Renal & Adrenal MRI — Characterising Masses

Renal & Adrenal MRI

For two organs full of incidental lumps, MRI’s tissue characterisation — fat, blood, enhancement — often makes the call CT can’t, without radiation.

Adrenal: the chemical-shift trick

Most incidental adrenal nodules are benign adenomas rich in intracytoplasmic (microscopic) fat. On chemical-shift MRI, such fat causes signal to drop on opposed-phase compared with in-phase images — confidently diagnosing a lipid-rich adenoma.

Signal drop on opposed-phase = lipid-rich adenoma. No drop needs further work-up (lipid-poor adenoma, phaeochromocytoma, metastasis, malignancy) with washout CT or biochemistry.

Renal masses

Cysts: MRI characterises complexity and enhancement, applying the Bosniak classification to estimate malignant risk.
Solid tumours: detecting enhancement (the key sign of a solid neoplasm), and distinguishing angiomyolipoma (macroscopic fat) from renal cell carcinoma.
Staging: venous (renal vein/IVC) tumour thrombus — MRI maps its extent for surgery.

When MRI over CT

MRI is preferred when iodinated contrast or radiation is best avoided (renal impairment, pregnancy, young patients, repeated surveillance), for problem-solving indeterminate CT findings, and for enhancement assessment via subtraction when a lesion is intrinsically high signal.

Reference: Silverman SG et al. Bosniak classification of cystic renal masses, version 2019. Radiology 2019;292:475–88.

Educational summary for clinicians; correlate with biochemistry and MDT. Not medical advice.