Posted By Dr. Eric Baron on May 18, 2020 |

Last updated on October 20th, 2020 at 06:53 am

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Chiari malformation is a common anatomical variation, specifically type I which this blog summarizes. It is most often a benign and asymptomatic finding found incidentally during routine imaging of the brain when an MRI or CT is done for other reasons, including headache. The difficulty is often trying to associate the likelihood of a patient’s symptoms with the Chiari malformation. Internet searching will give you a very long list of reported symptoms caused by Chiari malformation, many of which are inaccurate. Chiari malformation that is truly related to a patient’s symptoms typically include a “pegged” appearance of the cerebellar tonsils (back and bottom part of the cerebellum) which are pointed rather than rounded, suggesting compression at the cervicomedullary junction (area where the brainstem and upper cervical spinal cord merge between the bottom of the skull and upper cervical spine). When this appearance is present, the patient often does have symptoms that correlate to the Chiari. Unfortunately, most of the time the Chiari malformation is not as extensive, making it more difficult to determine if some of the patient’s symptoms are correlated or not. A contrast brain MRI which includes a cine flow (cine-phase contrast) study can be helpful in determining the extent of compression and subsequent blockage of normal cerebrospinal fluid (CSF) flow throughout the craniocervical junction. A cervical MRI without contrast is also recommended to rule out a cervical syrinx (enlarged area in the center of the spinal cord), which can sometimes be associated with Chiari. If a cervical syrinx is found, an MRI of the remaining thoracic and lumbar spine should also be performed.

Reference: “When Your Brain is Falling Out: My Chiari Diagnosis” –

In general, Chiari malformation cerebellar tonsillar herniation is considered to be within normal anatomical variation in the following:
-First decade (0-10 years): 6mm or less
-Second and third decades (10-30 years): 5mm or less
-Fourth-eighth decades (30 to 80 years): 4mm or less
-Ninth decade (greater than 80 years): 3mm or less


Some mild or borderline Chiari malformations can be associated with extensive symptoms, while other times an extensive Chiari malformation is found, but the patient lacks any Chiari symptoms. So, a detailed history of symptoms including headache and associated features is crucial in determining whether a Chiari malformation is clinically relevant or not. This is more useful than basing treatment decisions purely on the extent of tonsillar herniation in Chiari. History is also important in excluding other disorders which can cause a reversible “pseudo-Chiari”, caused by a different disorder such as intracranial hypotension CSF leak, or low-pressure headache) or idiopathic intracranial hypertension (IIH) (previously known as pseudotumor cerebri).


According to the International Classification of Headache Disorders 3rd Edition (ICHD3), Chiari headache caused by Chiari type I malformation is usually occipital or suboccipital, of short duration (less than 5 minutes) and provoked by cough or other Valsalva-like maneuvers (straining in the abdominal region such as when having a bowel movement). It remits after the successful treatment of the Chiari malformation.


Diagnostic criteria require Chiari malformation to have at least two of the following:

1. Either or both of the following:
a) Headache has developed in temporal relation to the Chiari or led to its discovery
b) Headache has resolved within 3 months after successful treatment of the Chiari


2. Headache has one or more of the following three characteristics:
a) Precipitated by cough or other Valsalva-like maneuver
b) Occipital or suboccipital location
c) Lasting less than 5 minutes


3. Headache is associated with other symptoms and/or clinical signs of brainstem, cerebellar, lower cranial nerve and/or cervical spinal cord dysfunction. (These may include symptoms such as hoarseness, slurred speech, swallowing or choking difficulty, unsteadiness, dizziness, vertigo, tongue weakness, trigeminal or glossopharyngeal neuralgia, tinnitus, absent gag reflex, facial numbness, autonomic symptoms (syncope, slow heart rate (bradycardia), drop attacks), loss of pain and temperature sensation of the upper torso and arms (from syrinx), loss of muscle strength in the hands and arms (from syrinx)


According to ICHD3 criteria, diagnosis of Chiari malformation by MRI requires a 5-mm caudal descent of the cerebellar tonsils or 3-mm caudal descent of the cerebellar tonsils plus crowding of the subarachnoid space at the craniocervical junction as evidenced by compression of the CSF spaces posterior and lateral to the cerebellum, or reduced height of the supraocciput, or increased slope of the tentorium, or kinking of the medulla oblongata.


Unfortunately, we see many patients who have had Chiari decompression, but they continue to have chronic daily headache which often resembles their pre-surgery headaches. When you delve deeper into their pre-existing headaches, many times they describe headaches which had/have migrainous features (throbbing, pounding, pulsating pain quality with nausea (+/- vomiting) and/or photophobia and phonophobia (sensitivity to bright light and loud sound with bad headache flares)). Many times, the chronic daily headaches that patients continue to have after surgery are associated with some variable degree of these migrainous characteristics. Overall, they typically resemble a chronic migraine pattern, and many times treating the headaches as chronic migraine rather than being distracted and treating only as ongoing Chiari headache can provide significant improvement. Even more important is screening for these migrainous features prior to surgery, and if present, treatments targeting migraine and chronic migraine should always be exhausted first because pure Chiari headache is not going to cause migrainous features of throbbing, pounding, pulsating headache with nausea (+/- vomiting) and/or photophobia and phonophobia.


In addition to a chronic migraine appearing headache, patients who have had Chiari decompression frequently have associated occipital neuralgia (see education pages) in the back of the head and a component of chronic post-craniotomy headache. Post-craniotomy headache is technically similar to chronic post-traumatic headache since surgery is, well, certainly a form of trauma to the head. Chronic post-traumatic headache itself commonly has a chronic migraine clinical appearance (with or without pre-existing migraine history), and treating as such can often be very beneficial.


Successful treatment with significant improvement of chronic daily headache with chronic migraine characteristics following Chiari decompression surgery is often a difficult task requiring patience and a good headache specialist. Onabotulinum toxin A (as of 2010, still the only FDA approved chronic migraine treatment), according to the PREEMPT protocol with some additional dosing over the occipital nerves is often helpful. Daily medications used in migraine prevention can also be helpful, particularly ones that are good for not only migraine, but also occipital neuralgia and musculoskeletal pain such as anticonvulsants (topiramate, gabapentin, etc.), TCAs (amitriptyline, nortriptyline), or SNRIs (duloxetine, venlafaxine ER). Ensuring there is no ongoing chronic daily headache driver from rebound headache (medication overuse headache) is also crucial to improvement.

Author: Dr. Eric Baron