Dermatologic Therapy | 2021
A rare site of subcutaneous lipoma on the middle finger: Case report and analysis of affected sites in 126 cases at a single institution
Abstract
Dear Editor, Lipomas are among the most common tumors. They consist of fat tissue and can occur anywhere in the body. Common sites are the head and neck, shoulders, chest, abdomen, and upper back. Digital lipoma is very rare, with few case reports. We report a case of lipoma on the middle finger and the results of a retrospective study on lipoma sites at our institution. A 75-year-old Japanese man presented with a painless nodule on the middle finger. He had noticed the nodule 10 years before, and it had gradually enlarged. Physical examination revealed a scalysurfaced, pinkish, soft elastic subcutaneous mass of 35 23 15 mm in diameter on the dorsal side of the right middle finger (Figure 1A). Initially, we suspected the tumor to be a lipoma, giant cell tumor of the tendon sheath, or neurilemmoma. Ultrasonic echography revealed a soft, variably hypovascular, subcutaneous echogenic mass with a mosaic inside (Figure 1B-D). Gross observation during the surgical operation revealed a soft, well-defined yellowish lobulated mass (Figure 1E). Histopathologically, mature adipocytes were fractionated and proliferated to incomplete fibrous septum (not shown). Based on these clinical and pathological findings, the patient was finally diagnosed with subcutaneous lipoma on the finger. Until today 36 cases of lipoma arising on the finger have been described. The clinical features of digital lipoma were reported as swelling, soft, fluctuant, mobile, and generally painless. The covering skin is usually normal. When the joints are compressed, a digital lipoma can limit flexibility and cause pain. Of the digits, the index and middle fingers are most commonly affected. Although some reports have described the etiology of lipoma to involve genetic, traumatic, and metabolic factors, these remain unclear. The incidence of digital lipoma has been reported as only 1% among subcutaneous lipomas. To confirm the results of the previous studies, we analyzed the affected sites of 126 cases (a total of 112 patients) which were histopathologically diagnosed as lipoma at the Hokkaido University Hospital from 2011 to 2019 (institutional review board approval number: 0200-0009, which deemed this retrospective analysis appropriate for a waiver of informed consent). Of the 112 patients, 11 patients had two or more lipomas at different regions. The patients clinical profile and the affected sites are summarized in Figure 1F. The patients ages range from 19 to 81 years, with a mean of 53.7 years (median: 55 years). The male:female ratio is 51:61. Of the 126 cases, 25 (19.8%) are located in the head and neck, 68 (54.0%) in the trunk, 17 (13.5%) in the upper extremities, and 13 (10.3%) in the lower extremities. The most frequent site is the upper back (28.6%). There was only one case of lipoma on the finger (the present case, 0.8%). The present results of lipoma distribution at our single institution are consistent with previous reports, which found lipomas to occur frequently on the upper back or the head and neck. In conclusion, finger lipomas are relatively rare, but if we find a subcutaneous mass on the fingers, we should consider lipoma as a differential diagnosis.