Septocutaneous gluteal artery perforator (sc-GAP) flap for breast reconstruction: how we do it The nerve to the quadratus femoris muscle This nerve arises from the anterior divisions of the ventral rami of L4-L5 and S1 and leaves the pelvis caudal to the piriformis muscle. The nerve to the obturator internus muscle This nerve, arising from the anterior divisions of the ventral rami of L5 and S1-S2, leaves the pelvis caudal to the piriformis muscle and medial to the sciatic nerve. The pudendal nerve The pudendal nerve, arising from the anterior divisions of the ventral rami of S2-S4, leaves the pelvis caudal to the piriformis muscle as the most medial nerve. PREOPERATIVE RADIOLOGICAL IMAGING Numerous radiological imaging modalities are available to identify perforator branches in advance, facilitating surgical planning and shortening operative time.18,23 At this moment, the most widely applied modalities in the preoperative evaluation and planning of perforator flap procedures are Doppler ultrasound (DUS) and CT angiography (CTA).18 Both these imag- ing techniques are widely available and relatively inexpensive. CT allows for beautiful 3D reconstructions, showing location, size and course of the perforators with high accuracy. Both modalities come with some disadvantages though. Doppler is associated with long imaging times, low accuracy and high interobserver variability.18,24 CTA, on the other hand, suffers from exposure to ionizing radiation, which is an important drawback in the often (relatively) young patients, especially as the ovaries are within the field of view.25,27 Magnetic resonance angiography (MRA) might overcome these disadvantages. Several authors have recently demonstrated that MR angio- graphy is suitable as preoperative imaging modality to evaluate the perforator bran-ches of the DIEA en SGA.18,20,22,28,29Excellent soft-tissue contrast and the absence of ionizing radiation are important advantages of MRI. Dis- advantages of MRI, however, include limited availability and relatively long acquisition times. For now, experience with contrast-enhanced MR angio- graphy (CE-MRA) in the preoperative workup of patients undergoing DIEP or S-GAP flap procedures is still scarce. Although studies comparing MRA and CTA/DUS generally report excellent results for MRA, the diversity in applied MRA techniques is large. Spatial resolution, applied contrast me- dia (conventional extracellular contrast agents versus blood pool contrast agents), field strength (1.5 Tesla versus 3 Tesla magnets) and the applica- 94
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