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Abdomen » Kidneys/Ureters
Renal Angiomyolipoma
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Presentation
37-year-old woman with microscopic hematuria. She does not report other discomforts. She has a maternal history of tuberous sclerosis.
A sonogram was requested as part of screening.
 
 
Caption: Longitudinal sonogram of the right kidney.
Description: Longitudinal sonogram reveals a hypercoecogenic nodule with partially defined edges, cortical with exophytic projection in the lower pole.
 
 
Caption: Longitudinal sonogram of the right kidney.
Description: Longitudinal sonogram reveals a hypercoecogenic nodule with partially defined edges, cortical with exophytic projection in the lower pole. Zoom view.
 
 
Caption: Longitudinal sonogram of the left kidney.
Description: Longitudinal sonogram reveals a hypercoecogenic nodule with partially defined edges, cortical with exophytic projection in the upper pole.
 
 
Caption: Longitudinal sonogram of the left kidney.
Description: Longitudinal sonogram reveals a hypercoecogenic nodule with partially defined edges, cortical with exophytic projection in the upper pole. Zoom view.
 
Differential Diagnosis
When an AML has typical appearances there is essentially no differential. If atypical, especially when fat-poor, other lesions to consider include:

- Retroperitoneal liposarcoma invading the kidney: 
* presence of a large vessel extending into the renal cortex suggestive of AML; iposarcoma is hypovascular,
* renal parenchymal defect at the site of tumour contact favours exophytic angiomyolipoma- claw sign,
* calcifications suggest liposarcoma.
- Adrenal myelolipoma.
- Renal cell carcinoma (RCC)
* may contain fat: lipid necrosis or osseous metaplasia
- Oncocytoma: may contain fat.
- Wilms tumour: may contain fat.
- Perirenal fat entrapment / renal junctional parenchymal defect.1

 
Final Diagnosis Angiomyolipoma
 
Discussion
Renal angiomyolipomas (AML) are a type of benign renal neoplasm encountered both sporadically and as part of a phakomatosis, most commonly tuberous sclerosis. They are considered one of a number of tumours with perivascular epitheloid cellular differentiation (PEComas) and are composed of vascular, smooth muscle and fat elements. They can spontaneously haemorrhage, which can be fatal. AMLs usually have characteristic radiographic appearances2.

The cornerstone of diagnosis on all modalities is the demonstration of macroscopic fat, however in the setting of haemorrhage, or when lesions happen to contain little fat, it may be difficult to distinguish an AML from a renal cell carcinoma3.

The sonographic features are:

- Tend to appear as hyperechoic lesions on ultrasound, located in the cortex and with posterior acoustic shadowing4.
- In the setting of tuberous sclerosis, they may be so numerous that the entire kidney is affected, appearing echogenic with the loss of normal corticomedullary differentiation4.
- Contrast-enhanced ultrasound5:
  * tend to enhance peripherally.
  * decreased central enhancement, compared with normal cortex.

Angiomyolipomas found incidentally usually require no therapy (when small), although follow-up is recommended to assess for growth. Small solitary AMLs (< 20 mm) probably do not require follow-up due to their slow growth6.
Larger AMLs, or those that have been symptomatic, can be electively embolised and/or resected with a partial nephrectomy. Lesions that present with retroperitoneal haemorrhage often requires emergency embolisation as a life-saving measure. mTOR inhibitors (e.g. everolimus) have been shown to significantly decrease AML size and may help to preserve renal function in tuberose sclerosis patients3.

 
Case References
1. Hélénon O, Merran S, Paraf F et-al. Unusual fat-containing tumors of the kidney: a diagnostic dilemma. Radiographics. 1997;17 (1): 129-44. doi:10.1148/radiographics.17.1.9017804 - Pubmed citation.
2. Logue LG, Acker RE, Sienko AE. Best cases from the AFIP: angiomyolipomas in tuberous sclerosis. Radiographics. 23 (1): 241-6. doi:10.1148/rg.231025109 - Pubmed citation.
3. Eble JN. Angiomyolipoma of kidney. Semin Diagn Pathol. 1998;15 (1): 21-40. Pubmed citation.
4. Harriet J. Paltiel Sonography of Pediatric Renal Tumors January 2007 (volume 2 issue 1 Pages 89-104 DOI: 10.1016/j.cult.2007.01.004)
5. Malhi H, Grant EG, Duddalwar V. Contrast-Enhanced Ultrasound of the Liver and Kidney. Radiol. Clin. North Am. 2014;52 (6): 1177-1190. doi:10.1016/j.rcl.2014.07.005 - Pubmed citation.
6. Maclean DF, Sultana R, Radwan R et-al. Is the follow-up of small renal angiomyolipomas a necessary precaution?. Clin Radiol. 2014;69 (8): 822-6. doi:10.1016/j.crad.2014.03.016 - Pubmed citation.

 
Technical Details
Ultrasound scanner. - Voluson 730 PRO. General Electric.
Transducer. – 2 - 6MHz convex array
Scanning in longitudinal planes.
 
Follow Up The angiomyolipomas found did not require therapy (they are small), although follow-up was recommended to assess for growth.
 
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