Angiolipoma

Angiolipomas are are rare soft tissue tumours composed of mature adipocytes and vessels. They most commonly arise in the subcutaneous tissues of the extremities.

Please refer to the epidural (spinal) angiolipoma article for a specific discussion. The remainder of this article describes the general features of peripheral angiolipomas.

Terminology

Given the heterogeneous and relatively non-specific histological features, it is unsurprising that the literature is replete with alternative names. In many instances, these probably represent separate entities. Some terms that have been used include haemangiolipomas, vascular lipomas, and and fibromyolipomas. None of these are recognised in the WHO classification of soft tissue and bone tumours (5th edition, 2020) ⁷.

Additionally, older literature subclassified these lesions into infiltrating and non-infiltrating variants ¹. The latter is typically found in muscles or less commonly in solid organs. They are thought to be separate entities having, in addition to different localisation, different histology (larger vessels), appearance (infiltrating rather than encapsulated) and demographics (older adults), and are not included under the term angiolipoma in the WHO classification of soft tissue and bone tumours ⁷.

And lastly, angiolipomas should not be confused with renal angiomyolipoma or adrenal myelolipoma.

Epidemiology

Typically occur in adolescents and young adults and are more common in males ^2,3,7. An autosomal dominant pattern of inheritance is identified in a minority of cases ⁷.

Clinical presentation

Angiolipomas present as multiple small (<2cm;2 cm) subcutaneous nodules, often tender. They are most frequently located on the forearm (most common location), trunk and upper arm. They are more common in males. ^2,3,7.

Pathology

Angiolipomas usually appear as yellow and/or red circumscribed encapsulated nodules or masses ⁷.

They are composed of variable amounts of thin-walled branching blood vessels and mature adipose tissue (adipocytes). The vessels frequently contain fibrin thrombi ⁷. Some tumours are almost entirely fat whereas others are almost entirely composed of blood vessels leading to variable macroscopic, microscopic and imaging features ⁷.

These fat-poor lesions are known as cellular angiolipomas and can mimic Kaposi sarcoma and angiosarcoma histologically ⁷.

There are no specific molecular markers ⁷.

Radiographic features

As expected, these masses contain adipose tissue with prominent vascular supply.

Infiltrating angiolipoma is nonencapsulated and can contain phleboliths, heterotopic bone, and calcium salts. There are authors who conclude that it should be classified as an "intramuscular haemangioma" ^2,4.

Ultrasonography

AppearMost often angiolipomas have oval shape and well-defined margins (the lateral tumour capsules tends to lesser visualised). They frequently appear as well-circumscribed, homogeneousheterogeneous and hyperechoic masses with sparse or no vascularisation on colour Doppler flow. There is no acoustic enhancement and calcification ^5,6,8,9.

MRI

Angiolipomas demonstrate signal intensity characteristics of mature adipose tissue. Vascular elements are T1-hypointense and T2 hyperintense and enhance vividly following administration of contrast ³.

Angiography

Catheter angiography demonstrates prominent coarse neovascularity. During the capillary phase, contrast staining is typically seen ¹.

Treatment and prognosis

Treatment is predominantly surgical.

Differential diagnosis

• lipoma

• haemangioma

• Kaposi sarcoma

• angiosarcoma