The patient went on to have a biopsy of the frontal lesion.
MICROSCOPIC DESCRIPTION: The section shows fragments of cerebral tissue containing multiple localised deposits of tumour tissue, which appear to be adjacent to small blood vessels. The tumour deposits vary in size and shape, with the largest ones showing central necrosis. The tumour is cellular, composed of crowded elongate cells with oval nuclei. There are occasional rosettes or tubules surrounded by tumour cells. Tumour cell nuclei show generally granular nucleoplasm and, frequently, small nucleoli. There are scattered mitotic figures at a rate of 20/50 hpf. The Ki67 index is approximately 30% of tumour cells.
The neuroendocrine nature of the cells is confirmed with positive cytoplasmic staining for chromogranin, synaptophysin and CD56. Staining for TTF-1 shows a very occasional single tumour cell nucleus positive. About 30% of tumour cells show moderately strong staining for ACTH. Cells are negative for somatostatin.
The features are those of metastatic neuroendocrine tumour, lacking morphologic features of small cell carcinoma. Applying criteria for neuroendocrine tumours described in the WHO Classification of Tumours of the Digestive System, Bosman et al, IARC, Lyon, 2010, this tumour would be categorised in the "neuroendocrine tumour grade 3" group. In the 2004 WHO categorisation of lung tumours, the terminology would be "atypical carcinoid".
FINAL DIAGNOSIS: Left frontal tumour - metastatic neuroendocrine tumour (G3) showing evidence of ACTH production.
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