MR evaluation of Chiari I malformations at 0.15 T.

Twelve patients with known or presumed Chiari I malformations and two with clinical diagnoses of multiple sclerosis were examined by magnetic resonance (MR) imaging. MR confirmed or established the diagnosis of Chiari I malformation in all 14 cases. The spin-echo technique with a short time to echo (TE = 40 msec) and a short time to recover (TR = 1000 msec) provided optimum imaging of tonsillar position, hydromyelia cavities, and cervicomedullary "kinking." Long TE (greater than 80 msec) and TR (greater than 2000 msec) increase the signal intensity of cerebrospinal fluid and may obscure the pathology. Sagittal, transaxial, and coronal images provided complementary data; sagittal and coronal views best imaged the abnormal spinal cord and tonsils, but slitlike cavities were best seen on transaxial images. Cervicomedullary kinking was found in 10 (71%) of 14 patients and in 90% of the hydromyelic patients. This high incidence suggests that in other radiologic techniques tonsillar herniation masks the kinking. Symptoms of the Chiari I malformation overlap those of demyelinating diseases and brain tumors. Our early experience suggests MR is the preferred noninvasive procedure for identifying Chiari I malformation. Moreover, the ability to portray the variable cavity morphology of hydromyelia directly offers the potential for improved shunt placement.