What are the possible causes and treatments for left lower quadrant (LLQ) pain radiating to the back?

Left Lower Quadrant Pain Radiating to Back

Obtain CT abdomen and pelvis with IV contrast immediately, as this is the preferred diagnostic test with 98-100% accuracy for identifying diverticulitis and other serious causes of left lower quadrant pain. 1, 2

Immediate Assessment for Emergency Features

Before imaging, rapidly assess for red flag symptoms that require emergent intervention:

• Fever with severe abdominal tenderness and guarding suggests perforation with peritonitis requiring emergent surgery 1
• Inability to pass gas or stool with abdominal distension indicates possible large bowel obstruction (present in 90% of cases) requiring urgent intervention 1
• Signs of shock (rapid breathing, rapid heartbeat, confusion, hypotension) indicate sepsis requiring immediate resuscitation and antibiotics 1
• Bloody stools with hemodynamic instability warrant emergent evaluation 1

If any of these features are present, initiate resuscitation and obtain emergent surgical consultation while proceeding with imaging. 1

Diagnostic Imaging Strategy

CT abdomen and pelvis with IV contrast is rated 8/9 (usually appropriate) by the American College of Radiology and should be obtained in nearly all patients with left lower quadrant pain. 1 This modality:

• Detects diverticulitis with 98-100% sensitivity and 99-100% specificity 2
• Identifies complications including abscess, perforation, fistula, and obstruction 1
• Reduces hospital admissions by >50% through accurate risk stratification 1
• Reveals alternative diagnoses such as renal colic, colitis, epiploic appendagitis, and malignancy 3, 4

Key CT findings to identify:

• Intestinal wall thickening with pericolonic fat stranding confirms diverticulitis 1
• Extraluminal gas or intra-abdominal fluid indicates perforation requiring surgery 1
• Abscess size determines drainage strategy (≥4 cm requires percutaneous drainage) 1
• Pericolonic lymphadenopathy >1 cm suggests malignancy rather than diverticulitis and warrants colonoscopy 1, 5

Special Population Considerations

For premenopausal women, obtain pelvic/transvaginal ultrasound first to evaluate for ectopic pregnancy, ovarian torsion, or pelvic inflammatory disease before proceeding to CT. 6, 1 Pregnancy testing is mandatory before CT in women of reproductive age. 1

If IV contrast is contraindicated (GFR <30 mL/min/1.73m²), CT without contrast is acceptable though less accurate for detecting abscesses (rated 6/9 by ACR). 6, 1

Most Likely Diagnoses

The differential diagnosis for left lower quadrant pain radiating to the back includes:

Diverticulitis (most common in adults, especially >65 years):

• Annual incidence 180 per 100,000 in the US 2
• Classic triad of left lower quadrant pain, fever, and leukocytosis present in only 25% of cases 1
• Pain radiating to back occurs due to retroperitoneal inflammation 3

Renal colic/urolithiasis:

• Left-sided kidney stones cause flank pain radiating to groin but can present as left lower quadrant pain 4
• Typically colicky pain with hematuria 3

Colitis (infectious, ischemic, or inflammatory):

• Often accompanied by diarrhea, which helps differentiate from diverticulitis 4

Epiploic appendagitis:

• Self-limited inflammation of colonic fat appendages 4
• Managed conservatively with NSAIDs 4

Treatment Algorithm Based on CT Findings

Uncomplicated Diverticulitis (85% of cases)

Conservative management without antibiotics is appropriate for immunocompetent patients. 1, 2 This approach includes:

• Clear liquid diet with gradual advancement as tolerated 1
• Pain control with acetaminophen (avoid NSAIDs and opioids when possible) 2
• Outpatient management if patient can tolerate oral intake 1

Reserve antibiotics for specific high-risk groups only:

• Persistent fever or chills despite conservative management 2
• Increasing leukocytosis 2
• Age >80 years 2
• Pregnancy 2
• Immunocompromised status (chemotherapy, high-dose steroids, organ transplant) 2
• Chronic medical conditions (cirrhosis, chronic kidney disease, heart failure, poorly controlled diabetes) 2

When antibiotics are indicated, use oral amoxicillin/clavulanic acid or cefalexin plus metronidazole for maximum 7 days. 2 Alternative regimens include Ertapenem 1g q24h or Eravacycline 1 mg/kg q12h. 1

Complicated Diverticulitis with Small Abscess (<4 cm)

Antibiotic therapy alone for 7 days without drainage is recommended. 1 Use:

• Oral regimen if patient can tolerate: amoxicillin/clavulanic acid or cefalexin plus metronidazole 2
• IV regimen if unable to tolerate oral: ceftriaxone plus metronidazole, or piperacillin-tazobactam 2

Complicated Diverticulitis with Large Abscess (≥4 cm)

Percutaneous drainage combined with IV antibiotics is required. 1 Use:

• Ceftriaxone plus metronidazole OR piperacillin-tazobactam 2
• Stop antibiotics at 4 days if source control is adequate and patient is immunocompetent and non-critically ill 1
• Continue up to 7 days in immunocompromised or critically ill patients 1
• Never continue antibiotics beyond 7 days in uncomplicated cases, as this increases resistance without improving outcomes 1

Perforation with Peritonitis or Septic Shock

Emergent laparotomy with colonic resection is required. 2 Initiate:

• Meropenem 1g q6h by extended infusion, OR Doripenem 500 mg q8h by extended infusion, OR Imipenem/cilastatin 500 mg q6h by extended infusion 1
• Aggressive fluid resuscitation and vasopressor support as needed 1

Postoperative mortality is 10.6% for emergent colon resection versus 0.5% for elective procedures, emphasizing the importance of early diagnosis. 2

Critical Pitfalls to Avoid

• Do not routinely prescribe antibiotics for uncomplicated diverticulitis in immunocompetent patients - this increases antibiotic resistance without improving outcomes 1, 2
• Do not perform routine colonoscopy after CT-confirmed diverticulitis unless abscess, perforation, or fistula is present, or for age-appropriate cancer screening 1
• Do not miss malignancy - pericolonic lymphadenopathy >1 cm on CT suggests cancer rather than diverticulitis and requires colonoscopy 1, 5
• Do not use clinical diagnosis alone - misdiagnosis rates are 34-68% without imaging 1
• Do not continue antibiotics beyond 7 days - if infection persists, obtain repeat imaging to assess for inadequate source control rather than extending antibiotics 1

Follow-Up Considerations

If symptoms persist or recur after initial treatment:

• Weight loss, anemia, or change in bowel habits warrant colonoscopy despite prior normal imaging 5
• Repeat CT is generally not indicated unless new symptoms develop or significant time has passed 5
• Consider gastroenterology referral for functional bowel disorder management if structural pathology has been excluded 5