Deep soft tissue leiomyoma of the thigh

ARTICLE

Auteur(s) : Haruko Uemura, Sinichi Koba, Masakazu Otu, Noriyuki Misago, Yutaka Narisawa

Division of Dermatology, Department of International Medicine, Faculty of Medicine, Saga University, 5-1-1 Nabeshima, Saga city, Saga 849-8501, Japan

Leiomyoma is a relatively well-known, smooth muscle-derived tumor, accounting for approximately 4% of benign soft-tissue tumors [1]. Cutaneous soft-tissue leiomyomas are classified according to their localization into superficial leiomyoma, which arises from the skin or superficial subcutaneous layer and is commonly encountered in dermatological practice, and deep soft-tissue leiomyoma (DSTL) which originates from the deep subcutaneous layer. Superficial leiomyomas include pilar leiomyoma arising from the erector pili muscle, angioleiomyoma from vascular smooth muscle, and genital leiomyoma from the smooth muscle of the scrotum, vulva, or nipple. DSTL arising in subcutaneous soft tissue are very rare. We report the case of a DSTL that arose in the thigh.

A 52-year-old woman first noticed a subcutaneous mass in the left thigh about one month prior to the first examination. In the left femoral region, there was an elastic-soft, subcutaneous mass, 4 cm in diameter, without skin changes. There was no spontaneous pain, tenderness, or radiating pain, and the mass was mobile. She did not have other muscular tumors or family history. MRI revealed a 38×25×19-mm well-defined, subcutaneous mass partially in contact with the fascia in the deep layer of subcutaneous adipose tissue in the left anterior thigh. At surgery, a well-defined, smooth-surfaced mass was observed in the deep layer of adipose tissue (figure 1A). The mass was not adherent to the surrounding tissue. There was no relapse. Histopathologically, the tumor was well-demarcated from the surrounding tissue, and composed of irregularly intertwining bundles of spindle-shaped cells with eosinophilic cytoplasm and fusiform nuclei (figure 1B). A “halo”, characteristic of smooth muscle cells, was also observed (figure 1C). No features of malignancy were noted. Immunohistochemistry showed that the tumor cells were positive for α-SMA, desmin, and vimentin, and negative for S-100 protein (figures 1D-F). The histopathological and immunohistochemical findings led to a diagnosis of deep soft-tissue leiomyoma.

Leiomyoma is a benign smooth muscle tumor with a predilection for the uterus and skin, and which very rarely arises in deep soft tissue. Clinically, superficial leiomyomas, which are primarily encountered in dermatological practice, arise in the dermis and upper subcutaneous adipose tissue, averaging less than 2 cm in diameter [2]. On the other hand, DSTL present as a well-defined, elastic-firm mass, affect persons with a mean age of 37 years, with a male-to-female ratio of about 1:1, have a predilection for the lower extremities, and, compared with superficial leiomyomas, present as a larger mass with a mean diameter of 6.5 cm [3, 4]. They are characteristically painful, and must be differentiated from other painful tumors such as glomus tumors, angiolipomas, spiradenomas and schwannomas. In this patient, the subcutaneous mass was well-defined and was located in the deep subcutaneous adipose tissue and it was a smaller-than-average size for a leiomyoma; therefore, the preoperative diagnosis of leiomyoma was difficult.

Histopathologically, DSTL is well-demarcated and composed of irregularly intertwining bundles of spindle-shaped cells with eosinophilic cytoplasm and blunt-ended, fusiform nuclei. Hyaline material is present in the stroma in many patients [5], and calcification is observed in more than 50% of patients [6]. Immunohistochemically, these leiomyomas are positive for vimentin, desmin, and α-SMA, as observed in this patient.

In contrast to superficial leiomyoma, the pathogenesis of DSTL has not been previously discussed and remains unclear. DSTL may originate from several large vessels that consist of smooth muscles in their walls. But in this patient, there were no characteristic features of frequently encountered angioleiomyoma, such as the angiocentric proliferation of smooth muscle cells, and the simple proliferation of smooth muscle cells was observed. These features were relatively similar to those of leiomyomas in other organs, such as uterine myoma, and we speculate that the origin of DSTL may be the ectopic smooth muscles.

Acknowledgements

References

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