Contributed by Celina Montemayor Garcia, MD, PhD1, Carolina Sandoval Garcia, MD2; Taryn Bragg, MD2; Neha J Patel, MD3, and Shahriar Salamat, MD, PhD1
Departments of 1Pathology and Laboratory Medicine, 2Neurological Surgery, and 3Pediatrics, University of Wisconsin-Madison, Madison, WI, USA
CLINICAL HISTORY AND IMAGING
An 11 year old boy presents with a 1-year history of sharp sacral pain radiating to the buttock and legs, left greater than right. His past medical history is unremarkable. No focal neurologic deficits are noted on examination. However, he has a pronounced antalgic gait with a crouched, widened stance. MRI of the lumbosacral spine (Figure 1) respectively reveals a sagittal T1 weighted image with a slightly hypointense lesion extending from S1 to S3. The lesion is hyperintense on T2, and in the T1 weighted sagittal image the mass exhibits homogeneous contrast enhancement after Gadolinium injection. The axial imaging post-contrast redemonstrates the lesion within the spinal canal. The inferior aspect is located asymmetric to the left and on lower cuts there is likely extension along an exiting nerve root due to thickening and enhancement of the left S3 nerve root (not shown). No other lesions are identified within the cervical, thoracic, or lumbar spine.
The patient underwent S1 and S2 laminectomies for tumor resection with use of intraoperative microscope and intraoperative monitoring (SSEP, EMG, and bladder sphincter monitoring). Intraoperatively, the mass was dumbbell-shaped with a small intradural and a large extradural component. The extradural portion had a well-defined capsule. Once de-vascularized, the extradural component was amputated from the intradural segment. It was easily separated from the bone. The calcified intradural component was easily separated from the dura. Several rootlets appeared to terminate within the mass and were sacrificed to allow for complete resection.
GROSS AND MICROSCOPIC PATHOLOGY
The surgical specimen consisted of 13 tan-brown rubbery fragments of tissue ranging from 0.2x0.1x0.1cm to 1.5 x 1.5 x 1.0 cm.
The H&E stained sections reveal an epithelioid neoplasm mostly surrounded by dura but also infiltrating the adjacent soft tissue and superficially one accompanying bony fragment. The tumor cells contain moderate cytoplasm, enlarged nuclei and enlarged magenta nucleoli (Figure 2). Atypical mitotic figures are frequently seen ranging between 4-5 per 10 high-power field. There is no specific organization in the arrangement of the tumor cells. Although a somewhat acinar pattern is hinted, the reticulin stain is completely negative. PAS highlights the basal lamina surrounding these cells (Figure 3).
Various antibodies employed reveal diffuse nuclear positivity with S100 antibody in the tumor cells (Figure 4) and diffuse cytoplasmic positivity with melanoma cocktail antibody (not shown). Neurofilament, GFAP and synaptophysin identify the adjacent nerve fibers and benign ganglion cells (Figure 5). The tumor cells are negative with desmin, myogenin, CD68, chromogranin and the cytokeratin cocktail antibodies.
Electron microscopy reveals epithelioid cells with enlarged nuclei, moderate cytoplasm that includes the usual complement of organelles such as mitochondria and rough endoplasmic reticulum (Figure 6). In addition, many cells are noted to contain pre-melanosomes and mature melanosomes (Figure 7). Redundant cytoplasmic processes are present. Often the neoplastic cells are surrounded by basal lamina, and some cells reveal simple intercellular junctional complexes (Figure 8). No other specific specialization is noted at electron microscopic levels. What is the diagnosis?