CASE 5075 Published on 10.08.2006

Renal angiomiolypoma


Uroradiology & genital male imaging

Case Type

Clinical Cases


Henrique Rodrigues, Pedro Belo Oliveira, Artur Costa


63 years, female

Clinical History
We present a case of a 63 years old woman with sudden intense right flank pain. Ultrasound detected a large volume of retroperitoneal fluid, and a right kidney mass with intense posterior attenuation of the echoes. CT confirmed the presence of retroperitoneal hemorrhage and a lipomatous kidney mass.
Imaging Findings
A previously healthy 63 years old female, recurred to the urgency service of our hospital with sudden intense right flank pain. On physical examination patient had a tender right flank mass, tachycardia and hypotension. In the abdominal X-ray we saw an increased opacity in the right flank with bowel loops deviated to the left (Fig 1). Ultrasound showed a large heterogeneous retroperitoneal fluid collection, and a 16 cm renal mass with areas of low and high echogenity, originating intense posterior attenuation of the echoes, aspect that was suggestive of a lipomatous tumor (Fig 2). Abdominal CT was performed in the same day. Images obtained before intravenous contrast depicted a retroperitoneal collection with high attenuation, in relation with hemorrhage (Fig 3). The renal tumor caused rupture of renal capsule and was primarily constituted by adipose tissue and some strands with soft tissue attenuation. After contrast, acquisitions were made in corticomedullary and nephrographic phases. We detected normal enhancement in renal parenchyma, and that the mass has some nodular structures that enhance like vascular segments, aspect that was in relation with the presence of pseudoaneurysms (Fig 4, 5). There was no active bleeding at the moment of the exam. Patient was submitted to a nephrectomy and the pathologist confirmed the radiological hypothesis of an angiomyolipoma.
Angiomyolipomas (AML) are hamartomas containing variable amounts of fat, smooth muscle and blood vessels. More frequent in young women, and usually measuring 2-5 cm, might reach 15 cm [1]. AML might be associated with Tuberous sclerosis and Lymphangiomyomatosis. Eighty percent of patients with Tuberous sclerosis have AML, typically multiple and bilateral. However less than 40% of patients with AML have Tuberous sclerosis [1,2]. Malignant transformation is unknown. Local lymph node enlargement and even foci in the liver, spleen are reflections of multicentric disease rather than metastases [2]. The classic sonographic appearance in approximately 80% of time is a homogeneous, well-defined cortical mass that is as echogenic as renal fat. Although these characteristics are very suggestive a differential diagnosis with renal cell carcinoma (RCC) needs to be done [3]. The presence of an anechoic rim, intra-tumoral cysts, calcifications and absence of acoustic shadowing is very suggestive of RCC [4]. At CT fatty components are almost always identifiable, and detection of small areas of attenuation values less than – 20 UH is sufficient for the diagnosis. The presence of angiomatous component may lead to heterogeneous enhancement [2]. Problems may arise in tumors with very small fatty component. A paper published by Jeong Kon Kim et col stated that high tumor attenuation was more common in AML with minimal fat than RCC; AML with minimal fat usually show homogeneous enhancement rather than heterogeneous enhancement; The mean amount of tumor enhancement is greater in RCC than in AML with minimal fat in both the corticomedullary and the early excretory phases, and threshold enhancement values of 115 HU in the corticomedullary phase and 56 HU in the early excretory phase have the highest accuracy for differentiating AML with minimal fat from RCC; An early washout pattern was observed in patients with RCC; Only patients with RCC have intratumoral calcification [5]. MR signal reflects the high lipid content of these lesions (signal that parallels that of the subcutaneous tissue). Jeong Kon Kim et col also showed the contribution of this technique in establishing the diagnosis of minimal fat AML. They gave particular emphasis to the signal intensity index and tumor-to-spleen ratio. The signal intensity index was calculated as follows: [(TSIin – TSIopp)/(TSIin)] x 100, where TSIin is tumor signal intensity on in-phase images and TSIopp is tumor signal intensity on opposed-phase images. The tumor-to-spleen ratio was calculated as follows: {[(TSIopp/SSIopp)/(TSIin/SSIin)] – 1} x 100, where SSIin is spleen signal intensity on in-phase images and SSIopp is spleen signal intensity on opposed-phase images. For differentiation of AMLs from non-AMLs, sensitivity and specificity were 96% and 93%, respectively, with a signal intensity index of 25% and 88% and 97%, respectively, with a tumor-to-spleen ratio of –32% [6]. The most feared complication is hemorrhage. These lesions are unlike to bleed if smaller than 4 cm [1,2] Small lesions are not treated; large and symptomatic lesions are resected or embolized [1,2].  
Differential Diagnosis List
Renal angiomiolypoma  
Final Diagnosis
Renal angiomiolypoma  
Case information
DOI: 10.1594/EURORAD/CASE.5075
ISSN: 1563-4086