A breast tissue expander is a temporary, balloon-like implant placed under the skin or chest muscle after a mastectomy to gradually stretch the remaining tissue, creating enough space to eventually hold a permanent breast implant. It’s the first step in a two-stage breast reconstruction process that has been the standard approach for about 50 years due to its reliability and versatility. Most expanders are filled with saline over several weeks through a small built-in port, though newer versions use carbon dioxide gas that patients can control at home.
How a Tissue Expander Works
Think of a tissue expander as a tough, deflated silicone shell with a small internal port. A surgeon places it in the chest during or after mastectomy surgery, then gradually fills it with saline (sterile salt water) over a series of office visits. Each injection stretches the overlying skin and muscle a little more. The goal is to preserve the breast skin envelope and slowly rebuild the breast mound so it can accommodate a permanent silicone or saline implant later.
During surgery, the expander is partially filled. Patients generally tolerate an initial fill of about 20% of the expander’s total volume, though some surgeons fill up to 50% or even 75% at the time of placement. A more aggressive initial fill means fewer office visits afterward but puts more immediate stress on the healing skin, so the right starting volume depends on the quality of the tissue and blood supply after mastectomy.
Where the Expander Is Placed
Surgeons place tissue expanders in one of two positions: above the chest muscle (prepectoral) or below it (subpectoral). For decades, placing the expander under the pectoralis muscle was the default. It provides good tissue coverage over the device, but it comes with trade-offs. Subpectoral placement involves cutting and lifting the chest muscle, which causes more postoperative pain and can lead to something called animation deformity, where the breast visibly shifts when you flex your chest. This affects more than 70% of patients with submuscular placement.
Prepectoral placement is a newer approach that leaves the chest muscle untouched. Instead, the expander sits above the muscle, wrapped in a supportive biological mesh. Pain scores are significantly lower at every measured time point, from 12 hours to 30 days after surgery, compared to subpectoral placement. Not everyone is a candidate, though. The best outcomes with either technique tend to occur in nonsmokers with a BMI under 29 who haven’t had radiation therapy, where complication rates can be as low as 8.6%.
The Expansion Schedule
After you’ve healed enough from the initial surgery, you’ll return to your surgeon’s office every one to two weeks for saline injections through the expander’s port. The port contains a small magnet so the surgeon can locate it through your skin, then inserts a needle to add saline. Each fill adds a measured amount, gradually increasing the volume until the expander reaches the desired size. The process typically takes several weeks, depending on how much volume needs to be added and how your tissue responds.
A newer alternative, the AeroForm tissue expander, skips office visits almost entirely. This device contains a small internal canister of carbon dioxide gas and comes with a handheld remote controller. You press a button to release 10 cc of gas at a time, up to three doses per day with at least three hours between doses. In clinical trials submitted to the FDA, the median time to complete expansion was 21 days with the CO2 device compared to 46 days with traditional saline fills. Total time from expander placement to completed reconstruction dropped from about 137 days to 109 days.
What It Feels Like
The expansion phase is not painless. After the initial placement surgery, expect minor swelling and bruising that can last up to eight weeks, along with tightness across your chest, muscle spasms, and mild to moderate pain. Many people describe a persistent pressure or stretching sensation, especially in the days following each fill. Itching and shooting electrical sensations are common as nerves heal. Some numbness or reduced sensitivity in the breast area can last months or become permanent.
Most patients go home the day after expander placement surgery. For at least a week, you’ll need to sleep on your back propped up with pillows. Driving is off the table until you’ve been off prescription pain medication for at least 24 hours and any surgical drains have been removed. Plan on four to six weeks before returning to normal daily activities and at least six weeks before adding strenuous exercise.
The Exchange to a Permanent Implant
Once the expander reaches its target size, there’s a waiting period before the second surgery to swap it for a permanent implant. This pause lets the stretched tissue recover and reestablish its blood supply. Some surgeons historically waited six months, but the preferred timeline has shortened considerably. The median wait is about 2.5 months, with a range from as little as two weeks to over a year depending on individual circumstances.
The exchange surgery itself is typically shorter and less involved than the original placement. The surgeon removes the expander through the existing incision and inserts a permanent silicone or saline implant. Some patients also have additional shaping procedures at this stage to refine symmetry or adjust the fold beneath the breast.
Complications to Be Aware Of
Tissue expander reconstruction is generally reliable, but complications do occur. Infection is the most common concern, affecting roughly 17% of patients in one large study. About three-quarters of infections required the expander to be surgically removed rather than treated with antibiotics alone, with an overall explantation rate of about 13% due to infection. Skin flap problems, where the tissue over the expander loses adequate blood supply, can also occur, particularly with aggressive early filling.
Radiation therapy significantly raises the stakes. In patients who received radiation, the major complication rate more than doubled, jumping from about 21% to 45%. Still, even among radiated patients, roughly 70% ultimately achieved a successful implant-based reconstruction, and another 10% went on to reconstruction using their own body tissue instead. If radiation is part of your cancer treatment plan, your surgical team will factor this into the timing and approach.
MRI Safety With a Tissue Expander
The magnetic port inside most tissue expanders creates a problem for MRI scans. These devices are officially labeled “MR Unsafe,” meaning patients with an expander in place are typically told they cannot have an MRI. The concerns include the magnet in the port potentially moving, heating up, or reversing polarity inside the MRI’s powerful magnetic field.
In situations where an MRI is medically necessary, some radiologists will proceed with specific precautions: using a lower-strength scanner (1.5 Tesla or less), wrapping the chest firmly with an elastic bandage to stabilize the port, positioning the patient face-down, and monitoring them continuously throughout the scan. This is a case-by-case decision that weighs the risks of the MRI against the clinical need for imaging. Once the expander is exchanged for a permanent implant, this restriction no longer applies, since permanent implants don’t contain magnets.