Prenatal hydrocolpos: imaging findings and differential diagnosis.

Prenatal hydrocolpos is characterized by fluid distension of the vagina. Hydrocolpos can be caused by multiple underlying etiologies and often demonstrates overlapping imaging features compared to other cystic abdominal and pelvic lesions. The purpose of the current pictorial essay is to provide a systematic prenatal magnetic resonance imaging (MRI) approach to differentiating the primary etiologies leading to hydrocolpos. After discussing the fundamental embryological processes involved in vaginal development, the current essay discusses the most common causes of hydrocolpos with their associated prenatal and postnatal imaging features. An approach to distinguishing the more common differential diagnoses is provided. Given the implications of parental counseling and postnatal management, this essay provides an important approach for narrowing differential diagnoses based on prenatal imaging.