Disappearance of the Hummingbird Sign after Shunt Surgery in a Case of Idiopathic Normal Pressure Hydrocephalus

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A 79-year-old man presented with a slowly progressive gait disturbance. Brain MRI demonstrated ventriculomegaly and the hummingbird sign. A lumbar puncture showed no abnormalities of the cerebrospinal fluid. The improvement of the gait disturbance after the ventriculoperitoneal shunt led to a diagnosis of idiopathic normal pressure hydrocephalus. Interestingly, postoperative brain MRI demonstrated the disappearance of not only ventriculomegaly, but also the hummingbird sign. The disappearance of the hummingbird sign suggests that an increase in the cerebrospinal fluid in the lateral and third ventricles could cause the compression of the superior surface of the midbrain tegmentum, which manifests as the hummingbird sign.