Answer: B. Leiomyosarcoma

Histological description:The tumor shows variable histology. In some areas there are well-formed fascicles of smooth muscle cut in both parallel and cross-section planes of section, characterized by cells with eosinophilic cytoplasm and elongated rounded-edged nuclei. Although relatively bland, then the least atypical area shows hypercellularity with scattered hyperchromatic enlarged nuclei and increased mitotic activity. Other areas of the tumor show much more pronounced pleomorphism and a less recognizable fascicular growth pattern.

Discussion. Leiomyomas of the bladder differ from the normal muscularis propria in that the former has compact smooth muscle fibers arranged haphazardly, whereas the latter is composed of well-organized discrete bundles of smooth muscle. Leiomyomas of the bladder have a uniform histology throughout and have no atypia except uncommonly focal degenerative cytological atypia unaccompanied by mitotic activity and not associated with hypercellularity. Leiomoyosarcomas of the bladder can vary within a single lesion in terms of its grade, as in the current case, but will never have areas that resemble a leiomyoma. Consequently, if a smooth muscle tumor with the histology of a leiomyoma is seen on a TUR, pathologists can diagnose it as benign even though the lesion may not have been completely sampled. If a low grade leiomyosarcoma is diagnosed on TUR, a comment must be added that there may be grade heterogeneity and that a higher grade component cannot be excluded if the lesion has not been completely resected.

Smooth muscle neoplasms of the urinary bladder: a clinicopathologic study of 51 cases.
Lee TK, Miyamoto H, Osunkoya AO, Guo CC, Weiss SW, Epstein JI.
Am J Surg Pathol. 2010 Apr;34(4):502-9.