Renal Angiomyolipoma Mimicking a Well-Differentiated Retroperitoneal Liposarcoma

Abstract

A 37-year-old Burmese woman presented with an incidentally found retroperitoneal fat-containing tumor. The tumor was 9 cm in the longest diameter, surrounding the right kidney, and composed of homogenous adipose tissue with thickened septum-like structures and spotty nonadipose structures, which were enhanced on contrast-enhanced computed tomography and magnetic resonance imaging. The tumor did not show either a beak sign or synchronous angiomyolipoma-like lesion in the kidneys. The tumor had irregular septa, thin blood vessels, and spotty small soft-tissue nodules. The tumor did not contain any heterogeneously enhanced solid lesions suspicious for dedifferentiated liposarcomas. Based on these imaging findings, a clinical diagnosis of a well-differentiated liposarcoma was made. Under the consensus of a multidisciplinary cancer board, she was recommended to undergo core-needle biopsy to confirm the clinical diagnosis. However, she declined to undergo biopsy for financial reasons. She underwent kidney-sparing retroperitoneal tumor resection. Histopathologically, the tumor was an angiomyolipoma with positive immunostaining for HMB45 and Melan A. The present case suggests the importance of core-needle biopsy prior to surgical intervention for retroperitoneal fat-containing tumors.

A Large Retroperitoneal Liposarcoma Mimicking an Angiomyolipoma on Pre-operative Imaging: A Case Report

“…In the literature, there are some cases of renal AMLs mimicking WDLs due to similarities in radiographic imaging [ 6 , 7 , 8 , 9 ]. It is important to correctly diagnose these entities, as AMLs and WDLs have different treatment modalities.…”

“…Renal AMLs are benign; however, the biggest clinical concern with these tumors is the risk of retroperitoneal hemorrhage, which can be life-threatening. Indications for treating these tumors are a size of ≥4 cm and the presence of symptoms regardless of size [ 9 ].…”

“…CT and MRI are the standard imaging tools used for the evaluation of retroperitoneal liposarcomas and can help distinguish the composition, relationship to neighboring organs, size, and enhancement [ 1 ]. Typically, AMLs and WDLs are both large fat-containing lesions which make them difficult to distinguish on MRI and CT, however, there are three distinctions that can be made in imaging to help identify the lesion correctly [ 8 , 9 , 10 , 11 ]. Should the observed mass be identified as an AML, a CT scan will reveal defects in the renal parenchymal structure, attributed to its expansion within the renal parenchyma.…”

Giant Angiomyolipoma Masquerading as Perinephric Abscess: A Diagnostic Conundrum

“…The classic triad of symptoms associated with renal masses of flank pain, palpable mass and haematuria were historically found in 37% -41% of patients with AML [8]. Rare reports of angiomyolipoma mimicking renal cell carcinoma, Wilm's tumour and retroperitoneal liposarcoma are found in literature [9] [10] [11]. A few rare reports are present in which patients with ruptured angiomyolipomas presented with unexplained fever [12] [13].…”

Radiologische Bildgebung bei Primären Sarkomen der Niere: eine multizentrische Studie

“…Intratumorales Fett wird im Rahmen von Fallstudien zu renalen Liposarkomen als wichtiger diagnostischer Hinweis beschrieben(Parizi et al 2019). Anzumerken ist in dieser Hinsicht, dass gut differenziertes Fettgewebe sowohl bei Lowgrade-Liposarkomen als auch bei benignen fettreichen AML vorkommt, sodass sich die radiologische Abgrenzung gelegentlich schwierig gestalten kann(Fuse et al 2020). Dennoch lassen sich bei AML in der Bildgebung regelmäßig charakteristische Zeichen identifizieren, welche diese häufige Diagnose untermauern -darunter das angular interface sign als Ausdruck der Tendenz von benignen exophytischen Läsionen, spitzwinklig in das Nierenparenchym hineinzureichen, Neovaskularisationen als Kennzeichen eines atypischen Gefäßwachstums sowie eine hypodense Umrandung des Tumors in nativen CT-Sequenzen(Shaaban et al 2016).…”