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Diagnosis: Angiomyolipoma (monophasic or fat poor)

Angiomyolipoma (AML) are tumours consisting of perivascular epithelioid cells (cells which are found surrounding blood vessels and which resemble epithelial cells). A tumour of this kind is known as a PEComa, from the initials of perivascular epithelioid cell. Older literature may classify them as hamartoma (benign tumours consisting of cells in their correct location but forming a disorganised mass) or choristoma (benign tumours consisting of normal cells in the wrong location). PEComas are themselves a kind of mesenchymal tumour.

An AML is composed of varying proportions of vessels, smooth muscle cells and fat cells. However, many pathologically confirmed AMLs are not suspected on preoperative imaging due to an absence of radiographically evident fat. The histological findings in these fat poor AMLs can be typical or can be monophasic, with minimal or not evident adipocytes. Clinical outcomes in patients with fat poor AMLs have
been reported to be excellent in several small series.

AML composed predominantly (95% or more) of a single component (adipose tissue or smooth muscle) is called monophasic AML. If 95% or more of the tumor is smooth muscle it is called "fat poor angiomyolipoma" (Lane BR, et al. Clinical correlates of renal angiomyolipoma subtypes in 209 patients: classic, fat poor, tuberous sclerosis associated and epithelioid. J Urol. 2008;180:836-43. [PubMed link]).

See the chapter Renal Neoplasms - Part 2 - of our tutorial (this chapter appears only in Spanish version).

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References

• Munjal K, Agrawal S, Munjal S. Leiomyomatous angiomyolipoma of kidney. Urol J. 2009;6(2):87. [PubMed link]
• Aydin H, Magi-Galluzzi C, Lane BR, Sercia L, Lopez JI, Rini BI, Zhou M. Renal angiomyolipoma: clinicopathologic study of 194 cases with emphasis on the epithelioid histology and tuberous sclerosis association. Am J Surg Pathol. 2009;33(2):289-97. [PubMed link]
• Lane BR, Aydin H, Danforth TL, Zhou M, Remer EM, Novick AC, Campbell SC. Clinical correlates of renal angiomyolipoma subtypes in 209 patients: classic, fat poor, tuberous sclerosis associated and epithelioid. J Urol. 2008;180(3):836-43. [PubMed link]
• Kim JY, Kim JK, Kim N, Cho KS. CT histogram analysis: differentiation of angiomyolipoma without visible fat from renal cell carcinoma at CT imaging. Radiology. 2008;246(2):472-9. [PubMed link] [Free full text]
  

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