Can A Child Grow Out Of Chiari?

March 31st, 2009 -- Spontaneous resolution - meaning Chiari that goes away on its own - has been documented in the medical literature, but is poorly understood. Though it is certainly every patient's (and parent's) highest hope, how often it occurs, why it occurs, and who it occurs to is largely unknown. Now, a report in the Journal of Neurosurgery: Pediatrics from a group of doctors at Duke University (Waldau et al.) offers some clues as to one possible mechanism underlying the near miracle of spontaneous resolution.

Chiari & Syringomyelia News has reported on cases of spontaneous resolution, primarily among children, and this journal article cites several such examples (Figure 1). Despite these reports it is very difficult to estimate how often this might occur. Certainly, a handful of case reports compared to hundreds of thousands of confirmed cases implies that it is a very rare event; however, it is impossible to know how many cases might have resolved on their own without anyone knowing about it.

Further, it is not known how or why Chiari can resolve on its own, although there are several logical possibilities. First is if the underlying cause of the herniation resolves or heals by itself. For example, Chiari can be caused by a spinal fluid leak which lowers the pressure in the spine compared to the brain and essentially pulls the cerebellum down. Some such CSF leaks are known to heal by themselves over time, so some cases could be due to an initial CSF leak which heals.

A different possibility involves the relative growth of the skull and the brain. A leading theory for a major cause of Chiari is a small posterior fossa (the part of the skull where the cerebellum is situated) which forces a normal sized brain out of the skull. There is a significant body of research which supports this theory in part and researchers have begun to focus on the potential dynamic nature of Chiari in children by looking at the relative growth rates of the skull versus the brain. In other words, if for a period of time the brain grows faster than the skull, then a problem can develop. However, if at a later time the skull catches up with its growth, then perhaps the problem, or the herniation, could resolve itself. Given the tremendous growth which children go through, this is certainly a reasonable theory.

It was this theory that the Duke researchers decided to explore when they encountered a case of spontaneous resolution in a young boy. The child was first seen at the age of 3 for seizures. The doctors determined that he had a genetic disease known as tuberous sclerosis which was causing the seizures. However, during their testing, they also found that he had a 13mm Chiari malformation (Figure 2).

Figure 2: MRIs Showing 13mm Chiari at Age 3 (A) and Complete Resolution at Age 7 (B)

Morpho1.gif

Despite its size and shape, the doctors could find no symptoms or problems directly attributable to the Chiari and there was no syrinx. When the boy was seen again at age 5, it was noted that the tonsils had ascended partially, and by the time he was 7, they had risen back into the skull (Figure 2 B).

In order to understand how this may have occurred, the Duke team used morphometric analysis to measure the volume of both the posterior fossa and the cerebellum from the MRIs at 3 years of age and 7 years of age. Techniques to calculate these values have been published previously. To minimize error, the researchers took the average of the results from five different experts who performed the measurements.

Interestingly, they found that all four volume measurements - posterior fossa and cerebellum at age 3 and 7 - were within published normal ranges for children that age (Figure 3); however over that period of time the posterior fossa grew 11.5% compared to only 4% for the cerebellum (Figure 4). In other words, at age 3 the cerebellum was much larger relative to the space available than at age 7. The authors of this study did not do so, but other publications have focused on looking at just such a ratio. Regardless, the data is suggestive that the relative growth rates of the posterior fossa skull and cerebellum may have played a role in the Chiari resolving naturally.

Due to his genetic condition, which involves masses in the brain, this patient is not a good one to generalize from; however, the approach the researchers took in tracking morphometric changes over time is interesting and applying it to more and different Chiari patients may provide some valuable insights.

It is also worth noting that cases such as this paint a picture of Chiari as a dynamic condition, in which not only symptoms can change, but the underlying structure can change as well. This is contrast to the traditional view that a person is born with Chiari and remains that way.


Figure 1: Published Cases of Spontaneous Resolution Cited In This Study

Author Age at Diagnosis Age at Resolution or Improvement
Avellino 5 10.5
Avellino 5 16
Castillo 9 13
Guillen 6 12
Sun 11 13
Jatavallabhula 1.5 6
Sudo 13 16
Sun 7 13

Figure 3: Posterior Fossa and Cerebellum Volumes at Age 3 and 7

Age 3 Age 7 Growth
PFV (cm3) 180 201 11.5%
CV (cm3) 143 149 4.08%

Figure 4: Chart of PFV and CV Growth From Age 3 To 7

Morpho2.gif

Note: The difference in growth between the posterior fossa and cerebellum was statistically significant


Related C&S News Articles:

Spontaneous Resolution Of Chiari

Spontaneous Resolution

Is Surgery Necessary If There Are No Symptoms?

Study Explores The Natural History Of Chiari