Brain tissue pressure gradients are dependent upon a normal spinal subarachnoid space.

Reports from our laboratory have shown that regional brain tissue pressure (RBTP) gradients develop in response to supratentorial but not posterior fossa extradural masses. We undertook this experiment to discover the mechanism of this differing response. RBTP was measured in the right and left frontal lobes (RF, LF), temporal lobes (RT, LT), midbrain (MB), and cerebellum (CB) of ten pigs. Balloons were expanded in the epidural space at C2 to occlude the subarachnoid space. A temporal extradural mass was expanded incrementally. The C2 balloon was deflated after temporal mass expansion. Expansion of the cervical balloon resulted in a homogeneous rise in RBTP. Expansion of the temporal mass resulted in the development of small RBTP gradients with the following relationship: RT > LT = LF > RF = CB > MB. In comparison with a previous series of animals without cervical balloons, animals in this series demonstrated higher global ICP in response to equal size masses and smaller RBTP gradients. Cervical balloon deflation resulted in decreased global ICP and increased RBTP gradients. The development of RBTP gradients in response to expanding supratentorial masses therefore appears to be at least partially dependent upon the presence of a normal communication between the supratentorial space and the spinal subarachnoid space.