What are the differential diagnoses for a patient presenting with left lower quadrant (LLQ) abdominal pain and vomiting for 6 weeks, with no other symptoms or medical concerns, and an unremarkable computed tomography (CT) scan?

Differential Diagnoses for Chronic LLQ Pain with Unremarkable CT

With an unremarkable CT scan after 6 weeks of left lower quadrant pain and vomiting, the most likely diagnoses shift from structural pathology to functional bowel disorders, gynecologic causes (in women), or less common entities that may not be evident on standard CT imaging. 1, 2

Primary Differential Diagnoses

Functional Bowel Disorders

• Irritable bowel syndrome (IBS) becomes the leading diagnosis when structural pathology has been excluded by CT imaging 2
• Pain related to bowel movements or dietary triggers strongly supports this diagnosis 2
• The 6-week duration with vomiting fits the pattern of functional gastrointestinal disorders 2

Gynecologic Pathology (if female patient)

• Endometriosis, ovarian pathology, or pelvic inflammatory disease must be considered in premenopausal women 1, 2
• Cyclical pain patterns suggest gynecologic etiology requiring pelvic/transvaginal ultrasound 2
• Standard abdominal CT may miss subtle gynecologic pathology that would be visible on dedicated pelvic imaging 1

Colonic Pathology Not Visible on CT

• Early inflammatory bowel disease (IBD) such as Crohn's disease or ulcerative colitis may present with normal CT in early stages 3, 4
• Colitis of various etiologies can cause chronic symptoms 3
• Fecal impaction should be considered, though typically visible on CT 3

Urologic Causes

• Intermittent urolithiasis with passed stones or chronic urinary tract pathology 3, 4
• Left-sided renal or ureteral pathology may not always be evident on CT without specific protocols 3

Musculoskeletal and Abdominal Wall Pathology

• Rectus sheath pathology or abdominal wall disorders 3
• Musculoskeletal pain referred to the LLQ 4

Rare but Important Considerations

• Epiploic appendagitis - a self-limited condition that may resolve by time of imaging or be subtle 3, 4
• Early or atypical diverticulitis - though CT has 98-100% sensitivity, very early disease might be missed 5
• Occult malignancy - pericolonic lymphadenopathy >1 cm would suggest this, but absence doesn't exclude early disease 1, 2

Critical Next Steps

Immediate Red Flag Assessment

• Evaluate for emergency symptoms: fever, inability to pass gas/stool, severe tenderness with guarding, bloody stools, or signs of shock require immediate emergency evaluation 1, 6
• Check for peritonitis signs: diffuse tenderness, guarding, rebound tenderness, or absent bowel sounds 6
• Assess vital signs: hypotension, tachycardia, or altered mental status suggest serious pathology 6

Additional Diagnostic Workup

For women of reproductive age:

• Obtain pelvic/transvaginal ultrasound as the preferred initial imaging for gynecologic pathology 1, 2
• Consider gynecology referral if ultrasound reveals pathology or clinical suspicion remains high 2

For persistent symptoms without clear diagnosis:

• Consider MRI abdomen and pelvis if CT was equivocal, with sensitivity of 86-94% and specificity of 88-92% for inflammatory conditions 2
• Gastroenterology referral for functional bowel disorder management or colonoscopy if not age-appropriately screened 2
• Colonoscopy is warranted if there is weight loss, anemia, or change in bowel habits despite prior normal imaging 2

Important Pitfalls to Avoid

Do not assume normal CT excludes all pathology:

• Clinical misdiagnosis rates range from 34-68% even with imaging 1, 6
• Functional disorders are diagnoses of exclusion but are common 2
• Pain localization alone is insufficient - 24% of appendicitis cases have no right lower quadrant findings, and 7% of diverticulitis cases have no LLQ findings 7

Do not repeat CT without new symptoms:

• Repeat CT is generally not indicated unless new symptoms develop or significant time has passed 2
• Consider alternative imaging modalities (ultrasound, MRI) based on suspected pathology 2

Do not overlook gynecologic causes in women:

• Standard abdominal CT should be supplemented with pelvic ultrasound in premenopausal women 1, 2