PMC4756087_01
(a) Computer tomography scan shows a lobulated paraaortic retroperitoneal mass. (b) The neoplasm extends through the left primitive iliac vein until the bifurcation, encasing the external left iliac vein. (c) The neoplasm compresses pelvic structures.
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The computer tomography (CT) showed a retroperitoneal mass of 11 x 9 x 7 cm with extrinsecal compression of the sigmoid colon and urinary bladder (Fig. 1a). In addition, there were multiple para-aortic and left iliac lymphadenopathies measuring up to 50 mm of diameter (Fig. 1b and c).
Microscopic details of the neoplasm showing the characteristic "merkeloid" open dusty chromatin with eccentric nucleoli and a solid and trabecular growth pattern. There are multiple abnormal mitotic figures.
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Pathologically, the mass was a white grayish retroperitoneal mass 12 cm in diameter, histologically composed of small to medium round cells, and with a high nuclear-to-cytoplasmic ratio with an area of vague trabeculae that was highly suggestive of MCC (Fig. 2).
The neoplasm shows paranuclear CK20 staining.
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Immunohistochemistry confirmed this finding, as the mass was positive for CD56, synaptophysin, CKAE/AE3, and a characteristic paranuclear cytokeratin (CK) 20 staining (Fig. 3).