BENIGN FOCAL RENAL TUMORS

Diagnostic Radiology

BENIGN FOCAL RENAL TUMOURS - Angiomyolipoma
This is a homogeneous, highly echogenic, usually rounded lesion in the renal parenchyma containing blood vessels, muscle tissue and fat, as the name suggests. They are usually solitary, asymptomatic lesions, found incidentally on the scan, although the larger lesions can haemorrhage, causing haematuria and pain. Angiomyolipomas are also associated with tuberose sclerosis, when they are often multiple and bilateral. Because the contrast between the hypoechoic renal parenchyma and the hyperechoic angiomyolipoma is so great, very small lesions in the order of a few millimetres can easily be recognized. It may be difficult confidently to differentiate an angiomyolipoma from a malignant renal neoplasm, particularly in a patient with haematuria.

Angiomyolipomas tend to be smaller and more echogenic than renal cell carcinomas, and sometimes demonstrate shadowing, which is not normally seen in small carcinomas. When doubt persists, CT is often able to differentiate in these cases by identifying the fat content of the lesion.

Adenoma
The renal adenoma is usually a small, well-defined hyperechoic lesion, similar in appearance to the angiomyolipoma. It is felt that adenomas are frequently early manifestations of renal carcinoma as distinct from a benign lesion6 and the two may be histologically indistinguishable. Renal adenomas are often found in association with a renal cell carcinoma in the same or contralateral kidney, although these are radiologically indistinguishable from metastases.

Because of the controversy surrounding the distinction between adenomas and small renal cell carcinomas, the management of patients with these masses is uncertain. Most incidentally discovered, small (less than 3 cm), parenchymal renal masses are slow-growing and may be safely monitored with CT or ultrasound, particularly in the elderly.

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