Lacrimal sac fistulas are rare developmental abnormalities that occur during embryogenesis, forming an epithelialized tract from the common canaliculus, lacrimal sac, or nasolacrimal duct to the overlying skin. The external os is usually found just inferiorly to the medical canthus. The incidence is around 1 in 2000 live births, and the literature is limited to case reports or small series.

Causation has not been established, but theories include incomplete closure of the embryonic fissure, inflammatory processes, or amniotic banding causing failure of the developing nasolacrimal drainage system to close properly, leaving a fistula.

Lacrimal sac fistulas may be asymptomatic with spontaneous resolution. The most common symptom is epiphora (possibly with mucoid component), but this is a nonpainful entity. Two common complications that may arise are localized eczema and acute dacryocystitis.

This is an embryological, developmental disorder without race or sex predilection. There have been reports of lacrimal sac fistulas running in some families, occasionally with an autosomal-dominant or recessive inheritance pattern. These are not generally associated with systemic disease, but associations have been made with the following disorders:

• Down syndrome
• VACTERL association
• CHARGE syndrome
• Preauricular fistula
• Hypospadias 
• Ectrodactyly-ectodermal dysplasia-clefting syndrome

Asymptomatic patients are generally observed closely, while symptomatic and infected patients undergo surgical correction. Outcomes are generally very good.