Symmastia is a physical condition where the tissue or breast implants merge across the midline of the chest, eliminating the intermammary cleft, commonly known as cleavage. The two distinct breast mounds appear continuous across the sternum, rather than being separated by a natural groove. While symmastia can be present on one side, it typically manifests as a bilateral merging of tissue or implant pockets.
Physical Characteristics of Symmastia
The most noticeable feature of symmastia is the appearance of a single, continuous breast mound, often described colloquially as a “uni-boob” or “bread loafing.” This is caused by the skin and underlying soft tissue lifting away from the sternum, allowing the breast volume to be displaced inward. The lack of a defined central inframammary fold contributes to the merged look.
If the condition is acquired after breast augmentation, the breast implants may move inward toward the center of the chest. This inward migration can cause the nipples to appear rotated outwards as the implant volume shifts medially. Beyond the cosmetic change, some people report discomfort, unstable implants, and difficulty finding bras that fit or provide adequate support.
Understanding the Primary Causes
Symmastia has two distinct origins: a rare congenital form and a more common acquired form following surgery. Congenital symmastia is a developmental anomaly present from birth where tissues fail to attach firmly to the sternum, sometimes due to an abnormal collagen arrangement. This form is very rare, with only a few cases documented in medical literature.
Acquired, or iatrogenic, symmastia is the most frequent presentation, arising as a complication of breast augmentation or reconstruction surgery. The primary mechanism involves over-dissection of the medial portion of the surgical pocket created to hold the implant. This excessive dissection weakens or tears the connective tissue that normally anchors the skin and fascia to the sternum, allowing the two implant pockets to communicate across the midline.
Contributing factors include using implants too wide for the patient’s chest anatomy, which forces the creation of a pocket that extends too far medially. Placing the implant in the subglandular plane (above the pectoral muscle) carries a higher risk compared to submuscular placement due to less structural support. Overly large implants can also stretch the central tissues, allowing the implant to migrate toward the center of the chest.
Surgical Correction and Treatment
The correction of symmastia is a specialized revision procedure that requires addressing the compromised internal anatomy to recreate the lost midline separation. The surgeon’s goal is to close the communication between the two implant pockets and re-anchor the soft tissues to the sternum. This is a technically demanding surgery due to the high risk of recurrence caused by pre-existing tissue weakness.
A core technique used is capsulorrhaphy, which involves surgically tightening the inner wall of the scar capsule around the implant using internal sutures. This medial plication closes the overly loose pocket and secures the implant within its designated space. The sutures firmly re-attach the capsule and subdermal tissue to the sternal periosteum, recreating the sternal attachment point that defines the cleavage.
In more complex or recurrent cases, surgeons may employ specialized materials to reinforce the repair. These materials include synthetic mesh or acellular dermal matrix (ADM), which is tissue derived from human or animal sources. This material acts as an internal sling to provide strong, stable support, helping prevent the implant from migrating inward again. The procedure often requires changing the implant itself, such as replacing oversized implants with narrower ones or changing the placement from subglandular to submuscular for better support.