What are the primary renal causes and management strategies for hypertension in a newborn within the first few weeks of life?

Renal Causes of Neonatal Hypertension

The most common renal causes of hypertension in newborns are umbilical arterial catheter-associated thromboembolism (particularly renal artery or vein thrombosis), congenital renal structural abnormalities, and acute tubular necrosis. 1, 2, 3, 4, 5

Primary Renal Causes

Thromboembolic Disease (Most Common)

• Umbilical arterial catheter-associated thrombosis is the leading renal cause of neonatal hypertension, occurring in up to 2% of NICU admissions 2, 3, 5
• Renal artery thrombosis presents with sustained severe hypertension (mean arterial pressure >85 mmHg), often therapy-resistant even with aggressive treatment 1
• Renal venous thrombosis shows decreased venous blood flow on Doppler ultrasound with abnormal waveforms 1
• These thromboembolic events can cause complete arterial occlusion requiring nephrectomy when medically uncontrollable 1

Congenital Renal Structural Abnormalities

• Renal dysplasia, hypoplasia, and polycystic kidney disease are significant causes 4, 5
• Obstructive uropathy and posterior urethral valves can present with hypertension in the first weeks of life 5
• These structural abnormalities accounted for 4 of 23 identified causes in one 10-year review 4

Acute Renal Parenchymal Disease

• Acute tubular necrosis was the single most common identified cause (7 of 23 cases with identified etiology) in neonates with hypertension 4
• Interstitial nephritis, though less common, can present with severe hypertension requiring treatment 4
• Renal parenchymal disease is a major category of neonatal hypertension causes 2, 3

Renovascular Disease

• Renal vascular abnormalities (excluding catheter-related thrombosis) accounted for 8 of 23 identified causes 4
• Renovascular disease has the worst prognosis, with hypertension often persisting beyond infancy 3

Diagnostic Approach

Initial Screening (Perform Immediately)

• Urinalysis, BUN, serum creatinine, and plasma renin activity (PRA) - if all normal, diagnostic studies can be postponed as hypertension tends to be benign and self-limited 4
• If any of these are abnormal, a renal cause is present in 68% of cases and warrants immediate further investigation 4
• Renal Doppler ultrasound to assess for thrombosis, structural abnormalities, and blood flow patterns 1, 5

Advanced Imaging When Initial Studies Abnormal

• Renal angiography if Doppler suggests arterial thrombosis or severe renovascular disease 1
• MAG3 renal scan to assess differential kidney function, particularly before considering nephrectomy 1
• These studies should be performed urgently in therapy-resistant hypertension with cardiac or neurologic involvement 1

Management Strategies

Medical Management

• First-line agents: ACE inhibitors (enalaprilat IV) and hydralazine for acute management 1
• Calcium channel blockers and beta-blockers are additional options, though data in neonates are extremely limited 2, 3
• Critical caveat: Even aggressive multi-drug therapy may fail in complete renal artery occlusion 1

Surgical Intervention

• Nephrectomy is indicated when hypertension remains medically uncontrollable and causes cardiac dysfunction or hypertensive encephalopathy 1
• This should be considered when MAG3 scan shows minimal function in the affected kidney 1
• Prognosis after nephrectomy for unilateral disease is excellent, with normal development at 6-12 month follow-up 1

Treatment Thresholds

• Sustained mean arterial pressure >85 mmHg requires immediate treatment 1
• Development of hypertensive encephalopathy or cardiac dysfunction mandates urgent intervention, potentially including surgery 1

Prognosis and Follow-up

Resolution Patterns

• In 57% of neonatal hypertension cases, no cause is identified 4
• When urinalysis, BUN, creatinine, and PRA are normal, hypertension is non-malignant, short-lived, and always resolves spontaneously 4
• Even when a cause is identified, hypertension generally resolves by 1 year of age unless renovascular disease is present 3, 4

Poor Prognostic Indicators

• Abnormal urinalysis, elevated BUN/creatinine, or elevated PRA predict persistent hypertension 4
• Renovascular disease has the highest risk of persistent hypertension requiring long-term treatment 3
• Two hypertensive deaths occurred in the group with abnormal preliminary studies 4

Critical Pitfalls to Avoid

• Do not delay renal Doppler ultrasound in any neonate with sustained hypertension, as thromboembolic disease requires urgent diagnosis 1, 2
• Do not perform extensive diagnostic workup if urinalysis, BUN, creatinine, and PRA are all normal - these infants have benign, self-limited hypertension 4
• Do not continue medical management indefinitely in therapy-resistant hypertension with end-organ damage when unilateral renal disease is present - nephrectomy can be life-saving and curative 1
• Do not assume hypertension will resolve in renovascular disease - these patients often require prolonged or permanent treatment 3