Anatomy of the TRAM - DIEP AND SIEA Flaps

The abdominal tissue outlined in orange with yellow shading depicts the sking tissue that is used for reconstruction with the SIEA, DIEP and TRAM reconstruction.  Superfically, they look the same.  However, below the skin and fat level, they are quite different anatomically and in terms of post-operative functional recovery. 

This area of the body often has excess skin and subcutaneous tissue, especially after child bearing.  The area is marked inferiorly roughly by the suprapubic crease and superiorly just above the umbilicus.  Laterally the area extends to near the anterior superior iliac spine - the high bony prominence of the anterior hips.

When this tissue is removed, the remaining skin from the abdomen is stretched and re-draped to close the abdominal wound, and a new umbilicus is formed surgically.  On the outside, the results are virtually the same as those seen with a tummy tuck.  Depending on the breast reconstruction procedure though, what happens on the inside is quite different.

This figure depicts the tissue deep to the abdominal wall. A single rectus muscles is seen extending from the rib cage just under the breasts to the pubic bone inferiorly on the left side of the patient (right on the screen).  These muscle are partially removed from the abdomen in the TRAM procedure along with the overlying fascia, subcutaneous fat and skin.  The DIEP flap and SIEA flap spare this muscle  The DIEP flap requires operating on and around this muscle.  Intercostal muscle branches that travel from the spinal cord to the rectus muscle perforate the muscle lateraly and travel medially. Some of these nerves are not preserved when harvesting a TRAM or DIEP flap.  The blood vessels to the rectus muscles are pictured - the deep inferior epigastric artery and vein.  These vessels course under and through the rectus muscles and send several branches that pierce (perforate) the muscle and supply the overlying skin and subcutaneous tissue of the abdomen.  The perforator vessels together with the deep inferior epigastric vessels supply the DIEP flap.  This flap does not require the removal of muscle or fascia.

On the right side of the patient are pictures the SIEA vessels.  They lie more superficial and do not require muscle dissection to harvest the flap.

This schematic depicts a cross section of the TRAM flap revealing the deep inferior epigastric artery and vein deep to the rectus muscle.  The rectus muscle is taken together with its overlying fascia and the skin and muscle.  The loss of the abdominal muscle and fascia in the donor area can lead to increased abdominal morbidity post-operatively.

TRAM Flap in Cross-Section

This schematic depicts a cross section of the DIEP flap revealing the deep inferior epigastric artery and vein together with their perforators that pierce the muscle and supply the overlying fat and skin.  Because the muscle and fascia are left behind, the patients are felt to have less donor area morbidity.  Dissecting the small perforator vessels free of muscle may however increase the chance of flap loss and fat necrosis.  Therefore, smokers and patients requiring large reconstructions may be better candidates for TRAM reconstruction. 

DIEP Flap in Cross Section

The SIEA flap relies on superfical vessels just below the skin surface.  The SIEA flap allows for less operative dissection, no muscle or fascia injury, and less operating time.  This flap is technically more demanding that the DIEP flap because of the small vessel size, and should only be performed by experienced microsurgeons and microsurgical teams.  Some patients do not have adequate superficial inferior epigastric vessels - a determination that is made intraoperatively.  The decision is made on the basis of vessel size.  These patients can typically be reconstructed with the DIEP flap.

SIEA Flap in Cross Section