Renal Imaging
Renal Imaging - Use of ultrasound, CT, MRI, radionuclide scans and other imaging in nephrology.
Practical orientation: Use ultrasound for obstruction and chronicity; use CT or MRI when anatomy, stones, masses or vascular questions require more detail.
Renal ultrasound
| Indication | Use |
|---|---|
| AKI/CKD evaluation | Kidney size, obstruction, cysts, echogenicity, masses. |
| Biopsy guidance | Percutaneous kidney biopsy. |
| Transplant kidney | Perinephric fluid, obstruction, vascular assessment. |
| Bladder | Retention and post-void residual. |
Ultrasound interpretation
| Finding | Consider |
|---|---|
| Bilaterally small kidneys | Chronic kidney disease or scarring. |
| Bilaterally large kidneys | Diabetes, obesity/hyperfiltration, AIN, infiltrative disease, HIVAN, ADPKD. |
| Asymmetry >1 cm | Renovascular disease, infarction, pyelonephritis, congenital abnormality or RVT. |
| Hydronephrosis | Urinary obstruction; false negatives occur early or with volume depletion/RP fibrosis. |
| Increased echogenicity | Intrinsic parenchymal disease, but not reliable alone for CKD. |
| Complex cyst | Needs CT/MRI characterization. |
| Solid mass | Contrast CT or MRI unless contraindicated. |
CT
| Test | Best uses |
|---|---|
| Noncontrast CT | Stones, calcification, obstruction localization, chronic cortical thinning. |
| Contrast CT | Mass, complex cyst, abscess, malignancy staging, vascular lesions, infarction. |
| CT urography | Hematuria evaluation when high-risk urothelial cancer is possible. |
MRI/MRA
MRI is useful for complex cysts, small masses, renal artery stenosis and pregnancy when CT would otherwise be considered. Use gadolinium cautiously in advanced CKD; macrocyclic/newer agents are preferred when contrast MRI is necessary and alternatives are inadequate.
Radionuclide renal scan
| Radiotracer | Function | Clinical use |
|---|---|---|
| DTPA | Glomerular filtration. | GFR estimate and obstruction. |
| MAG3 | Tubular secretion. | Split function and obstruction, especially reduced renal function. |
| DMSA | Cortical tubular retention. | Scarring, infarction, split cortical function. |
Other imaging
| Test | Use |
|---|---|
| Angiography | Definitive vascular diagnosis/treatment for RAS, FMD and medium/large-vessel vasculitis. |
| Pyelography | Suspected ureteral obstruction when CT/US are inconclusive or contrast excretion poor. |
| VCUG | Vesicoureteral reflux. |
| PET | Selected ADPKD cyst infection or transplant lymphoproliferative disease. |
| Plain radiograph | Radiopaque stones and nephrocalcinosis; largely replaced by CT for many indications. |