What is the initial approach to a middle-aged female presenting with acute abdomen?

Differential Diagnosis of Acute Abdomen in a Middle-Aged Female

Immediate Hemodynamic Assessment

Begin by immediately assessing hemodynamic stability—check for tachycardia, hypotension, fever, or signs of shock, as these indicate potential bowel ischemia, perforation, or sepsis requiring emergency intervention. 1

• Tachycardia is the most sensitive early warning sign of surgical complications and should trigger urgent investigation, even before other symptoms develop 2
• The combination of fever, tachycardia, and tachypnea predicts serious complications including anastomotic leak, perforation, or sepsis 2
• Hemodynamically unstable patients require immediate IV crystalloid resuscitation and emergency surgical consultation 1, 3

Physical Examination Priorities

Evaluate for peritoneal signs—guarding, rebound tenderness, and rigidity—which suggest perforation or ischemia and mandate urgent surgical consultation. 1

• Assess for abdominal distension, which has a positive likelihood ratio of 16.8 for bowel obstruction 1
• Pain out of proportion to physical examination findings should raise suspicion for acute mesenteric ischemia 2
• Asymmetric gaseous distention with emptiness of the left iliac fossa is pathognomonic for sigmoid volvulus 2

Essential Laboratory Investigations

Order a complete blood count, metabolic panel, and lactate level immediately, as these guide diagnosis and severity assessment. 1, 3

• Leukocytosis >14,000 suggests infection, ischemia, or inflammation; marked elevation indicates potential bowel ischemia 1
• Low bicarbonate, elevated lactate, and elevated pH indicate intestinal ischemia 1
• High C-reactive protein has superior sensitivity and specificity compared to white blood cell count for ruling in surgical disease 2
• A pregnancy test is mandatory in all women of reproductive age before imaging, even at age 55 if any possibility of pregnancy exists 1, 3, 2

Common Pitfall: Normal Labs Don't Exclude Serious Disease

Many serious infections present with normal white blood cell counts in elderly patients, and normal lactate does not exclude internal herniation or early ischemia. 1, 2

Differential Diagnosis by Frequency

The most common causes in middle-aged females presenting with acute abdomen include:

• Non-specific abdominal pain (30-41% of cases) 4, 5
• Acute appendicitis (15.9-28.1% of cases requiring surgery) 2, 4, 5
• Acute cholecystitis (9-11% of cases) 4, 5
• Bowel obstruction (4-5% of cases, accounting for 15% of acute abdominal pain admissions) 2, 4, 5
• Diverticulitis (more common in this age group) 2

Gynecological Causes Specific to Middle-Aged Females

In women of reproductive age, always consider gynecologic conditions such as ectopic pregnancy, ovarian torsion, tubo-ovarian abscess, or pelvic inflammatory disease. 3, 2

• Ectopic pregnancy: TVUS has a positive likelihood ratio of 111 for finding adnexal mass without intrauterine pregnancy 6
• Ovarian torsion: CT has 74-95% sensitivity and 80-90% specificity 6
• Tubo-ovarian abscess: CT findings include thick-walled fluid density in adnexal location with septations 6
• Ruptured hemorrhagic cyst: Irregular peripherally enhancing adnexal cyst with hemorrhagic pelvic free fluid 6

Age-Specific Considerations

Middle-aged and elderly patients have higher likelihood of malignancy, diverticulitis, and vascular causes of acute abdominal pain. 2

• Weight loss and rectal bleeding are highly suggestive of colorectal cancer, which causes 60% of large bowel obstructions in this age group 1
• Previous abdominal surgery has 85% sensitivity for adhesive small bowel obstruction, which accounts for 55-75% of small bowel obstructions 1, 2
• Elderly patients often present with atypical symptoms and may have normal laboratory tests despite serious pathology 1, 3, 2

Imaging Algorithm Based on Pain Location

The location of pain guides the initial imaging approach: 1, 3, 2

Right Upper Quadrant Pain

• Ultrasonography is the initial imaging of choice, with 81% sensitivity and 83% specificity for cholecystitis 1, 3, 2

Right or Left Lower Quadrant Pain

• CT abdomen and pelvis with IV contrast is recommended, with >95% sensitivity for appendicitis and high accuracy for diverticulitis 1, 3, 2

Diffuse or Nonlocalized Abdominal Pain

• CT abdomen and pelvis with IV contrast is the imaging modality of choice, changing diagnosis in 49% of cases and management in 42% of patients 1, 3, 2

Pelvic Pain with Suspected Gynecological Etiology

• If β-hCG is positive: Transvaginal ultrasound is the single best diagnostic modality for evaluating suspected ectopic pregnancy 6
• If β-hCG is negative: CT abdomen and pelvis with IV contrast for suspected adnexal torsion or tubo-ovarian abscess 6

Critical Pitfall: Don't Delay Imaging

Delaying imaging based on clinical impression alone can lead to missed diagnoses, as CT changes diagnosis in approximately 50% of cases with nonspecific pain. 1, 3

• Plain radiographs have limited diagnostic value and should not be routinely used, except in cases of suspected bowel obstruction 3, 2
• Ultrasound remains the primary imaging technique in young and female patients to limit radiation exposure 7

Initial Management Approach

For hemodynamically stable patients without peritoneal signs:

• Supportive care including IV fluids, antiemetics, and bowel rest 1
• Antibiotics should only be used if infection is suspected, not as routine treatment for all abdominal pain 1, 3
• Serial examinations are essential, as clinical status can change rapidly 4, 8

For patients with peritonitis, perforation, or septic shock:

• Emergency surgical consultation is necessary 1, 3
• Immediate IV crystalloid resuscitation 1, 3
• Broad-spectrum antibiotics if infection is suspected 6

Red Flags Requiring Urgent Surgical Evaluation

• Severe pain out of proportion to physical findings (suggests mesenteric ischemia) 2
• Signs of peritonitis (rigid abdomen, rebound tenderness) 1, 2
• Hemodynamic instability (suggests bleeding or sepsis) 1, 3, 2
• Abdominal distension with vomiting (suggests bowel obstruction) 1, 2
• Abrupt or instantaneous onset of severe pain (suggests vascular catastrophe) 2

Special Considerations for Immunocompromised Patients

If the patient is immunocompromised, consider specific entities such as neutropenic enterocolitis, cytomegalovirus colitis, or Clostridioides difficile colitis, which have high mortality if misdiagnosed. 6