Validation of a 3D-printed model of cryptoglandular perianal fistulas.

INTRODUCTION: Visualising the course of a complex perianal fistula on imaging can be difficult. It has been postulated that three-dimensional (3D) models of perianal fistulas improve understanding of the perianal pathology, contribute to surgical decision-making and might even improve future outcomes of surgical treatment. The aim of the current study is to investigate the accuracy of 3D-printed models of perianal fistulas compared with magnetic resonance imaging (MRI). METHODS: MRI scans of 15 patients with transsphincteric and intersphincteric fistulas were selected and then assessed by an experienced abdominal and colorectal radiologist. A standardised method of creating a 3D-printed anatomical model of cryptoglandular perianal fistula was developed by a technical medical physicist and a surgeon in training with special interest in 3D printing. Manual segmentation of the fistula and external sphincter was performed by a trained technical medical physicist. The anatomical models were 3D printed in a 1:1 ratio and assessed by two colorectal surgeons. The 3D-printed models were then scanned with a 3D scanner. Volume of the 3D-printed model was compared with manual segmentation. Inter-rater reliability statistics were calculated for consistency between the radiologist who assessed the MRI scans and the surgeons who assessed the 3D-printed models. The assessment of the MRI was considered the 'gold standard'. Agreement between the two surgeons who assessed the 3D printed models was also determined. RESULTS: Consistency between the radiologist and the surgeons was almost perfect for classification (κ = 0.87, κ = 0.87), substantial for complexity (κ = 0.73, κ = 0.74) and location of the internal orifice (κ = 0.73, κ = 0.73) and moderate for the percentage of involved external anal sphincter in transsphincteric fistulas (ICC 0.63, ICC 0.52). Agreement between the two surgeons was substantial for classification (κ = 0.73), complexity (κ = 0.74), location of the internal orifice (κ = 0.75) and percentage of involved external anal sphincter in transsphincteric fistulas (ICC 0.77). CONCLUSIONS: Our 3D-printed anatomical models of perianal fistulas are an accurate reflection of the MRI. Further research is needed to determine the added value of 3D-printed anatomical models in preoperative planning and education.

The complexity of cryptoglandular fistula-in-ano can be predicted by the distance of the external opening to the anal verge; implications for preoperative imaging?

BACKGROUND: Many surgeons believe that the distance from the external opening to the anal verge (DEOAV) predicts the complexity of a cryptoglandular fistulas-in-ano and, therefore, predicts the need for additional imaging. However, there is no evidence to support this. The primary aim of this study was to determine if DEOAV can predict the complexity of a fistula. Secondary aims were clinical outcome and identification of those patients that might not benefit from preoperative imaging. METHODS: All patients having surgery for cryptoglandular fistula-in-ano between January 2014 and December 2016 were evaluated. Preoperative imaging was used to classify fistulas as simple or complex. The DEAOV was measured preoperatively and was divided into categories ≤ 1 cm, 1-2 cm, or > 2 cm. The relationship between the DEOAV and complexity of the fistula was investigated. Clinical outcome was recorded and a group of patients that might not benefit from preoperative imaging was identified. RESULTS: A total of 103 patients [m:f = 65:38, median age 47 (range 19-79) years] were included. Magnetic resonance imaging identified 39 simple and 64 complex fistulas. The percentage of simple fistula was 88% in fistulas with DEAOV ≤ 1 cm, 48% in DEAOV 1-2 cm and 38% in > 2 cm. There was a significant difference between the complexity of the fistula and the distance to the anal verge (p < 0.001). The overall healing rate was 88%. CONCLUSIONS: The complexity of perianal fistula depends on the DEAOV. We propose that preoperative imaging should be performed in fistulas with external opening > 1 cm from the anal verge.