Contributed by Gulisa Turashvili, MD, PhD, Sonal Varma, MD, Sandip SenGupta, MD, John P. Rossiter, MB, BCh, PhD
Department of Pathology and Molecular Medicine, Queen`s University and Kingston General Hospital, Kingston, Ontario, Canada
CLINICAL HISTORY AND RADIOLOGY
A 64 year old man with a history of hyperlipidemia and hypertension presented to neurosurgery clinic with progressive pain in the left lower limb and mid-back. Sagittal (Fig. 1a) and axial (Fig. 1b) T1-weighted MRI of the lumbar spine showed a 1.3 x 1.1 x 1.2 cm homogeneously enhancing, intradural, ovoid and slightly lobulated solid mass at the L4 vertebral level. The lesion occupied the majority of the thecal sac, with resulting splaying and compression of the nerve roots of the cauda equina. The MRI features favored a nerve root meningioma with a differential of a schwannoma, while metastatic disease was thought to be a less likely diagnostic consideration. The patient underwent elective lumbar laminectomy L3 through L5. The lesion was identified by ultrasound before opening the dura. The tumor was found to arise from a lumbosacral nerve root and had a purple-brown appearance. It was elevated out of the cauda equina and the surrounding proximal and distal nerves were separated from the mass before its complete gross removal. The patient recovered uneventfully from the procedure with no neurological deficits and remains recurrence-free one year after the diagnosis.
Macroscopic examination of the resected mass showed a tan, focally hemorrhagic nodule with a rubbery consistency, measuring 1.3 x 1.3 x 1.1 cm in greatest dimensions. Microscopic evaluation of hematoxylin-phloxine-saffron (HPS) stained sections showed a well circumscribed nodular tumor mass, comprised of several relatively sharply circumscribed, moderately cellular and highly vascular lobular units and surrounded by dense collagenous tissue (Fig. 1c). In a few locations the cellular elements of the tumor had a more disorganized arrangement and irregular interface with the surrounding collagenous tissue. At low power the lobular elements were noted to contain frequent thin-walled blood vessels, some of which had a "staghorn" configuration (Fig. 1d). At medium to high power an additional dense network of smaller diameter vessels, including capillaries, was seen (Figs. 1e, 1f). Many of the vessels were lined by a single layer of relatively plump endothelial cells. Dispersed within this vascular network were stromal cells with moderately pleomorphic oval to elongated medium-sized nuclei, frequently containing small to intermediate sized nucleoli (Fig. 1f). Approximately 3 mitoses per 10 high power fields and scattered small foci of erythropoiesis (Fig. 1g) were seen. There was no evidence of tumor necrosis. There were thin bundles of peripheral nerve in several locations towards the periphery of the mass, but also curving around lobular elements deep within the mass. Reticulin staining highlighted the vascular network and a dense network of reticulin fibers subdividing small groups or individual tumor cells from each other (Fig. 1h).
Ki-67 immunostaining (Fig. 1i) showed an approximately 30% proliferative index by visual assessment and 34% by ImageJ automated scoring. The vascular and cellular stromal elements showed strongly positive immunostaining for vimentin, CD34 (Fig. 1j), CD99 (Fig. 1k) and BCL2 (Fig. 1l). CD31 immunostaining highlighted the extensive vascular network and also showed a predominantly membranous pattern of staining in a high proportion the stromal cells (Fig. 1m). These cells also exhibited strongly positive factor VIII related antigen immunolabeling (Fig. 1n). Many perivascular and stromal cells showed strong immunostaining for smooth muscle actin (SMA) (Fig. 1o) and weak to moderate staining for muscle specific actin (MSA). With the exception of some of the larger vascular profiles, desmin immunostaining was negative. The tumor cells were negative for S-100, EMA, GFAP, NSE, synaptophysin, chromogranin, inhibin and pan-cytokeratin. Peripheral nerve tissue, likely derived from a spinal nerve root, was highlighted by neurofilament (Fig. 1p) and NSE immunostaining. What is your diagnosis?