Figure 1: Sagittal MRI scan demonstrating a pre-operative Chiari malformation with cervical syrinx (left), and the same patient 6 months post-operatively demonstrating resolution of the Chiari malformation as well as almost complete resolution of the syrinx (right). The foramen magnum is represented by the dashed red line. Before surgery the patient’s cerebellar tonsils extended 13mm below the foramen magnum (double arrow-head white line), and the tonsils ‘plug’ the craniocervical junction. Following surgery the tonsils are no longer plugging the foramen magnum and can be seen well above their previous level, the amount of cerebrospinal fluid around the brainstem at the craniocervical junction is now normal, and the large pre-operative cervical syrinx (yellow star) has almost completely disappeared.
What is a Chiari malformation? A Chiari malformation is a structural abnormality at the hindbrain, where the cerebellar tonsils herniate through the opening at the bottom of the skull, known as the foramen magnum. The cerebellum is the balance organ of the brain, and sits behind the brainstem at the back of the head. The tonsils are the bottom most part of the cerebellum and normally sit within the skull just above the foramen magnum, however in patients with a Chiari malformation the tonsils extend through the foramen magnum and compress the brainstem and upper part of the spinal cord at the craniocervical junction. In many patients a Chiari malformation can be asymptomatic, however some people experience headaches particularly with coughing, straining or bending over, and some patients also develop fluid accumulation within their cervical spinal cord, known as a cervical syrinx or syringomyelia (from the Greek words syrinxreferring to a fluid filled structure, and myelum meaning ‘of the spinal cord’). Most Chiari malformations are congenital and related to structural development of the foetus, however in some patients they can be acquired such as with an intracranial mass lesion or after a traumatic brain injury. Most patients develop symptoms in youth or young adulthood, but in some instances patients may not notice symptoms related to their Chiari malformation until a much older age, even though they most likely have had this condition their whole life.
The condition was first described by the 19th Century Austrian pathologist Hans Chiari and can be graded by the degree of cerebellar tonsil descent below the foramen magnum (measured in millimetres) as well as the presence or absence of other associated pathologies, such as a syrinx, hydrocephalus, or a tethered spinal cord. The most common symptom associated with a Chiari malformation is exertional or strain related headaches, but many other symptoms can be associated with a Chiari, especially in the presence of a cervical syrinx. The diagnosis is easily made with an MRI brain scan; imaging should also include the whole spine to exclude syringomyelia and/or a tethered cord. Cerebrospinal fluid flow studies can also be performed, which may demonstrate disturbance of fluid flow at the craniocervical junction.
Common symptoms of a Chiari malformation:
· Headaches, particularly aggravated by coughing or sneezing;
· Neck pain;
· Numbness in the hands, and sometimes feet;
· Difficulty swallowing;
· Difficulty breathing
Treatment generally depends on the degree of disability that the symptoms are producing. Headaches should initially be managed with simple oral analgesia. When headaches are severe and interfering with the patient’s quality of life and are not responding to conventional treatment it may be reasonable to consider surgical intervention. Surgical correction of a Chiari malformation is a major procedure performed under a general anaesthetic. The operation requires making an incision at the back of the head, removing part of the occipital skull bone above the foramen magnum as well as the posterior arch of the first cervical vertebra, opening the dura mater (the lining, or ‘skin’ of the brain), resecting any adhesions, performing an expansile duraplasty with the patient’s own harvested tissue, and then finally closing the wound watertight. Most people will need several days in hospital recovering from surgery, and then a few more weeks of rest before resuming work or study. There are known risks associated with this operation, however when performed successfully it can greatly improve or completely resolve the patient’s pre-operative symptoms. For patients with a cervical syrinx secondary to a Chiari malformation surgery is almost always recommended to limit injury to the spinal cord; fortunately however following correction of a Chiari malformation the syrinx frequently resolves as well, as can be seen in the figure above (right). Once treated Chiari malformations rarely recur therefore successful surgery can often cure this disease process, however in patients with syringomyelia that does not correct with Chiari decompression surgery a shunt procedure is sometimes required.
Where can you find out more about Chiari malformations? For more information, please visit these excellent patient resources: