Response to the Letter to the Editor by Haneline

In Response:

We understand the concerns of the responders; however, because limited literature is available concerning the connection between manipulation and cerebellar perfusion, we can only rely on hypotheses. Until now, predominantly case reports and small case series have linked vertebrobasilar insufficiency to therapeutic neck manipulations. To the best of our knowledge, this is the first study that investigates directly the local perfusion rather than the blood flow of the supplying arteries using Doppler sonography. In previous studies examining the effect of cervical spine manipulation on blood flow, blood flow was measured in the vertebral artery at a point midway between its origin and its disappearance into the foramen of the sixth transverse cervical process (V1 segment).1, 2, 3 Measurements of extracranial vertebral artery blood flow proximal to the point of restriction may have limited clinical value as some part of the blood flow may escape via the many collaterals of the vertebral artery (ie, the spinal and muscular branches). Therefore, the assessment of the effect of cervical spine manipulation on blood flow to the hindbrain may be more clinically valid if measurements are made distal to the believed point of restriction, as is the case in transcranial Doppler sonography or single photon emission computed tomography.

The relation between upper cervical spine manipulation and hypoperfusion in the anterior lobe of the cerebellum remains hypothetical. We expected to find a hypoperfusion in the posterior inferior cerebellar artery (PICA) region but found a decreased perfusion in the superior cerebellar artery (SCA) region. One of the hypotheses may be that end-to-end anastomoses may compensate hypoperfusion in other regions of the cerebellum. End-to-end anastomoses exist between the SCA, PICA, and anterior inferior cerebellar artery (AICA). The most important and constant anastomosis is that between the SCA and the PICA, for which the name of Lazorthes has been proposed.4 The communicating arteries are normally small and cannot immediately deliver the required amounts of blood if one of the major arteries is suddenly occluded. They can, however, provide alternative sources of blood in the event of a progressively occluded artery. Therefore, we can assume that manipulation induces occlusion of one vertebral artery (left in this case), which results in hypoperfusion in the PICA region and will be compensated, through anastomoses, mainly by the SCA but also by the AICA, which will become hypoperfused. To investigate this hypothesis, injection with 99mTc ECD should be given earlier (1-2 minutes before the manipulation) so that what happens with the blood flow can be explored. It should also be interesting to know how the cerebral blood flow is influenced the next 24 hours. This requires the same protocol but with a longer time frame between manipulation and injection. However, because this investigation is quite costly and rather invasive, it is not that easy to do this study over and over again.

According to the responders, cerebellar hypoperfusion may have occurred following several other aspects of the procedure that was used, such as head positioning or movements. The mechanism on how manipulation can influence the cerebellar blood flow is still not known. Manipulation is composed of a head position and a thrust. We think that the hypoperfusion exists as a consequence of neck movements in combination with rapid stretching of the vessel. For certainty, the same study should be redone without the thrust component.

We are convinced that this study contributes to the knowledge of the effect of cervical spine manipulation on cerebellar perfusion. There is a need for further investigations regarding the relationship between both because, until now, minimal fundamental research has been done to prove this link.