Marco Losa, MD1, Manfredi C. Carta, MD1, Karl Frontzek, MD1, Niklaus Krayenbühl, MD2, Werner Wichmann, MD3, Elisabeth J. Rushing, MD1
Departments of 1Neuropathology, 2Neurosurgery, 3Neuroradiology, University Hospital of Zurich
A previously healthy 44-year-old female presented to the emergency department with sudden onset, bilateral throbbing headaches of two weeks duration. Three days prior to admission, she experienced several episodes of vomiting. Neurological examination was unremarkable and funduscopic examination showed no evidence of papilledema. CT and MRI of the head revealed a partially cystic, hemorrhagic mass with discrete calcifications in the cerebellomedulllary cistern with compression of the midbrain, of the foramina of Luschka bilaterally and of the foramen of Magendie (Figs 1A, 1B, and 1C). The radiographic differential diagnosis favored either subependymoma or medulloblastoma. The patient was admitted to the neurosurgical unit and underwent a craniotomy with gross total tumor resection. Postoperative recovery was unremarkable.
The resected specimen consisted of multiple grey-white fragments with a slimy consistency and measured 0.9 x 0.7 x 0.6 cm in aggregate. Microscopically, the tumor was well-circumscribed and was organized into compact lobules separated by glial septa and thickened vessels. There was neither evidence of necrosis nor microvascular proliferation. The back-to-back, monomorphic tumor cells harbored clear cytoplasm and contained large clefted nuclei (Fig 1D). Perivascular rosettes were inconspicuous; however, occasional ependymal canals were visible. Immunohistochemical preparations for NHERF1/EBP50 highlighted ring-like microlumina and occasional dot-like and surface structures (Fig 1E), whereas immunostain for EMA was negative. Mitotic figures were not observed and the MIB1 proliferation index was less than 3%. GFAP immunolabeled the glial septa and intermingled reactive astrocytes (Fig 1F). In addition, the IHC panel showed negativity for CK8a, IDH, Synaptophysin, CD10, CKpanB, CD56 and Pax8. Ultrastructural examination revealed numerous intermediate (adherens) junctions as well as microvilli along cell borders (Fig 1G). What is your diagnosis?