Findings from their NIH-supported study, “MRI Measures of Posterior Cranial Fossa Morphology and CSF Physiology in Chiari Malformation Type I,” have been published online by the journal Neurosurgery.
CMI is characterized by tonsillar herniation, a condition in which a part of the brain, the cerebellar tonsils, has descended out of the skull into the spinal area. The resulting crowding causes compression of parts of the brain and spinal cord and disrupts the normal cerebrospinal fluid physiology. Symptoms include severe headaches, gait problems, numbness and motor weakness.
“The traditional determination of a diagnosis of CMI is a descent by the cerebellar tonsils of greater than 5 millimeters,” said the study’s principal investigator and the article’s first author, Noam Alperin, Ph.D., professor of radiology and biomedical engineering and Director of the Physiologic Imaging and Modeling Lab. “The problem is that some patients who fit that definition have no symptoms, and some patients with a small descent have severe symptoms.
“Defining CMI based on tonsilar herniation alone was detrimental to realizing the multi-factorial nature of this disorder,” said Alperin. “For every 10 patients diagnosed with CMI who have corrective surgery, which involves removing a portion of the skull bone and/or brain tissue, three have poor outcomes. Clearly we need a more comprehensive way of identifying appropriate surgical candidates.”
The conclusions, however, are anecdotal, said Alperin. The study set out to compare certain MRI-generated measurements of the posterior cranial fossa and cranio-cervical junction in 36 symptomatic CMI subjects and 37 control subjects. The CMI group was further divided based on symptomatology into “typical” and “atypical” subgroups.
A total of 20 morphologic and physiologic measures were made, 10 of which demonstrated significant differences between the CMI and control groups. The results suggest that the use of these measures provides a more complete and symptomatically relevant characterization of CMI than can tonsillar herniation alone.
“This offers a new perspective on what is now a poorly understood problem for a neurosurgeon to treat,” said Alperin. “We have a treatment that is effective when you have CMI, so we need a better way to identify CMI. That way, only people who can benefit will undergo the surgical treatment.”
The next step, he said, should be a full-scale study to determine if these findings hold true over a larger group of subjects.
Other Miller School researchers participating in the study were an engineering student, James Ryan Loftus; a medical student, Carlos J. Oliu; Ahmet Bagci, Ph.D., senior research associate in radiology; Sang H. Lee, M.S., systems analyst in radiology; and Barth Green, M.D., professor and Chairman of Neurological Surgery.
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