Genitourinary Radiology
Core concepts
Know renal anatomy and the Bosniak classification of cystic renal masses, from simple cyst (I) to clearly malignant (IV, with solid enhancing components). Understand the imaging features of renal cell carcinoma (clear cell: hypervascular; papillary: hypovascular), angiomyolipoma (macroscopic fat), and transitional cell carcinoma (filling defect in the collecting system). Master the CT urography phases: unenhanced, nephrographic, excretory. Recognize the signs of acute pyelonephritis (striated nephrogram), emphysematous pyelonephritis (gas in parenchyma), and renal abscess. Understand adrenal imaging: adenoma (low density <10 HU on unenhanced CT, rapid washout), pheochromocytoma, and metastases. Know prostatic and bladder imaging basics, including PI-RADS concepts and bladder cancer staging.
Traps
Do not diagnose a simple cyst if the wall is thickened, septated, or calcified; assign the Bosniak category and recommend follow-up or surgery accordingly. A hyperdense renal lesion on unenhanced CT may be a hemorrhagic cyst or a solid tumor-use enhancement to distinguish. Beware mistaking a parapelvic cyst for hydronephrosis. Adrenal lesions with high unenhanced attenuation are not adenomas.
Rule of thumb
Enhancement is the discriminator: measure Hounsfield units before and after contrast; a lesion that enhances is solid until proven otherwise.
Worked example
A 3 cm renal lesion with a thick irregular wall and nodular enhancement is Bosniak IV and warrants surgical excision, whereas a 1 cm smooth thin-walled cyst is Bosniak I and requires no follow-up.