Rare Presentation of Angiolipoma Affecting an Intact Achilles Tendon

Musculoskeletal lipomatous lesions are common in soft tissues. However, these are rarely associated with tendon sheaths or tendon compartments. Moreover, angiolipoma of the Achilles tendon is yet to be described. Here, we report an angiolipoma of an intact Achilles tendon, which has not been described previously. A 54-year-old woman presented with a two-year history of a palpable mass in the posterior aspect of the left ankle. The mass caused an intermittent localized pain while walking and a catching phenomenon induced by the plantar dorsiflexion movement of the ankle joint. Magnetic resonance imaging revealed a well-circumscribed, oval lesion on the lateral aspect of the Achilles tendon. The location and shape of the lesion had changed over time, suggesting that the lesion was moving in and out around the Achilles tendon. At the surgery, the tumor was confirmed under the crural fascia. Histopathological examination revealed that the tumor comprised mature adipocytes covered peripherally with a fibrovascular capsule. Based on these features, the tumor was diagnosed as an angiolipoma. Angiolipomas are typically treated surgically by simple excision, and lipomatous lesions of the tendon sheath are not different. From this case report, angiolipomas are rare but should be considered in the differential diagnosis and treatment of Achilles tendon tumors.