The average age at presentation is 41 years. Females slightly outnumber males. It is seen in adolescents but occasionally is first encountered in older individuals. Rarely it is seen in several members of one family. The most common symptom is pain, especially headache that is usually felt in the back of the head, and is aggrevated by coughing and straining.
Weakness is also prominent, especially in the hands.
I malformation is usually not associated with other brain anomalies. However, spinal cord, skull base, and spine lesions are common in this disorder. Dissection of CSF through the ependyma to form cavitation within the substance of the spinal cord is termed syringomyelia. Therefore the term syrinx, or syringomyelia, is used to describe any abnormal accumulation of CSF within the spinal cord. Surgical treatment is the treatment of choice for symptomatic Chiari I malformation.