Vascular leiomyoma is a benign soft tissue tumour with a predilection for middle-aged women. It is most often seen in the extremities, particularly in the lower leg. The typical lesion is a small, slow-growing subcutaneous nodule. These tumours are often unexpected or preoperatively confused with other soft tissue tumours including low-grade sarcomas, leading to wide surgical excision. This may partly be due to the relatively few studies delineating the characteristic imaging features of this entity. Here, the imaging findings of a case of vascular leiomyoma in the ankle are presented. Literature review of the magnetic resonance imaging findings of published reports and series of vascular leiomyomas of the extremities is also performed.

A 46-year-old man presented to the Department of Orthopaedics and Traumatology, Pamela Youde Nethersole Eastern Hospital in February 2004 with a 3-month history of self-detected left thigh mass. It was of spontaneous onset with no history of trauma, associated pain, weakness, or numbness. The patient had full range of movement and no lymphadenopathy was noted. Magnetic resonance imaging (MRI) [ Fig 1] revealed a large area of infiltrative soft-tissue Hong Kong Med J 2019;25:149-51 https://doi.org/10.12809/hkmj164921 thickening at the medial aspect of the left distal thigh and involved the subcutaneous layer. The lesion measured 8.4 × 3.4 × 11.2 cm (anteroposterior × transverse × longitudinal) and was characterised by T1-weighted (T1W) hypointense to isointense and T2-weighted (T2W) fat-suppressed hyperintense signals with internal heterogeneity. Internal foci of hypointensity in the T2W fat-suppressed images were noted. An internal reticular pattern of septal thickening was also found. There was enhancement after gadolinium contrast administration. The margin of the lesion was well delineated from the underlying vastus medialis and sartorius muscles with no features of muscular invasion or destruction. The knee joint was unremarkable and bone marrow signal was normal. The neurovascular bundle was also intact. Overall features were non-specific for either inflammatory or neoplastic pathology.Microscopic examination of an incisional biopsy over the left vastus medialis with a wedge of skin and subcutaneous tissue revealed infiltrate in the subcutis and to a lesser extent the deep dermis. The infiltrate consisted of lymphocytes and a low number of plasma cells. Immunohistochemical stains showed mainly T-cells and some B-cells. Occasional areas with aggregates of paler histiocytic cells were present and suggested granuloma formation. Stains for acid-fast bacilli and fungus were negative. The paler histiocytic cells were S100-positive and showed lymphophagocytosis (Fig 2). Molecular study by polymerase chain reaction showed no clonal T-cell proliferation. The overall features were suggestive of Rosai-Dorfman disease (RDD).Radical excision of the lesion was performed subsequently and included the epimysium of the gracilis, sartorius and aponeurosis of the vastus medialis. The excision margin in the radial excision of the lesion was 2 cm. Microscopic examination revealed that the mass in the subcutis was composed of nodules or aggregates of lymphohistiocytic cells separated by areas of fibrosis. The cellular aggregates were composed of dark areas with plasma cells and lymphocytes and pale areas with CASE REPORT FIG 1. (a) Axial T1-weighted magnetic resonance (MR) image showing a large area of infiltrative soft tissue thickening involving the subcutaneous layer at the medial aspect of the thigh with hypo-to iso-intense signals (arrow). (b) Axial T2-weighted fat-suppressed MR image showing hyperintense signals with internal heterogeneity and foci of hypointensities. Internal reticular pattern of septal thickening was pre...

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