This 45-year-old male patient presents with right upper quadrant pain.
Answer: 3. Renal angiomyolipoma
● Angiomyolipoma (AML) is the most common benign solid renal neoplasm observed in clinical practice1.
● Prevalence ranges from 0.2 to 0.6%, females being affected more than males2.
● 80% are sporadic while 20% are associated with tuberous sclerosis complex1.
● As the name suggests, the tumor consists of varying amounts of three elements1:
- Angio: Dysmorphic blood vessels
- Myo: Smooth muscle components
- Lipoma: Mature adipose tissue
● Hyperechoic due to fat component.
● Fat-poor AML can be difficult to diagnose on ultrasound and differentiation from a renal cell carcinoma (RCC) can also be challenging in these cases3.
● Up to 1/3rd cases of AML can show acoustic shadowing which is not seen with RCC1.
● Unenhanced CT
- Fat in lesions can be seen as hypodense areas with average HU values less than -10 HU. The presence of fat is however nonspecific and fat has been reported in RCCs as well3. In such cases, other associated features like larger size, necrosis, invasive/irregular margins, renal vein/ IVC involvement and metastases can help aid diagnosis3.
- Fat-poor AMLs appear as homogeneously hyperdense on unenhanced CT.
- Calcification is unusual and should raise the possibility of an alternative diagnosis like RCC1.
- Intra-tumoral hemorrhage can be also seen, especially in tumors larger than 4cm1.
● Contrast enhanced CT
- Larger lesions can have dilated tortuous vessels and aneurysms, which makes them susceptible to intra-tumoral hemorrhage3. A small aneurysm is seen in the lesion depicted in Figure 1.
- Fat-poor AMLs show homogenous persistent and gradual enhancement3.
● Fat-rich AMLs appear hyperintense on T1 and T2-weighted images owing to their lipid content. Fat suppressed images and in/out phase imaging, aids confirmation of fat.
● Fat-poor AMLs appear as hypointense lesions on T2-weighted images, while fat-invisible AMLs are isointense as the signal is mainly from the muscle component of the lesion3.
● Classic angiomyolipoma1:
- Conservative management
- Lesions more than 4 cm and with intratumoral aneurysms measuring more than 5mm are at increased risk of spontaneously bleeding, and may need active management.
● Fat-poor AMLs and fat-invisible AMLs may need biopsy for confirmation as these can be difficult to differentiate from RCCs1.
● AMLs associated with tuberous sclerosis complex have increased risk of spontaneous bleeding1 and are more likely to need active management.
● Treatment options include1:
- Arterial embolization
- Partial nephrectomy
- mTOR inhibitor sirolimus has been useful in a few subtypes.
1. Jinzaki M, Silverman S, Akita H, Nagashima Y, Mikami S, Oya M. Renal angiomyolipoma: a radiological classification and update on recent developments in diagnosis and management. Abdominal Imaging. 2014;39(3):588-604.
2. Vos N, Oyen R. Renal Angiomyolipoma: The Good, the Bad, and the Ugly. Journal of the Belgian Society of Radiology. 2018;102(1).
3. Park B. Renal Angiomyolipoma: Radiologic Classification and Imaging Features According to the Amount of Fat. American Journal of Roentgenology. 2017;209(4):826-835.