Breast Implant MRI : Teaching Points

Case Report 

Follow up case of subpectoral silicone implant with no old scans available.

MR findings

Both breasts suggest well defined regular silicone implants in deep pectoral region with intact capsule. Subtle heterogeneity of the silicone signal at places is MR flow or interphase related with no linguine sign positivity to suggest any intra or extracapsular rupture of silicone. The contour of implant at places is depressed suggesting partial collapse (more seen in left breast implant anteriorly. Pectoral muscles appear normal. Both breast show tiny bright foci – possibly cysts with rest normal with no axillary lymphadenopathy.

Teaching Points by Dr MGK Murthy, Dr GA Prasad, MR Technologist Narasimhulu

Breast implants are categorized by lumen number, filler type, and surface contour. Breast implants are commonly positioned either deep to the glandular tissue (retroglandular or subglandular) or deep to the pectoralis major muscle (retropectoral or subpectoral).

Fibrous tissue develops around the implant as a normal physiologic response to a foreign body; this process is termed “encapsulation.” Early postoperative complications are - hematoma and infection. Late postoperative complications are- capsular contracture, silicone granuloma formation, and implant rupture.

Capsular contracture - abnormal constriction of the fibrous capsule that surrounds the breast implant which can occur anytime after surgery, but most commonly occurs within the first few postoperative months and is more frequently observed with smooth-surfaced silicone implants and subglandular implants. Capsular contracture is predominantly a clinical diagnosis. Radiographic findings, which are not always present, include a change in the shape of the implant (i.e., rounding, irregularity, infolding, or tenting); thickening of the fibrous capsule, which is best shown on ultrasound; and peri-implant calcifications.

Implant Rupture- Silicone implant rupture can be -  intracapsular or extracapsular with most common being intracapsular (77–89%). MRI has a high sensitivity (72–94%) and specificity (85–100%) for the diagnosis of silicone implant rupture. The hallmark of intracapsular rupture on MRI is the linguine sign, representing layers of collapsed elastomeric shell floating in silicone gel contained by the fibrous capsule.  Signs of minimally collapsed intracapsular rupture include the “teardrop sign,” the “keyhole” or “noose” sign, and the “subcapsular line” sign. These signs represent small amounts of silicone outside the implant shell but contained within the fibrous capsule. MR findings of extracapsular rupture include the presence of free silicone separate from the implant seen as discrete foci of isointense to low signal intensity on T1 fat-suppressed images and of high signal intensity on water-suppressed T2- weighted images.

Silicone granulomas - may enhance similar to breast carcinomas and may be difficult to distinguish on the basis of imaging criteria alone, thus requiring biopsy.