A dynamic theory for hydrocephalus revealing benign intraspinal tumours: tumoural obstruction of the spinal subarachnoid space reduces total CSF compartment compliance.

Hydrocephalus may rarely be the revealing symptom of intraspinal tumours. This form of presentation is more common in malignant spinal cord tumours due to subarachnoid dissemination and meningeal tumoural infiltration up to the intracranial basal cisterns. In contrast, in benign intraspinal tumours the mechanism of hydrocephalus has been a subject of controversy and various explanations have been proposed. We discuss different pathophysiological hypotheses and propose a mechanical explanation based on current knowledge of cerebrospinal fluid (CSF) dynamics. We hypothesize that hydrocephalus in benign intraspinal tumours is the result of alteration of craniospinal compliance distribution. Intraspinal tumours may decrease the compliance of the caudal spinal portion, thereby reducing overall CSF space compliance. In this condition, minimal changes to other implicated factors such as CSF protein concentration, intracranial CSF flow resistance due to arachnoiditis or intracranial vascular compliance may have a greater effect on CSF dynamics. After tumour removal, hydrocephalus disappears rapidly due to spinal compliance recovery.