More Findings On Chiari & Abnormal Skull Geometry

November 30, 2007 -- Over the past few years, several research studies have shown that people with Chiari tend to have small posterior fossas. The posterior fossa is the depression on the inside of the back of the skull and is where the cerebellum is situated. This finding has led many to refer to Chiari as a problem involving underdevelopment of the skull which in turn crowds a normal sized brain.

Now, a study from Birmingham Children's Hospital in England (Sgouros et al.), and published in the September 2007 issue of the Journal of Neurosurgery: Pediatrics, has found that the skull abnormalities associated with Chiari extend to the entire skull base, not just the posterior region.

In the study, Dr. Sgouros and his colleagues were looking to expand on their previous findings involving posterior fossa size and Chiari. In their earlier work, they had compared various measurements of the posterior fossa in children with Chiari, children with both Chiari and syringomyelia, and a control group of normal children. While they did find a small posterior fossa volume like other researchers, they only found this difference among the children with both Chiari and syringomyelia. In other words, the children with just Chiari tended to have normal sized posterior fossas, but the children with both Chiari and syringomyelia had small posterior fossas. In explaining this finding, the researchers pointed out that other research studies had failed to separate the two groups and that a group of subjects with a high percentage of syringomyelia patients would result in a significant difference for the entire group.

To investigate this finding further, and try to determine why there was a difference between the children with Chiari only and with both Chiari and syringomyelia, the researchers decided to look at the entire skull base, not just the posterior measurements. Specifically, they compared 4 distances and 3 angles (see Figure 1) of 14 children with Chiari only, 16 children with both Chiari and syringomyelia, and a control group of 42 children without Chiari or other skull type problems. The group used computer aided analysis of MRIs to acquire the data.

Figure 1: Skull Base Distances and Angles Measured


Interestingly, they found that in both the CM and CM/SM group, 3 of the four distances and 2 of the 3 angles were significantly different from the control group (see Table 1). The geometric differences mean that children with Chiari tend to not only have small posterior fossas, but the front of the skull base tends to be longer than normal. Since the growth of one portion of the skull can affect other portions of the skull, it is not clear if these findings are due to the small posterior fossa or a direct result of a developmental problem.

In comparing the children with Chiari only to those with both CM and SM, the scientists found two measurements which were significantly different between the groups. The authors admit it is difficult to interpret this finding and draw any conclusions from it, but they do raise an interesting question. Namely, is Chiari with syringomyelia simply a more severe form of Chiari, or does it represent something distinctly different.

It is natural to assume that syringomyelia comes with more severe cases, but if there is more than one underlying cause for Chiari, it could be the case that Chiari by itself is due to one thing, and Chiari with syringomyelia is due to something else entirely. Regardless, continued advances in quantifying the geometric characteristics of the Chiari skull could lead to significant advances in understanding the root cause(s), improving diagnoses, and refining surgical treatments.

Table 1
Skull Base Distances and Angles, CM, CM& SM, Control

Control CM CM/SM Sig
1 135 145 151 Y
2 110 122 123 Y
3 96 97 101 N
4 34 29 29 Y
1 58 75 63 Y
2 46 50 40 N
3 32 31 27 Y

Note: Sig refers to whether the difference between the CM groups and the control group is statistically significant and not likely due to chance.

Related C&S News Articles:

Small Posterior Fossa Linked To Chiari Related Syringomyelia

Children With Chiari Symptoms Due To Shunting Found To Have Small Posterior Fossa Volume

Is Chiari 0 For Real? Research Shows Small Posterior Fossa In Chiari 0 Patients

Chiari Link To Small Posterior Fossa Confirmed In Adults