Contributed by Caterina Giannini, MD1, Kenneth C. Spengel, DO, FCAP2, Patrice C. Abell Aleff3, Michael Rivera, MD1, John T. Wald, MD4
Departments of 1Anatomic Pathology, Pathology and Laboratory Medicine; 3Electron Microscopy, Biochemistry and Molecular Biology; 4Neuroradiology,
Diagnostic Radiology, Mayo Clinic, Rochester, MN; 2MAWD Pathology - Liberty Hospital, North Kansas City, MO
A previously healthy 24-year-old white female patient presented to the emergency room with back pain. The pain, which had been ongoing for the past four days, started in her lower back and wrapped around her left leg down below the knee. It was constant and worsened with any activity. Bladder and bowel function were unaffected. The patient denied any prior history of back pain or back injury. She did not have any history of trauma. On physical examination, no focal neurological findings were noted.
An MRI was obtained, which demonstrated a prominent lesion within the spinal canal beginning at L1-L2 and extending to the L3-L4 disc level (Figure 1). The lesion appeared to be intradural and extramedullary in location, below the level of the conus, and measuring 7.3 (vertical) x 1.7 (AP) x 2 cm (transverse). The mass was slightly heterogeneous on T2-weighted images and isointense on T2-weighted sequences compared to the cord. Following contrast administration, the lesion demonstrated relative homogeneous enhancement on fat-saturated T1-weighted sequences. It did not extend into the foramen. There did not appear to be any evidence of bone destruction of the vertebral bodies. The main differential diagnosis included myxopapillary ependymoma, paraganglioma, and spinal schwannoma.
L2-L3 laminectomies were performed. Opening of the dura revealed a dark and hemorrhagic mass with evidence of recent subarachnoid hemorrhage inferiorly. A clear plane was observed around the tumor inferiorly. Nerve roots were displaced anteriorly and laterally while the proximal end was difficult to see. The distal two-thirds of the tumor were easily removed while the proximal end of the tumor appeared to intimately involve several large nerve roots and the tip of the conus medullaris. All visible tumor was removed with only microscopic residual near the conus.
Multiple irregular tan fragments of soft tissue measuring in aggregate 5 x 5 x 1.8 cm were submitted for pathological examination. The formalin-fixed biopsy samples were processed with standard technique and stained routinely with H&E as well as with antibodies against cytokeratin (CAM5.2), EMA, progesterone receptor, GFAP, S-100 protein, synaptophysin, chromogranin, inhibin and Melan-A. The tumor was composed of monomorphous polygonal cells without a distinct growth pattern (Figure 2). Cytologically, the tumor cells contained round, relatively uniform nuclei with small central nucleoli. While most of the cells contained granular slightly eosinophilic cytoplasm (Figure 3), some cells showed a fine peripheral clear vacuolation, at times, confluent throughout the cytoplasm imparting a pale appearance (Figure 4). Focal intracellular yellowish pigment was noted in some cells (Figure 3). Proliferative activity was low with only rare mitotic figures identified (Figure 5). No invasive features or tumor necrosis were identified. Immunohistochemically, all cells showed strong positivity for inhibin (Figure 6) and Melan-A (Figure 7), while weak to moderate reactivity was seen with synaptophysin in over 50% of tumor cells (Figure 8). Immunostains for S100 protein, CAM5.2, EMA, progesterone receptor (PR), chromogranin, and TTF-1 were negative. Ki-67 labeling index was low (< 2%).
Formalin-fixed paraffin-embedded tumor was reprocessed for ultrastructural studies. Clusters of polygonal cells with abundant cytoplasm and regularly shaped nuclei as well as dispersed chromatin were present. The cytoplasm contained abundant smooth endoplasmic reticulum (Figure 9) and mitochondria with tubulovesicular cristae (Figure 10). Occasional dense core secretory granules were present (Figure 11). Intercellular junctions were scant and poorly formed. What is your diagnosis?