Which lesion is a small fatty tumor less than 5 mm in diameter with specific echogenicity to differentiate from cortex and sinus?

Which lesion is a small fatty tumor less than 5 mm in diameter with specific echogenicity to differentiate from cortex and sinus?

• A. Angiomyolipoma
• B. Adenoma
• C. Lipoma
• D. Oncocytoma

Answer: (C)

A lesion composed of mature fat in the kidney tends to appear as a tiny, well-defined, homogeneous structure with very bright echogenicity on ultrasound. When it’s small, under 5 mm, this fat-traction appears as a discrete, uniform echogenic focus that can be distinguished from the renal cortex, which is less echogenic, and from the surrounding sinus fat, which is expected to be very echogenic but part of a larger fat-containing region rather than a separate, well-circumscribed mass. This combination—small size, uniform fat content, and clear margins—fits a lipoma best. Angiomyolipoma also contains fat but includes vascular and smooth muscle components, often giving a more heterogeneous or varied appearance and isn’t defined as a small purely fatty lesion. Adenoma and oncocytoma are solid renal tumors without the fat-dominant, uniformly echogenic characteristics described here.

A lesion composed of mature fat in the kidney tends to appear as a tiny, well-defined, homogeneous structure with very bright echogenicity on ultrasound. When it’s small, under 5 mm, this fat-traction appears as a discrete, uniform echogenic focus that can be distinguished from the renal cortex, which is less echogenic, and from the surrounding sinus fat, which is expected to be very echogenic but part of a larger fat-containing region rather than a separate, well-circumscribed mass. This combination—small size, uniform fat content, and clear margins—fits a lipoma best.

Angiomyolipoma also contains fat but includes vascular and smooth muscle components, often giving a more heterogeneous or varied appearance and isn’t defined as a small purely fatty lesion. Adenoma and oncocytoma are solid renal tumors without the fat-dominant, uniformly echogenic characteristics described here.