What is the differential diagnosis for worsening lower abdominal pain?

Differential Diagnosis for Worsening Lower Abdominal Pain

For acute lower abdominal pain that has been steadily worsening over 24 hours, the differential diagnosis must prioritize life-threatening conditions first, followed by common surgical emergencies, then inflammatory and infectious causes.

Life-Threatening Causes (Evaluate First)

• Mesenteric ischemia presents with pain out of proportion to physical examination findings and carries 30-90% mortality if untreated, progressing to infarction, perforation, and peritonitis 1, 2, 3
• Ruptured abdominal aortic aneurysm manifests as severe lower abdominal and back pain with hypotension, with mortality exceeding 50% even with prompt intervention 1, 3
• Perforated viscus presents with abdominal rigidity, rebound tenderness, and peritoneal signs requiring immediate surgical evaluation 1, 2
• Aortic dissection involving the abdominal aorta causes severe abdominal pain with abrupt onset and carries particularly high mortality in women due to atypical presentation 2, 3

Common Surgical Emergencies

Right Lower Quadrant Pain

• Acute appendicitis is the most common surgical pathology causing lower quadrant pain, accounting for approximately one-third of emergency department presentations with acute abdominal pain, most common in ages 10-30 years 4, 2, 5
• Right colonic diverticulitis is less frequent than left-sided but must be considered in right lower quadrant presentations 4
• Intestinal obstruction presents with abdominal distension and vomiting, accounting for 4-5% of acute abdominal pain cases 4, 1, 2

Left Lower Quadrant Pain

• Acute sigmoid diverticulitis is the most common cause of left lower quadrant pain in adults, occurring in 10-20% of patients with diverticulosis, with 25% experiencing recurrent episodes 4
• Colonic volvulus accounts for 15-20% of large bowel obstruction cases and presents with sudden onset abdominal distension 4
• Colorectal cancer causes 60% of large bowel obstructions and may present with progressive pain, rectal bleeding, and unexplained weight loss 4

Inflammatory and Infectious Causes

• Colitis (infectious, ischemic, or inflammatory bowel disease) can cause diffuse or localized lower abdominal pain 4, 6
• Inflammatory bowel disease (Crohn's disease or ulcerative colitis) causes pain during disease flares, with 50-70% of IBD patients experiencing pain during active disease 2
• Complicated diverticulitis with abscess formation, fistula, or perforation requires imaging to detect and may necessitate surgical or interventional radiology procedures 4

Genitourinary Causes

• Ureteral stone is a less frequent but important cause of right lower quadrant pain 4
• Gynecologic pathology must be considered in women of childbearing age, including ectopic pregnancy, ovarian torsion, tubo-ovarian abscess, and ruptured ovarian cyst 4, 5

Critical Diagnostic Approach

For nonlocalized or unclear lower abdominal pain with worsening symptoms, CT of the abdomen and pelvis with IV contrast is the preferred initial imaging modality, altering diagnosis in 49% of patients and changing management in 42% of cases 4, 1, 2

• CT has sensitivity greater than 95% for detecting diverticulitis and can identify complications such as abscess, perforation, or fistula 4, 1
• CT angiography is the gold standard for diagnosing mesenteric ischemia and aortic pathologies 1, 2, 3
• For right upper quadrant pain suggesting biliary disease, ultrasonography is the initial test of choice 4, 1
• Plain radiographs have limited diagnostic value and should not delay definitive imaging 1, 2, 3

Essential Laboratory Evaluation

• Complete blood count to evaluate leukocytosis 1
• Elevated lactate suggests ischemia or sepsis 1
• Metabolic panel, liver function tests, amylase, and lipase 1
• Mandatory beta-hCG testing in all women of reproductive age before CT imaging 1, 2

Critical Clinical Pearls

• Pain out of proportion to physical findings is the hallmark of mesenteric ischemia and should trigger immediate CT angiography 1, 2, 3
• Hemodynamic instability (tachycardia, hypotension, tachypnea) suggests bleeding or sepsis requiring immediate resuscitation 4, 1
• Elderly patients may present with atypical symptoms and require more extensive evaluation even with normal laboratory tests 1
• Imaging may be unnecessary in patients with classic presentation of uncomplicated diverticulitis (left lower quadrant pain, fever, leukocytosis) and previous history of diverticulitis, but should be strongly considered given the worsening nature of symptoms 4
• Patients with obvious signs of diffuse peritonitis requiring immediate laparotomy do not need preoperative imaging 4