The pathogenesis of syringomyelia continues to be an enigma. The patency of the central canal and its role in the pathogenesis of communicating syringomyelia continues to elicit controversy. The case reported here provides an opportunity to retest some of the hypotheses of syringomyelia. A 33 year old female presented with sensory disturbances over the left upper extremity and trunk and was diagnosed to have panventriculomegaly with communicating syringomyelia. She was initially treated with ventriculoperitoneal shunting. As there was no change in her neurological status following shunt, this was followed by foramen magnum decompression with excision of an arachnoid veil covering the fourth ventricular outlet. She had clinical and radiological improvement after foramen magnum decompression. Five months later she had reappearance of the symptoms of syringomyelia and was found to have shunt dysfunction and holocord syrinx. She improved following shunt revision. This case is being reported to highlight the following points: 1. In patients with communicating syringomyelia and hydrocephalus, shunt dysfunction can present with symptoms of syringomyelia without the classical clinical features of shunt dysfunction, 2. In patients with communicating syringomyelia, the central canal of the spinal cord acts as an "exhaust valve" for the ventricular system, and, 3. studies about the patency of the central canal are reviewed in the context of this case and the role of the central canal in the pathogenesis of communicating syringomyelia is reviewed.