<unk><unk> , also known as<unk> , is a condition affecting the brain.  It consists of a downward displacement of the cerebellar tonsils through the foramen magnum (the opening at the base of the skull), sometimes causing non-communicating hydrocephalus as a result of obstruction of cerebrospinal fluid (CSF) outflow.  The cerebrospinal fluid outflow is caused by phase difference in outflow and influx of blood in the vasculature of the brain. It can cause headaches, fatigue, muscle weakness, difficulty swallowing (sometimes accompanied by gagging), choking and vomiting, dizziness, nausea, tinnitus, impaired coordination, neck pain, unsteady gait (problems with balance), poor hand coordination (fine motor skills), numbness and tingling of the hands and feet, and speech problems (such as hoarseness).
Less often, people with<unk><unk>  may experience ringing or buzzing in the ears (tinnitus), weakness, slow heart rhythm, curvature of the spine (scoliosis) related to spinal cord impairment, abnormal breathing, such as central sleep apnea, characterized by periods of breathing cessation during sleep, and, in severe cases, paralysis.
Arnold–Chiari malformation
Brain Stem Gliomas
Adult brain tumors
Brain stem tumor
Glioblastoma multiforme
Primary central nervous system lymphoma
Chiasmal Syndrome
Glioma