Angiomyolipoma

The lesion is defined as a benign tumour composed of variable admixtures of adipose tissue, smooth muscle (spindled or epithelioid), and thick-walled blood vessels. The age range of angiomyolipoma is from 30-72 years, with a mean of 50 years {1373}. It is seen equally in males and females {604}. A small number are associated with tuberous sclerosis. Angiomyolipomas are usually single, with 60% located in the right lobe, 30% in the left lobe, 20% in both lobes and 8% in the caudate lobe {1373}. They are sharply demarcated but not encapsulated, fleshy or firm and, when sectioned, with a homogeneous yellow, yellow-tan or tan appearance, depending on their content of fat.

Histopathology. Angiomyolipomas are composed of adipose tissue, smooth muscle and thick-walled, sometimes hyalinized blood vessels in varying proportions. Morphologically and phenotyp-ically they are believed to belong to a family of lesions characterized by proliferation of perivascular epithelioid cells {2197}. The smooth muscle is composed of spindle-shaped cells arranged in bundles, or larger more rounded cells with an 'empty' (glycogen-rich) cytoplasm or an eosinophilic, epithelioid appearance. The nuclei of the spindle cells are elon

Fig. 8.65 Lymphangioma. Lymphatic channels of variable size contain clear pink fluid.

Fig. 8.64 Sclerosed haemangioma. Pale hyalinized nodule with remnants of obliterated vessels.

gated with blunt ends, but the larger smooth muscle cells can have large, hyperchromatic nuclei with prominent nucleoli. The microscopic appearances are extensively varied and may imitate several malignant tumours, e.g. leio-myosarcoma, malignant fibrous histiocy-toma and hepatocellular carcinoma

Fig. 8.65 Lymphangioma. Lymphatic channels of variable size contain clear pink fluid.

{1971}. A characteristic feature of angio-myolipoma is the presence of extra-medullary haematopoiesis. The smooth muscle cells contain variable quantities of melanin and express the melanoma markers HMB-45 and Melan-A. They also express muscle specific actin and smooth muscle actin.

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