A 6-month-old infant has rapidly enlarging head circumference (99th centile) with sunset sign, prominent scalp veins, and irritability. CT brain shows dilated lateral and third ventricles with a normal fourth ventricle. This pattern of hydrocephalus is caused by obstruction at which site?
- A Aqueduct of Sylvius (cerebral aqueduct) ✓
- B Foramina of Luschka and Magendie
- C Arachnoid granulations
- D Choroid plexus
Explanation
Dilatation of the lateral and third ventricles with a normal-sized fourth ventricle indicates obstruction between the third and fourth ventricles, i.e., at the cerebral aqueduct (aqueduct of Sylvius). Aqueductal stenosis is the most common cause of congenital obstructive hydrocephalus and can be acquired (post-infectious, post-haemorrhagic). Obstruction at the foramina of Luschka and Magendie causes fourth ventricle and superior dilatation (Dandy-Walker malformation pattern). Arachnoid granulation dysfunction causes communicating hydrocephalus with all ventricles dilated. The fourth ventricle is downstream of the aqueduct, so it remains normal when the block is at the aqueduct.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.