A 45-year-old man presents with sudden severe headache, progressive drowsiness, and bilateral sixth nerve palsies over 6 hours. CT head reveals dilated lateral and third ventricles with a small, rounded hyperdense lesion at the foramen of Monro. There is no mass effect elsewhere. What is the most likely diagnosis?
- A Pilocytic astrocytoma of the cerebellum
- B Colloid cyst of the third ventricle ✓
- C Choroid plexus papilloma
- D Subependymoma of the fourth ventricle
Correct answer: B. Colloid cyst of the third ventricle
Explanation
Colloid cyst classically presents at the foramen of Monro, causing intermittent or acute obstructive hydrocephalus with positional headaches and sudden neurological deterioration. CT shows a rounded hyperdense lesion at the foramen of Monro. These are benign cysts lined by columnar epithelium. Treatment is surgical excision (endoscopic or open) or stereotactic aspiration. Cerebellar astrocytoma would not cause this presentation (Robbins, 10th ed.; Greenberg).
Reference: Greenberg's Handbook of Neurosurgery, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.