A 42-year-old man is brought to the emergency room in an ambulance after suffering a grand mal seizure at home. There is no history of recent illness, fever, headache, seizures, or head trauma. He drinks alcohol occasionally and denies any other drug use. Neurologic exam shows the patient to be ale and oriented. No focal abnormalities are noted. A CT scan of the head reveals multiple punctate calcifications, and two enhancing cystic lesions with surrounding edema. What is the most likely diagnosis?