A breast expander, formally called a tissue expander, is a temporary inflatable device placed under the skin or chest muscle after a mastectomy to gradually stretch the remaining tissue and create space for a permanent breast implant. It works like a slowly inflating balloon: over several weeks, the expander is filled little by little until the skin and muscle have stretched enough to accommodate the final implant. This two-stage approach is the most common method of implant-based breast reconstruction.
How the Two-Stage Process Works
The expander is typically placed during the same surgery as the mastectomy, though it can also be placed months or even years later. A surgeon creates a pocket either beneath or on top of the chest muscle and inserts the deflated expander. Over the following weeks, the expander is gradually filled to increase its volume. Once the tissue has stretched to the desired size and had time to recover and reestablish blood supply, the expander is removed in a second surgery and replaced with a permanent implant.
The expansion phase usually takes several weeks to a few months. After the target volume is reached, most surgeons wait an additional period before the exchange surgery to let the stretched tissue settle and heal. The total timeline from expander placement to final implant varies, but many patients complete the process within three to six months.
Where the Expander Gets Placed
Surgeons place the expander in one of two positions: under the chest muscle (subpectoral) or on top of it (prepectoral). For decades, placing it under the muscle was the standard approach. It provides good coverage over the expander, but it comes with trade-offs. Because the pectoralis muscle gets lifted and manipulated during surgery, postoperative pain tends to be higher. More than 70% of patients with subpectoral placement experience animation deformity, where the reconstructed breast visibly shifts when the chest muscle contracts.
Prepectoral placement, where the expander sits above the muscle in a pocket reinforced with a surgical mesh, has become increasingly popular. Studies comparing the two approaches show significantly lower pain scores at every measured time point, from 12 hours after surgery through the first month. Patients also avoid the animation deformity issue entirely because the chest muscle is left untouched. Not every patient is a candidate for prepectoral placement, though. Factors like skin thickness and blood supply after mastectomy help determine which approach a surgeon recommends.
Saline vs. Carbon Dioxide Expanders
Traditional expanders are filled with saline (sterile saltwater) through a small port embedded in the device. During office visits every one to two weeks, a nurse or surgeon locates the port, inserts a needle through the skin, and injects a measured amount of saline. Each fill session stretches the tissue a bit more. This method works well but requires repeated office visits and needle sticks, which many patients find uncomfortable.
A newer option uses carbon dioxide gas instead of saline. The AeroForm expander lets patients control the expansion themselves using a handheld remote. Each press releases 10 cubic centimeters of gas, and patients can expand up to three times per day. This means up to 210 cc of expansion per week, compared to what a single office visit might deliver. In clinical comparisons, patients using the carbon dioxide expander completed expansion in an average of 45 days versus 87 days for saline. The total reconstruction timeline, from placement to final implant, was also shorter: 94 days compared to 143 days.
The carbon dioxide expander also showed lower complication rates overall (32.4% versus 46.0%) and zero surgical-site infections compared to 5.4% with saline. Because there are no needle sticks, there’s no risk of accidentally puncturing the expander or introducing bacteria through the skin during fills.
What Expansion Actually Feels Like
The physical sensation varies from person to person, but the most common description is tightness and pressure, similar to the feeling of overstretching a muscle. One patient described it as having coconut shells attached to the body, except they’re under the skin. Because a mastectomy cuts nerves in the chest, many patients experience numbness over the expanded area, which creates an odd disconnect between pressure and surface sensation.
Pain is most noticeable in the 18 to 36 hours after each fill session. Muscle relaxers and over-the-counter pain relievers help manage the discomfort. Between fills, most patients adjust to the new volume and the tightness eases. Sleeping can be challenging, especially in the early weeks. Many patients find that sleeping slightly elevated or on their back is more comfortable than their usual position.
Complications to Know About
A large study of prepectoral expander reconstruction found the most frequent complications were fluid buildup around the expander (8.7%), infection or skin redness (8.2%), and expander loss requiring removal (4.2%). Bleeding complications, expander exposure through the skin, and skin flap death each occurred in roughly 2% of cases. Most complications are manageable, but expander loss means starting the reconstruction process over or switching to a different approach.
Radiation therapy significantly raises the risk. Among patients who received radiation during or after expansion, the major complication rate jumped from 21.2% to 45.4%. Despite this, about 70% of radiated patients still achieved a successful implant-based reconstruction, and another 10% moved to reconstruction using their own body tissue instead.
MRI Scans and Magnetic Ports
Most tissue expanders contain a small magnetic port that helps the surgeon locate the fill site through the skin. This magnet creates a problem with MRI machines, which use powerful magnetic fields. Expanders with magnetic ports are officially labeled “MR Unsafe,” meaning MRI is generally avoided while an expander is in place. If imaging is needed during the expansion period, doctors typically use ultrasound or CT scans instead.
That said, research has shown that MRI can be performed on patients with magnetic-port expanders when special precautions are taken. Some radiologists choose to proceed with MRI on a case-by-case basis when the diagnostic benefit outweighs the risk. If you have a tissue expander and need an MRI for any reason, the key step is making sure every member of your medical team knows the expander is in place before scheduling the scan.