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Abstract
Background and purpose We describe the development of a novel endovascular cerebrospinal fluid (CSF) shunt device, intended for transdural deployment through a transvenous transfemoral approach into the cerebellopontine angle cistern, for the treatment of communicating hydrocephalus. The implant mimics the function of the arachnoid granulations by diverting excess cerebrospinal fluid from the subarachnoid space into a dural venous sinuses.
Materials and methods Review of published literature points to an intracranial to dural venous sinus estimated time-averaged pressure gradient of 3–5 mmHg, with transient venous pressure increases of 40 mmHg occurring during coughing, sneezing, or straining events. The design must include a valve capable of resisting venous blood reflux into the subarachnoid space during these spikes, while permitting a target antegrade CSF flow rate of 10 mL/hr at the normal physiologic pressure gradient. An in vitro intracranial and venous pressure circuit, capable of acquiring instantaneous pressure and flow data at the location of the valve, was developed to evaluate valve dynamic characteristics. Implant size was selected based on anatomical boundaries for transdural deployment at the inferior petrosal sinus, hemodynamic resistance of CSF flow, and the associated postural hydrostatic pressure column effect.
Results The resulting endovascular shunt prototype is comprised of a polyurethane shunt body that resides within venous blood flow and possesses a full-length 0.016’ diameter inner lumen to enable CSF flow. The shunt length of 35 mm creates a hydrostatic pressure gradient of <3.5 mmHg, 10 times lower than the postural 35 mmHg gradient seen in conventional ventriculo-peritoneal shunts, thereby mitigating the siphon effect. A self-expanding low-profile nitinol malecot that expands to a 3.0 mm height and 3.6 mm width at the cisternal end provides effective transdural implant stability to inhibit device migration, while enabling endovascular retrieval using conventional snare or stent-retriever tools. Performance evaluation of differential pressure slit valve prototypes (n=230) allowed convergence to an optimal configuration comprising two 3 mm length slits, 180° opposed, positioned at the venous-end of the shunt body that repeatedly satisfies the required hydrodynamic parameters in a fatigue-resistant manner.
Conclusion A novel tubular low-profile endovascular valved CSF shunt that mimics the function of the arachnoid granulations has been successfully developed and built for transdural deployment via the transvenous route. CSF Outflow into the venous sinuses may simplify valve requirements by re-establishing the physiologic venous pressure regulation in patients with communicating hydrocephalus and avoiding the postural siphon effect via a low-profile implant.
Disclosures A. Malek: 2; C; CereVasc LLC. 3; C; Stryker Neurovascular, Microvention-Terumo. 4; C; CereVasc LLC. C. Heilman: 2; C; CereVasc LLC. 4; C; CereVasc LLC.