Contributed by Melanie H. Hakar, DO1, Benjamin P. Liu, MD2, Craig M. Horbinski, MD3
Departments of 1Pathology, 2Radiology and 3Neuropathology, Northwestern University, Chicago, IL.
A 24-year-old man presented with new onset of generalized tonic clonic seizure. Prior to admission, the patient reported an enlarging painless scalp mass for the previous two months, without having sought medical attention. MRI of the brain revealed a 7.7 cm heterogeneously enhancing mass with a large subgaleal extracalvarial/extracranial component and a smaller intracranial enhancing component along the dura on T1 weighted images (Figures 1 and 2). Noncontrast CT showed abnormal calvarial sclerosis concerning for osseous involvement (Figure 3). The patient underwent biparietal craniectomy and sub-total resection of the mass with residual tumor involving the superior sagittal sinus. The cranium, dura, and subgaleal mass were submitted for evaluation.
Histologic examination revealed a dural-based tumor growing into the overlying skull table, composed of spindle cells arranged in large nodules and sheets with interdigitating thin collagen bundles (Figure 4). The tumor cells featured variably open and clumpy chromatin with brisk mitotic activity (Figure 4). There was abundant admixed lymphocytic inflammation and scattered macrophages with eosinophils present. No whorls, psammoma bodies, herringbone pattern, or intranuclear cytoplasmic pseudoinclusions were present. CD20 (Figure 5) and CD45 (Figure 6) showed strong, diffuse positivity. The tumor cells were positive for Bcl-6 (Figure 7) and CD10 (Figure 8). Immunostains for CD3, Bcl-2, CD34, EMA, S100, SMA, desmin, CD56, CD1a, and ALK1 were negative in tumor cells. Ki-67 proliferation index was 70%. Mitotic count was 10 per 10 HPF. What is your diagnosis?