What is the initial workup for a new rectal mass?

Initial Workup for a New Rectal Mass

The initial workup for a new rectal mass should include digital rectal examination with rigid sigmoidoscopy, biopsy for histopathological examination, complete blood count, liver and renal function tests, carcinoembryonic antigen (CEA), and imaging studies including endorectal ultrasound (ERUS) or rectal MRI. 1

Diagnostic Approach

Step 1: Clinical Examination

• Digital rectal examination to assess:
  • Distance from anal verge
  • Size and consistency of mass
  • Fixation to surrounding structures
• Rigid sigmoidoscopy to:
  • Precisely measure distance from anal margin (tumors ≤15 cm are classified as rectal)
  • Visualize the mass

Step 2: Tissue Diagnosis

• Biopsy of the mass for histopathological examination 1
  • Essential for definitive diagnosis
  • Differentiates adenocarcinoma (95-98% of rectal masses) from other pathologies

Step 3: Laboratory Tests

• Complete blood count
• Liver and renal function tests
• Carcinoembryonic antigen (CEA) 1

Step 4: Imaging Studies

• Local staging:

  • Endorectal ultrasound (ERUS): Preferred for early tumors (cT1-T2) 1
  • Rectal MRI: Recommended for all tumors, especially intermediate to advanced cases 1
    • Provides superior assessment of:
      • T stage
      • Circumferential resection margin (CRM)
      • Sphincter involvement
      • Mesorectal fascia involvement

• Distant staging:

  • CT or MRI of liver and abdomen
  • Chest X-ray or CT scan of thorax 1

Step 5: Complete Colonic Evaluation

• Complete colonoscopy (pre- or postoperatively if the tumor is obstructive)
• If colonoscopy not possible due to obstruction:
  • Virtual colonoscopy or barium enema 1

Important Considerations

Histopathological Assessment

• Biopsy should be evaluated for:
  • Tumor type and grade
  • For early lesions (T1), assessment of submucosal invasion depth using Haggitt's or Kikuchi (sm) classification 1
  • Vascular and neural invasion

Multidisciplinary Evaluation

• All cases should be discussed at a multidisciplinary team conference 1
• This ensures appropriate staging and treatment planning

Pitfalls to Avoid

• Inadequate local staging: Failure to obtain proper imaging can lead to under-treatment or over-treatment
• Incomplete colonoscopy: Missing synchronous lesions
• Relying solely on clinical examination: Digital examination alone is insufficient for accurate staging
• Overlooking non-adenocarcinoma pathologies: While rare, other entities like lymphoma, GIST, neuroendocrine tumors, and even benign conditions can present as rectal masses 2

Special Considerations

• In very early tumors (some cT1), local excision may be considered if properly staged 1, 3
• For more advanced tumors, preoperative treatment planning is essential 1, 3

By following this systematic approach to the workup of a new rectal mass, clinicians can ensure accurate diagnosis and appropriate staging, which are critical for determining the optimal treatment strategy and improving patient outcomes.