## Anatomy of Congenital Dacryocystitis **Key Point:** The plica lacrimalis (valve of Hasner) at the distal end of the nasolacrimal duct is the most common site of obstruction in congenital dacryocystitis. ### Nasolacrimal Duct Anatomy and Obstruction Sites | Anatomical Site | Frequency of Obstruction | Clinical Presentation | | --- | --- | --- | | Plica lacrimalis (valve of Hasner) | 90% | Most common in congenital cases; usually resolves by 12 months | | Lacrimal canaliculi | Rare | Canalicular agenesis or stricture; requires probing | | Lacrimal sac | Rare | Dacryocystocele; may require marsupialization | | Common lacrimal duct | Rare | Complete agenesis; surgical intervention needed | **High-Yield:** The valve of Hasner is a mucosal fold at the opening of the nasolacrimal duct into the inferior meatus of the nasal cavity. Failure of this valve to canalize during fetal development (around 6 months gestation) results in congenital nasolacrimal duct obstruction (CNLDO) in approximately 6% of newborns. **Mnemonic:** **HASNER** — **H**asner's valve is at the **A**nterior end (distal opening) of the nasolacrimal duct into the **N**ose, and is the most common site of **ER** (embryologic) obstruction. ### Clinical Significance 1. **Presentation:** Epiphora and mucoid discharge from birth or within the first few weeks of life. 2. **Natural History:** 90% of cases resolve spontaneously by 12 months with conservative management (warm compresses, gentle massage of the lacrimal sac). 3. **Intervention:** Probing is indicated if obstruction persists beyond 12 months or if acute dacryocystitis develops. **Clinical Pearl:** Dacryocystoceles (blue dome cysts) can form if the nasolacrimal duct is obstructed at both ends (plica lacrimalis distally and common canaliculus proximally), trapping fluid within the lacrimal sac. 
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.