What is the appropriate evaluation and management for a 20-year-old female presenting with flank pain?

Evaluation and Management of Flank Pain in a 20-Year-Old Female

Non-contrast CT of the abdomen and pelvis is the imaging study of choice for evaluating flank pain in this patient, with 98-100% sensitivity and specificity for detecting urinary stones and identifying alternative diagnoses. 1

Initial Clinical Assessment

The diagnostic approach must first distinguish between renal colic and other causes based on specific pain characteristics:

• Classic renal colic presents as colicky, wave-like severe pain that is independent of body position, radiating into the groin or genitals with abrupt onset 2, 1
• Pain that worsens after prolonged static positioning or with external flank pressure suggests musculoskeletal origin (paraspinal muscles, facet joints) rather than stone disease 1, 3
• Pain that significantly worsens with external pressure indicates pyelonephritis, kidney infection, or perinephric abscess rather than nephrolithiasis 4

Critical Red Flags Requiring Urgent Evaluation

• Fever, chills, or signs of systemic infection 1
• Inability to urinate or decreased urine output 1
• Visible blood in urine 1
• Vital signs showing shock or hemodynamic instability 2

Diagnostic Workup

Urinalysis

• Hematuria (even microscopic) shifts probability toward stone disease 1
• Absence of pyuria essentially excludes urinary tract infection with excellent negative predictive value 3
• Unremarkable urinalysis excludes most significant renal pathology 3

Imaging Selection

Non-contrast CT abdomen/pelvis is the gold standard with the following advantages 1, 5, 6:

• 98-100% sensitivity and specificity for stones regardless of size, location, or composition
• Detects stones as small as 1-2mm
• Identifies extraurinary causes in approximately one-third of patients 1, 5
• No contrast agent needed, avoiding nephrotoxicity and allergic reactions
• Completed within 5 minutes

Ultrasound is first-line only if the patient is pregnant to avoid radiation exposure 1. However, ultrasound has significant limitations:

• Only 72% sensitive for large stones (>5mm) in proximal ureter 1
• 29% sensitive overall for stones of any size 1
• Absence of hydronephrosis makes larger ureteral stones (>5mm) less likely, with ultrasound being up to 100% sensitive for hydronephrosis 1

Alternative Diagnoses to Consider in Young Females

Given the patient's age and sex, the differential extends beyond urolithiasis:

Gynecologic Causes

• Benign adnexal masses 1, 3
• Pelvic congestion syndrome 1, 3
• Ectopic pregnancy if delayed menses 2

Gastrointestinal Causes

• Right colonic diverticulitis 1, 3
• Gastroenteritis and colitis 1, 3
• Inflammatory bowel disease 1, 3

Other Urinary Tract Pathology

• Spontaneous ureteral rupture (presents with sudden onset abdominal/flank pain) 7
• Page kidney from subcapsular hematoma causing secondary hypertension 8

Management Based on Imaging Results

If Stone Disease Confirmed

• Stones <5mm typically pass spontaneously 1
• Larger stones or those causing complete obstruction may require endoscopic removal 1
• Instruct patient to maintain high fluid intake and strain urine to catch stones 2
• Provide rapid analgesia (diclofenac intramuscular injection preferred) within 30 minutes 2

If No Stone Identified

• Only 14% require hospitalization and 4% undergo surgical intervention when no CT diagnosis is made 1
• Consider musculoskeletal evaluation with physical examination focusing on costovertebral angle tenderness, spinal range of motion, and paraspinal muscle tenderness 3
• Evaluate retroperitoneal processes if imaging pursued 3

If Alternative Diagnosis Found

• 41% require hospitalization and 22% undergo surgical or image-guided intervention when non-appendiceal CT diagnosis is made 1
• Management directed at specific diagnosis identified

Follow-Up Protocol

• Telephone follow-up 1 hour after initial assessment and analgesia administration 2
• Fast-track radiology within 7 days if managed outpatient 2
• Urgent urology appointment within 7-14 days if calculus identified requiring intervention 2
• Failure of analgesia after 1 hour mandates immediate hospital admission 2

Common Pitfalls to Avoid

• Do not assume all flank pain is kidney-related—positional nature of symptoms is key to distinguishing musculoskeletal from renal causes 1
• Do not rely on plain radiography (KUB), which is only 29% sensitive overall for stones 1
• Do not delay imaging in young females—consider gynecologic causes that may require urgent intervention 2
• Do not miss ectopic pregnancy in women with delayed menses presenting with flank pain 2