Introduction: Hypoplasia of the internal carotid artery is a rare cause of congenital Horner syndrome. Birth trauma is the most common identifiable cause. We report a case of congenital Horner syndrome associated with ipsilateral hypoplasia of the internal carotid artery.
Observation: A 5-month-old boy presented with left Horner syndrome with myosis, iris hypopigmentation, and enophthalmia. Cranial magnetic resonance imaging was normal. Cerebral angiography showed hypoplasia of the left internal carotid artery. The anterior and middle cerebral arterial flow was supplied through the communicating arteries. Computed tomography demonstrated hypoplasia of the left carotid canal.
Conclusion: Infants with isolated congenital Horner syndrome with no history of birth trauma require complete investigation by a pediatrician. CT or MRI imaging should be discussed to search for associated abnormalities.