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Left kidney mass in a 45 year old woman

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Q1: What is the most likely diagnosis?

Contrast enhanced computed tomography (see p 722) showed a retroperitoneal haematoma (asterisks) anterior to the left kidney, displacing ventrally the anterior layer of renal fascia (arrows). There was a space occupying lesion within the kidney (black arrows), consisting of fat and convoluted vessels (open arrows). Note the thickened posterior renal fascia (short arrows). These findings are consistent with the occurrence of a recent haemorrhage from the angiomyolipoma.

Q2: What is the treatment?

The present strategy for the management of angiomyolipoma is to preserve normal renal parenchyma by performing renal sparing surgery or renal arterial embolisation, in order to prevent future haemorrhaging and to preserve renal function.1 An asymtomatic angiomyolipoma 4 cm or larger should be monitored at every six months with computed tomography or ultrasonography.

In this case the patient underwent left partial nefrectomy. Two years after discharge, she remains well and is followed up every six months.


Angiomyolipoma is an uncommon mesenchymal hamartoma of the kidney containing variable amounts of fat, smooth muscle, and blood vessels.2 The prevalence of angiomyolipoma in the general population is approximately 0.3%. It can be associated with tuberous sclerosis complex (20%), while sporadic cases of angiomyolipoma (80%) are typically found in middle aged women. Its main clinical manifestation is flank pain caused by spontaneous perinephric haemorrhage, which is positively correlated to the size of the neoplasms: among angiomyolipomas 4 cm or larger, 50%–60% bleed spontaneously. Angiomyolipoma is the only benign tumour of the kidney that can be diagnosed almost exclusively by means of imaging. The diagnosis relies on the detection of intratumoral fat on computed tomography, which is characteristic.3

Final diagnosis

Haemorrhage from an angiomyolipoma.

Angiomyolipoma of the kidney

  • Histology: hamartomas containing smooth muscle, fat, and blood vessels

  • Radiological features: the presence of fat, which appears hypodense on computed tomography, is virtually diagnostic of angiomyolipoma

  • Associations: tuberous sclerosis complex (20%)

  • Complications: spontaneous bleed

  • Treatment: large, symptomatic lesions may be resected or embolised


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