Abdominal and Pelvic Masses: MCCQE1 Study Guide

Introduction

The evaluation of abdominal and pelvic masses is a frequent and critical clinical scenario encountered in Canadian medical practice. For the MCCQE1, candidates are expected to demonstrate the CanMEDS Medical Expert role by formulating a broad differential diagnosis based on anatomical location, patient age, and clinical presentation.

Understanding the epidemiology specific to the Canadian population (e.g., prevalence of colorectal cancer, AAA screening guidelines) is essential for high performance.

Anatomy and Quadrant-Based Differential Diagnosis

A systematic approach based on abdominal quadrants is the most effective strategy for the MCCQE1.

Clinical Approach: The MCCQE1 Framework

Follow these steps to maximize your score on Clinical Decision Making (CDM) cases.

Canadian Guidelines and Screening

Knowledge of CTFPHC (Canadian Task Force on Preventive Health Care) guidelines is high-yield for the MCCQE1.

1. Abdominal Aortic Aneurysm (AAA)

• Definition: Aortic diameter >3.0 cm.
• Screening Guideline: One-time screening with abdominal ultrasound for men aged 65 to 80.
• Rationale: Reduces mortality from AAA rupture.
• Women: Screening not routinely recommended (lower prevalence).

2. Colorectal Cancer (CRC)

• Screening Guideline: Asymptomatic adults aged 50 to 74.
• Modality: Fecal Immunochemical Test (FIT) every 2 years OR Flexible Sigmoidoscopy every 10 years.
• Symptomatic Mass: Diagnostic Colonoscopy (not screening).

3. Ovarian Cancer

• Guideline: No routine screening recommended for the general population (CA-125 and Transvaginal US have high false-positive rates and do not reduce mortality).

4. Cervical Cancer

• Guideline: Routine screening (Pap test) every 3 years starting at age 25.

Key Clinical Entities

Abdominal Aortic Aneurysm (AAA)

• Risk Factors: Smoking (strongest), Male, Age, HTN, Atherosclerosis.
• Presentation: Asymptomatic (incidental), pulsatile mass, back pain.
• Rupture Triad: Hypotension + Pulsatile Mass + Back/Flank Pain.
• Management:
  • <5.0 cm: Surveillance US (frequency depends on size).
  • >5.5 cm (men) or >5.0 cm (women) or Rapid expansion (>0.5 cm/6mo): Surgical repair (EVAR or Open).

Colorectal Carcinoma

• Right-sided (Cecum/Ascending): Occult bleeding, iron deficiency anemia, fatigue. Mass often palpable.
• Left-sided (Sigmoid/Rectum): Obstruction, change in bowel habits, “pencil stools”, frank blood.
• Diagnosis: Colonoscopy with biopsy.

Uterine Fibroids (Leiomyomata)

• Epidemiology: Very common benign monoclonal tumours.
• Presentation: Menorrhagia, pelvic pressure/pain, “lumpy-bumpy” uterus on exam.
• Management: Observation if asymptomatic. Medical (OCP, GnRH agonists) or Surgical (Myomectomy, Hysterectomy, Embolization) for symptoms.

Mnemonics for MCCQE1

To help remember the causes of abdominal distension/masses:

Key Points to Remember for MCCQE1

1. Iron Deficiency Anemia: In an adult male or post-menopausal female, this is GI malignancy until proven otherwise. Do not just treat with iron; investigate the GI tract.
2. Pulsatile Mass: Do not palpate vigorously. Order an urgent Ultrasound if stable. If unstable (hypotension), go directly to the OR (if known AAA) or FAST scan/CT if diagnosis unclear but patient stable enough.
3. Sister Mary Joseph Nodule: Palpable nodule at the umbilicus representing metastasis from a pelvic or abdominal malignancy (often gastric or pancreatic).
4. Courvoisier’s Sign: Palpable, non-tender gallbladder with jaundice suggests malignancy (pancreatic head), not gallstones.
5. Pediatrics: A flank mass in a child is likely Wilms Tumour (nephroblastoma) or Neuroblastoma. Wilms tumour typically does not cross the midline; Neuroblastoma does.

Sample Question

Scenario: A 68-year-old male presents to his family physician for a routine health maintenance visit. He has a history of hypertension controlled with amlodipine and has smoked 1 pack of cigarettes daily for 40 years. He has no specific complaints. On physical examination, his BMI is 28 kg/m². Abdominal examination reveals a non-tender, pulsatile mass in the epigastrium, slightly superior to the umbilicus. The mass is estimated to be approximately 4 cm in width. Peripheral pulses are intact.

Which one of the following is the most appropriate next step in the management of this patient?

• A. Reassurance and annual physical examination
• B. Computed tomography (CT) angiography of the abdomen
• C. Abdominal ultrasound
• D. Immediate referral for vascular surgery consultation
• E. Magnetic resonance imaging (MRI) of the abdomen

Explanation

The correct answer is:

• C. Abdominal ultrasound

Detailed Explanation:

• Diagnosis: The clinical presentation is highly suggestive of an Abdominal Aortic Aneurysm (AAA). The patient has significant risk factors: older age, male gender, and a significant smoking history. The finding of a pulsatile epigastric mass is classic.
• Guideline: According to the Canadian Task Force on Preventive Health Care (CTFPHC) and general surgical guidelines, abdominal ultrasound is the screening and diagnostic modality of choice for asymptomatic AAAs. It is non-invasive, cost-effective, and highly sensitive/specific for measuring the aortic diameter.
• Why C is correct: Ultrasound will confirm the diagnosis and accurately measure the size of the aneurysm to determine if it meets criteria for surveillance or intervention.
• Why A is incorrect: A pulsatile mass in a 68-year-old smoker is pathological until proven otherwise. Ignoring it could lead to rupture and death.
• Why B is incorrect: While CT angiography provides detailed anatomical information for surgical planning, it involves radiation and contrast exposure. It is typically reserved for pre-operative planning after an aneurysm has been diagnosed and reached a size threshold requiring intervention, or if rupture is suspected.
• Why D is incorrect: Immediate referral is premature without imaging confirmation and sizing. Vascular surgery referral is generally indicated if the aneurysm is >5.0-5.5 cm or rapidly expanding.
• Why E is incorrect: MRI is not the first-line modality for diagnosis due to cost and availability, though it can be used if CT is contraindicated.

References

1. Canadian Task Force on Preventive Health Care. (2017). Recommendations on screening for abdominal aortic aneurysm in primary care. CMAJ.
2. Medical Council of Canada. (2023). MCCQE Part I Clinical Decision Making and Multiple Choice Question Objectives.
3. Toronto Notes. (2024). Gastroenterology and General Surgery Sections.
4. UpToDate. (2024). Clinical presentation, evaluation, and management of renal masses.
5. Society of Obstetricians and Gynaecologists of Canada (SOGC). Clinical Practice Guidelines on Adnexal Masses.