Answer

The diagnosis is cellular angiolipoma.

Discussion

Cutaneous angiolipomas are the benign tumors of proliferating mature adipose tissue and capillary-sized blood vessels. They commonly occur in the subcutaneous fat of upper limbs, especially forearm of young adults and less commonly over the trunk.^[1] Rarely, they can involve extradural, breast, oral, intra-articular, and bronchial sites. Familial cases have rarely been reported.^[1] Clinically, they present as tender or painful nodule with erythematous or bluish surface.^[1] Pain can be variable and depends upon the amount of vascularity of the lesion.^[1] They are more often multiple than solitary. Multiple angiolipomas have been reported in association with diabetes mellitus, use of antiretroviral therapy (particularly with indinavir and saquinavir), and HIV infection.^[1] Angiolipomas are classified into infiltrating and noninfiltrating types. Infiltrating types are more aggressive in nature and produce unusual symptoms due to infiltration of muscular, osseous, fibrocollagenous, and neural tissues and mimic malignant neoplasm.^[2] Noninfiltrating types are more common and present as painful, soft, cutaneous nodules in younger individuals.^[2] In our case, because of subcutaneous location and no associated pain in the nodule, the differentials we considered were rheumatoid nodule, subcutaneous granuloma annulare, solitary neurofibroma, and sarcoidosis.^[1]

In contrast to other forms of lipomas including ordinary lipoma, angiolipomas are not associated with any characteristic cytogenetic abnormality, which may point towards a different pathogeneses from that of lipomas.^[3]

Histology reveals well-encapsulated tumor comprising of mature adipocytes and varying proportions of irregular, anastomosing small blood vessels. The presence of luminal microthrombi and absence of cellular atypia, pleomorphism, and mitotic figures of both adipose and angiomatous components are very characteristic.^[1] Cellular angiolipoma differs from angiolipoma by its predominant vascular component, which usually occupies more than 90% of the tumor area. In cellular angiolipoma, spindle cells are found to be present between the proliferating blood vessels and thought to be of pericyte origin.^[4],[5] In our case, the proliferating capillaries constituted more than 90% of the tumor mass and imparted an “angiomatous growth pattern.” In case of a cellular angiolipoma, the presence of proliferating vessels with variable number of interstitial spindle cells sometimes poses diagnostic difficulty, especially while differentiating it from Kaposi's sarcoma, capillary hemangioma, spindle cell hemangioma, and spindle cell lipoma.^[5]

Noninfiltrating angiolipomas can be treated by enucleation while infiltrating angiolipomas need a wide excision including normal surrounding tissue.^[2] Our case demonstrates that although angiolipomas are conventionally associated with pain, they can present as a painless subcutaneous nodule and pose diagnostic difficulty in differentiating them from other benign tumors and inflammatory lesions.

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Conflicts of interest

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