An 8-month-old child is brought with rapidly increasing head circumference, full fontanelle, 'setting sun' sign, and irritability. Cranial ultrasound reveals dilated lateral and third ventricles with a normal fourth ventricle. What is the ANATOMICAL site of obstruction?
- A Foramen of Luschka and Magendie (Dandy-Walker malformation)
- B Foramina of Monro (interventricular foramina)
- C Aqueduct of Sylvius (cerebral aqueduct) ✓
- D Subarachnoid space over cerebral convexities
Correct answer: C. Aqueduct of Sylvius (cerebral aqueduct)
Explanation
Dilation of the lateral ventricles AND third ventricle with a NORMAL fourth ventricle localizes the obstruction to the aqueduct of Sylvius (connecting the third and fourth ventricles). This is aqueductal stenosis, the most common cause of non-communicating (obstructive) hydrocephalus. If foramina of Monro were obstructed, only one or both lateral ventricles would dilate with a normal third and fourth. Dandy-Walker malformation involves the fourth ventricle and posterior fossa cysts. Subarachnoid space obstruction causes communicating hydrocephalus with all ventricles dilated.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.