Seiff S R, Shah L
Department of Ophthalmology, University of California, San Francisco 94143.
Arch Ophthalmol. 1990 Sep;108(9):1326-9. doi: 10.1001/archopht.1990.01070110142039.
The mechanism by which optic nerve sheath fenestration relieves papilledema associated with increased intracranial pressure has not been clearly defined. A model was constructed to determine if the induction of fluid flow along the nerve sheath and through the fenestration could account for a reduction in pressure around the optic nerve, as might be expected according to Bernoulli's equation of fluid dynamics. The model states that as the velocity of a fluid increases, the pressure it exerts decreases. The model simulated fluid spaces corresponding to the intracranial vault, chiasm, and optic nerves. The unfenestrated model showed direct transmission of elevated intracranial pressure to the nerves, consistent with the production of papilledema. When one nerve was fenestrated, fluid flow along the nerve was initiated and pressure in that nerve sheath dropped substantially. In addition, pressure in the unfenestrated sheath dropped due to fluid communication across the chiasm. These lower intrasheath pressures were consistent with the bilateral resolution of papilledema after unilateral fenestration. The reduced intrasheath pressures persisted even when the intracranial pressure was again elevated to pathologic levels as long as active fluid flow continued along the nerve sheaths. Thus, induction of cerebrospinal fluid flow along the optic nerve sheath by fenestration appears to locally reduce the pressure around the optic nerve, in spite of persistently elevated intracranial pressure. This is in accordance with what would be predicted by Bernoulli's equation.
视神经鞘开窗术缓解与颅内压升高相关的视乳头水肿的机制尚未明确界定。构建了一个模型，以确定沿神经鞘并通过开窗诱导的液流是否可以解释视神经周围压力的降低，正如根据流体动力学的伯努利方程所预期的那样。该模型表明，随着流体速度增加，其施加的压力降低。该模型模拟了与颅内腔、视交叉和视神经相对应的流体空间。未开窗的模型显示颅内压升高直接传递至神经，这与视乳头水肿的产生一致。当一条神经开窗时，沿该神经开始出现液流，该神经鞘内的压力大幅下降。此外，由于通过视交叉的液体连通，未开窗鞘内的压力也下降。这些鞘内较低压力与单侧开窗后视乳头水肿的双侧消退一致。只要沿神经鞘持续存在活跃的液流，即使颅内压再次升高至病理水平，鞘内压力降低仍会持续。因此，尽管颅内压持续升高，但通过开窗诱导脑脊液沿视神经鞘流动似乎可局部降低视神经周围的压力。这与伯努利方程的预测相符。
