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Letter regarding the endovascular transdural cerebrospinal fluid shunt device

We read the article by Heilman et al with great interest. Their idea is very clever and has the potential to solve the problems inherent in ventriculoperitoneal shunt device application. However, we would like to highlight some issues with their study from the viewpoint of the anatomy of the petroclival region. The aim of the device was described as “diverting excess CSF from the intracranial subarachnoid space to the adjacent cerebral venous system through an endovascular transdural shunt device”. The anatomical architecture of the subarachnoid and subdural spaces in the retroclival area differs from the calvarial region. 3 The arachnoid membrane lying over the clivus was reported as being the “anterior pontine membrane”, which was clearly documented in the literature. Consequently, it is not easy to determine whether the tip of the shunt catheter is anchored in the subdural or subarachnoid space, since it will first enter the subdural space (figure 1). Difficulties may be encountered in passing the tip of the device through the arachnoid membrane, which may be thin or thick. The inferior petrosal sinus (IPS) may not drain the cerebrospinal fluid sufficiently well through the subdural space, if the tip of the device is not located in the subarachnoid compartment. Antiplatelet drugs are required prior to deployment of the device in the IPS to prevent thrombosis. The dura mater in the petroclival region has a rich blood supply. Piercing the posterior wall of the IPS will cause bleeding at the puncture point, and therefore venous bleeding disseminating to the subdural or subarachnoid spaces may result in dramatic complications facilitated by antithrombotic drugs. The thickness of the dura mater in this region presents another potential problem. Rupture of the wall of the intracranial aneurysm during endovascular coiling is an endovascular surgeon’s nightmare. However, a large mass of coils could be embedded inside the IPS and yet not cause rupture complications, which demonstrates the thickness of the dura mater. Consequently, piercing the petroclival dura mater is not an easy procedure in practice. Duvernoy has described the inferior petrosal vein draining to the IPS around the junction of the IPS and jugular foramen. Although Duvernoy found this vein in 30% of his dissections of 50 cadaveric heads, it is rarely noted in the literature. Doppman has also commented on the existence of a connection between the IPS and the bridging brainstem veins as being the explanation for brainstem injury complications during IPS sampling procedures; therefore, the presence of this venous variation may cause fatal venous bleeding during device deployment. Tubbs et al has reported the inferior petroocciptal vein in the neighborhood of the IPS. This vessel was found to have an close relationship with the overlying IPS and was separated only by a thin layer of bone. This may be another variation within the IPS region that needs to be considered during device deployment.