostains are negative. Immunohistochemical stain for S100 highlights spindle cells surrounding the small blue cells (Image 19), which were not readily apparent with H & E staining. Proliferation index, as determined by Ki-67 (MIB-1) expression, is approximately 1 to 3% (Image 20).