NephrologyTier 2Topic

Imaging - renal tract ultrasound

Role

First-line, radiation-free imaging of the kidneys, ureters (poorly visualised unless dilated), and bladder - assesses size, cortical thickness, cysts, masses, hydronephrosis, and bladder residual volume
Investigation of choice for suspected obstruction, AKI/CKD workup, initial renal mass characterisation, and in pregnancy/children where radiation is avoided

Findings and what they mean

Small, echogenic kidneys - chronic, often irreversible renal disease
Normal-sized or enlarged echogenic kidneys - an acute process, or infiltrative/polycystic disease
Cortical thinning + hydronephrosis - chronic obstruction

Cysts and Doppler

Bosniak classification - risk-stratifies renal cysts by ultrasound/CT appearance (I-II benign, IIF-III indeterminate needing follow-up/further imaging, IV likely malignant)
Doppler ultrasound adds renal artery resistive index and can screen for renal vein thrombosis or renal artery stenosis (operator-dependent)

Acting on findings

Guides the urgency of further workup - hydronephrosis on ultrasound in a patient with AKI prompts urgent decompression assessment
Post-void bladder residual volume identifies bladder outlet obstruction/urinary retention contributing to upper tract dilatation

Conditions

Obstructive uropathy, autosomal dominant polycystic kidney disease (cyst counting for diagnostic criteria), renal cell carcinoma, chronic kidney disease staging correlation

Limitations

Operator- and body-habitus-dependent - a normal ultrasound does not fully exclude early obstruction or a small stone, and CT is used when suspicion remains high

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