Avoiding Denervation of Rectus Abdominis in DIEP Flap Harvest: The Importance of Paraneural Perforators

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Sir: We read with great interest the article entitled “Avoiding Denervation of Rectus Abdominis in DIEP Flap Harvest: The Importance of Medial Row Perforators” (Plast Reconstr Surg. 2008;122:710–716). The authors documented that nerve branches enter the rectus muscle mainly from its posterior surface more medial than the lateral row perforators.1,2 As medial row perforators were not related to these motor nerves, the authors suggested that these perforators are ideal for inclusion in abdominal flaps.1 We agree with the authors that the dissection of a dominant lateral row perforator, although usually more straightforward due to a short intramuscular course,3 carries higher risk of muscle denervation. The authors confirmed with histologic analysis the presence of a nerve plexus running with the lateral branch of the deep inferior epigastric artery, but not with the medial branch. Despite this important finding, we believe that the dissection of a medial row perforator may present risk of rectus muscle innervation, as well. Interestingly, Hammond et al.4 reported that although most nerves enter the muscle in the lateral third, nerves were also noted to pass two-thirds of the way under the muscle to enter the medial third. It is also our experience that, during deep inferior epigastric artery perforator flap dissection, occasionally motor nerves are noted to enter the muscle at the junction of its middle and medial thirds. Moreover, a medial row perforator may present a long and oblique intramuscular course (Fig. 1) that traverses the motor nerves, and its dissection may jeopardize the anatomic continuity of these nerves.Fig. 1.: Medial row perforator (long arrow) and lateral branch of the deep inferior epigastric artery (arrowhead). The perforator pierces the muscle at a distance 31.36 mm from its medial border, which corresponds to half the width of the muscle (57.58 mm). The perforator will follow a long oblique intramuscular course and will pierce the deep fascia (short arrow) 14.21 mm from the rectus medial border.Computed tomography–microangiography revolutionized the planning of abdominal flaps and enabled us to identify perforators from the deep inferior epigastric system that follow a retromuscular plane and then either pierce the deep fascia in the linea alba (paramuscular perforators) or pierce the most medial part of the muscle, have a short vertical intramuscular course, and then pierce the deep fascia (paraneural perforators). Both types of perforators essentially have a retromuscular course and, most importantly, a paraneural course, since they emerge medial to the rectus motor nerve supply. To ensure the paraneural course of the perforators with the minimal medial trajectory, we have included in our criteria only those vessels that perforate the undersurface of the muscle less than 15 mm from its medial border (Fig. 2). This distance corresponds to one fourth of the rectus width on average, which is unlikely to involve segmental nerves.1,2,4Fig. 2.: Paraneural perforator (arrow) and lateral branch of the deep inferior epigastric artery (arrowhead). After taking a retromuscular course, the perforator pierces the muscle at a distance 10.82 mm from its medial border, which corresponds to one-fifth of the muscle’s width (60.21 mm). The perforator will follow a short rectilinear intramuscular course and will pierce the deep fascia (short arrow) 4.74 mm from the rectus medial border.We reviewed retrospectively the computed tomography–microangiography scans of patients who underwent breast reconstruction in our unit and recorded that 25.8 percent of the abdominal walls had a dominant paramuscular perforator and 20.6 percent had a dominant paraneural perforator. In other words, in almost 50 percent of cases, a deep inferior epigastric artery perforator flap could be based on a perforator with no impact on rectus muscle innervation. Between a dominant lateral row perforator and a dominant medial with long intramuscular course perforator, we favor the latter, because it is more centrally located and is not associated with a nerve plexus, as Rozen et al.1,2 have documented. Andreas Gravvanis, M.D., Ph.D. Department of Plastic Surgery Dimitris D. Dionyssiou, M.D. Department of Plastic Surgery Lekha Chandrasekharan, D.M.R.D., D.N.B. Department of Radiology Ian Francis, F.R.C.R., F.R.C.S. Department of Radiology Roger W. Smith, F.R.C.S., M.Chir.(Plast.)