20 Therefore, we have chosen to assess CSF flow with the real-time MR imaging technique, pencil beam imaging (PBI). However, this is difficult, even with a very fast version of the cine phase contrast sequence, because it produces images that are weighted averages of the phasic behavior over many cardiac cycles and is therefore unable to show transient changes in CSF flow that result from a physiologic challenge and in which the duration of the transient changes is just a few cardiac cycles. Therefore, it is logical to propose that an imaging test for patients with CMI include an assessment of the CSF flow response after a physiologic challenge. 16, 18 This result is believed to be related to transient alterations in CSF flow across the foramen magnum. Symptoms experienced by patients with CMI can be induced or exaggerated by physiologic alterations such as coughing or the Valsalva maneuver. 3, 4, 11 ⇓– 13, 15 Despite success in showing group differences in CSF flow between symptomatic and asymptomatic patients with CMI, 3, 4, 15, 19 critical questions remain concerning the management of an individual patient with CMI presenting for treatment, such as whether and when surgery should be performed and how a patient without typical clinical or MR imaging features should be managed. 10 ⇓ ⇓ ⇓ ⇓ ⇓ ⇓ ⇓– 18 During the past 2 decades, attempts have been made to use cine phase contrast MR imaging to noninvasively assess CSF flow abnormalities in patients with CMI and to provide an objective test for assessment of disease severity. Many of the symptoms and signs associated with CMI are due to abnormal CSF circulation between the head and spine, secondary to foramen magnum obstruction produced by herniated cerebellar tonsils. This scenario is believed to have led to overuse of surgical treatment. 5 ⇓ ⇓– 8 Therefore, in the absence of an objective assessment test for CMI that correlates well with the severity of the clinical findings, a decision for surgery is often based entirely on the clinical judgment and management philosophy of the treating neurosurgeon. 1 ⇓ ⇓ ⇓ ⇓– 6 The issue under debate is that some patients who meet the MR imaging criteria for CMI diagnosis are asymptomatic and some with <5-mm tonsillar herniation may have typical symptoms of CMI. ABBREVIATIONS: A CSF CSF flow waveform amplitude CMI Chiari I malformation FR CSF CSF flow rate PBI pencil beam imaging SV CSF CSF stroke volumeĪlthough the diagnosis of Chiari I malformation (CMI) by MR imaging can be easily made by using a simple definition of >5-mm downward displacement of the cerebellar tonsils through the foramen magnum, management of this condition remains challenging and controversial.
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