Background
The deep inferior epigastric perforator flap (DIEP) has become an increasingly popular option for postmastectomy reconstruction because of decreased abdominal wall donor-site morbidity.  Perforator flaps such as the DIEP flap may have a greater incidence of venous congestion, and several methods have been described to improve venous outflow.   Salvage techniques such as venous supercharging and interconnection of the superficial and deep venous systems have been described by other authors.  The concept of retrograde venous drainage has been described previously in reverse radial forearm flaps, but its use with DIEP flaps for breast reconstruction has not been reported.  We present a new option for augmenting venous outflow in DIEP breast reconstruction by creating an anastomosis between a vena comitante of the deep inferior epigastric artery with the retrograde venous limb of the internal mammary vein (IMV).
Methods
A series of fifteen DIEP flaps were prepared by anastomosing the deep inferior epigastric artery with the internal mammary artery and one vena comitante with the antegrade IMV.  An additional venous anastomosis was then made between the second vena comitante and the remaining IMV in a retrograde direction.  Venous congestion was assessed before releasing the antegrade IMV anastomosis after inflow had been established and outflow was based solely only on the retrograde system.  Intraoperative duplex ultrasound was utilized to demonstrate the direction of venous blood flow away from the flap and into the retrograde IMV.  Serial measurements of flap viability including color, temperature, turgor, and Doppler signal were then monitored throughout the patients hospital stay. 
Results
Fifteen consecutive DIEP flaps were created for breast reconstruction using the above described retrograde IMV over a three month period. Each flap had its venous outflow augmented with an anastomosis of a vena comitante to the retrograde limb of the IMV.  After creating the arterial and retrograde venous anastomoses and establishing flow through the flap, no evidence of venous congestion was seen. Retrograde directional blood flow was demonstrated using intraoperative duplex imaging of the venous anastomosis with the retrograde IMV.  All fifteen flaps were successful and displayed no evidence of venous congestion. 
Conclusions
The clinical course of the retrograde augmented DIEP flaps was robust without development of venous congestion.  Utilization of a venous anastomosis to the retrograde IMV provides a large caliber vessel which should improve venous outflow when compared to an antegrade IMV anastomosis alone.  Intraoperatively we show that no significant venous congestion develops with flow which is limited to only a retrograde venous anastomosis. The combination of this outflow with an antegrade anastomosis should provide superior venous outflow when compared to single vein anastomoses.  Intraoperative duplex ultrasound was used to confirm these findings, and supports the use of a retrograde venous IMV anastomosis to improve DIEP flap survivability.  In addition to the method presented here, drainage of the superficial inferior epigastric venous system using a retrograde IMV anastomosis would also be possible.