The majority of patients who are diagnosed with Chiari malformation have what is called Arnold Chiari Malformation Type 1, as opposed to Type 2, which is a much rarer condition. The information below will help you better understand the differences between Arnold Chiari Malformation Type 1 and Type 2, as well as how each differ in diagnosis, treatment and recovery.

Differences Between Arnold Chiari Malformation Type 1 and Type 2

Both Type 1 and Type 2 Arnold Chiari malformations are developmental in nature. This means they have been present since birth as a result of how your body formed.

In Arnold Chiari malformation Type 1, an area at the back of the skull, the posterior fossa, does not grow large enough to accommodate an area at the back of the brain, the cerebellum. This forces the cerebellum through a hole at the base of the skull, the foramen magnum, through which the spinal cord exits. The portion extending outside the skull is called the cerebellar tonsils.

In Type 2 Chiari malformation, there are several skull base and intracranial abnormalities that occur in addition to displacement of the cerebellum is displaced through the foramen magnum.  It typically occurs along with a special form of spina bifida called myelomeningocele, in which the spinal canal and spine do not close completely as they should. This can lead to many complications.

Differences Between Diagnosis

Diagnosis of Arnold Chiari malformation Type 1 and Type 2 tends to happen very differently. Most people born with a Type 2 have other congenital defects that are noticeable at birth, such as spina bifida. Type 2 malformations are always accompanied by symptoms, which can be severe.

In contrast, Type 1 malformations may be asymptomatic and undetected well into adulthood. In fact, they are often discovered incidentally during diagnostic imaging for an entirely different condition. Some people with asymptomatic Arnold Chiari malformation Type 1 may go their whole lives without knowing it is there or experiencing problems as a result. If your doctor suspects you may have an Arnold Chiari malformation Type 1, he or she will typically confirm the diagnosis using MRI imaging.

Differences Between Treatment

Arnold Chiari malformation Type 1 may not require any treatment.   Type 2 almost always requires surgery soon after birth to correct other accompanying issues, such as closing the myelomeningocele and/or draining extra cerebrospinal fluid within the skull using a shunt.  It is relatively uncommon that Type 2 Chiari malformation patients require direct decompression of the malformation itself.

Because Arnold Chiari malformation Type 2 patients often have coexisting additional conditions, there may be other surgeries involved that can impact recovery time. These additional surgeries are often required shortly following birth and can vary, depending upon the severity of the malformation and which, if any, other conditions are present.

Two Very Different Conditions

Now that you have a better understanding of Arnold Chiari malformation Type 1 and Type 2, you can see how they differ in severity, the frequency with which they occur and how they are diagnosed. Patients with Type 1 malformations often go their entire life with minimal to no symptoms and never require any surgical intervention.  Patients with Type 2 malformations generally require early surgical intervention shortly after birth and may have lifelong symptoms that require other treatments. If you find you still have questions about the two different forms, be sure to bring them up with your doctor, who can provide further clarification.

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