CHIARI-1 MALFORMATIONS - ASSESSMENT WITH PHASE-CONTRAST VELOCITY MR

PURPOSE: To assess movement of the medulla, tonsils, and upper cervica l cord as well as that of the posterior fossa cerebrospinal fluid path ways in both normal subjects and those with Chiari I malformations. ME THODS: Nine healthy volunteers and eight patients with Chiari I malfor mations were examined with phase-contrast cine MR. With a region-of-in terest cursor, the directions and intensities of the brain and cerebro spinal fluid were assessed and intensity-versus-time graphs generated. RESULTS: Cerebrospinal fluid flow patterns of the patients with Chiar i I malformations were normal except for absence of valleculla flow. I n addition, increased velocities (10 times normal) of the tonsils of a ll patients with Chiari I malformations together with posterior moveme nt of the medulla (rather than the expected anterior movement seen in volunteers) occurred. CONCLUSIONS: Increased velocities of the tonsils may be the result of the carotid systolic pulse being delivered to a structure (the tonsil) without the normal surrounding cerebrospinal fl uid, resulting in impact of the tonsils in the confined foramen magnum and a consequent caudocranial recoil. An alternative explanation woul d include the Bernoulli effect caused by the confined location of the tonsils. There may be a decrease in the peak tonsillar velocities afte r surgery.