Department of Pathology, University of Oklahoma Health Sciences Center

NeuroSim Case #03: 10 year-old girl with a hemispheric mass and hydrocephalus

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What are your differential diagnoses?

    The pathologic features in this case clearly point to a papillary tumor arising in the cerebral hemisphere. The first issue of concern is whether this is a primary or secondary tumor. Metastatic papillary carcinoma in a 10 year-old girl is very unusual, particularly without a confirmed history of papillary carcinoma in locations outside the brain. For all practical purpose, this tumor should be viewed as a primary tumor.

    The first differential diagnosis to consider is choroid plexus papilloma. Most choroid plexus papillomas occur as exophytic mass that protrude into the ventricle. The imaging results of a hemispheric mass that bulged into the ventricles is not the most common picture of a choroid plexus papilloma. The degree of pleomorphism and the age of this patient is not very compatible with choroid plexus carcinoma; most of them are seen in infants. The fact that the tumor cells have a palisading arrangement, a nuclear free mantle around blood vessels, and the absence of basement membrane suggest a diagnosis of papillary ependymoma. The age group and the location of this tumor is compatible with a papillary ependymoma.

 FSim03-HEx60.gif (37987 bytes) Click thumbnail to see picture again.

Intraoperative consultation: Tissue of this tumor was submitted for a frozen section diagnosis. The squash preparation of the tumor gave a "glial pattern"  featured by glial cells with very elongated thin cytoplasmic processes. The frozen section had histopathologic features of a papillary neoplasm as the picture being shown here. The frozen section diagnosis was  "papillary neoplasm consistent with papillary ependymoma". Retrospectively, the mismatch between a "glial pattern" in the squash preparation with a "papillary pattern" in the frozen section was an important hint to the correct diagnosis.

Patterns of ependymoma: Ependymoma is a notorious imposter. When they are cellular, they may suggest small blue cell tumors such as medulloblastoma; when they are relatively less cellular, they may closely mimic an astrocytoma or pilocytic astrocytoma. The papillary variant can mimic choroid plexus papilloma, metastatic papillary carcinoma, and other papillary tumors. The clear cell ependymoma can mimic oligodendroglioma, central neurocytoma, and metastatic clear cell carcinomas. Recognition of ependymoma in intraoperative consultation is very important because gross total resection remains a very important favorable parameter in the treatment of ependymal tumors. 

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