List seven causes of urethral stricture.

Infection
1. Neisseria gonorrhoeae infection (most common)
2. Tuberculosis

Trauma
3. Instrumentation (e.g., TURP)
4. Catheter placement

Neoplasia (rare)
5. Polyps (inflammatory, transitional cell papilloma)
6. Malignant primaries: transitional cell cancer (80%), squamous cell cancer(15%)
7. Prostate cancer