Pseudoangiosarcomatous features in medullary thyroid carcinoma spindle-cell variant. Report of a case studied by FNA and immunohistochemistry.

We report a case of medullary thyroid carcinoma (MTC), spindle cell variant, which exhibited striking histological pseudovascular clefts and abortive lumina, closely mimicking an angiosarcoma. The patient is a 72-yr-old-man who presented facial rash and a solid nodule in the right lobe of the thyroid gland. The fine-needle aspiration (FNA) showed bloody background containing loosely groups of fusiform and plasmocytoid cells with coarse chromatin and eosinophilic granular cytoplasms. Microscopically, the tumor exhibited spindle-cell pattern intermingled with a striking angiosarcoma-like pattern characterized by the presence of abortive lumen and clefts containing erythrocytes. Dense hyaline extracellular amyloid was present. The tumor cells were strongly positive for cytokeratin, chromogranine-A, synaptophysine, serotonin, calcitonin, and CEA. TTF-1 was weakly positive. Stains for CD34 and CD31 were negative. This case illustrates that the spindle cell variant of MTC may exhibit an infrequent angiosarcoma-like appearance which may be misdiagnosed as angiosarcoma.