Experimental syringomyelia: the relationship between intraventricular and intrasyrinx pressures.

The influence of ventricular pressure changes on syrinx pressure was investigated in this study of experimental canine kaolin-induced syringomyelia. The pressures of the ventricles, syrinx, and cervical subarachnoid space were measured. A complete ventriculosubarachnoid block occurred in the animals with syringomyelia. The baseline syringeal pressures exceeded those of both the ventricles and the subarachnoid space. Raising ventricular pressure elevated the syringeal pressure, but aspiration of ventricular fluid did not acutely lower the pressure. These findings suggest a ventriculosyrinx valve effect that may inflate the syrinx during transient rises of intracranial pressure. A respiratory pressure pattern was found in the syrinx similar to that of the ventricles and subarachnoid space. This wave was reduced but not abolished by ligating the subarachnoid space distal to the syrinx. The arterial pulse was much diminished within the syrinx at rest. These findings indirectly support the possibility that transmission of thoracic pressures to the spinal subarachnoid space with compression of the syrinx is a principal force that enlarges the syrinx.