A. Wadhwa1, S.E. Wayson1, D. Dalecki2, N.A. Wilson1,2 1University Of Rochester, Department Of Surgery, Rochester, NY, USA 2University Of Rochester, Department Of Biomedical Engineering, Rochester, NY, USA
Introduction: Anorectal malformations (ARMs) are congenital anomalies characterized by complete or partial absence of the anorectal canal with or without a perineal fistula. Surgical correction aims to achieve anatomic reconstruction, establish healthy bowel function, and avoid fecal/urinary incontinence. Appropriate location of the neoanus at the center of the anal sphincter complex (ASC) is a main tenant of surgical repair and mislocation is a common complication requiring reoperation. Electrical stimulation is the gold standard for intraoperative location of the ASC, but this technique is imprecise, assumes ASC symmetry, and muscle contraction forces decrease with repeated stimulation. We hypothesize that transperineal ultrasound (US) can be used to non-invasively visualize the ASC and locate the midline of the anal canal using an ex-vivo ferret model of imperforate anus. The long-term objective of this project is to develop a novel transperineal US system to non-invasively locate the ASC intraoperatively in patients with ARMs.
Methods: A ferret model was used as the ferret ASC is similar in size to a human infant. After IACUC approval, the animals were euthanized, the tail was removed, and hair was removed using depilatory cream. A skin flap was sutured over the anal opening to mimic imperforate anus. Transperineal B-mode US images of the ASC were acquired using an 8-MHz Verasonics linear array transducer. The transverse US image was computed for the plane directly below the sutured skin using Matlab. Anatomical structures were outlined and midline anal opening width was measured in B-mode images and photographs. Volumetric reconstruction of the ASC was generated in FIJI.
Results: The midline anal opening width was measured in the transverse plane in a photograph (1A) and US image (1B). There is a 1.90 mm difference between the photograph and the US image [11.4 mm vs 13.3 mm]. Coronal (1C) and sagittal (1D) US images of the ASC are shown with internal and external anal sphincter, anal canal, and skin outlined. 3D US image reconstruction enabled visualization of the ASC throughout its volume (1E).
Conclusions: These data establish proof-of-concept that transperineal US can be used as a tool for non-invasive 3D visualization of the ferret ASC and identification of the midline ex-vivo. The long-term goal of this work is to expand this US system to guide incision placement at the time of posterior sagittal anorectoplasty. Future experiments will increase the sample size, refine the accuracy and precision of midline measurements, and locate the center of the canal. The project establishes the pre-clinical foundation for developing a dedicated non-invasive quantitative US imaging system to guide reconstructive surgery for ARMs.