Real-Time Subcutaneous Arterial Navigation for Thinning of an Anterolateral Thigh Flap Using Photoacoustic Imaging and Projection Mapping: A Case Report

Thinning of anterolateral thigh flap is challenging. Anatomical studies have shown variations in arterial branching patterns in the subcutaneous layer, which were suspected to be the reason for the high frequency of thinning failures. We attempted to visualize subcutaneous arterial courses preoperatively and perform thinning of perforator flaps using this information appropriately. We accumulated evidence on the accuracy of noninvasive vascular visualization using photoacoustic tomography (PAT). In the present case, we applied a medical imaging projection system (MIPS), which enabled real-time surgical navigation using indocyanine green (ICG) emission signals, to use photoacoustic information intraoperatively during the flap thinning procedure. A 69-year-old woman underwent half-tongue resection using the pull-through method for right-sided tongue cancer. Preoperative PAT was performed 5 days before surgery. The 12 × 6-cm area took ~8 min to scan. We used an ICG test card containing ICG-positive control material cut into strips to show tentative artery lines by projection mapping. The transparent vascular map was laminated and sterilized. MIPS captured ICG fluorescence signals that penetrated the anterolateral thigh flap and continuously projected the purple area on the reverse side of the flap, guiding the position of the tentative arteries. A 20 × 6.5-cm anterolateral thigh flap was elevated with the distal part of the reconstructed tongue and proximal de-epithelialized part to fill the pull-thorough tunnel in the submandibular region. Active bleeding was observed when cutting marginal fat tissue near the purple line of the distal ALT flap projected by MIPS. The study protocol did not include a highly invasive trial for MIPS-guided thinning; therefore, we removed minimal marginal fat tissue. The ALT flap showed no postoperative complications while maintaining conversation and swallowing functions. We present the concept of subcutaneous arterial real-time navigation surgery using PAT and MIPS for safe, easy, and fast flap thinning procedures in the future.