Small (<1 cm) incidental echogenic renal cortical nodules: chemical shift MRI outperforms CT for confirmatory diagnosis of angiomyolipoma (AML)

Excerpt

Non-calcified echogenic renal cortical nodules are commonly detected with abdominal ultrasound (US). The majority of these nodules represent benign angiomyolipomas (AMLs), which are present in 0.3–2.1 % of the population at autopsy [1]. The increased echogenicity (in the absence of calcification) of renal AML is due to the presence of gross or mature fat within the nodule [2]. Although renal AMLs are typically markedly echogenic, echogenicity may vary depending upon the relative proportion of fat, smooth muscle and blood vessels within the nodule [3, 4]. Renal cell carcinoma (RCC) is traditionally considered to be less echogenic than renal cortical parenchyma, although the echogenicity of RCC varies with its size. Forman et al. [5] demonstrated that one-third of RCCs less than 3 cm in size are as echogenic as “classic” AML. In a recent meta-analysis, Farrelly et al. [6] demonstrated that nearly half of small RCCs are more echogenic than renal cortical parenchyma and 11.5 % are as echogenic as renal sinus fat. The increased echogenicity of small RCC is attributed to cell arrangement with increased internal interfaces and the presence of internal degeneration or haemorrhage [7]. Nodule heterogeneity, intratumoural cysts and the presence of a hypoechoic rim are specific sonographic findings that favour echogenic RCC; while posterior acoustic shadowing is a specific sonographic finding that favours AML [6]. Although these differentiating sonographic findings are specific, they lack the sensitivity required to discriminate between AML and RCC when a small echogenic renal cortical nodule is detected in everyday practice [6]. …