A 28-year-old woman undergoes surgical excision of a benign skin lesion on her back. During the follow-up visits, she develops a hypertrophic scar. Which is the most common cause of hypertrophic scar formation in this patient?

Explanation

## Hypertrophic Scar Formation ### Pathophysiology of Hypertrophic Scars **Key Point:** Hypertrophic scars result from **excessive deposition of Type I collagen** with a relatively organized (parallel to skin surface) fiber arrangement. This is distinct from keloids, which also have excessive Type I collagen but in a markedly disorganized, nodular pattern. ### Comparison: Normal Scar vs. Hypertrophic Scar vs. Keloid | Feature | Normal Scar | Hypertrophic Scar | Keloid | | --- | --- | --- | --- | | **Collagen Type** | Predominantly Type I (organized) | Excessive Type I (organized, parallel) | Excessive Type I (thick, disorganized nodules) | | **Fiber Arrangement** | Organized, parallel bundles | Organized, parallel to skin surface | Random, haphazard, nodular | | **Extends Beyond Wound** | No | No (stays within wound borders) | **Yes** (extends beyond original wound) | | **Regression** | Stable over time | May regress spontaneously over months–years | Rarely regresses | ### Mechanism of Hypertrophic Scar Formation 1. **Prolonged inflammatory phase** → increased TGF-β1 signaling 2. **Excessive fibroblast proliferation and collagen synthesis** → predominantly Type I collagen 3. **Impaired collagen remodeling** → net accumulation of collagen 4. **Fibers arranged parallel to the skin surface** → raised but organized scar 5. **Scar remains within original wound boundaries** — key distinguishing feature from keloid ### Why the Other Options Are Wrong - **Option B (Type III collagen, disorganized):** Type III collagen is the early provisional collagen in granulation tissue; it is normally replaced by Type I during remodeling. Hypertrophic scars are characterized by excess Type I, not Type III. Disorganized arrangement is more characteristic of keloids. - **Option C (Inadequate angiogenesis):** Poor angiogenesis leads to impaired healing and chronic wounds, not hypertrophic scars. - **Option D (Premature termination of inflammatory phase):** Premature termination of inflammation would impair healing; hypertrophic scars are associated with *prolonged*, not premature, inflammation. ### Clinical Pearl **High-Yield (Robbins & Cotran Pathologic Basis of Disease):** Hypertrophic scars are characterized by **excessive Type I collagen deposition with fibers arranged parallel to the skin surface**, remaining within the original wound boundaries. Keloids, by contrast, show thick, disorganized collagen bundles extending beyond the wound margins and are more common in darkly pigmented individuals with a genetic predisposition. **Mnemonic:** **"Hypertrophic = Type I, organized, within borders"** — Hypertrophic scars have excess Type I collagen in an organized pattern and do NOT extend beyond the wound. Keloids = excess Type I, disorganized, extends beyond wound.