Spontaneous autoinflation of saline-filled mammary implants: postoperative volume determination by magnetic resonance...

Autoinflation of saline-filled mammary implants has recently been reported in the literature. Except for a few controversial hypotheses, the cause of autoinflation has not been clarified. The need to remove implants for accurate measurement of fill volume has been a deterrent to studies of autoinflation. To measure in situ volumes of saline-filled mammary implants, a noninvasive technique using magnetic resonance imaging (MRI) was developed. Measurements were performed manually on every MRI slice by tracing the outline of the implant with a hand-driven cursor. The accuracy of this MRI technique was assessed by measurements of tissue expanders containing known volumes of saline. To evaluate for autoinflation in mammary implants, a prospective clinical study to compare initial fill volumes of saline-filled mammary implants with 3- and 18-month postoperative volumes, calculated from magnetic resonance imaging (MRI) studies, was designed. A total of 12 patients (23 breast implants) implanted between 1994 and 1996 was included in the study. Volume data were compared by statistical analysis. MRI-determined volumes 3 months postoperatively were significantly larger than reported initial fill volumes, indicating that most saline-filled mammary implants included in the study autoinflated to some extent. Comparison of MRI-determined volumes 3 and 18 months postoperatively revealed no significant differences, indicating that saline-filled mammary implants remain stable and inflated between 3 and 18 months postoperatively. As a result of this study we believe that autoinflation of saline-filled mammary implants occurs more frequently than previously thought.