Posterior fossa metastasis
Confusion and ataxia.
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Posterior fossa mass that primarily lies in the midline of the superior cerebellum, separate from the fourth ventricle. It has heterogeneous T1 and T2 signal, and on post contrast imaging there is heterogeneous enhancement with central low signal. There is a broad dural attachment to the inferior surface of the left tentorium cerebelli, where it extends around the anterior edge and lines the superior surface.
Few foci of blooming artifact, which is likely blood product. Peripheral diffusion restriction. Surrounding in FLAIR signal in the cerebellum, tectal plate and medial left occipital lobe most in keeping with vasogenic edema. There is partial effacement of the fourth ventricle and complete effacement of the inferior cerebral aqueduct with resultant obstructive hydrocephalus.
The patient proceeded to craniotomy and resection.
MICROSCOPIC DESCRIPTION: Paraffin sections show fragments of a densely hypercellular tumour. This is composed of cells with pleomorphic round and oval vesicular nuclei, many with conspicuous nucleoli and a variable amount of pale cytoplasm. These are arranged in variably sized solid aggregates within a dense fibrous stroma. Frequent mitotic figures are noted and there are several foci of tumour necrosis. Some of these show dystrophic calcification. Immunohistochemistry shows strong nuclear staining in tumour cells for oestrogen receptor (+++; >90%) and strong membrane staining for E-cadherin. HER-2 is negative (+; <5%). No staining for progesterone receptor, TTF-1, CDX-2, GCDFP or cytokeratin CK7 is seen in tumour cells. The features are of metastatic undifferentiated carcinoma and are consistent with an origin from breast.
DIAGNOSIS: "Posterior fossa tumour": Metastatic undifferentiated carcinoma consistent with an origin from breast.
This breast metastasis could potentially be mistaken for a meningioma because of the broad dural attachment but it "just not quite right" for a meningioma, and metastasis should always be considered. In this case the patient had a known history of breast cancer resected a few years earlier.