Brainstem hypointense shadow is described in neuroimaging, and the brainstem hypointense shadow described during cranial CT examination is mostly seen in brainstem infarction, brainstem inflammation, and brainstem occupying lesions. The reasons are: 1. Brainstem infarction is mostly seen in the elderly, and patients have an acute onset, often accompanied by dizziness, headache, limb weakness, sensory impairment, distorted eyes and mouth, choking and coughing, and in severe cases, unconsciousness, incontinence and even life-threatening. 2. Patients with brainstem inflammation have a subacute onset, mostly due to viral infection and demyelination, and patients are often accompanied by headache, dizziness, ataxia, limb weakness, etc. 3. 3. Brainstem occupying lesions are usually seen in patients with intracranial primary tumors, which have a slow onset, or in patients with lung cancer and other tumors that have metastasized to the brainstem. The specific cause should be combined with the patient’s medical history and other laboratory tests to confirm the diagnosis.