Nerve Regeneration and Return of Sensation following Breast Reconstruction with Abdominal Flaps
Maurice Nahabedian, MD, FACS
Associate Professor of Plastic Surgery
Director: Center for Reconstructive and Aesthetic Surgery of the Breast
Johns Hopkins Medical Institutions
Breast reconstruction with abdominal flaps such as the pedicle TRAM, free TRAM, and DIEP flap are frequently associated with a loss of sensation in the new breast. This results from transection of the nerves providing sensation to the transplanted abdominal skin and fat. With the recent advancements and new information regarding nerve regeneration, there is an increased emphasis on performing techniques that will increase the probability for nerve regeneration to occur. However, in order to understand how this occurs, a brief discussion on the anatomy and physiology of nerve injury and regeneration is necessary.
The sensation to the skin in the abdominal region is provided primarily from the intercostal nerves that are in proximity to the rib cage. There are 6 to 8 intercostal sensory nerves that enter each of the paired rectus abdominis muscles. These nerves course through the muscle and fat and provide sensation to the overlying skin. They are of extremely small size and difficult to see without visual magnification. When a peripheral sensory nerve such as the intercostal nerve is transected, the distal portion of the nerve degenerates; however, the proximal portion does not and retains the capacity for nerve growth. All peripheral sensory nerves are encased within a conduit called the myelin sheath that does not degenerate even if transected. During the elevation of a TRAM flap, the sensory nerves entering the flap are transected resulting in degeneration of the distal or flap portion of the nerves, thus rendering the flap insensate. However, the conduits within the flap do not degenerate. Following a mastectomy, the nerves entering the breast from the surrounding skin and chest wall are also transected. The remaining transected nerve ends along the edge of the mastectomy site and chest wall remain viable and possess the capacity for nerve growth. When the TRAM flap is transplanted to the breast site, the mastectomy site nerves can randomly enter the conduits within the TRAM and provide some degree of sensation. Unfortunately, the random return of sensation does not occur in all patients because the viable nerve endings may not ever attach to a conduit within the flap. In the event that a random attachment is made, nerve regeneration is an extremely slow process proceeding at a rate of only 1 millimeter per day or 1 inch per month, thus it generally takes approximately 1 year before any return of sensation can occur. The likelihood of successful nerve regeneration and return of sensation may be increased when a viable nerve surrounding the TRAM flap is directly attached to a nerve within the flap and when patients are young. Nerve regeneration is unlikely to occur in patients of advanced age (greater than 60 years) due to biological factors affecting the ability of older nerves to regenerate.
The spontaneous return of sensibility in breasts reconstructed with autologous tissue, in which no two nerves were directly attached, has been studied. Thirty-three patients were included and the average time from the date of the breast reconstruction to the date of the sensory testing was 25 months. Parameters evaluated included objective touch-pressure, pain, temperature, and vibratory measurements. Findings related to touch-pressure demonstrated that 66% of patients regained at least a level of protective sensation and 31% of these patients were able to detect light touch. Thirty-four percent of patients did not regain sensation on the surface of the flap and only responded to deep pressure. The other findings included the ability to detect pain in 88%, cold in 82%, heat in 64%, and vibratory sensation in 100% of patients. Flaps greater than 3 years old demonstrated an improved sensibility score (p=0.0014). The susceptibility of flaps to thermal injury is partially explained by these findings. Flaps with poor sensation that are exposed to an external heat source such as a heating pad or sunlight, may not transmit the appropriate temperature and pain signals to the brain, and can result in a burn to the reconstructed breast.
The return of sensibility following breast reconstruction with TRAM flaps in which two nerves were directly coapted has also been studied. Nerve coaptation was between the 11th intercostal nerve within the flap and the 4th intercostal nerve that is the primary nerve supplying sensation to the normal breast. Fifteen patients following immediate reconstruction with TRAM flaps were compared to 16 control patients in whom no nerve coaptation was performed. Follow-up for all groups ranged from 4 to 41 months. Parameters evaluated included touch, pain, and temperature. Findings included a gradual return of sensation beginning at about 6 months for the nerve coaptation group whereas the control group did not demonstrate a return of sensation for about 1 year.
It can be concluded from these studies that at least a partial return of sensation can be expected in greater than 50% of women after 1 year following breast reconstruction using ones own tissue. The sensibility within a flap increases with time. Nerve coaptation appears to result in a more rapid return of sensation and may result in improved sensation.
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