I have vague flank (side) pain without fever, urinary, gastrointestinal, or neurological symptoms; what evaluation and management should I pursue?

Evaluation and Management of Vague Flank Pain Without Fever or Other Symptoms

For a patient with isolated, vague flank pain and no fever, urinary symptoms, gastrointestinal complaints, or neurological deficits, obtain a non-contrast CT of the abdomen and pelvis as the first-line imaging study, which provides 98-100% sensitivity and specificity for detecting urinary stones and identifies alternative diagnoses in approximately one-third of cases. 1

Initial Clinical Assessment

Key Historical Features to Elicit

• Determine whether pain is position-dependent: Pain that worsens or improves with specific body positions (e.g., prolonged sitting, standing, or lying) suggests a musculoskeletal origin involving paraspinal muscles, facet joints, or referred pain from lumbar spine pathology. 1

• Assess pain character and timing: Classic renal colic presents as colicky, wave-like severe pain that is independent of body position, radiates into the groin or genitals with abrupt onset, and occurs in paroxysms. 1 In contrast, constant dull aching pain that varies with movement points toward musculoskeletal causes. 2

• Inquire about recent trauma or unusual physical activity: Even minor or occult trauma can cause rib fracture, muscle strain, or costochondritis that manifests as flank pain. 2

• Review medication history: NSAIDs, potassium supplements, iron, or bisphosphonates can cause gastrointestinal symptoms that may present as flank discomfort. 2

Physical Examination Priorities

• Palpate the costovertebral angle and paraspinal muscles: Tenderness to percussion over the kidney suggests renal pathology, while tenderness along muscle groups or reproducible pain with palpation indicates musculoskeletal origin. 1

• Perform straight-leg raise testing and neurologic examination: Assess for radiculopathy if there is any suspicion of lumbar spine involvement, checking knee strength, ankle reflexes, and sensation. 2

• Examine the skin: Look for herpes zoster rash, which can present with flank pain before the rash appears. 1

Diagnostic Imaging Strategy

First-Line Imaging

• Order non-contrast CT abdomen and pelvis immediately: This study detects urinary stones with 98-100% sensitivity and specificity, identifies hydronephrosis, and reveals alternative diagnoses (including diverticulitis, colonic pathology, ovarian masses in women, and musculoskeletal abnormalities) in roughly one-third of patients. 1, 2

• Consider low-dose CT protocols when available: These maintain 92-99% sensitivity for stone detection while significantly reducing radiation exposure. 1

Alternative Imaging in Specific Populations

• Use ultrasound as first-line in pregnant patients or those with severe contrast allergy: Ultrasound demonstrates up to 100% sensitivity for hydronephrosis but only 24-57% sensitivity for direct stone visualization, particularly for stones <5 mm. 1

• Recognize ultrasound limitations: Absence of hydronephrosis makes stones >5 mm unlikely, but secondary signs of obstruction may not appear within the first 2 hours of symptom onset. 1

• Combine ultrasound with plain abdominal radiography (KUB) if CT is unavailable: This combination increases sensitivity for clinically significant stones to 79-90%. 1

When to Add Contrast

• Reserve contrast-enhanced CT for specific scenarios: Use when non-contrast CT is nondiagnostic, when there is strong suspicion of complicated infection despite absence of fever, or when clinical improvement does not occur after initial therapy. 1 Contrast adds diagnostic information in only 5-18% of cases and alters management in merely 2-3% of patients. 1

Laboratory Evaluation

Essential Tests

• Obtain urinalysis with microscopy: Check for hematuria (even microscopic), pyuria, bacteriuria, crystals, and casts. 1 Note that more than 20% of patients with confirmed urinary stones have negative urinalysis for hematuria, so absence of blood does not exclude stone disease. 1

• Measure serum creatinine: Assess baseline renal function before any imaging. 1

• Perform urine pregnancy test in all women of reproductive age: Rule out ectopic pregnancy before proceeding with imaging. 1

Management Based on Imaging Results

If Urinary Stones Are Identified

• Stones <5 mm typically pass spontaneously: Provide analgesia with NSAIDs (e.g., intramuscular diclofenac 75 mg), instruct the patient to maintain high fluid intake, strain urine to catch stones, and arrange fast-track radiology follow-up within 7 days if managed outpatient. 1

• Stones >5 mm or complete obstruction require urologic referral: Arrange urgent urology appointment within 7-14 days for consideration of endoscopic removal. 1

• Reassess pain control within 1 hour: Failure of analgesia after 1 hour mandates immediate hospital admission. 1

If No Stones but Alternative Diagnosis Found

• Manage according to the identified pathology: Examples include antibiotics for pyelonephritis, surgical consultation for diverticulitis, or gynecologic evaluation for ovarian masses. 1

• Consider gastrointestinal causes if imaging is unrevealing: Right colonic diverticulitis, inflammatory bowel disease, gastroenteritis, or severe constipation can all present as flank pain. 1

If Imaging Is Completely Normal

• Evaluate for musculoskeletal causes: Consider costochondritis, muscle strain, rib fracture, or lumbar spine pathology with referred pain. 2

• Trial of conservative management: Recommend activity modification, heat application, and NSAIDs for musculoskeletal pain. 2

• Consider empiric acid suppression therapy if gastrointestinal origin is suspected: A trial of proton pump inhibitors is reasonable when esophageal or gastric causes are possible. 2

• Arrange close follow-up within 1-2 weeks: Instruct the patient to return immediately if pain worsens, fever develops, or new symptoms appear. 1

Critical Red Flags Requiring Urgent Evaluation

• Develop fever, chills, or signs of sepsis: These suggest obstructive pyelonephritis or urosepsis and mandate immediate hospital admission for intravenous antibiotics and possible decompression. 1

• Hemodynamic instability or shock: Requires emergent evaluation for conditions such as ruptured abdominal aortic aneurysm or ectopic pregnancy. 1

• Inability to urinate or decreased urine output: Suggests complete bilateral obstruction or bladder outlet obstruction requiring urgent intervention. 1

• Progressive neurologic deficits: Including motor weakness, saddle anesthesia, or bowel/bladder dysfunction, which may indicate cauda equina syndrome. 2

Common Pitfalls to Avoid

• Do not assume all flank pain is kidney-related: The positional nature of symptoms is a key distinguishing feature; musculoskeletal pain typically varies with movement and position, whereas renal colic does not. 1

• Do not delay imaging in women of reproductive age: Gynecologic emergencies such as ectopic pregnancy or ovarian torsion may require urgent intervention. 1

• Do not miss ectopic pregnancy: Always obtain beta-hCG testing before imaging in women with delayed menses presenting with flank pain. 1

• Do not rely solely on urinalysis: A normal urinalysis does not exclude significant urologic pathology, as over 20% of patients with confirmed stones have negative urinalysis. 1

• Do not order contrast-enhanced CT routinely: It provides additional diagnostic information in only 5-18% of cases and should be reserved for specific clinical scenarios. 1