Fetal mri of obstructive hydrocephalus: a review proposing a surgical etiology-based approach

Ventriculomegaly (VM) is the fetal central nervous system (CNS) anomaly most commonly represented in prenatal imaging. It is defined as a lateral ventricle of dimensions greater than or equal to 10 mm; it can be unilateral or bilateral. More generally, hydrocephalus is defined as an imbalance between brain parenchyma and cerebrospinal fluid (CSF) due to an abnormal increase of the latter within the ventricles in an almost bilateral manner. To identify ventriculomegaly and categorize its severity, the appropriate imaging and measurement methods are crucial. Clinical outcomes vary greatly because of the wide differential diagnosis. Furthermore, there is a significant chance that these causes may recur in subsequent pregnancies. Pregnancy care and counseling depend on a precise diagnosis of the underlying cause.

We retrospectively reviewed our institutional fetal MR imaging database (4568 examinations) from 2005 until 2024. We focused on obstructive hydrocephalus and, according to rigorous inclusion/exclusion criteria (Table 1), we enrolled 201 cases.

We analyzed isolated aqueduct stenosis (36.3%); hemorrhagic events (30.3%); rhombencephalosynapsis (7.5%); dural sinus malformation (6%); midline cysts (5.4%); diencephalic-mesencephalic junction (DMJ) dysplasia (3.5%); infectious lesions (3%); tumors (2.5%); Chiari 1 (1.5%); Walker Warburg disease (1%); not otherwise specified (3%).

We discuss the different etiologies of obstructive hydrocephalus in our population and propose an etiology-based approach that allows the clinician and radiologist to reach the correct differential diagnosis and provide an indication for possible fetal surgery.

Hydrocephalus arises from embryological abnormalities or acquired insults, requiring precise neuroimaging for diagnosis and management. A thorough imaging approach aids in etiological diagnosis, surgical planning, and essential counseling.