SCI and VP Shunt: Do These Letters Work Together?

In their case report, Dr. Colle and colleagues describe the occurrence of post-operative spinal cord ischaemia (SCI) after fenestrated endovascular aneurysm repair (FEVAR) for a pararenal aortic aneurysm in the presence of a pre-existing ventriculoperitoneal (VP) shunt.¹ The decision was made to proceed with FEVAR in the setting of a previous open repair of an infrarenal abdominal aortic aneurysm with aortobifemoral grafting. Neurosurgery who had been consulted pre-operatively, recommended against placement of a spinal drain, assuming the VP shunt would maintain low cerebrospinal pressures. The procedure went well, with a proximal landing zone at the 8th thoracic vertebra, and distal landing zone extending into the aortobifemoral graft, and no neurological defects were detected intra-operatively. However, one hour post-operatively the patient was noted to have bilateral lower extremity paralysis. This improved somewhat with blood pressure control and placement of a spinal catheter. The drain was kept in place for 72 hours, with pressure maintained at 8–10 cmH₂0. The patient experienced partial recovery, and was discharged at 22 days, able to ambulate independently.

This patient continued to experience elevated cerebrospinal pressures despite cerebrospinal fluid (CSF) drain placement post-operatively. The report concluded that a VP shunt is unlikely to provide sufficient drainage in this patient population, probably secondary to intra-operative positioning with head elevation. This patient's shunt had been placed two months prior to the scheduled FEVAR for symptoms of normal pressure hydrocephalus and involved an adjustable differential pressure component and gravitational component to compensate for pressure changes caused by positioning shifts from supine to upright. The goal of gravitational valves in these shunts is to prevent over drainage of CSF, which can lead to severe headaches, nausea, and subdural bleeds.² However, in this patient who was lying flat with his head propped up on a pillow, the gravitational component of the shunt was partially obstructed, leading to incomplete CSF drainage instead.

SCI is a well documented and feared complication after complex endovascular aneurysm repair. There is abundant literature describing the placement of CSF drains pre-operatively, especially in those who require long segment aortic coverage. These serve to prevent SCI by decreasing cerebrospinal pressure placed on the cord, with up to a 50% risk reduction.³ However, as Dr. Colle and colleagues point out, there are no guidelines on peri-operative CSF drainage in patients with VP shunts. Although it would seem having a pre-existing VP shunt would be protective against increased cerebrospinal pressure, their case demonstrates the opposite. Recommendations for pre-operative care in this patient population include ensuring VP shunt patency, as well as spinal drain placement; intra-operative positioning is also key, to maintain the patient in a horizontal position keeping the shunt valve open for adequate drainage. Pre-operative collaboration with neurosurgical colleagues who understand the mechanics of these shunts may be key to preventing this complication. Although the cohort of patients with VP shunts undergoing endovascular aneurysm repair may be small, understanding the intricacies of CSF drainage pathways is crucial to ensuring good outcomes and preventing the development of SCI.