What are the symptoms of pyelonephritis and can it be diagnosed with a computed tomography (CT) scan?

Pyelonephritis Symptoms and CT Diagnostic Role

Pyelonephritis typically presents with fever (>38°C), chills, flank pain, nausea, vomiting, or tenderness at the costovertebral angle, with or without symptoms of cystitis, and CT imaging is not indicated for initial evaluation of uncomplicated pyelonephritis but should be performed if the patient remains febrile after 72 hours of appropriate antibiotic therapy. 1

Clinical Presentation of Pyelonephritis

Key Symptoms

• Fever (>38°C)
• Chills
• Flank pain or tenderness at the costovertebral angle
• Nausea and vomiting
• Systemic inflammation signs (fatigue)
• Bladder symptoms (urgency, dysuria, frequency) in approximately 80% of cases 1

Important Clinical Considerations

• Up to 20% of patients may lack bladder symptoms 1
• Diabetic patients often present atypically, with up to 50% lacking the typical flank tenderness 1
• Clinical presentation can range from mild flank pain with low-grade fever to septic shock 1
• Urinalysis typically shows pyuria and/or bacteriuria 1
• Urine culture yielding >10,000 colony-forming units of a uropathogen per milliliter is the confirmatory diagnostic test 1

Role of CT in Pyelonephritis Diagnosis

When CT is NOT Indicated

• Initial evaluation of uncomplicated pyelonephritis in otherwise healthy patients 1
• Patients who respond to appropriate antibiotic therapy within 72 hours 1

When CT IS Indicated

• Patient remains febrile after 72 hours of appropriate antibiotic therapy 1
• Immediate deterioration in clinical status 1
• High-risk patients:
  • Diabetic patients 1
  • Immunocompromised patients 2
  • History of urolithiasis or prior renal surgery 2
  • Suspected complications (abscess, emphysematous pyelonephritis) 1

CT Findings in Pyelonephritis

• Acute uncomplicated pyelonephritis:

  • Renal enlargement
  • Wedge-shaped heterogeneous areas of decreased enhancement ("striated nephrogram") 3
  • Global enlargement, poor parenchymal enhancement in diffuse forms 2

• Complicated pyelonephritis:

  • Intrarenal or perirenal abscess
  • Emphysematous changes (gas in renal parenchyma)
  • Pyonephrosis (pus in collecting system) 3

Diagnostic Algorithm for Suspected Pyelonephritis

1. Initial Diagnosis: Based on clinical presentation (fever, flank pain) and urinalysis showing pyuria/bacteriuria

2. Obtain Cultures: Urine culture and blood cultures if sepsis is suspected 1

3. Initial Imaging:

   • For uncomplicated cases in healthy adults: No imaging needed 1
   • For patients with risk factors (history of stones, renal dysfunction, high urine pH): Ultrasound to rule out obstruction 1

4. Follow-up Imaging:

   • If fever persists >72 hours on appropriate antibiotics: Contrast-enhanced CT 1
   • If clinical deterioration occurs at any point: Immediate contrast-enhanced CT 1
   • For pregnant women: Ultrasound or MRI instead of CT 1

Special Considerations

High-Risk Populations

• Diabetic patients may have painless pyelonephritis (50% lack typical flank tenderness) and are more prone to complications 1, 4
• Elderly, immunocompromised, and patients with structural abnormalities require closer monitoring and more aggressive imaging 5

Diagnostic Pitfalls

• Relying solely on bladder symptoms may miss pyelonephritis (20% lack these symptoms) 1
• Ultrasound alone is insensitive for uncomplicated pyelonephritis but can detect abscesses and focal bacterial nephritis 4
• CT findings of pyelonephritis can mimic renal infarction, lymphoma, or interstitial nephritis 2

CT remains the gold standard for assessing pyelonephritis severity and complications when indicated, but should not be used routinely for uncomplicated cases that respond to antibiotics within 72 hours 1, 2.