Genitourinary Imaging
What the exam tests
GU imaging covers renal masses, urolithiasis, prostate MRI, bladder cancer, adrenal lesions, and female pelvic imaging. Expect multiphasic CT/MRI, PI-RADS, Bosniak classification, and stone protocols.
Core rules
- A renal mass is enhancing if it increases by ≥20 HU after contrast; simple cysts are near water density and do not enhance.
- Bosniak classification: I and II are benign; IIF requires follow-up; III and IV usually require surgery.
- Noncontrast CT is the test of choice for suspected ureteral stone in most patients.
- PI-RADS uses T2-weighted, diffusion-weighted, and dynamic contrast sequences; a score of 4 or 5 typically prompts targeted biopsy.
Worked example
A 62-year-old has an incidental 3.5-cm solid renal mass. Multiphase CT shows enhancement of 45 HU on the nephrographic phase. Reasoning: true enhancement confirms a solid renal neoplasm, most likely renal cell carcinoma. The next step is staging and urologic evaluation; a partial nephrectomy may be considered if technically feasible. A simple cyst would show near-water density and no enhancement.
Traps
Mistaking pseudoenhancement for a solid mass; calling a Bosniak IIF cyst benign; using PI-RADS without adequate DWI; and missing that a stone protocol should be noncontrast.
Key points
- Enhancement of ≥20 HU suggests a solid renal mass.
- Bosniak III/IV lesions usually require surgery.
- Noncontrast CT is first-line for suspected urolithiasis.
- PI-RADS 4-5 lesions warrant targeted biopsy.
- Adrenal lesions are characterized by density and washout.