What is the appropriate workup for an adult patient presenting with a rectal mass?

Workup for Rectal Mass

Begin with digital rectal examination (DRE) and rigid proctoscopy with biopsy to obtain tissue diagnosis, followed by complete colonoscopy, laboratory evaluation, and staging imaging with endorectal ultrasound for early lesions or MRI for more advanced disease. 1, 2

Initial Clinical Assessment

Physical Examination and Tissue Diagnosis

• Perform DRE and rigid proctoscopy with biopsy as the essential first diagnostic steps to establish histopathological diagnosis and measure distance from the anal verge (tumors ≤15 cm are classified as rectal) 1, 2
• Document the exact location, size, mobility, and relationship to the anal sphincter during DRE 2
• Obtain multiple biopsies during rigid proctoscopy for histopathological confirmation (95-98% will be adenocarcinomas) 2

Complete Endoscopic Evaluation

• Complete colonoscopy to the cecum is mandatory to exclude synchronous colorectal tumors, which occur in a significant proportion of patients 1, 2
• If obstruction prevents complete colonoscopy initially, perform it within the first postoperative year 1

Laboratory Workup

Obtain the following baseline laboratory tests: 1, 2

• Complete blood count
• Liver function tests
• Renal function tests
• Carcinoembryonic antigen (CEA) level

Staging Imaging

Local Staging Strategy

The choice between endorectal ultrasound (ERUS) and MRI depends on clinical T stage: 1, 2

• For early tumors (cT1-T2): Use ERUS to assess depth of invasion and guide decisions about local excision versus radical surgery 1, 2
• For all other tumors (most T3, T4): Use rectal MRI as the primary local staging modality 1, 2

MRI Assessment Should Evaluate:

• T stage and depth of invasion 2, 3
• Circumferential resection margin (CRM) status—critical for determining need for neoadjuvant therapy 2, 3
• Extramural vascular invasion 2
• Relationship to anal sphincter complex 2
• Regional lymph node involvement (though nodal staging remains challenging even with MRI) 2, 3

Distant Metastasis Evaluation

Assess for metastatic disease with: 1, 2

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

PET-CT may be useful for detecting occult synchronous tumors or metastases at initial presentation, though it is not routinely required 3

Multidisciplinary Team Review

All rectal mass cases should be discussed at a multidisciplinary conference including radiologists, surgeons, radiation oncologists, medical oncologists, and pathologists to determine optimal treatment strategy 2

For patients over 70 years, perform formal geriatric assessment or frailty screening before treatment planning 2

Common Pitfalls to Avoid

• Do not rely on flexible sigmoidoscopy alone—rigid proctoscopy provides more accurate measurement of tumor distance from the anal verge, which is critical for treatment planning 1
• Do not skip complete colonoscopy—synchronous lesions must be identified before definitive treatment 1, 2
• Do not use ERUS for locally advanced tumors—MRI is superior for assessing CRM involvement and selecting patients for neoadjuvant therapy 1, 2, 3
• Consider non-malignant etiologies in appropriate clinical contexts—rectal masses can rarely represent prostate cancer invasion, amebomas, or other non-colorectal pathology 4, 5