Genitourinary Radiology
Stones and obstruction
Non-contrast CT is the reference standard for urinary calculi. Size predicts outcome: stones under 5 mm usually pass spontaneously, those over 10 mm rarely do. Grade hydronephrosis as mild (calyceal blunting), moderate (ballooning of calyces and pelvis) and severe with cortical thinning.
Renal masses
Apply the Bosniak classification (2019 version) to cystic lesions: categories I and II are benign, IIF requires follow-up, III requires surgery or biopsy and IV is clearly malignant. Enhancement of septa or wall and nodularity upgrade a lesion. Among solid tumours, clear cell carcinoma is hypervascular and heterogeneous, papillary carcinoma is hypovascular, and chromophobe carcinoma is homogeneous. Macroscopic fat suggests angiomyolipoma. A central scar suggests oncocytoma but cannot exclude carcinoma.
Prostate and bladder
PI-RADS v2.1 scores the peripheral zone predominantly by diffusion-weighted imaging and the transition zone by T2-weighted imaging; dynamic contrast enhancement upgrades equivocal peripheral zone lesions. Bladder cancer staging hinges on whether the detrusor muscle is invaded.
Adrenals and variants
An unenhanced density below 10 Hounsfield units identifies a lipid-rich adenoma. A column of Bertin is normal cortex, not a mass.
Traps
Peripelvic cysts mimic hydronephrosis. Pseudoenhancement can falsely upgrade a cyst on CT. Testicular torsion is a clinical and Doppler diagnosis and surgery must never be delayed for imaging.
Rule of thumb
Adrenal incidentaloma under 10 HU on unenhanced CT = lipid-rich adenoma; no further work-up is required.