An Infratentorial Tumor in a 44‐Year‐Old Female Patient

Clinical History

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. 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.

Microscopic Pathology

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 of microvascular proliferation. The back‐to‐back, monomorphic tumor cells harbored clear cytoplasm and contained large clefted nuclei (Figure 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 (Figure 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 (Figure 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 (Figure 1G). What is your diagnosis?

Figure 1.

Diagnosis

Clear cell ependymoma (CCE).

Discussion

Clear cell along with tanycytic and papillary ependymoma represent three morphological ependymoma variants without prognostic significance 1, 2. In limited biopsies, CCE may be mistaken for oligodendroglioma. Unlike oligodendroglioma, CCE is well‐circumscribed, lacks the 1p19q co‐deletion and is IDH‐wildtype. In contrast to the current case, most cases are found in children, especially in the supratentorial compartment. In the past, electron microscopy was a helpful tool for distinguishing morphologically ambiguous cases 4. The ultrastructural features of ependymal tumors comprise microlumina with microvilli and cilia as well as runs of intermediate junctions. IHC with EMA, which immunostains surface structures and dot‐like microlumina has largely obviated the need for EM. NHERF/EBP50, an organizer of polarity structures, has been recently reported to stain 35% of ependymomas that lacked reactivity for EMA 3. This case underscores the value of this diagnostic marker.