Scallop Prolapse Definition
Scallop prolapse refers to the abnormal displacement of one or more specific segments (scallops) of the mitral valve leaflets into the left atrium during systole, typically due to torn chordae tendineae or myxomatous degeneration of the valve tissue.
Anatomical Context
The mitral valve consists of two leaflets (anterior and posterior), with the posterior leaflet divided into three scallops:
- P1 (lateral/anterolateral scallop)
- P2 (middle scallop) - most commonly affected
- P3 (medial/posteromedial scallop)
The anterior leaflet similarly has three segments (A1, A2, A3) 1.
Mechanism and Pathophysiology
Scallop prolapse occurs when:
- Chordae tendineae rupture or elongate, causing the affected scallop to lose its normal anchoring to the papillary muscles
- Myxomatous degeneration weakens the leaflet tissue itself, particularly in conditions like Barlow's disease or fibroelastic deficiency
- The unsupported scallop moves superiorly beyond the mitral annular plane into the left atrium during ventricular systole 1
This abnormal motion prevents proper leaflet coaptation, resulting in mitral regurgitation (MR).
Clinical Significance
Diagnostic Identification
The specific scallop(s) involved must be identified because:
- Surgical repair feasibility depends heavily on which scallops are affected 1
- Single P2 scallop prolapse has the highest likelihood of successful and durable surgical repair 1
- Multiple scallop involvement or anterior leaflet prolapse requires more complex repair techniques and referral to high-volume centers 1
Imaging Characteristics
On echocardiography, prolapse is distinguished from normal leaflet motion by:
- The leaflet tip moving above the mitral annular plane into the left atrium
- This differs from "anterior leaflet override" in secondary MR, where leaflets remain tethered below the annulus despite appearing to overlap 2
Common Pitfalls
Do not confuse scallop prolapse with:
- Anterior leaflet override - seen in functional/secondary MR where the anterior leaflet appears to override the posterior leaflet but both remain tethered into the ventricle, never crossing above the annular plane 2
- Systolic anterior motion - where the anterior leaflet moves toward the septum, not into the atrium
The P2 scallop is most frequently involved due to its redundancy and variable thickness under systolic pressure, though isolated P3 prolapse can occur, particularly with ischemic papillary muscle rupture 3.