What does preserved or lost corticomedullary differentiation on ultrasound indicate in a patient with a history of kidney disease, diabetes, or hypertension?

Corticomedullary Differentiation on Ultrasound

Preserved corticomedullary differentiation (CMD) on ultrasound generally indicates early-stage or less severe kidney disease, while loss of CMD suggests advanced chronic kidney disease with significant parenchymal damage and fibrosis. 1

What Preserved CMD Indicates

Preserved CMD is reassuring but does NOT exclude significant kidney disease, particularly in patients with diabetes, hypertension, or early-stage CKD. 1

• Early CKD (Stages 1-2) commonly maintains normal CMD because structural architecture remains largely intact despite functional impairment (eGFR ≥60 mL/min/1.73 m²). 2

• Diabetic kidney disease characteristically presents with preserved CMD and normal-sized kidneys despite progressive functional decline, making ultrasound findings falsely reassuring in this population. 1, 2

• Acute kidney injury frequently shows preserved CMD regardless of creatinine elevation, as structural damage has not yet occurred. 3

• Infiltrative disorders (such as amyloidosis or lymphoma) can maintain CMD while significantly reducing kidney function. 1

What Loss of CMD Indicates

Loss of CMD is a marker of advanced parenchymal damage and typically indicates chronic, irreversible kidney disease. 1

• Advanced CKD with cortical thinning and loss of CMD suggests end-stage or near-end-stage renal disease with extensive fibrosis. 1, 4

• Poor CMD combined with small kidneys (<9 cm) indicates chronic, irreversible damage and generally contraindicates kidney biopsy due to high risk and low diagnostic yield. 1, 4

• Loss of CMD in renal artery stenosis indicates non-viable kidney parenchyma and predicts poor response to revascularization. 1

Critical Clinical Context for Interpretation

In Diabetic Patients

Normal CMD and kidney size are common in diabetic nephropathy and should NOT provide false reassurance. 1, 2

• Diabetic kidney disease maintains normal structural appearance on ultrasound while eGFR declines and albuminuria progresses. 1, 2

• Diagnosis requires laboratory testing (eGFR and UACR), not imaging findings. 2

• Up to 30% of patients with presumed diabetic kidney disease have alternative diagnoses on biopsy, particularly when CMD is lost or kidneys are asymmetric. 2

In Hypertensive Patients

Hypertensive nephrosclerosis typically shows poor CMD, increased cortical echogenicity, and reduced kidney size in advanced stages. 1, 5

• Simple renal cysts and poor CMD are the most common ultrasound findings in chronic hypertension. 5

• Preserved CMD with hypertension and declining eGFR should prompt evaluation for renovascular disease (renal artery stenosis). 1

In Renal Artery Stenosis

Assessment of CMD is critical for determining kidney viability and predicting revascularization benefit. 1

• Viable kidney: Distinct cortex >0.5 cm with preserved CMD, kidney length >8 cm, resistive index <0.8. 1

• Non-viable kidney: Loss of CMD, kidney length <7 cm, resistive index >0.8, albumin-creatinine ratio >30 mg/mmol. 1

• Loss of CMD predicts poor response to revascularization and should influence decision-making against intervention. 1

Diagnostic Limitations and Pitfalls

Ultrasound findings have minimal impact on diagnosis and management in patients with diabetes or hypertension—laboratory testing is essential. 1

• In a series of 1,007 CKD patients, ultrasound abnormalities were detected in only 26.8%, contributed to diagnosis in only 5.9%, and affected management in only 3.3%. 1

• Preserved CMD can occur with severe acute kidney injury (creatinine up to 10.5 mg/dL), making it unreliable for assessing severity of acute dysfunction. 3

• Normal kidney size does not exclude CKD, as size is initially preserved in diabetic nephropathy, minimal change disease, FSGS, and infiltrative disorders. 1, 2

• Increased cortical echogenicity is nonspecific and subjective, occurring in only 10.3% of CKD patients and providing limited diagnostic value. 1

When Ultrasound IS Indicated

Ultrasound should be reserved for specific clinical scenarios, not routine CKD surveillance. 1

• History of kidney stones or obstruction (to detect hydronephrosis). 1

• Suspected renal artery stenosis (flash pulmonary edema, resistant hypertension, rapidly declining eGFR). 1

• Family history of polycystic kidney disease. 1

• Acute kidney injury of unknown etiology (to exclude obstruction). 1

• Asymmetric kidney size or function (suggesting renovascular disease or unilateral pathology). 1

Essential Management Principle

Regardless of ultrasound findings, all patients with diabetes, hypertension, or suspected kidney disease require laboratory assessment with eGFR and UACR to diagnose and stage CKD. 1, 2

• CKD is defined by eGFR <60 mL/min/1.73 m² OR albuminuria (UACR ≥30 mg/g) persisting ≥3 months, independent of imaging findings. 1, 2

• Preserved CMD with declining eGFR or albuminuria still represents significant kidney disease requiring treatment. 2