Typical symptoms associated with CM include severe headache (often brought on by coughing and straining), neck pain, and sensory and motor deficits. Although CM is considered to be a congenital malfomation, the onset of symptoms occurs mainly during adulthood. Also puzzling is the fact that the presence or absence of these symptoms does not correlate with the anatomical severity of herniation. Tonsilar herniation is often found accidentally in asymptomatic persons,15 whereas severe symptoms are often associated with only mild herniation. Hence, the evaluation of the anatomical herniation alone is of limited prognostic value and therefore a better understanding of CM pathophysiology is needed.
Tonsilar herniation is assumed to obstruct partially CSF flow between the cranium and the spinal canal, modifying the local craniocervical hydrodynamics. Several authors have evaluated parameters such as tonsilar motion, cord displacement, and CSF velocities at the craniospinal junction in patients with CM by using phase-contrast MR imaging.5,8,11,17,21 Wolpert, et al.,21 reported greater caudal velocities of tonsils, and Pujol, et al.,17 reported higher tonsilar pulsations in patients harboring CM compared with those in control volunteers. In a similar study, Hofmann, et al.,11 found an increase in maximal systolic and diastolic cord displacement rates in patients with CM. Bhadelia, et al.,8 measured systolic and diastolic CSF flow velocities at four different regions in the craniospinal junction by using MR imaging. They reported statistically significant lower maximal CSF velocities in patients with CM only at the anterior subarachnoid space at the foramen magnum level. On the other hand, Armonda, et al.,5 measured significantly reduced CSF velocities only dorsal to the spinal cord at the level of C-2. This discrepancy in results is not surprising given that CSF velocities have been found to exhibit considerable intersubject variability.3,7,20 Although higher tonsillar velocities and cord displacement rates as well as reduced CSF velocities have been documented in patients with CM, these parameters cannot explain the pathophysiology of the defect including the presence and severity of symptoms.
Despite these remaining questions, posterior fossa decompression surgery has been the treatment of choice in patients with CM. The aim of decompression surgery is the alleviation of hindbrain congestion by removing a portion of bone at the base of the skull. A variety of surgical decompression procedures—with or without opening of the dura mater, opening of the dura with or without closing or patching—have been proposed.13,16 Both successes and failures of decompression have been reported.4,6 The absence of standard guidelines for surgical treatment may be due to the lack of noninvasive means of quantifying the effect of decompression surgery on craniospinal biomechanical properties. Using a recently described MR imaging—based method of measuring intracranial elastance and pressure,2 investigators from our lab reported a significant increase in ICC following decompression surgery in patients whose symptoms improved.19 To establish further the role of ICC in CM, in the present study we quantified ICC in patients with symptomatic CM and in controls. We also compared the sensitivity of ICC with that of local hydrodynamic parameters in detecting abnormal craniospinal biomechanics in patients suffering from CM.
volumetric flow rate
change in intracranial volume
Raksin PBAlperin NSivaramakrishnan ASurapaneni SLichtor T: Noninvasive intracranial compliance and pressure based on dynamic MR imaging of blood flow and cerebrospinal fluid flow: review of principles, implementation, and other noninvasive approaches. Neurosurg Focus 14(4):E42003Neurosurg Focus 14(4):
Sivaramakrishnan AAlperin NSurapaneni SLichtor T: Evaluating the effect of decompression surgery on cerebrospinal fluid flow and intracranial compliance in patients with Chiari malformation using magnetic resonance imaging flow studies. Neurosurgery 55:1344–13512004Neurosurgery 55:
This study was supported in part by the Ed and Gayle Labuda Charitable Fund of the Vanguard Charitable Endowment Program.