A 10-year-old boy is brought to the pediatrician with 1 month of headache, nausea, and vomiting. fundoscopy depicting swelling of the optic nerve head (papilledema) are strongly suggestive of increased intracranial pressure (ICP). MRI of the brain after contrast reveals an abnormal mass with calcifications located at the third ventricle. Which of the following is the most likely cause of this patient’s symptoms?