{"id":15124,"date":"2026-03-19T00:00:53","date_gmt":"2026-03-18T23:00:53","guid":{"rendered":"https:\/\/dev.institutchiaribcn.com\/enfermedades\/arnold-chiari-i-syndrome\/"},"modified":"2026-03-30T12:54:01","modified_gmt":"2026-03-30T10:54:01","slug":"arnold-chiari-syndrome","status":"publish","type":"enfermedades","link":"https:\/\/institutchiaribcn.com\/en\/arnold-chiari-syndrome\/","title":{"rendered":"Arnold-Chiari I Syndrome"},"content":{"rendered":"

Last update: 03\/19\/2026, <\/strong>Dr. Miguel B. Royo Salvador<\/strong><\/a>, Medical License Number 10389.<\/strong> Neurosurgeon and Neurologist.<\/strong><\/p>\n

Definition<\/strong><\/h2>\n

Arnold-Chiari I syndrome<\/strong> consists of herniation of the lower part of the brain \u2013 the cerebellar tonsils \u2013 and the lower cerebellum through the occipital foramen into the vertebral canal, without other associated spinal cord malformations. For some, the descent of the cerebellar tonsils must be greater than 5 mm, for others 3 mm, and for some it may be 0 mm, or impacted tonsils with a compatible clinical picture.<\/p>\n

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Figure 1.- Diagram showing cerebellar tonsil descent and the consequent increase in the supracerebellar space as the entire cerebellum shifts toward the vertebral canal in Arnold-Chiari I syndrome.<\/em><\/p>\n

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Symptoms<\/strong><\/h2>\n

The clinical presentation of Arnold-Chiari I syndrome (ACIS) can manifest in various combinations of symptoms, the most frequent in our case series being (from most to least common): headache, neck pain, limb paresis, vision impairment, limb pain, paresthesia, sensory alteration, vertigo, swallowing difficulty, low back pain, memory impairment, altered gait, upper back pain, balance disturbance, dysesthesia, speech disorder, sphincter alteration, insomnia, vomiting, loss of consciousness, tremor.<\/strong><\/p>\n

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Types of Arnold-Chiari Syndrome<\/strong><\/h2>\n
\"arnold<\/div>\n

There are four classic types (I, II, III, IV) and two recently described types (\u201c0\u201d, \u201c1.5\u201d):<\/p>\n

Type I.<\/strong> Descent of the cerebellar tonsils without other central nervous system (CNS) malformations.<\/p>\n

Type II.<\/strong> Descent of the cerebellar tonsils with neurovertebral malformation, which may fix the spinal cord to the vertebral canal.<\/p>\n

Type III.<\/strong> Descent of the cerebellar tonsils with occipital encephalocele and cerebral abnormalities.<\/p>\n

Type IV.<\/strong> Descent of the cerebellar tonsils with cerebellar aplasia or hypoplasia associated with aplasia of the tentorium cerebelli.<\/p>\n

Type \u201c0\u201d. Cases have been reported with the clinical features of ACIS but without cerebellar tonsil descent.<\/p>\n

Type \u201c1.5\u201d.<\/strong> Recently described, Arnold-Chiari \u201c1.5\u201d syndrome involves cerebellar tonsil descent and brainstem herniation into the occipital foramen.<\/p>\n

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Causes of Cerebellar Tonsil Descent: Theories<\/strong><\/h2>\n

Cerebellar tonsil descent (CTD) may result from traction exerted on the spinal cord by malformations associated with certain forms of Arnold-Chiari syndrome; except in Type I, where tonsil descent is the only morphological alteration \u2013 in this case, several theories exist:<\/p>\n

– Conventional theories:<\/strong><\/p>\n