Microscopic features of mesothelioma of uncertain malignant potential of tunica vaginalis. A, Mesothelioma of tunica vaginalis. The smaller of the two resected tumors measuring 0.5 cm in diameter, is shown completely on low magnification (original magnification ×4). B, Both tumors were circumscribed and showed no evidence of invasion; the base of the stalk can be seen in the centre of the field (original magnification ×10). C, Both tumors were composed mostly of papillae with fibrovascular cores, lined by flat to cuboidal and focally columnar cells with bland nuclei. The fibrovascular cores were mostly paucicellular, but focally exhibited myxoid and hyalinized stroma (original magnification ×10). D, Focally, the neoplasm showed more complex growth with confluent cords and trabecullae (original magnification ×20). E, Smaller solid areas with spindle cells were also present (original magnification ×40). F, A single microfocus of coagulative necrosis was found in the larger tumor; this focus appeared in the vicinity of a stalk-like structure, raising the possibility of local torsion or infarct (original magnification ×40).