Abdominal Distension: MCCQE1 Preparation Guide

Introduction

Abdominal distension is a common presentation in both primary care and emergency settings across Canada. For MCCQE1 preparation, it is crucial to differentiate between functional disorders (like bloating) and pathological accumulation of substances (fluid, mass, gas).

As a future Canadian physician, you must apply the CanMEDS Medical Expert role to identify life-threatening causes such as bowel obstruction or perforated viscus, and the Communicator role to discuss sensitive topics like alcohol use or malignancy.

Etiology: The “F” Mnemonic

A classic mnemonic useful for the MCCQE1 to recall the causes of generalized abdominal distension is the 6 Fs.

Clinical Evaluation

History Taking

When preparing for the MCCQE1, focus on distinguishing features in the history that point towards a specific “F”.

• Timeline: Acute (obstruction, perforation) vs. Chronic (ascites, obesity).
• Associated Symptoms:
  • Pain: Colicky (obstruction) vs. Dull ache (hepatomegaly/splenomegaly).
  • Systemic: Fever (SBP, abscess), Weight loss (malignancy).
  • GI: Vomiting (proximal obstruction), Change in bowel habits (colorectal cancer).
• Risk Factors: Alcohol use, viral hepatitis risk (immigration from endemic areas, IVDU), heart failure history.

Physical Examination

Perform the abdominal exam in the correct sequence to avoid altering bowel sounds or causing guarding prematurely.

Differential Diagnosis & Pathophysiology

For the MCCQE1, you must be able to categorize the distension.

Investigations

Laboratory Studies

• CBC: Anemia (GI bleed/malignancy), Leukocytosis (infection/ischemia).
• Electrolytes/Creatinine: Hypokalemia (ileus), Dehydration (third spacing).
• Liver Enzymes/Function: INR and Albumin verify synthetic function (Cirrhosis).
• Beta-hCG: All females of childbearing age.

Imaging

Follow Choosing Wisely Canada recommendations to avoid unnecessary radiation.

1. Abdominal X-ray (Acute Abdominal Series):
   • First-line for suspected obstruction or perforation.
   • Look for: Air-fluid levels, dilated loops (>3cm SB, >6cm LB, >9cm Cecum), free air under diaphragm.
2. Abdominal Ultrasound:
   • Best for ascites, liver pathology, and pelvic masses (ovarian).
   • Doppler studies for Portal Vein Thrombosis/Budd-Chiari.
3. CT Abdomen/Pelvis:
   • Gold standard for undifferentiated distension, staging malignancy, or locating transition point in obstruction.

Diagnostic Paracentesis

Indicated for new-onset ascites or suspicion of Spontaneous Bacterial Peritonitis (SBP).

• Cell count & differential: Neutrophils ≥ 250/mm³ = SBP.
• Albumin: Calculate SAAG.
• Culture: In blood culture bottles.
• Cytology: If malignancy suspected.

Canadian Guidelines & Management

Management of Ascites (CASL Guidelines)

The Canadian Association for the Study of the Liver (CASL) recommends:

1. Salt Restriction: < 2000 mg (88 mmol) sodium per day.
2. Diuretics: Spironolactone (aldosterone antagonist) +/- Furosemide. Typical ratio 100mg : 40mg to maintain potassium balance.
3. Refractory Ascites: Large volume paracentesis (LVP) with albumin replacement (6-8g albumin per liter removed if >5L removed).
4. TIPS (Transjugular Intrahepatic Portosystemic Shunt): For select candidates.

Management of Obstruction

• Conservative: NPO, IV fluids, NG tube decompression (Gastric suction).
• Surgical: If strangulation, peritonitis, or failure of conservative management.

Key Points to Remember for MCCQE1

• SAAG differentiates portal hypertension from other causes of ascites.
• Shifting dullness is the most reliable physical exam finding for detecting ascites.
• Ovarian cancer should be high on the differential for persistent bloating in post-menopausal women.
• Air under the diaphragm on upright CXR indicates a perforated viscus (surgical emergency).
• Volvulus (Sigmoid > Cecal) typically appears as a “coffee bean” sign on X-ray.
• Always check pregnancy status in women of reproductive age presenting with abdominal distension.

Sample Question

Explanation

The correct answer is:

• C. Perform a diagnostic paracentesis

Detailed Explanation: This patient presents with signs suggestive of Spontaneous Bacterial Peritonitis (SBP): fever, abdominal pain, tachycardia, and worsening hepatic encephalopathy (confusion, asterixis) in the setting of known cirrhosis and ascites.

• Option C is correct: Diagnostic paracentesis is the gold standard and mandatory first step to diagnose SBP. The diagnosis is confirmed if the ascitic fluid absolute neutrophil count (ANC) is ≥ 250 cells/mm³. Delaying this procedure delays diagnosis and appropriate antibiotic tailoring.
• Option A is incorrect: While empiric antibiotics (like ceftriaxone) are the treatment for SBP, samples for cell count and culture should be obtained before or immediately concomitant with starting antibiotics to ensure accurate diagnosis and future stewardship. However, obtaining the fluid is the diagnostic priority.
• Option B is incorrect: A CT scan may show ascites but cannot diagnose SBP (a microbiological/cellular diagnosis). It delays the definitive test.
• Option D is incorrect: Lactulose and rifaximin treat hepatic encephalopathy. While this patient has HE, the precipitating cause (likely SBP) must be identified and treated first.
• Option E is incorrect: NG tube is used for decompression in bowel obstruction or GI bleed, which is not the primary clinical picture here.

References

1. Medical Council of Canada. MCC Objectives for the Qualifying Examination Part I.
2. Toronto Notes 2024. Gastroenterology: Abdominal Distension & Ascites.
3. Canadian Association for the Study of the Liver (CASL). Guidelines for the Management of Ascites in Cirrhosis.
4. Choosing Wisely Canada. Gastroenterology Recommendations.
5. Feldman, M., Friedman, L. S., & Brandt, L. J. (2020). Sleisenger and Fordtran’s Gastrointestinal and Liver Disease. Elsevier.