Looking Back: When Is A Syrinx Not A Syrinx?

When is a syrinx not a syrinx? Although it sounds like the set-up line to a bad joke, for some people it is a question of critical importance. While the increased use of MRI's has certainly revolutionized the diagnosis of Chiari, for a number of people, it has also led to a finding which can be difficult to interpret. The reality is that if you put enough people in an MRI machine, you will find that some of them have syrinxes - or something like a syrinx - even though they don't necessarily have any related symptoms.

In September, 2002, Dr. Ulrich Batzdorf - a somewhat legendary neurosurgeon in the Chiari world - along with his colleague Dr. Langston Holly, examined this phenomenon in a paper published in the Journal of Neurosurgery. In the paper, they proposed that there are a set of people which have what they call slitlike syrinx cavities. They define the slitlike syrinx cavity as being narrow in width, not accompanied by factors that disrupt CSF flow, like Chiari, and generally asymptomatic in nature.

To examine this phenomenon, the team retrospectively looked at the medical and imaging records of 32 patients, with slitlike syrinxes, who they had seen between 1992 - 2000. The group was comprised of 18 men and 14 women with an average age of 40. Thirteen of the group underwent an MRI because of spinal pain (see Table 1), while others had an MRI because of abnormal sensations, numbness, and radicular pain.

Table 1
Presenting Symptoms Which Prompted MRI

Symptom Number of Patients
Spinal pain 13
Radicular pain 7
Paresthesia 6
Numbness 5
Muscle spasm 1

Obviously, the MRI's revealed a syrinx like cavity in each person. On average, the syrinxes were less than 2mm wide, and in no case was the spinal cord enlarged due to the syrinx. Sixteen of the patients had a cavity in the cervical region, 12 in the thoracic, and 4 in both. Nine of the group actually had multiple cavities.

Neurological exams were completely normal for 12 patients, while 20 had minor sensation or motor related findings. There were no indications of many of the signs that are normally present in syringomyelia.

The patients were tracked for an average of 38 months and were evaluated with follow-up MRI's and neurological exams. During that time, 31 of the 32 were treated non-surgically, primarily with medicine and physical therapy. One person underwent surgery for a herniated disc. Overall, 6 people improved, 19 remained unchanged, and 7 got worse. A different underlying problem - such as a peripheral nerve problem - was found to the be the cause of symptoms in 16 people. The authors point out that nerve conduction studies were very useful in identifying the true underlying problem in these cases.

Follow-up MRI's showed that not a single cavity changed in size during the 3 years. Similarly, follow-up neurological exams were uneventful. (see Table 2).

Table 2
Condition At Long-Term Follow-Up

Status Number of Patients
Improved 6
Deteriorated 7
No Change 19

Batzdorf and Holly believe that the slitlike syrinx cavity is not actually a syrinx, but is a remnant of the central canal which is visible on MRI in some people. The central canal is the very center of the spinal cord. When we are children, it is like an open tube, but as we age, it collapses and becomes closed off. Early theories on syrinx formation held that CSF flow was blocked by a Chiari and flowed back into the central canal from the brain. However, this has since been shown not to be true since the central canal is closed in most adults.

The researchers believe that in some people, the canal doesn't collapse completely, and thus can look like a thin syrinx on an MRI. In fact, a study by Petit-Lacour of 794 MRI's, found that 1.5% of the images showed a visible central canal, with cavities ranging in diameter from 2mm - 4mm.

So when is a syrinx not a syrinx? For some, when it is found incidental to another problem and really just represents the natural structure of their spinal cord.

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