Chiari malformation does not obstruct cerebrospinal fluid flow during coughs

Chiari malformation is characterised by the herniation of the cerebellar tonsils through the foramen magnum. It is commonly assumed that the tonsils obstruct normal cerebrospinal fluid (CSF) flow, resulting in cough-associated headaches. However, the mechanisms that cause these headaches are unknown, leading to varied and often unsatisfactory treatment outcomes for patients with Chiari. In this study real-time phase contrast MRI (PC-MRI) was used to determine whether the tonsils restrict CSF flow during coughs, and shape models of the posterior fossa were used to identify morphological differences between patients with and without cough headache. Twenty Chiari patients with cough headache, seven without, and twelve age and sex matched controls underwent MR imaging of the head and neck. 3D models of the hindbrain, CSF and vertebrobasilar arteries were constructed from T1-weighted MRI. PC-MRI was collected at the foramen magnum and mid-C3 to measure CSF flow, plus arterial and venous flow. The shape models showed that the CSF space anterior to the pons was narrower in Chiari patients than in controls. Additionally, the CSF space around the vertebrobasilar arteries was more restricted in patients with cough headache than those without. The flow of CSF across the foramen magnum was not restricted, and CSF velocities were ∼2 times greater in Chiari patients than in controls. These findings suggest that overcrowding of the posterior fossa creates high velocity CSF flow across the pons, medulla, and vertebrobasilar arteries. This high velocity flow through the restricted CSF space may stress the cranial vasculature and contribute to headache.