Urethral Stricture

Urethral stricture is a pathologic narrowing of the urethral lumen caused by fibrosis of the corpus spongiosum (spongiofibrosis) surrounding the urethra. The process begins with mucosal injury to the urethral epithelium, progresses through submucosal inflammation, and culminates in dense fibrotic scar formation that reduces luminal diameter and impairs urinary flow. At the molecular level, urethral injury activates a wound healing cascade that becomes dysregulated, leading to excessive fibrosis rather than normal tissue repair. Initial epithelial disruption triggers platelet degranulation and release of platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF-β). TGF-β is the master fibrotic cytokine - it activates resident fibroblasts through SMAD2/3 signaling pathway, inducing their differentiation into myofibroblasts (characterized by alpha-smooth muscle actin expression). Myofibroblasts produce excessive extracellular matrix (ECM) components, particularly collagen types I and III, fibronectin, and proteoglycans. Simultaneously, TGF-β suppresses matrix metalloproteinase (MMP) expression while upregulating tissue inhibitors of metalloproteinases (TIMPs), creating an imbalance favoring collagen deposition over degradation. The resulting dense scar tissue (spongiofibrosis) is poorly vascularized, inelastic, and progressively contracts, narrowing the urethral lumen. Iatrogenic causes are the most common etiology...