What causes left side pain, and how should it be treated in a patient with unknown age and medical history?

Left Side Pain: Diagnostic and Management Approach

Initial Diagnostic Imaging

CT abdomen and pelvis with IV contrast is the most appropriate initial investigation for left-sided pain, providing superior diagnostic accuracy (98%) for identifying the broad differential diagnosis including diverticulitis, colitis, inflammatory bowel disease, urolithiasis, gynecologic pathology, and vascular emergencies. 1

Why CT is First-Line

• CT detects critical findings including small quantities of extraluminal air indicating perforation, bowel wall pathology, pericolic abnormalities, vascular pathology, and intraabdominal fluid collections—all of which have significant mortality implications if missed 1

• CT guides appropriate management regardless of patient sex or body habitus, with sensitivity and specificity approaching 100% for most acute abdominal pathology 1

• Unenhanced CT is acceptable when IV contrast is contraindicated, with similar accuracy (64-68% vs 68-71%) in elderly patients with acute abdominal pain 1

Alternative Imaging Modalities

• Transabdominal ultrasound may reduce unnecessary CT examinations by identifying patients without surgical abdomen, particularly when directed to the area of maximal pain 1

• Transvaginal ultrasound is appropriate first-line in premenopausal women when gynecologic pathology is clinically suspected 1, 2

• Plain radiography is not useful as initial imaging because CT is more sensitive and specific for all relevant pathology including extraluminal air, bowel obstruction, and urolithiasis 1

• MRI is not appropriate for initial evaluation due to lower sensitivity for extraluminal air and urinary calculi, longer acquisition time, and greater susceptibility to motion artifacts in symptomatic patients 1

Common Causes by Age and Presentation

Most Common: Acute Diverticulitis

Diverticulitis is the most common cause of left lower quadrant pain in adults, with prevalence increasing from 10% at age 40 to 70% in elderly patients. 1

Critical Diagnostic Considerations

• Clinical diagnosis alone is unreliable with misdiagnosis rates of 34-68% 1, 3

• The classic triad (left lower quadrant pain, fever, leukocytosis) is present in only 25% of diverticulitis cases 1

• Elderly patients present atypically: only 50% have lower quadrant pain and only 17% have fever 3

• Mortality increases dramatically with age: 1.6% in patients <65 years, 9.7% in patients 65-79 years, and 17.8% in patients >80 years 3

When Imaging May Not Be Required

Imaging may be deferred in patients with typical symptoms, prior history of diverticulitis with similar presentation, and no evidence of complications—such patients may be treated medically without imaging 1

Other Common Causes

The differential diagnosis includes 1, 4:

• Colitis and inflammatory bowel disease
• Epiploic appendagitis
• Bowel obstruction or hernia
• Urolithiasis or pyelonephritis
• Ovarian and fallopian tube pathology (in women)
• Fecal impaction
• Spontaneous retroperitoneal or rectus sheath hemorrhage

Management Based on CT Findings

Uncomplicated Diverticulitis

• Outpatient management with oral antibiotics is appropriate for most cases of uncomplicated diverticulitis 1

• Early CT diagnosis can reduce hospital admission by >50% and shorten hospital length of stay 1

Complicated Diverticulitis

Treatment depends on specific complications identified on CT: 1, 3

• Free perforation with diffuse peritonitis: Immediate emergency surgical consultation for laparotomy with colonic resection 3

• Large abscess (≥4 cm): Percutaneous CT-guided drainage PLUS IV antibiotics for 4 days 3

• Small abscess (<4 cm): IV antibiotics alone for 7 days without drainage 3

• Locally perforated diverticulitis without drainable collection: Medical therapy 1

Critical Laboratory Markers

• C-reactive protein >170 mg/L predicts severe diverticulitis with 87.5% sensitivity 3

• However, 39% of patients with complicated episodes have CRP <175 mg/L, so normal CRP does not exclude complicated disease 3

• Lactate level should be obtained in patients with suspected sepsis or hemodynamic instability 3

Red Flags Requiring Emergency Evaluation

Immediate emergency department evaluation is mandatory for: 5

• Fever with inability to pass gas or stool
• Severe tenderness with guarding or peritoneal signs
• Hemodynamic instability (hypotension, tachycardia)
• Vomiting or bloody stools
• Signs of shock

Hemodynamically Unstable Patients

For patients presenting with hypotension and suspected complicated diverticulitis: 3

1. Initiate aggressive fluid resuscitation with crystalloids to restore systolic blood pressure >90 mmHg 3

2. Start broad-spectrum IV antibiotics immediately (carbapenem therapy) before imaging 3

3. Obtain emergent CT as soon as hemodynamically stable enough for transport 3

4. Do not delay antibiotics waiting for imaging in hypotensive patients, as mortality increases significantly with delayed treatment in septic shock 3

Recurrent or Chronic Left-Sided Pain

When Initial Workup is Negative

If CT and colonoscopy exclude structural pathology, functional bowel disorders become the most likely diagnosis. 5

Additional Considerations

• Pain related to bowel movements or dietary triggers points toward irritable bowel syndrome 5

• Cyclical pain in women suggests gynecologic etiology requiring pelvic ultrasound if not already performed 2, 5

• Weight loss, anemia, or change in bowel habits warrant repeat colonoscopy despite prior normal study 5

Follow-up Colonoscopy

Colonoscopy should be performed after an episode of complicated diverticulitis in patients without recent colonoscopy to rule out colorectal cancer, which may present with similar symptoms 2

When to Repeat Imaging

• Repeat CT is generally not indicated unless new symptoms develop or significant time has passed 5

• MRI abdomen and pelvis may be considered if CT was equivocal, with sensitivity of 86-94% and specificity of 88-92% for inflammatory conditions 5

• New pericolonic lymphadenopathy >1 cm on repeat imaging suggests malignancy rather than benign causes 5

Symptomatic Pain Management

For symptomatic treatment of mild to moderate pain, acetaminophen or NSAIDs are first-line agents. 6

• Choice depends on pain type and patient risk factors for NSAID-related adverse effects (gastrointestinal, renovascular, cardiovascular) 6

• For insufficient relief, acetaminophen/opioid combinations targeting separate pathways are reasonable 6

• Severe acute pain is typically treated with potent opioids, though caution is warranted given misuse potential even for short-term treatment 6

Critical Pitfalls to Avoid

• Do not rely on clinical examination alone to determine severity, as elderly patients present atypically and misdiagnosis rates are high 1, 3

• Do not assume low inflammatory markers exclude serious pathology, as significant proportions of complicated cases have normal or mildly elevated markers 3

• Do not delay surgical consultation in high-risk presentations with hemodynamic instability or peritoneal signs 3

• Consider cumulative radiation exposure when ordering multiple CT scans, especially in younger patients 2

• In boys with left-sided abdominal pain, carefully examine the testes with the patient standing, as testicular torsion can present as referred left abdominal pain 7