Can frequent Urinary Tract Infections (UTIs) cause kidney damage visible on a Computed Tomography (CT) scan?

Can Frequent UTIs Cause a Kidney to "Disappear" on CT Scan?

A kidney cannot literally disappear from a CT scan due to frequent UTIs, but severe recurrent pyelonephritis can cause progressive renal damage leading to a small, scarred, non-functioning kidney that may appear markedly atrophied or difficult to visualize on imaging.

Understanding Renal Damage from Recurrent UTIs

Mechanism of Kidney Damage

• Recurrent urinary tract infections, particularly when they ascend to involve the kidney parenchyma (pyelonephritis), trigger an inflammatory process that forms microabscesses which can coalesce into larger abscesses 1
• The inflammatory reaction within the renal parenchyma can lead to pyelonephritic scarring, especially when infections are inadequately treated or occur at a young age 2
• Renal scarring represents permanent damage to kidney tissue and is the most consequential long-term complication of acute pyelonephritis 3

What Actually Happens to the Kidney

• Repeated episodes of pyelonephritis cause progressive renal scarring that can result in a shrunken, atrophic kidney with severely reduced or absent function 2
• Long-term complications from renal scarring include hypertension, reduced kidney function, and potentially chronic renal failure 1, 2
• A severely scarred kidney may appear significantly smaller on CT imaging compared to the contralateral kidney, but it doesn't truly "disappear" - it becomes atrophic

Risk Factors That Increase Kidney Damage Risk

Structural Abnormalities

• Vesicoureteral reflux (VUR) is a major risk factor that facilitates ascending infection and renal damage even with bacteria of "low virulence" 2
• Congenital urinary tract anomalies, obstructive uropathies, and mechanical obstruction disrupt normal urinary flow and increase pyelonephritis risk 1, 4
• Renal calculi, urethral or bladder diverticula, and altered bladder function predispose to recurrent infections 4

Host and Clinical Factors

• Young age at time of infection increases susceptibility to permanent renal scarring 2
• Inadequate or delayed antibiotic therapy is a critical predisposing factor for pyelonephritic scars 2
• Diabetes mellitus, pregnancy, and genetic predisposition increase infection risk 1, 4

When to Pursue Imaging

Indications for CT Imaging

For patients with recurrent complicated UTIs, CT urography (CTU) is the primary imaging test recommended, providing detailed anatomic depiction of the entire urinary tract including assessment for scarring, obstruction, and congenital anomalies 5

• Imaging should be considered in patients with nonresponse to conventional therapy, frequent reinfections or relapses (particularly within 2 weeks of treatment), or known underlying risk factors 5
• CTU includes unenhanced, nephrographic, and excretory phase images (5-20 minutes after contrast) and is excellent for detecting congenital anomalies and obstruction 6, 5
• Ultrasound of kidneys and bladder is appropriate as initial screening, particularly in children, and can diagnose hydronephrosis in early stages 6

What Imaging Should NOT Be Done

• Routine imaging is not recommended for uncomplicated recurrent UTIs due to low yield of anatomic abnormalities 5
• Standard contrast-enhanced CT of abdomen/pelvis is not optimally tailored for urothelial evaluation 5

Critical Clinical Pitfalls

Prevention of Renal Scarring

• Treatment of acute pyelonephritis with appropriate antibiotics within 48 hours of fever onset is crucial to lower the risk of renal scarring 3
• Early recognition of obstructive uropathies by sonographic screening and undelayed diagnosis with consequent treatment of symptomatic UTI may reduce the incidence of long-term renal damage 2
• Early identification of reflux after symptomatic UTIs is important for preventing progressive damage 2

Common Misconceptions

• Not all patients with pyelonephritis present with fever - absence of fever does not exclude the diagnosis 4
• Bilateral pyelonephritis should raise high suspicion for underlying structural or functional abnormalities of the urinary tract 4
• The distinction between upper and lower tract UTI is clinically difficult but critically important, as permanent renal damage occurs when infection involves the kidneys 7

Bottom Line for Clinical Practice

If a patient reports that a kidney has "disappeared" on CT scan in the context of frequent UTIs, this likely represents severe chronic pyelonephritis with resultant renal atrophy and scarring rather than actual disappearance. The appropriate workup includes CT urography to assess for underlying structural abnormalities, obstruction, or other treatable causes of recurrent infection 5. The focus should shift to protecting the remaining kidney function through prompt treatment of infections, identifying and correcting any anatomic abnormalities, and preventing future episodes 2, 3.