Understanding the vascular anatomy of zone IV in DIEA perforator flaps

Abstract

**Introduction**: The deep inferior epigastric artery perforator (DIEP) flap has become a mainstay of microsurgical breast reconstruction due to its low donor site morbidity and comparable success rates. However, there exists a longstanding controversy over the perfusion reliability of zone IV, so much so that current practice commonly advises this area is routinely discarded despite the mechanism behind zone IV necrosis not being fully understood. The authors review and investigate the vascular anatomy of zone IV with the aim of outlining the reasons for necrosis. **Methods**: A PubMed and Embase search was performed regarding zone IV of the DIEP flap and its perfusion. A review of archival injection studies performed by the authors was undertaken to identify the arterial and venous maps of the abdomen. Unembalmed abdominal wall and full body specimens were used for cadaveric studies to demonstrate the arterial anastomotic patterns and venous drainage pathways of the deep inferior epigastric, superficial inferior epigastric, superficial circumflex iliac and intercostal systems. **Results**: Cadaveric injection studies demonstrated the presence of true and choke anastomoses between all lower abdominal arterial branch systems. True and choke anastomoses occur within the subdermal plexus between the lower abdominal arterial branches, the plexus upon which demand is increased following flap transfer to supply the tissue and therefore most susceptible to arterial insufficiency. Arterial insufficiency was noted to arise as a result of low or lack of perfusion of zone IV from medial and lateral row perforators on perfusion studies. Venous studies found that the dominant venous drainage is through large caliber superficial epigastric and circumflex iliac veins, a system which is interrupted in flap elevation and redirected to the perforator venae comitantes, with inter-territory communicating oscillating veins also becoming a limiting factor between territories. **Conclusion**: The mechanism behind the common failure of zone IV in the DIEP flap is explained with studies demonstrating both potential arterial and venous limiting factors. The authors conclude that the mechanism is indeed multifactorial, however suggest that when zone IV in DIEP tissue transfer is required, fat below Scarpa’s fascia is excised and the contralateral SIEV is preserved for use as an additional venous anastomosis.