Management of Bilocular Cyst at the Anal Verge
A bilocular cyst at the anal verge should be completely surgically excised to establish definitive diagnosis, rule out malignancy, and prevent complications such as infection, fistulization, or malignant degeneration. 1, 2
Initial Diagnostic Approach
Clinical Evaluation
- Obtain focused medical history including duration of symptoms, presence of pain, swelling, discharge, or changes in bowel habits 3
- Perform complete physical examination with digital rectal examination to assess the cyst's location, size, consistency, and relationship to surrounding structures 3
- Check for signs of infection (erythema, warmth, fluctuance, purulent discharge) or systemic illness 3
Laboratory Investigations
- For uncomplicated cysts without signs of infection, routine biochemical investigations are not required based on available evidence 3
- If signs of infection or systemic illness are present, obtain complete blood count, inflammatory markers (C-reactive protein, procalcitonin), and serum glucose to rule out diabetes mellitus 3
Imaging Studies
Advanced imaging is essential for preoperative planning and to characterize the cyst fully. 2, 4
- MRI is the preferred imaging modality as it provides superior soft tissue characterization, defines the cyst's relationship to the anal sphincter complex, and identifies any associated anomalies such as presacral extension or fistulous tracts 2, 4, 5
- CT scan or endoanal ultrasound are acceptable alternatives when MRI is unavailable or contraindicated 3, 4
- Fistulography may be useful if a fistulous tract is suspected 4
Key Imaging Features to Assess
- Cyst wall characteristics (thin-walled vs. thick-walled) 2
- Unilocular vs. multilocular architecture 2
- Presence of septations or internal debris 2
- Associated sacral bone defects or calcifications 2
- Connection to anal canal, rectum, or presacral space 2, 4
Differential Diagnosis Considerations
The bilocular nature and anal verge location require excluding several entities 1, 2, 4:
- Anal gland/duct cyst (most common benign cystic lesion in this location, occurring in only 0.05% of anal surgeries) 1
- Developmental cysts (epidermoid, dermoid, tailgut cysts) 2
- Anal canal duplication (rare congenital malformation, can present in adults) 4
- Anorectal abscess (if inflammatory features present) 3
- Cystic neoplasms requiring histopathologic exclusion 2, 5
Surgical Management
Indications for Surgery
Complete surgical excision is indicated in all cases for the following reasons 1, 2, 4:
- Establish definitive histopathologic diagnosis
- Rule out malignancy definitively
- Prevent complications (infection with fistulization, bleeding, malignant degeneration)
- Achieve cure and prevent recurrence
Surgical Approach
- Transanal excision is appropriate for simple anal gland/duct cysts confined to the anal canal 1
- Posterior sagittal approach is preferred for cysts with presacral extension or associated anomalies 4
- Ensure complete excision with intact cyst wall when possible to minimize recurrence risk 2, 4
Timing of Surgery
- Elective surgical excision should be performed once diagnosis is established and imaging completed 1, 2, 4
- If signs of acute infection are present, consider whether immediate drainage is needed versus antibiotic therapy followed by delayed definitive excision 3
Important Caveats
- Do not assume benignity based on imaging alone—histopathologic confirmation is mandatory as malignant degeneration can occur in developmental cysts 2
- Incomplete excision leads to recurrence—ensure complete surgical removal with adequate margins 2, 4
- Consider associated anomalies, particularly in female patients where anal canal duplication and presacral cysts may coexist 4
- Avoid simple aspiration or incision and drainage as definitive treatment, as this does not provide tissue diagnosis and has high recurrence rates 1, 2