Preoperative Computed Tomographic Angiography for Deep Inferior Epigastric Artery Perforator Flaps: Important Information for the Reporting Radiologist

Abstract

Sir: The use of preoperative imaging for perforator flaps with computed tomographic angiography is being increasingly sought by reconstructive surgeons internationally. This has been particularly sought before the deep inferior epigastric artery perforator flap, where imaging with computed tomographic angiography has been shown to reduce operating times and improve operative outcomes.1,2 However, there are significant differences in the scanning protocol and the techniques for reconstruction for abdominal wall computed tomographic angiography compared with routine abdominal computed tomographic angiography that require implementation. Without these changes, perforators are not adequately imaged, venous and soft-tissue contamination occurs, and the images are not suitable for surgical correlation. In recent visits by the current authors to multiple international centers, it has become apparent that although the scanning protocols have been instituted adequately, the interpretation of the scan data has been less than could otherwise be achieved. The three-dimensional reconstruction of scan data is essential for accurate interpretation, perforator mapping, and presentation to the surgeon. In our previous publications on the use of preoperative computed tomographic angiography, we have described the scanning technique that we use to optimize visualization of perforators.3–5 In terms of positioning the patient, this consists of maintaining the patient in the operative position (supine), without compressive clothing, and scanning the range of the flap only (pubic symphysis to 4 cm above the umbilicus). The scanning protocol involves triggering the contrast bolus at the common femoral artery and scanning the patient in the caudocranial direction (to match filling of the deep inferior epigastric artery). The three-dimensional image reconstructions are the most important part of postscan processing. We use two major techniques: volume-rendered technique reconstructions are used for mapping the cutaneous course of perforators, and maximum intensity projection reconstructions are used for assessing the intramuscular course of perforators.4 Volume-rendered technique reconstructions require the use of a color look-up table, and we have developed a color look-up table that optimally displays the subfascial and subcutaneous course of perforators and highlights the location at which perforators pass through the anterior rectus sheath. This color look-up table is designed to make subcutaneous fat completely transparent, maximize the surface contours of the rectus sheath, and color the skin pink to allow structures to be distinguished from each other. We have found use of this color look-up table to be an essential component of reviewing these scans. The color look-up table can be implemented by using the data shown in Figure 1, or by downloading our color look-up table from the free-to-use Web site (http://insideinspace.com/). Alternatively, the color look-up table or other details can be requested by e-mailing the corresponding author.Fig. 1.: Color look-up table and ray cast lighting properties in Siemens Syngo InSpace 4D (Syngo InSpace 4D, version 2006A; Siemens Medical Solutions, Erlangen, Germany).Although volume-rendered technique images (using our color look-up table) are optimized for visualizing the subcutaneous and subfascial course of perforators (Fig. 2, above), the intramuscular course is optimally seen with maximum intensity projection reconstructions. We use thick axial maximum intensity projection images (both thick contiguous 20/20-mm and thick overlapping 50/20-mm maximum intensity projection images) to demonstrate the intramuscular course of the perforators (Fig. 2, below).Fig. 2.: Computed tomographic angiogram of the abdominal wall vasculature. (Above) Volume-rendered technique reconstruction showing the cutaneous course of a 2-mm periumbilical perforator (arrow). (Below) Maximum intensity projection reconstruction showing the intramuscular course of the same perforator (arrow).The use of these techniques for image reconstruction can drastically improve the benefits of preoperative computed tomographic angiography and can be readily implemented by involving an interested radiology department. Without these finer details of scanning technique and processing, the imaging can frequently be misleading and inadequate. Warren M. Rozen, M.B.B.S., B.Med.Sc. Jack Brockhoff Reconstructive Plastic Surgery Research Unit Department of Anatomy and Cell Biology The University of Melbourne Timothy J. Phillips, M.B.B.S. Damien L. Stella, M.B.B.S. Department of Radiology Royal Melbourne Hospital Mark W. Ashton, M.B.B.S., M.D. Jack Brockhoff Reconstructive Plastic Surgery Research Unit Department of Anatomy and Cell Biology The University of Melbourne Parkville, Victoria, Australia