Indian Journal of Radiology and Imaging Indian Journal of Radiology and Imaging

: 2006  |  Volume : 16  |  Issue : 4  |  Page : 911--913

Large renal angiomyolipoma with extension in perinephric space: A case report

SV Phatak, PK Kolwadkar, D Rajderkar 
 Honorary Asst Prof. Radio-Diagnosis IGMC and Mayo Hospital, Nagpur, India

Correspondence Address:
S V Phatak
Honorary Asst Prof. Radio-Diagnosis IGMC and Mayo Hospital, Nagpur, R 203,«DQ»Devashish Apartments«DQ», 1 Bajaj Nagar South Ambazari Road, Nagpur 440010, Maharashtra

How to cite this article:
Phatak S V, Kolwadkar P K, Rajderkar D. Large renal angiomyolipoma with extension in perinephric space: A case report.Indian J Radiol Imaging 2006;16:911-913

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Phatak S V, Kolwadkar P K, Rajderkar D. Large renal angiomyolipoma with extension in perinephric space: A case report. Indian J Radiol Imaging [serial online] 2006 [cited 2020 Feb 22 ];16:911-913
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Full Text

A sixty-year-old lady presented with vague pain in right lumbar region. On clinical examination mass was felt. Sonography revealed a large hyperechoic mass in anterior cortex of right kidney. CT and MRI were done to further characterize the mass that revealed classical imaging features of Angiomyolipoma.


Angiomyolipoma is the most common benign renal neoplasm diagnosed radiologically. It is a hamartoma composed of vascular, fat and smooth muscle elements in varying amounts. Typically it is nonencapsulated slow growing and expansile replacing renal parenchyma and distorting the renal collecting system, but without destruction. They commonly show an extrarenal growth pattern with extension through the renal capsule into perinephric space. They are about 4.5 times more common in women as compared with men. Mostly are asymptomatic. Classic symptoms in symptomatic patients are flank pain, hematuria and hypotension may occur secondary to parenchymal, subcapsular or perirenal haemorrhage. [1] Clinically two distinct groups of patients are involved. The first are those with tuberous sclerosis. Their angiomyolipomas are usually bilateral and multifocal. And can occur at any age. And in either sex. The second group consists mainly women of 40-70yearsold.Lesions in this group are unilateral and focal. [2]


On gross examination these tumors are typically smoothly rounded or ovoid and circumscribed but not encapsulated. Size ranges from several centimeters to over 20 centimeters. With mean diameter of 9.4 centimeters. The growing tumor compresses and distorts the renal parenchyma and collecting system but not invasive. Many tumors have extended into the perirenal fat at the time of diagnosis although every AML is composed of fat, smooth muscle and abnormal blood vessels the relative amounts of these three constituents vary tremendously from tumor to tumor and in different foci of the same tumor. Histologically aggregrates of abnormal thick walled artery like blood vessels are admixed with varying amounts of adipose tissue and smooth muscle. Individual fat cells may vary considerably in size but otherwise resemble normal adipose tissue. The smooth muscle component characteristically pleomorphic but without mitotic figures. The vascular element is the most characteristic feature of the angiomyolipoma. The smaller arteries are devoid of elastica as are most of the layers but the distinctive feature is the relation of vascular adventitia to the smooth muscle element of the tumor: the latter will form a collar about the periphery of the vessel or will exhibit an intimate perpendicular orientation in relation to it. Some of these tumors consist almost entirely of adipose tissue or smooth muscle and this vascular -myomatous configuration may provide the only clue to the diagnosis. [3]

Plain radiographs show the distinctive feature of radiolucency in the tumor corresponding to fatty tissue. This is seen in less than 10%cases of AML.The most characteristic sonographic pattern is very hyperechoic with the adjacent renal parenchyma. This marked echogenicity is attributed to high fat content, with multiple acoustic interfaces between intracellular fat and the cell walls cellular architecture that is heterogeneousand the presence of multiple vessels in AML. [1] Unfortunately bright echogenicity is not specific for fat. Other lesions such as renal abscess, renal cell carcinoma, ,oncocytoma and cavernous hemangioma may create dense echopattern. Large AML may demonstrate a speed propagation artifact. This may be the only specific sign of fat. It results from sound traversing fat at slower speed, so that structures posterior to a fatty mass are artfactually displaced more distally than would be expected. [4] Three types of sonographic finding are described in AML.Echodense pattern, Mixed pattern and low sonodense pattern. [5] Fatty attenuation seen in renal tumour on CT is virtually diagnostic for AML.Detecting small amounts of fat may require thin section CT, use of small areas for attenuation measurements and use of unenhanced CT scans. The fatty content of the AML may be largely extrarenal and therefore tumor may be confused with other extrarenal lesions. [1] CT images of AML reflect the variable pathologic findings that may be present. Tumors composed primarily of fat will have a density similar to normal subcutaneous or retroperitoneal fat. Intermixed within this fatty mass are areas of tissue density that may correspond to smooth muscles, blood vessels, areas of haemorrhage or haemorrhagic breakdown. Rarely CT appearance will be entirely fatty without myomatous or vascular elements visible. (Lipoma like AML)[3] AML composed primarily of smooth muscle may have insufficient fat to be recognized by CT.Extension of AML beyond kidney is well demonstrated by CT.The perinephric spaces contains loose areolar tissue that is capable of marked expansion and therefore offers path of least resistance to the enlarging AML.Occasionally the entire perinephric space is filled by the tumor. Although a large perinephric component is often present, an intrarenal component can usually be recognized. [3] On MRI fat produces high signal intensity both on T1 and T2 weighted SE sequences because of the short T1 and moderately long T2 of fat. The multiplanar imaging of MRI also may be useful in evaluating fat containing masses adjacent to kidney by delineating the presence or absence of a cleavage plane between the tumor and kidney. MRI usually shows a plane between a retroperitoneal liposarcoma and the kidney but not between an AML arising from kidney. [6] Involvement of regional lymphnodes have been reported previously and most likely represents a second hamartomatous focus and not a metastasis. Its extension into renal vein and IVC is also reported. Extension into venous structures probably represents aggressive local invasion and is not evidence of malignant neoplasm. The possibilty remains that involvement of inferior vena cava is another hamartomatous focus because multicentricity is recognized in this tumor. [2]


1Jon W.Meilstrup et al other renal Tumors Seminars in RoentgenologyVol XXX, No.2 (April) 1995:168-184.
2A M Arenson et al Angiomyolipoma of the kidney extending into the inferior vena cava: sonographic and CT findings AJR December 1988; 151:1159-1161.
3John L.Sherman Angiomyolipoma: Computed tomographic pathologic correlation of 17 cases AJR 1981(December); 137:1221-26.
4Robert K Zeman et al Imaging approach to the suspected renal mass RCNA vol 23,No.3, September 1985:520-523.
5David S Hartman et al Angiomyolipoma: Ultrasonic-Pathologic correlation Radiology 1981; 139:541-458.
6Magnetic Resonance Imaging David D Stark, William G Bradley Vol 2,second edition Mosby year book 1992:1927