Neuroanatomy USMLE Step 1 Practice Question
A 45-year-old woman with metastatic breast cancer to the brain presents to the emergency department with a 2-day history of progressive headache, confusion, and nausea. Vital signs show hypertension (160/95 mmHg) and bradycardia (52 bpm). Brain MRI with and without contrast reveals obstructive hydrocephalus with enlargement of the lateral and third ventricles, but the fourth ventricle is normal in size. The obstruction is localized at the aqueduct of Sylvius on axial imaging. Which of the following is the most likely cause of the obstruction at this location?
Answer choices
- AMetastatic deposit compressing the midbrain and narrowing the aqueductCorrect answer
- BCommunicating hydrocephalus secondary to impaired cerebrospinal fluid absorption at the arachnoid granulations
- CEpendymitis causing thickening of the ependymal lining within the third ventricle
- DStenosis of the foramen of Monro preventing flow from the lateral ventricles
- EObstruction of the foramen of Luschka and foramen of Magendie
- FEnlargement of the pineal gland causing mass effect on the aqueduct
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