Diagnosis and testing
Figure 9. An MRI of the brain shows the cerebellar tonsils (arrow) herniating through the foramen magnum (yellow line).
Figure 10. An MRI of the neck shows a collection of CSF in the spinal cord (yellow arrow) called a syrinx.
Figure 11. A cine MRI movie shows a blockage of CSF flow (white) behind the tonsils and pistoning (up and down movement) of the tonsils.
The complex symptoms of Chiari I malformation can mimic other diseases – often leading to misdiagnosis and delay in treatment. At times, Chiari I is mistaken for fibromyalgia, chronic fatigue syndrome, migraine, multiple sclerosis, mental disorder, depression, sinus disease, trigeminal neuralgia, or other neurologic disorders. Some people wait for years before a diagnosis is made. Yet, an accurate diagnosis and plan of treatment is important to prevent permanent injury to the nervous system. The average patient suffers symptoms for 3 to 7 years before a diagnosis is made.
There is no specific test to confirm Chiari. Rather, a diagnosis is made by assessment of the patient’s symptoms, neurological exam, and MRI findings (i.e., tonsillar herniation, bone deformity, CSF blockage, syrinx).
A complete medical history and physical exam can determine if your symptoms are related to Chiari or another problem. A neurological exam detects problems with cranial nerves such as gag reflex, facial numbness, hoarseness, double vision, tremors, and vision problems. You may be asked to see an eye (ophthalmologist) or ear (otolaryngologist) specialist, or to undergo a sleep evaluation.
If Chiari is suspected, the doctor will order one or more imaging tests to confirm the diagnosis. Diagnostic tests may include:
MRI (magnetic resonance imaging) scan is a noninvasive test used to evaluate the brain, spinal cord, and surrounding CSF. MRI can identify the extent of cerebellar herniation (Fig. 9). The herniation may reach to the level of the first two vertebrae (C1 or C2) of the cervical spine. Herniation of the tonsils is often measured in millimeters (mm) below the foramen magnum. The classic definition of Chiari I is herniation greater than 5mm below the foramen magnum. However, the size of herniation seen on MRI does not closely correlate with symptoms. Someone without herniation may have severe symptoms while another with 20-mm herniation may have no symptoms.
Today the diagnosis of Chiari I is based on symptoms and CSF blockage. MRI of the neck and thoracic spine can detect abnormal collections of CSF within the spinal cord (Fig. 10). This fluid-filled cavity (syrinx) is surrounded by stretched tissues of the spinal cord.
Cine MRI scan is a special MRI study used to observe cerebrospinal fluid (CSF) flow (Fig. 11). With each heartbeat, CSF is forced out of the ventricle of the brain, into the cisterna magna, and down the spinal canal. When the heart relaxes, the CSF flow reverses. The movie-like cine MRI captures the fluid movement. The test can determine if, and by how much, a Chiari is blocking the back-and-forth flow of CSF between the brain and spine.
Learn more about Cine MRI:
Video Webinar: Cine MRI for Chiari Type I Malformation
w/ Mary Gaskill-Shipley, MD, Professor of Radiology and Section Chief in the Division of Neuroradiology at the University of Cincinnati
CT (computed tomography) scan is used to view the bony skull base and spinal column. It can detect thickened bone or previous trauma. CT can also be used to more clearly see bone abnormalities, such as basilar invagination or Ehler-Danlos syndrome.
X-rays of the neck may be taken in flexion and extension to view the bony vertebrae. These images can help your doctor identify any instability at the craniocervical area.
reviewed by: Andrew Ringer, MD, John M. Tew, MD,
Nancy McMahon, RN
University of Cincinnati Department of Neurosurgery