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Preliminary report of preoperative assessment of anterolateral thigh flap perforators using real‐time virtual sonography system

The anterolateral thigh (ALT) flap is considered to be useful for the reconstruction of soft-tissue defects of the head and neck and extremities. However, the flap harvest is not easy technically because of several anatomical variations of vascular pedicle. To overcome the difficulty and make flap harvest simpler and safer, multiple imaging techniques have been applied to surgical planning. Among them, computed tomographic angiography (CTA) can demonstrate the vascular anatomy and can aid perforator selection. Rozen et al. suggested that CTA is currently the standard in preoperative imaging for perforator flaps. However, preoperative imaging might not be always perfect, and the information of preoperative CTA cannot be projected onto the surface of operative field. Real-time virtual sonography (RVS) is a ultrasonography (US) diagnostic system that displays the real-time US image synchronized with previously acquired threedimensional computed tomographic scan imaging or magnetic resonance image. This system can show any cross-sectional image of computed tomographic (CT) volume data in real-time corresponding to the angle of the transducer, and synchronized images are seen side by side on the workstation monitor. The RVS system has been described as a novel and effective navigation tool for use in percutaneous radiofrequency ablation of hepatocellular carcinoma or sentinel lymph node detection in breast cancer. We applied RVS system for preoperative assessment of ALT flap perforators in two patients. Preoperative imaging of the lateral circumflex femoral arterial system was undertaken with three-dimensional computed tomographic angiography (3DCTA). RVS was performed with an ultrasound scanner (HI VISION Preirus, Hitachi Medical corporation, Japan) with a 14-6 MHz probe (EUP-L65) and a small magnetic sensor and magnetic generator. The magnetic generator was set up on either side of the patient’s hip, and CT volume data were transferred in the Sonography unit. It is important to achieve good synchronization between the virtual CT images and real-time US images. We selected an anterior superior iliac spine (ASIS) as a reference point. RVS system displayed the image corresponding to the movement of the transducer in the magnetic field. Synchronized images of the virtual CT and US were seen side by side on the monitor (Fig. 1). Using RVS system, we were able to detect the same vessels visualized by 3DCTA. The information about the perforators and main vessels of the flap was obtained from the examination. Although the flap harvest was performed successfully, the synchronization of the different forms of images was difficult and took relatively long *Correspondence to: Akira Saito, M.D., Ph.D., Department of Plastic and Reconstructive Surgery, Graduate School of Medicine, Hokkaido University, Kita 15, Nishi 7, Kita-ku, Sapporo 060-8638, Japan. E-mail: rogoredo84@gmail.com