Case Report: Acquired Horner Syndrome Secondary to Mediastinal Ganglioneuroblastoma in a Pediatric Patient

Introduction Horner syndrome is a rare condition resulting from disruption of the sympathetic nerve pathway to the eye with an estimated incidence in the United States of 1.42 per 100 000 pediatric patients aged younger than 19 years. Although it is more often congenital due to birth trauma, it can also be acquired and classically presents with ptosis, miosis, and anhidrosis. Neuroblastomas, although also rare, are considered the most significant hidden malignancy associated with pediatric Horner syndrome. Case Report A 2-year-old female patient presented with a complaint of uneven pupil sizes, with the right pupil being larger than the left since she was 10 months old. The patient’s parents reported no notable birth, medical, or surgical history and did not observe any one-sided sweating or facial flushing. Iris heterochromia and anisocoria were observed at the initial presentation, but no ptosis was noted. Subsequent follow-up revealed a possible upper lid ptosis with anisocoria greater in the dark. Magnetic resonance imaging was advised, which revealed a mediastinal ganglioneuroblastoma and confirmed the diagnosis of acquired Horner syndrome. Conclusion This case highlights the importance for eye care providers to recognize that Horner syndrome can present subtly and intermittently in pediatric patients. Given that it may be the first sign of a neuroblastoma, early diagnosis is crucial for effective management and treatment.