Figure 2: Chiari I malformation (dorsal/ventral view). Note the arrows pointing to the herniated cerebellar tonsils. (Adapted from Syringomyelia and the Chiari Malformations.)

Clinical symptoms of Chiari I are varied. Most patients present with symptoms of headache and/or neck pain; arm or hand numbness; weakness of the upper extremities; disruption of sensory (pain and temperature sensations); and leg weakness or gait difficulty.8,10 In more severe cases, patients may present with symptoms of lower cranial nerve deficit, such as hoarseness, difficulty swallowing, and visual disturbance.3,4,8

Posterior fossa decompression is most commonly used to treat Chiari I malformation.3,4,11 This is the removal of the bony foramen magnum and a cervical laminotomy to the level below the herniated tonsils. The goal in this procedure is to widen the foramen magnum sufficiently to alleviate compression of the subarachnoid spaces.3 Often this is followed by a duraplasty to relieve the alterations in CSF flow, which lead to syrinx formations, at the cervicomedullary junction.3,4 Hydrocephalus occurs in approximately 10% of Chiari I patients. Often, treatment of hydrocephalus via VP shunting will alleviate the symptoms associated with Chiari I. 3,4,12 For this reason it is imperative to identify the presence of hydrocephalus prior to surgical intervention. In most of the literature, the improvement is often seen in motor strength (50-85%),8,9,11 however there is little hope of improvement if muscle atrophy has occurred. Headaches and neck pain also improve in 60-80% of the patients. Symptoms associated with sensory function are less likely to improve. Additionally, patients presenting with syringomyelia are less likely to improve. 3,4,13