angiolipomas

Angiolipoma is a benign subcutaneous tumor composed of mature adipose tissue intermingled with proliferating blood vessels. It most often affects young adults and typically presents as tender, well-circumscribed subcutaneous nodules, most commonly on the forearms. Lesions can be solitary or, particularly in younger patients, multiple.

Histology and subtypes: Two histologic subtypes are recognized. The noninfiltrating (encapsulated) type is usually well defined and tends to be painful but does not invade surrounding tissues. The infiltrating type lacks a capsule and extends into adjacent fascia or muscle, and it tends to recur after excision.

Microscopic features include mature adipose tissue admixed with small capillary vessels and, frequently, fibrin microthrombi within the vascular channels. These features help distinguish angiolipoma from ordinary lipoma and from vascular lesions such as hemangioma.

Imaging and diagnosis: Ultrasound often reveals a vascular, hypoechoic or hyperechoic lesion; MRI can show a lesion with fat signal interspersed with enhancing vascular components. Definitive diagnosis is made histologically, usually after excision or biopsy.

Treatment and prognosis: Complete surgical excision is the preferred treatment. The noninfiltrating form has a low likelihood of recurrence, whereas infiltrating angiolipoma has a higher rate of local recurrence and may require wider excision. Malignant transformation is exceedingly rare.

Differential diagnosis includes lipoma with vascular proliferation, hemangioma, and angioleiomyoma.