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A left cerebellar lesion has intrinsic T1 signal and susceptibility artefact in keeping with blood product, which limits interpretation of diffusion imaging, heterogeneous enhancement with a number of cystic components. Non-enhancing high FLAIR signal surrounds the lesion and extends to the left cerebellar peduncle and is also present in the right cerebellar hemisphere.
Extensive mass effect in the posterior fossa with effacement of the cerebral aqueduct and partial effacement of the fourth ventricle, distortion of the medulla, cerebellar peduncles and basal cisterns. Mild dilatation of lateral and third ventricles, prominent superior cerebral aqueduct, with a periventricular rim of high FLAIR signal in keeping with hydrocephalus.
Cerebral blood volume (CBV) is mildly elevated around the periphery of the lesion. Spectroscopy (not shown) demonstrates elevation of choline, reversal of choline creatine ratio, reduced NAA and a lactate peak.
Conclusion: Left cerebellar mass with associated hydrocephalus most likely represents a metastasis.
The patient went on to have surgery confirming the diagnosis of cerebellar metastasis.
Paraffin sections show fragments of a densely hypercellular tumor. Tumor cells have moderately pleomorphic round and oval nuclei with finely granular cytoplasm and a variable amount of eosinophilic cytoplasm and are arranged predominantly in diffuse sheets. Poorly formed papillary and perivascular pseudo-rosettte like structures are noted. Moderate numbers of mitotic figures are identified. Scattered small foci of tumor necrosis are also seen.
Immunohistochemistry shows strong cytoplasmic staining in tumor cells for CD99, CD56 and synaptophysin. There is patchy strong cytoplasmic staining for epithelial membrane antigen (EMA) and patchy moderate staining for pancytokeratin AE1/AE3, neuron specific enolase (NSE) and chromogranin. No staining for TTF-1, tyrosinase, SOX10, S-100 protein, CDX2, estrogen receptor (ER) or cytokeratins (CK7; CK20) is seen in tumor cells. The features are of metastatic neuroendocrine carcinoma.
FINAL DIAGNOSIS: Metastatic neuroendocrine carcinoma.