What are the causes and treatments of left lower abdominal pain?

Left Lower Abdominal Pain: Causes and Treatment

Immediate Diagnostic Approach

CT abdomen and pelvis with IV contrast is the single most important test and should be obtained in nearly all patients with left lower quadrant pain, achieving 98-100% diagnostic accuracy. 1, 2 Clinical diagnosis alone is unreliable with misdiagnosis rates of 34-68%. 1

When to Image Immediately

• Obtain CT with IV contrast for any patient presenting with left lower quadrant pain who lacks a prior imaging-confirmed diagnosis 3
• The classic triad of left lower quadrant pain, fever, and leukocytosis occurs in only 25% of diverticulitis cases, making clinical diagnosis inadequate 1
• When all three criteria are present (left lower quadrant tenderness, CRP >50 mg/L, absence of vomiting), diagnostic accuracy reaches 97%, but this combination occurs in only 24% of patients 1

Special Population Considerations

• For premenopausal women with suspected gynecologic pathology, obtain pelvic/transvaginal ultrasound as the initial imaging study 1
• In pregnant patients, use ultrasonography or MRI instead of CT to avoid radiation exposure 1

Primary Differential Diagnoses

Diverticulitis (Most Common)

Acute diverticulitis is the leading cause of left lower quadrant pain, affecting 5-25% of patients with diverticulosis, with 70% of elderly patients having underlying diverticulosis. 2

CT Findings Confirming Diverticulitis:

• Intestinal wall thickening with pericolonic fat stranding 1
• Extraluminal gas or intra-abdominal fluid indicates perforation 1
• Abscess formation—measure size carefully as it determines drainage strategy 1

Critical Red Flag: Distinguishing Cancer from Diverticulitis

• Pericolonic lymphadenopathy >1 cm in short axis strongly suggests perforated adenocarcinoma rather than diverticulitis 1, 2
• This is the key distinguishing feature, as perforated colon cancer can perfectly mimic diverticulitis clinically and radiographically 2

Other Important Causes

• Renal colic and urinary tract infection 4
• Gynecologic disorders in women of reproductive age 4
• Epiploic appendicitis 4
• Inflammatory bowel disease 5
• Bowel obstruction—90% present with inability to pass gas, 65% with inability to pass stool 1

Emergency Red Flags Requiring Immediate Surgical Consultation

Any of the following mandate immediate emergency department evaluation and surgical consultation: 1, 2

• Fever with inability to pass gas or stool
• Severe abdominal tenderness with guarding or rebound (peritonitis)
• Vomiting
• Bloody stools
• Signs of shock (hypotension, tachycardia, altered mental status)
• Progressively worsening pain over several days
• Free air on imaging

Why These Matter:

• Perforation with peritonitis leads to fecal contamination, diffuse peritonitis, and septic shock 1
• Complete bowel obstruction causes bowel necrosis and perforation if untreated 1
• Abscess or fistula formation requires drainage or surgery 1

Treatment Algorithm Based on CT Findings

Uncomplicated Diverticulitis (No Abscess, Perforation, or Fistula)

Conservative management WITHOUT antibiotics is appropriate for immunocompetent patients with uncomplicated diverticulitis. 1

• Clear liquid diet with advancement as tolerated 1
• Pain control with oral analgesics 1
• Outpatient management is acceptable if patient can tolerate oral intake 1

When to Use Antibiotics in Uncomplicated Disease:

• Only use antibiotics in immunocompromised or elderly patients, limited to maximum 7 days 3, 1
• Ertapenem 1 g every 24 hours OR Eravacycline 1 mg/kg every 12 hours 1
• Do not continue antibiotics beyond 7 days in uncomplicated cases—this increases resistance without improving outcomes 1

Complicated Diverticulitis with Small Abscess (<3-4 cm)

• Antibiotic therapy alone for 7 days without drainage 1
• Use same antibiotic regimens as above 1

Complicated Diverticulitis with Large Abscess (≥3-4 cm)

• Percutaneous drainage combined with antibiotics for 4 days 1
• Stop antibiotics at 4 days in immunocompetent, non-critically ill patients if source control is adequate 1
• Continue up to 7 days in immunocompromised or critically ill patients, guided by clinical response and inflammatory markers 1

Septic Shock Presentation

• Meropenem 1 g every 6 hours by extended infusion OR Doripenem 500 mg every 8 hours by extended infusion OR Imipenem/cilastatin 500 mg every 6 hours by extended infusion 1

Perforation or Peritonitis

• Emergent surgery is mandatory 1

Follow-Up Colonoscopy Strategy

Colonoscopy is mandatory after complicated diverticulitis and after a first episode of uncomplicated diverticulitis, but may be deferred if a high-quality colonoscopy was performed within 1 year. 3

Timing:

• Delay colonoscopy by 6-8 weeks or until complete resolution of acute symptoms, whichever is longer 3
• Consider sooner if alarm symptoms present (weight loss, anemia, change in bowel habits) 6

Why This Matters:

• Malignancy can be misdiagnosed as diverticulitis—pooled prevalence of colon cancer is 1.9% among patients with diverticulitis, rising to 7.9% in complicated cases 3
• Advanced adenomas found in 4.4% and adenomas in 14.2% of patients undergoing colonoscopy after diverticulitis 3

Common Pitfalls to Avoid

• Never assume diverticulitis without imaging—clinical diagnosis alone has 34-68% misdiagnosis rate 1, 2
• Never miss colon cancer—lymphadenopathy >1 cm is the key differentiator from diverticulitis 1, 2
• Never continue antibiotics beyond 7 days in uncomplicated cases—no benefit, only increased resistance 1
• Never obtain routine colonoscopy after CT-confirmed diverticulitis except for age-appropriate screening, unless abscess, perforation, or fistula is present 1
• If signs of infection persist beyond 7 days, obtain repeat imaging to assess for inadequate source control rather than simply continuing antibiotics 1

Recurrent or Persistent Pain After Initial Workup

• If structural pathology excluded by CT and colonoscopy, functional bowel disorders become most likely 6
• Pain related to bowel movements or dietary triggers suggests irritable bowel syndrome 6
• Cyclical pain in women suggests gynecologic etiology requiring pelvic ultrasound 6
• New pericolonic lymphadenopathy >1 cm on repeat imaging suggests malignancy 6
• Consider gastroenterology referral for functional bowel disorder management if symptoms persist despite conservative measures 6