Neurodegenerative Diseases USMLE Step 1 Practice Question
A 2-day-old male presents with stridor, poor feeding, and recurrent apneic episodes requiring intermittent bag-mask ventilation. Vital signs show HR 155 bpm, RR 42/min, BP 65/38 mmHg, and SpO2 88% on room air. Examination reveals bilateral lower-extremity weakness and absent anal wink. Spinal MRI demonstrates a lumbosacral myelomeningocele with normal cerebrospinal fluid protein levels. Cranial nerve examination is intact. Which posterior fossa abnormality is most likely also present?
Answer choices
- ADownward displacement of cerebellar tonsils only
- BSmooth cerebral surface due to failed neuronal migration
- CDownward displacement of cerebellum and medulla through the foramen magnumCorrect answer
- DFailure of the forebrain to divide into two hemispheres
- EAgenesis of the cerebellar vermis with enlarged posterior fossa
- FEnlargement of the fourth ventricle with hydrocephalus secondary to aqueductal stenosis
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