[Deep soft-tissue leiomyoma]

Deep soft tissue leiomyomas (DSTL) are very rare. For this reason they are neither histologically, nor clinically reliably characterized, especially regarding their dignity. The authors present two cases of leiomyomas which grew from the deep soft tissue in the region of the head and perineum. Both cases involved women 43 and 63 years of age. Characteristically morphological traits, as e.g. good borderline of lesion, the presence of fibrous pseudocapsule, and classical morphologic appearance of leiomyoma were present in both cases. While in the first case the foci of dystrophic calcification within regressively altered foci of the tumour were found, the second case involved the presence of foci of myxohyalin degeneration of stroma. The first tumour contained also parts with a palisade arrangement of nuclei which gives a hint of resemblance to that of neurilemmoma. Mitoses did not exceed the HPF index of 2/10 in neither of the cases. Both cases were S-100 immunohistochemically negative, actin and human muscle actin were significantly positive, desmin was weakly or mediately positive, and vimentin significantly or mediately positive. The first case involved a clinical recurrence of a histologically verified leiomyoma after 5 years in the same location with MI being of zero value. Regarding the presented characteristics, the authors classify the described leiomyomas as DSTL. These tumours with an uncertain prognosis can metastatize despite their benign morphology. (Tab. 2, Fig. 4, Ref. 19.)