A 16-year-old male patient with a past medical history of congenital brain malformation presented for surveillance F-FDG PET/CT scan of left parotid acinic cell adenocarcinoma. F-FDG PET/CT revealed absence of gray matter activity in the bilateral cerebral hemispheres most consistent with hydranencephaly. Hydranencephaly is a rare congenital condition characterized by absent cerebral hemispheres replaced by cerebrospinal fluid-filled sacs. The etiology is hypothesized to be secondary to intrauterine bilateral internal carotid artery compromise. Most affected individuals die in utero or within weeks of birth; however, there are rare reported cases of prolonged survival as in our patient.