Definition and Overview
Tissue expansion is a surgical technique whereby the body is made to grow additional tissues, such as skin or bone. It goes by the principle of controlled mechanical overstretching, leading to the growth of cells. When the skin is stretched beyond the normal, several processes happen in the body: mitotic activity and vascularity increase, and collagen synthesis occurs, resulting in increased surface area of the skin. Melanocytes or the cells that give colour to the skin, also have increased activity, producing hyperpigmentation. However, colour returns to normal once expansion has been completed. Although no new hair follicles are created during tissue expansion, thinning of the hair is usually not noticeable unless a large degree of expansion is performed.
An inflatable device known as a tissue expander is implanted underneath the skin, and inflated over time to stretch the skin and allow it to grow. A capsule forms around the expander and a slight inflammatory reaction occurs, which eventually becomes more organised. The tissues grow permanently, although some degree of retraction is expected once the expander is taken out. It is commonly used for breast reconstruction, but it may also be used for other procedures. Defects of significant sizes can be replaced or covered with neighbouring tissues that have similar colour and texture. Tissue expansion is typically performed by plastic and reconstructive surgeons.
Who Should Undergo and Expected Results
Although the insertion of tissue expanders is most frequently performed for breast reconstruction, it may also be utilised for other purposes. For burn victims or patients with extensive wounds, tissue expansion can be performed on the skin of the buttocks or the back, so that excess skin can grow and be harvested for grafting to other sites.
Patients with phimosis, a condition wherein the foreskin of the penis cannot be retracted, can also undergo tissue expansion to manage the condition.
Tissue expansion has also become a useful tool in the management of various head and neck conditions. It has been used successfully for the management of alopecia and male pattern baldness. It may also be used for the reconstruction of the scalp for patients with significant scars on the area. For example, a patient with skin cancer on the scalp who underwent wide excision can have a hairless defect on the scalp, which may not be amenable to primary closure. Adjacent scalp tissue subjected to tissue expansion will retain its hair-bearing ability, making it ideal as a replacement. Other uses of tissue expansion in the head and neck region include expansion prior to performing a forehead flap, and for the reconstruction of defects of the external ear.
How is the Procedure Performed?
There are several stages involved in tissue expansion, namely the insertion of the expander, the expansion itself, and the reconstruction. For most cases, the creation of the defect precedes the expansion process; however, this may change, depending on the lesion to be addressed and the expected defect that will be formed. For example, if a benign but large nevus is to be removed, tissue expansion can be performed first, followed by subsequent excision of the lesion and reconstruction.
The first step in tissue expansion is the selection of the appropriate expander for insertion. Different kinds of silicone expanders are available in the market. The size of the expander should be larger than the size of the defect, with some experts suggesting a base approximately 2.5 times larger. In some instances, more than one expander may have to be inserted, allowing the expansion of different regions around the defect.
Once the proper expander has been selected, insertion is performed. The incision for expander insertion varies, depending on the definitive operation. The surgeon must be knowledgeable about the techniques of reconstruction and the anatomy, with emphasis on the blood supply. The incisions should ideally be made in areas where they can be incorporated into future incisions or adequately concealed. A radial or a tangential incision is usually performed.
The incision is carried down to the subcutaneous tissues, and a pocket is created. The expander should be able to fit about a 2 cm margin from the suture line. For this stage, hemostasis is crucial. The integrity of the expander unit is checked prior to insertion by injecting and removing air. The expander is then rolled up and inserted into the pocket, which usually lies between the subcutaneous tissues and the muscles. However, in some locations, such as in the forehead, it may be placed underneath the muscle. This confers additional protection for the hair follicles, and serves as an additional barrier to prevent extrusion of the expander. Once inserted, a sterile isotonic solution is injected into the filling port to facilitate the unrolling and placement of the expander.
The filling port is inserted next. When positioning the filling port, it is important to place it at a site where it is easily palpable. Many surgeons choose to suture the port to nearby tissues to maintain the right orientation. The filling port may also be externalised; however, this may increase the risk for infection. After insertion, the wound is closed in layers.
The next stage involves the expansion proper. Expansion typically begins 10 to 14 days after the insertion. This gives time for the wound to heal, preventing dehiscence. A topical anaesthetic is applied over the filling port. A butterfly needle is then inserted into the port under sterile conditions. The expander is then inflated with isotonic saline solution, making sure that good capillary refill over the flap is maintained. Expansion is performed weekly, until enough skin and soft tissue for reconstruction have been formed.
Possible Risks and Complications
Complication rates can range from 5% to as high as 60%, with increasing surgeon experience being associated with lower complication rates.
Hematoma formation in the expander pocket is best avoided with meticulous hemostasis. The development of a hematoma or seroma can result in infection and formation of a scar capsule.
One of the most serious complications of this procedure is expander exposure or extrusion. Thus, it is important to regularly inspect the wound after the procedure. If the skin flap is thinning, the removal of the isotonic solution may be necessary. The skin then retracts and is allowed to heal before further expansion is attempted. If the implant becomes exposed, it has to be removed immediately. The reconstruction may be performed at the same time as the removal, making use of whatever expanded tissue is already available.
Other complications with the use of an expander include deflation of the expander, migration, and skin necrosis over the expander or the filling port.
Breast reconstruction: Helping you become whole again. American Society of Plastic Surgeons. http://www.plasticsurgery.org/reconstructive-procedures/breast-reconstruction.html.
FDA update on the safety of silicone gel-filled breast implants: Executive summary. US Food and Drug Administration. http://www.fda.gov/MedicalDevices/ProductsandMedicalProcedures/ImplantsandProsthetics/BreastImplants/ucm259866.htm. Accessed Aug. 20, 2013.