An Uncommon Occipital Horn Arachnoid Cyst in a Newborn

This is a case of a full-term male newborn with the rare diagnosis of an arachnoid cyst that is located in the left occipital horn of the lateral ventricle. Prenatal ultrasounds demonstrated progressive dilation of the left lateral ventricle without additional anomalies. On day two of life, an ultrasound confirmed moderate to marked dilation of the left occipital horn. Magnetic resonance imaging revealed a dilated left occipital horn containing a well-circumscribed, cystic lesion with cerebrospinal fluid measuring 4.3×2.1 cm, consistent with an arachnoid cyst. Pediatric neurosurgery was consulted and recommended further evaluation and follow-up. This case highlights an unusual cyst location within the left occipital horn of the lateral ventricle in a newborn. Furthermore, it underscores the importance of early diagnosis and imaging to guide management.