A 28-year-old woman with known rheumatic mitral stenosis undergoes transthoracic echocardiography. The stenotic mitral valve shows commissural fusion and restricted leaflet motion. Which is the most common site of pathological involvement in rheumatic mitral stenosis?

Explanation

## Most Common Site of Pathology in Rheumatic Mitral Stenosis **Key Point:** Commissural fusion is the hallmark of rheumatic mitral stenosis; the commissures (anterolateral and posteromedial) are the primary sites of fibrosis and calcification, leading to restricted leaflet motion and stenosis. ### Anatomical Sites of Rheumatic Mitral Valve Involvement ```mermaid flowchart TD A[Rheumatic Mitral Valve]:::outcome --> B[Commissures]:::action A --> C[Leaflets]:::action A --> D[Chordae Tendinae]:::action B --> B1[Anterolateral commissure]:::decision B --> B2[Posteromedial commissure]:::decision B1 --> E[Commissural fusion - MOST COMMON]:::urgent B2 --> E C --> C1[Fibrosis and thickening]:::action D --> D1[Shortening and fusion]:::action E --> F[Restricted leaflet motion]:::outcome C1 --> F D1 --> F F --> G[Mitral stenosis]:::outcome ``` ### Pathological Sequence in Rheumatic MS 1. **Acute phase** → edema and inflammation of valve leaflets and commissures 2. **Healing phase** → fibrosis begins at commissures (high-stress zones) 3. **Chronic phase** → commissural fusion, leaflet thickening, chordal shortening 4. **End-stage** → calcification, rigid valve, severe stenosis ### Comparison of Valve Involvement Sites | Site | Frequency | Pathology | Echo Finding | | --- | --- | --- | --- | | **Commissures** | >95% | Fusion, fibrosis | Restricted leaflet separation, doming | | **Leaflets** | >90% | Thickening, fibrosis | Increased echogenicity, reduced mobility | | **Chordae tendinae** | 70–80% | Shortening, fusion | Reduced chordal length, restricted motion | | **Papillary muscles** | <10% | Hypertrophy (secondary) | Indirect effect from increased afterload | | **Aortic valve** | 30% | Concurrent involvement | Aortic stenosis or regurgitation | | **Tricuspid valve** | 10% | Concurrent involvement | Tricuspid regurgitation | **High-Yield:** Commissural fusion is the **defining feature** of rheumatic MS; it is visible on echocardiography as restricted separation of the anterior and posterior leaflets at the commissures ("hockey stick" appearance of anterior leaflet in parasternal long-axis view). **Clinical Pearl:** The anterolateral commissure is typically fused before the posteromedial commissure; bilateral commissural fusion leads to a funnel-shaped stenotic orifice. **Mnemonic — Rheumatic Mitral Valve Pathology: **CFCL** — Commissural fusion, Fibrosis, Calcification, Leaflet thickening. ## Echocardiographic Features of Commissural Fusion - **Parasternal long-axis view:** Anterior leaflet shows doming (convex appearance) due to restricted commissural opening - **Mitral valve area:** Planimetry shows reduced orifice area; commissural fusion limits opening - **Leaflet mobility:** Anterior leaflet shows restricted motion; posterior leaflet is often immobile - **Chordal involvement:** Shortened, fused chordae contribute to restricted motion **Warning:** Do NOT confuse commissural fusion (rheumatic) with mitral valve prolapse (myxomatous degeneration) or endocarditis (vegetations); these have different echo patterns and clinical presentations.