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Posterior Fossa Tumors
Medulloblastoma is the most frequent infratentorial tumor in neonates. Medulloblastomas are usually midline and arise from primitive neurons in the posterior medullary velum. They may compress and infiltrate the brainstem. They present with signs of brainstem dysfunction and increased intracranial pressure. Apnea may be the first sign of medulloblastoma.
Posterior fossa arachnoid cysts can produce apnea by brainstem compression (Figure 26.1). Apnea is more likely to occur with ventrally located cysts. The treatment for posterior fossa arachnoid cysts producing apnea is surgical decompression.


Figure 26.1.
[A] Ventrally located posterior fossa arachnoid cyst compressing the brainstem. [B] Decompressed posterior fossa arachnoid cyst. The apnea in this patient ceased after treatment.


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cerebellum clivus arachnoid cyst thalamus medulla oblongata pons mesencephalon (midbrain) cerebelum straight sinus tectum arachnoid cyst after surgical decompression Two options: (1) click on figure; or (2) pause pointer on structures indicated by arrows (figure must be centered).