A 32-year-old woman undergoes surgical excision of a benign skin lesion on her forearm. At 2 weeks post-op, the wound shows red, granular tissue with prominent blood vessels. At 6 weeks, the scar is pale and firm with minimal vascularity. Which feature best distinguishes the tissue present at 2 weeks from that at 6 weeks?

Explanation

## Granulation Tissue vs. Mature Scar ### Tissue at 2 Weeks (Late Proliferative Phase) **Granulation Tissue** is the hallmark: - **High cellularity**: abundant fibroblasts, myofibroblasts, macrophages - **Prominent angiogenesis**: new capillaries (appears red/beefy) - **Loose, immature collagen** (Type III predominates) - **Myofibroblasts** expressing α-smooth muscle actin (α-SMA) - **Minimal cross-linking** of collagen - **Active wound contraction** (myofibroblast-mediated) ### Tissue at 6 Weeks (Early Remodeling Phase) **Mature Scar Tissue**: - **Low cellularity**: fibroblasts sparse, macrophages absent - **Minimal vascularity**: capillaries regress, pale appearance - **Dense, mature collagen** (Type I predominates, Type III decreases) - **Myofibroblasts disappear** (apoptosis) - **Extensive cross-linking** of collagen fibers - **Scar contraction complete** ### Comparison Table | Feature | 2 Weeks (Granulation) | 6 Weeks (Mature Scar) | |---------|----------------------|----------------------| | **Appearance** | Red, granular, moist | Pale, firm, avascular | | **Cellularity** | High (fibroblasts, macrophages) | Low (sparse fibroblasts) | | **Vascularity** | Prominent capillaries | Minimal vessels | | **Collagen Type** | Type III (60–70%) | Type I (80–90%) | | **Collagen Cross-links** | Few | Extensive | | **Myofibroblasts** | Present (α-SMA+) | Absent (apoptosed) | | **Tensile Strength** | ~20% of normal | ~60–80% of normal | **Key Point:** The **transition from granulation tissue to scar** is characterized by: 1. **Loss of cellularity** (fibroblasts undergo apoptosis) 2. **Loss of vascularity** (capillary regression) 3. **Collagen maturation and cross-linking** (Type III → Type I) 4. **Disappearance of myofibroblasts** **High-Yield:** Granulation tissue is **vascular and cellular**; mature scar is **avascular and acellular**. This is the single best discriminator and is frequently tested. **Clinical Pearl:** A wound that remains red and granular beyond 3 weeks suggests **impaired remodeling** (chronic wound, infection, or poor perfusion). Excessive scar formation (keloid/hypertrophic scar) results from prolonged myofibroblast activity and excessive collagen deposition. **Mnemonic: GRAN** — **G**ranulation is **R**ed, **A**bundant cells, **N**ew vessels. [cite:Robbins 10e Ch 3]