What is the appropriate evaluation and management for a presacral (retro‑rectal) mass?

Evaluation and Management of Presacral (Retrorectal) Masses

For any presacral mass, obtain high-resolution pelvic MRI with contrast as the primary imaging modality, followed by surgical excision as definitive treatment in nearly all cases. 1, 2

Initial Diagnostic Workup

Imaging Strategy

• Pelvic MRI with contrast is the gold standard for characterizing presacral masses, providing superior soft tissue detail to assess the relationship to the mesorectal fascia, sacrum, rectum, and surrounding structures 3, 1
• MRI accurately differentiates cystic from solid lesions and identifies key features including septations, wall thickness, signal characteristics, and vascular invasion patterns 1, 4
• CT chest and abdomen/pelvis with contrast should be obtained to evaluate for metastatic disease if malignancy is suspected based on imaging characteristics 3
• Endorectal ultrasound may provide complementary information for lesions in close proximity to the rectal wall 1

Clinical Assessment

• Digital rectal examination with rigid proctoscopy to assess the relationship of the mass to the rectal wall and determine if there is mucosal involvement 3
• Do not perform enemas in patients with presacral masses due to risk of perforation, infection, and tumor seeding 5
• Assess for symptoms including pelvic pain, constipation, urinary dysfunction, or neurologic symptoms from sacral nerve compression 2, 6

Classification and Differential Diagnosis

Presacral masses are heterogeneous and classified as: 2, 6

• Congenital lesions (40%): tailgut cysts, dermoid cysts, teratomas, anterior meningoceles
• Neurogenic tumors (30%): schwannomas, neurofibromas, ependymomas
• Osseous lesions (10%): chordomas, osteosarcomas, giant cell tumors
• Inflammatory/infectious: abscesses, foreign body granulomas
• Miscellaneous: rectal carcinoma extension, metastases, lymphoma

Critical Imaging Features That Alter Management

Features suggesting malignancy requiring neoadjuvant therapy: 1, 6

• Invasion of adjacent structures (sacrum, rectum, pelvic sidewall)
• Irregular margins with infiltrative growth pattern
• Heterogeneous enhancement with necrotic areas
• Bone destruction or periosteal reaction
• Lymphadenopathy

Features suggesting benign lesions amenable to primary resection: 1, 4

• Well-circumscribed margins
• Homogeneous cystic appearance
• Thin regular wall without nodularity
• No invasion of surrounding structures

Tissue Diagnosis Considerations

Pre-operative biopsy is generally NOT recommended for the following reasons: 1, 2, 6

• Risk of tumor seeding along the biopsy tract
• Risk of infection, particularly with cystic lesions
• Incomplete sampling may miss malignant components
• Does not typically change the need for surgical excision

Biopsy should only be considered when: 1, 6

• Imaging suggests metastatic disease or lymphoma where systemic therapy would be first-line
• Suspected chordoma or sarcoma where neoadjuvant radiation may be beneficial
• Patient is not a surgical candidate and diagnosis would alter palliative management

Surgical Management

Surgical Approach Selection

The surgical approach depends on the superior extent of the lesion and suspected pathology: 7, 2, 6

Transanal approach (including TEM): 7

• Lesions with superior border below S3-S4
• Small lesions (<5 cm)
• Benign-appearing cystic lesions
• No sacral involvement
• Offers low morbidity with excellent visualization

Posterior (transcoccygeal or transsacral) approach: 2, 6

• Lesions extending to S3 or below
• Solid lesions requiring wider margins
• Allows direct access to presacral space
• May require partial sacrectomy for adequate exposure

Anterior (transabdominal) approach: 2, 6

• Lesions extending above S3
• Large lesions (>10 cm)
• Suspected malignancy requiring wide margins and lymphadenectomy
• Allows assessment of peritoneal cavity and vascular control

Combined abdominosacral approach: 2, 6

• Very large lesions spanning multiple levels
• Malignant tumors requiring en bloc resection
• Lesions with both pelvic and presacral components

Principles of Surgical Resection

• Complete excision with negative margins is mandatory for all presacral masses to prevent recurrence and establish definitive diagnosis 2, 6
• En bloc resection without tumor violation is critical for suspected malignancies 6
• Partial sacrectomy may be required for lesions adherent to or invading the sacrum, with preservation of at least S3 nerve roots bilaterally to maintain continence 2, 6
• Intraoperative frozen section should be considered to ensure margin adequacy 6

Management of Specific Lesions

Tailgut Cysts (Retrorectal Cystic Hamartomas)

• Complete surgical excision is mandatory despite benign appearance, due to risk of infection, recurrence, and rare malignant transformation (up to 13%) 4, 2
• Transanal or posterior approach is typically sufficient for lesions below S3 7, 4

Chordomas

• Neoadjuvant radiation therapy (50-70 Gy) should be administered prior to wide en bloc resection with high-dose radiation 6
• Requires aggressive surgical resection with wide margins including partial sacrectomy 6
• Multidisciplinary planning with orthopedic oncology and radiation oncology is essential 6

Rectal Neuroendocrine Tumors (NETs) in Presacral Location

• Lesions ≤2 cm: endoscopic or transanal excision is appropriate 3
• Lesions >2 cm or with muscularis propria invasion: low anterior resection or abdominoperineal resection with total mesorectal excision 3

Common Pitfalls to Avoid

• Never perform needle biopsy of cystic presacral lesions without multidisciplinary discussion, as this risks infection and tumor seeding 1, 2
• Do not assume all cystic lesions are benign—up to 13% of tailgut cysts harbor malignancy, and imaging cannot reliably exclude this 4, 2
• Avoid incomplete excision or cyst drainage procedures, as these result in high recurrence rates and potential malignant transformation 2, 6
• Do not delay surgical referral for "observation" of asymptomatic lesions, as growth, infection, or malignant degeneration may complicate subsequent resection 2, 6
• Ensure adequate preoperative imaging extends superiorly to at least L5-S1 to fully characterize the cranial extent and plan the appropriate surgical approach 1, 6