To substantiate the presence of hydrocephalus in the brains of Mpdz−/− mice, and to distinguish between metabolically active and inert, possibly necrotic tissue, we imaged the brains of Mpdz+/+ and Mpdz−/− mice by 18F‐fluorodeoxyglucose positron emission tomography (PET). The gene discussed is MPDZ; the disease is Hydrocephalus.