Implant — Linguine Sign
The linguine sign indicates intracapsular rupture with extensive shell collapse. Multiple adjacent curvilinear or wavy hypointense lines of the collapsed implant shell float within silicone gel, resembling linguine pasta. It is considered pathognomonic for intracapsular silicone implant rupture and represents a more advanced stage than the subcapsular line sign or keyhole sign.
Definition
An intracapsular rupture occurs when the elastomer shell of a silicone implant tears or disrupts, but the surrounding fibrous capsule (formed by the body’s foreign-body response) remains intact. In the linguine sign, the shell has collapsed extensively — multiple fragments of the ruptured envelope fold upon themselves and float freely within the extravasated silicone gel, all still contained by the fibrous capsule.
Imaging Appearance
Silicone-Sensitive Sequences (Key Diagnostic Sequence)
- Water-suppressed silicone-only sequences (e.g., silicone-selective inversion recovery) are the most sensitive for detecting the linguine sign
- Collapsed shell fragments appear as multiple wavy hypointense lines against the hyperintense silicone background
- The lines are irregular, curvilinear, and parallel or intertwined — distinct from the single thin line of an uncollapsed shell
T2-Weighted (Without Silicone Suppression)
- Silicone is hyperintense on T2; collapsed shell fragments appear as low-signal curvilinear lines
- Less specific than silicone-selective sequences but may raise suspicion
T1-Weighted
- Silicone is intermediate signal; shell fragments may be difficult to distinguish
- Not the primary diagnostic sequence for implant evaluation
MRI Without Contrast
- Contrast is not required for implant integrity evaluation per BI-RADS v2025
- Silicone-sensitive sequences and water-suppressed images are sufficient
Board Pearl
The linguine sign is pathognomonic for intracapsular silicone implant rupture. Multiple wavy dark lines (collapsed shell) floating in bright silicone on silicone-sensitive sequences = unmistakable diagnosis. This is a classic boards image — if you see “wavy noodle-like lines within silicone,” the answer is always intracapsular rupture.
Spectrum of Intracapsular Rupture Signs
The linguine sign exists on a continuum of increasing shell collapse:
| Sign | Shell Status | Appearance | Severity |
|---|---|---|---|
| Implant — Subcapsular Line Sign | Minimal tear, shell mostly intact | Single thin line just inside the shell | Early / minimal |
| Implant — Keyhole Sign | Small focal tear | Teardrop or keyhole-shaped silicone between shell and capsule | Early / focal |
| Linguine sign | Extensive collapse, shell fragmented | Multiple wavy hypointense lines floating in silicone | Advanced |
Board Pearl
The subcapsular line sign is the earliest and most subtle indicator of intracapsular rupture — a thin curvilinear line parallel to the inner shell surface. The linguine sign indicates more advanced rupture with greater shell collapse. Both remain intracapsular (silicone contained within the fibrous capsule).
Differential Diagnosis
| Finding | Key Distinguishing Feature |
|---|---|
| Normal radial folds | Extend from the periphery toward the center; do not float freely; continuous with the shell; no silicone between fold and capsule |
| Subcapsular line sign | Single thin line near the shell surface, not multiple wavy lines |
| Extracapsular rupture | Silicone extends beyond the fibrous capsule into surrounding breast tissue; may see free silicone granulomas |
| Gel bleed | Microscopic silicone diffusion through intact shell; no visible shell disruption on MRI |
Board Pearl
The most common pitfall is confusing radial folds with the linguine sign. Radial folds are normal invaginations of the intact shell that extend inward from the periphery and are contiguous with the shell wall. The linguine sign shows freely floating, wavy, discontinuous shell fragments — not tethered to the capsule margin.
Clinical Significance
- Intracapsular rupture is often asymptomatic — may be discovered incidentally on MRI performed for other indications
- The FDA recommends screening MRI for silent rupture starting 5–6 years after silicone implant placement and every 2–3 years thereafter
- Intracapsular rupture can progress to extracapsular rupture over time if not addressed
- Management: surgical consultation for explantation or implant exchange; not an emergency but warrants timely follow-up
- Extracapsular extension changes management urgency — look carefully for silicone outside the capsule
Pitfalls
- Radial folds mimicking rupture — the most common false positive. Radial folds are contiguous with the shell and do not float freely. Use multiple planes to confirm.
- Single-lumen vs. double-lumen implants — double-lumen implants have an inner and outer shell; the inner shell can appear as a line within silicone and should not be mistaken for rupture.
- Water droplets within silicone — small round hypointense foci (water signal) within the silicone on silicone-sensitive sequences can indicate shell permeability but are not the same as the linguine sign.
- Suboptimal silicone suppression — poor fat or water suppression can obscure the shell fragments. Ensure proper sequence selection.
- Assuming intracapsular = benign — always evaluate for extracapsular extension (silicone in breast tissue, axillary lymph nodes, or chest wall).
v2025 Context
- BI-RADS v2025 maintains the classification of implant-related findings under the breast MRI lexicon and reinforces that contrast is not required for implant integrity assessment alone
- The linguine sign remains the established descriptor for advanced intracapsular rupture across editions
- Silicone-sensitive sequences remain the recommended approach for implant evaluation