Impact of Surgical Timing on Anal Fistula Outcomes

This prospective cohort study evaluates whether the duration from symptom onset to surgical intervention influences key clinical outcomes in anal fistula.

The estimated required sample size is 90 patients, distributed evenly with 30 patients in each of the three groups. This sample was calculated using G*power software, assuming an alpha of 0.05, a power of 0.80, and a hypothesized medium effect size difference (0.3) between the groups using a one-way ANOVA test.

Study Procedures and Data Collection:

• Temporal Measurement: The primary exposure variable is the precise interval in days calculated by subtracting the documented symptom onset date from the surgery date. This onset date is captured from initial outpatient clinic notes, emergency department records, or primary care referrals.
• Preoperative Assessment: Magnetic Resonance Imaging (MRI) will be used to classify the fistula's complexity using Park's classification extended by St. James University Hospital, and the external opening location will be documented using Goodsall's rule.
• Intraoperative Protocol: Following an examination under anesthesia (EUA) with tract probing, the surgical intervention will be performed. Researchers will document the procedure type, operative time, estimated blood loss, extent of sphincterotomy, and any intraoperative findings.
• Postoperative Monitoring: Pain will be assessed using a 10 cm Visual Analog Scale (VAS) at 6 hours, 12 hours, 24 hours, 1 week, 2 weeks, and at clinic visits at 1, 3, 6, and 12 months. Fecal incontinence will be evaluated using the Wexner Cleveland Clinic Fecal Incontinence Score, with a clinically significant deterioration defined as a 2-point or greater increase. Clinical healing will be verified by digital rectal exam and proctoscopy.

Inclusion criteria

• Patients aged 18 years or older diagnosed with primary cryptoglandular anal fistula confirmed by clinical examination and preoperative imaging (MRI).
• Patients who will be undergoing definitive surgical intervention for anal fistula at Assiut University Hospital between 2026 and 2028.
• Complete medical records available, including documented symptom onset date (defined as first reported perianal pain, swelling, or discharge) and surgery date.
• Minimum postoperative follow-up of 12 months, with clinical assessment data on healing and recurrence.

Exclusion criteria

• Fistulas due to Crohn's disease, tuberculosis, malignancy, trauma, radiation, or obstetrical injury.
• Pregnant women.
• Recurrent anal fistulas or those with prior surgical intervention for the same fistula.
• Incomplete records or loss to follow-up before 6 months postoperatively.
• Patients with comorbidities precluding surgery (e.g., uncontrolled coagulopathy or active systemic infection).