Renal Angiomyolipoma: Preoperative Identification of Atypical Fat-Poor AML

Abstract

The preoperative distinction between benign and malignant renal masses is a well-known radiographic diagnostic challenge. With angiomyolipoma (AML) and renal cell carcinoma (RCC) representing the most common benign and malignant renal parenchymal lesions, respectively, differentiating these two entities is especially important due to their vastly different treatments and prognoses. Renal AML is typically composed of smooth muscle cells, dysmorphic blood vessels, and varying amounts of adipose tissue. In most cases, "typical" AML can be diagnosed by identifying macroscopic fat with ultrasound, computed tomography, or magnetic resonance imaging. However, approximately 4-5 % of AML tumors have fat that is grossly undetectable by conventional techniques, precluding a straightforward diagnosis. The overlapping radiographic features between "atypical" or "fat-poor" AML and RCC, especially in smaller (<3-4 cm) lesions, lead many patients with benign AML to undergo unnecessary surgery for suspected RCC when the diagnosis is not established beforehand. This review presents the most recent studies and developments in preoperative evaluation of fat-poor AML.

Intensity ratio curve analysis of small renal masses on T2‐weighted magnetic resonance imaging: Differentiation of fat‐poor angiomyolipoma from renal cell carcinoma

“…Of the reported radiological features, “low SI” and “homogeneity” on T2‐WI are characteristic of fpAML in standard MRI techniques . The fpAML feature of low SI on T2‐WI might result from its smooth muscle component; furthermore, it shows hyperattenuation on an unenhanced CT scan .…”

“…The fpAML feature of low SI on T2‐WI might result from its smooth muscle component; furthermore, it shows hyperattenuation on an unenhanced CT scan . The low SI on T2‐WI could be a key feature of fpAML in differentiating it from ccRCC (which typically presents with iso or high SI on T2‐WI) . This characteristic feature of fpAML is represented as “tumor SI” on the IR curve analysis.…”

“…Some quantitative evaluations including histogram analysis and texture analysis on unenhanced CT, and tumor‐to‐spleen ratio analysis on chemical shift MRI, have been proposed to diagnose SRM . Sasiwimonphan et al .…”

“…As they are often clinically misdiagnosed as RCC, fpAMLs account for the majority of benign renal tumors being resected. Some known radiological features of fpAML include slightly higher attenuation than renal parenchyma on an unenhanced CT scan because of their muscular component, homogeneity within the tumor on an unenhanced or enhanced CT scan, absence of a pseudocapsule and relatively lower intensity than renal parenchyma on a T2‐WI, and homogenously high SI on a diffusion‐weighted magnetic resonance image . These radiological characteristics are subjectively assessed; there are no clear objective criteria for assessing tumor SI, the extent of heterogeneity and the presence of a pseudocapsule.…”

Angiomyolipoma of the scrotum: report of a rarely seen case and review of the literature

“…However, our case was fat-poor, which led to its missed diagnosis on imaging studies. [7][8][9] The fat was present in microscopic sections and consisted of scattered individual adipocytes or small clusters of adipose cells, as shown in Figure 2. Only one case of scrotal AML has been reported previously in a 22-year-old man presenting with left orchialgia.…”