What are the causes and treatments of left flank pain?

Left Flank Pain: Causes and Management

Initial Imaging Approach

For most patients presenting with left flank pain, low-dose CT abdomen and pelvis without IV contrast is the preferred initial imaging modality, as it provides the highest diagnostic accuracy for both urinary tract stones and alternative diagnoses. 1

Primary Imaging Recommendations by Clinical Context

• Suspected urolithiasis (most common cause): Low-dose noncontrast CT is usually appropriate, with sensitivity and specificity approaching 98-100% for detecting ureteral stones regardless of size, location, or composition 2
• Pregnant patients: Ultrasound is the imaging tool of choice (rating 8/9) to avoid ionizing radiation, with reasonable sensitivity for stone detection and hydronephrosis 1
• Premenopausal women with possible gynecologic pathology: Pelvic/transvaginal ultrasound should be considered first 3
• Recurrent stone disease: Low-dose noncontrast CT (rating 7/9) or ultrasound for hydronephrosis evaluation are usually appropriate 1

Alternative Imaging Considerations

• Ultrasound combined with radiography: Provides sensitivity of approximately 79% for clinically significant stones, offering an acceptable alternative to CT when radiation exposure is a concern 1, 4
• CT with IV contrast: May be appropriate (rating 6/9) when alternative diagnoses need better characterization, particularly for inflammatory conditions or abscesses 1, 3
• Plain radiography alone: Usually not appropriate (rating 3/9) due to limited sensitivity and inability to guide toward alternative diagnoses 1

Common Causes of Left Flank Pain

Urologic Etiologies (Most Common)

• Nephrolithiasis/ureterolithiasis: The most frequent cause of acute flank pain, characterized by colicky pain with waves of severe discomfort 4, 2
• Hydronephrosis: May indicate obstruction from stones, strictures, or external compression 1
• Pyelonephritis/kidney infection: Pain typically worsens with external flank pressure (unlike stone pain), associated with fever and leukocytosis 4
• Renal infarction: Uncommon mimic presenting with constant progressive flank pain, elevated LDH, and mild hematuria 5
• Page kidney: Subcapsular hematoma causing renal compression and secondary hypertension, presenting with flank pain and hematuria 6
• Nutcracker syndrome: Compression of left renal vein between superior mesenteric artery and aorta, causing left renal vein thrombosis 7

Non-Urologic Etiologies

• Diverticulitis: CT with contrast is superior for evaluating disease severity, detecting complications like perforation or abscess 3
• Splenic pathology: Requires CT evaluation for proper characterization 8
• Pancreatic conditions: CT can identify pancreatitis or other pancreatic pathology 8
• Thoracic disc herniation: Rare cause that can mimic urinary system disorders, particularly far lateral T10-11 disc herniation 9
• Gastric or colonic pathology: Including left-sided colonic diverticulitis, inflammatory bowel disease 1, 3

Management Algorithm

For Suspected Urolithiasis

Step 1: Risk Stratification

• Assess for fever, leukocytosis, and signs of sepsis requiring urgent intervention 1
• Evaluate stone size and location on imaging to predict spontaneous passage 4
• Check for hydronephrosis indicating significant obstruction 1, 4

Step 2: Intervention Decision

• Septic patient with obstruction: Urgent decompression with retrograde ureteral stenting or percutaneous nephrostomy (PCN) 1
• Pregnant patient (20+ weeks) with infection and hydronephrosis: Retrograde ureteral stenting or PCN are usually appropriate 1
• Obstructing stone with persistent symptoms: Retrograde ureteral stenting is usually appropriate 1
• Conservative management candidates: Stones <10mm without infection or severe symptoms may pass spontaneously 2

For Non-Stone Etiologies

Infection/Pyelonephritis

• Look for pain worsening with external pressure, fever, and positive urinalysis 4
• CT may show perinephric stranding without obstructing stone 1
• Urgent PCN if septic with obstruction 1

Vascular Causes

• Renal infarction: Consider when leukocytosis and elevated LDH present without stone on imaging 5
• Page kidney: Suspect with hematuria, hypertension, and subcapsular hematoma on CT; manage conservatively with antihypertensive therapy 6
• Nutcracker syndrome: Diagnose with CT showing renal vein compression; confirm with intravascular ultrasound 7

Inflammatory/Structural Causes

• Diverticulitis: CT with contrast for severity assessment and complication detection 3
• Disc herniation: Consider MRI of thoracic spine if urologic workup negative and pain distribution atypical 9

Critical Pitfalls to Avoid

• Anchoring on nephrolithiasis: Always consider alternative diagnoses when imaging doesn't show stones or clinical presentation is atypical 6, 7
• Missing infection with obstruction: This combination requires urgent decompression to prevent sepsis and renal damage 1
• Radiation overexposure: Use low-dose CT protocols when appropriate, and consider ultrasound alternatives in young patients and those with recurrent stones 1
• Assuming fatty liver causes pain: Hepatic steatosis does not cause flank pain; investigate other etiologies separately 8
• Overlooking pregnancy: Always use ultrasound first in pregnant patients to avoid fetal radiation exposure 1
• Ignoring pain characteristics: Stone pain is colicky and doesn't worsen with external pressure, while infectious causes typically do 4