Anyone who has been to a tailor knows it’s important to get the measurements right when buying clothing. And we’ve all seen the amusement park sign “Children must be this tall to ride,” giving some indication of a safe age to experience certain attractions at the park.
As important as it is to have accurate measurements in these situations, in medicine it is even more critical. Neurosurgeons, for example, use increasingly sophisticated technology to measure structures and spaces in the brain and spinal areas. Armed with this information, they can make their best decisions about when and how to perform a procedure.
One such measurement was the subject of a recent paper by Dr. Richard C.E. Anderson of the Pediatric Neurosurgery Center at Columbia University Medical Center/NewYork-Presbyterian Hospital. He and his colleagues* published their findings in the Journal of Neurosurgery: Pediatrics.
To understand these findings, you first need to learn a bit about the condition and treatments studied:
The authors studied patients with a condition called Chiari Type 1 malformation. This condition may occur when the bones at the base of the skull and upper spine are not formed properly. When this occurs, the lower part of the brain, known as the cerebellum, may move downward through the bottom opening of the skull into the spinal area.
A Chiari Type 1 malformation may cause no symptoms, especially early in life. However, it may eventually cause any of a number of symptoms. These include headaches, neck pain, clumsiness and difficulty walking steadily. In addition, nerves coming from the brain and the spinal cord may be affected, leading to problems such as hoarse voice, difficulty swallowing and muscle weakness.
Fortunately, when symptoms do occur, there is surgical treatment. Commonly the neurosurgeon will enter the lower brain and upper spinal cord areas through the back of the head and neck. He will then remove a small amount of bone from the lower skull and upper spine. This relieves the pressure around the brain and nerves, alleviating the patient’s symptoms.
Usually, this procedure, which is known as posterior fossa decompression, is all that’s needed. But in more severe cases, the surgeon may need to perform additional procedures.
One procedure, known as anterior decompression, involves reaching the area from the front. In this case, the neurosurgeon will either make an incision through the mouth and throat area or, in a procedure known as endoscopic surgery, pass a small tube through the nose.
Other patients may require a procedure known as occipitocervical fusion. In this procedure, the upper spine is made more stable by fixing it to the skull with screws.
How to tell which patients need additional procedures? One clue is to measure one aspect of the craniovertebral junction, called the pBC2 line (stands for the line perpendicular to a line drawn between bony structures of the skull called the basion and the clivus). Some studies have shown when the pBC2 line is greater than 9 millimeters, patients are more likely to need procedures above and beyond the more standard posterior fossa decompression.
The importance of how we get to this measurement was the subject of the recent article by Dr. Anderson and his colleagues. They studied 31 patients who underwent two common tests used to diagnose Chiari Type 1 malformation: CT and MRI. These tests commonly give enough information for surgeons to estimate the size of structures and spaces.
Three neurosurgeons, one of whom was Dr. Anderson, reviewed the films independently. In doing so they were trying to answer two questions: Does the measurement vary depending on who’s measuring, or is it consistent? And do the CT and MRI produce the same measurement?
The researchers found that the values obtained for the pBC2 line were consistent between observers. Furthermore, the CT and MRI produced similar values.
Why might this be important? First of all, since the patients, as well as the neurosurgeons doing the measuring, came from three different institutions, it appears more likely that physicians from multiple facilities could use this information as a standard that helps them tailor treatment.
Second, since a CT scan involves radiation and an MRI does not, and since the results appear to be similar regardless of the test used, physicians may be able to get all the information they need to plan treatment by performing an MRI only. This is particularly important because many Chiari Type 1 malformations are diagnosed in children, a population particularly vulnerable to radiation.
The day we can be assured of a perfect fit by just ordering clothing in our size may be a ways off. But when it comes to surgical treatment, studies like the one performed by Dr. Anderson and his colleagues show promise in helping neurosurgeons plan the best procedures for their patients.
*Full list of authors: Todd C. Hankinson, M.D., M.B.A., Gerald F. Tuite, M.D., Dagmara I. Moscoso, M.S., Leslie C. Robinson, M.D., Pharm.D., M.B.A., James C. Torner, Ph.D., M.S., David D. Limbrick, Jr., M.D., Ph.D., Tae Sung Park, M.D., and Richard C.E. Anderson, M.D., for the Park-Reeves Syringomyelia Research Consortium Investigators