Introduction: Due to a longstanding controversy over the perfusion reliability of zone IV current 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 literature search and 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. 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.

Introduction: Due to a longstanding controversy over the perfusion reliability of zone IV current 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 literature search and 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. 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.

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Taylor: Then, now and later 0.5 mm. Are we all faced with becoming supermicrosurgeons or is bigger still best? Remember however, 'What goes around comes around'-and goes around again!