First and second year — the floor first, then every step
An echogenic renal lesion raises AML; ultrasound cannot prove fat and cannot distinguish a small echogenic RCC.
Orient first
AML is typically a well-defined hyperechoic renal mass. A small RCC can look identical.
Acoustic shadowing and a speed-of-sound artefact are suggestions, not proofs. The confirming test is non-contrast CT or MRI.
Colour Doppler may show internal vessels; their presence does not make the diagnosis and their absence does not exclude it.
Acquire the study
Scan both kidneys with a curvilinear probe; measure the lesion in three planes; apply colour Doppler with settings for slow flow.
Do not offer AML as a conclusion — offer it as the reason for non-contrast CT or MRI.
The manoeuvre
Confirm the mass arises from renal parenchyma on grey-scale, not from perinephric fat or the adrenal, by showing a claw of cortex around it.
Describe echogenicity against cortex at the SAME depth, posterior acoustic features, and internal colour Doppler flow.
Name non-contrast CT (or fat-saturated MRI) as the study that can prove macroscopic fat, rather than concluding AML.
What confirms it
A renal mass containing macroscopic fat, without calcification, is an angiomyolipoma until a rare fat-containing RCC is specifically suspected (calcification, invasion, lymphadenopathy).
What licenses you to exclude it
⚠️ ABSENCE OF VISIBLE FAT DOES NOT EXCLUDE AML — fat-poor AML is a real entity and needs the same work-up as any other solid renal mass.
Ultrasound cannot exclude AML and cannot confirm it. An echogenic renal lesion is an AML only when CT or MRI has shown fat.
The classic misread
Calling an echogenic renal lesion an angiomyolipoma on ultrasound alone.
Reference values
Each value carries the caveat that keeps it from being misused. Normal limits and diagnostic criteria are kept apart on purpose: a disease cut-off read as a normal range is the more dangerous mistake.
Diagnostic criteria
Renal mass · Size as used in T-staging and active-surveillance discussions
a named staging input: T1a is 4 cm or less, T1b is over 4 to 7 cm, T2 over 7 cm — TNM edition must be named; surveillance pathways use their own size bands
Size is one axis of T-stage; perinephric fat, venous and collecting-system invasion are others. Do not quote an edition year from memory — name "current TNM" and verify. Versioned criterion — verify against the current edition before clinical use.
CT · MRI · USG
Fat-containing lesions · Attenuation of macroscopic fatat or below −10 HU
Macroscopic fat in a renal mass makes angiomyolipoma the leading diagnosis (in the absence of calcification), and supports adrenal myelolipoma or ovarian dermoid in those organs — but fat-poor AML exists, so absence of fat excludes nothing.
CT
See it on real cases
Direct links to Radiopaedia — the reference article and worked cases with their images. Each opens on Radiopaedia.