The impact of intraoperative neurophysiological monitoring in spinal cord astrocytoma-surgery

Objective:

Surgery for intramedullary spinal cord tumors, especially intramedullary spinal cord astrocytomas, is associated with a high risk of new postoperative neurologic deficit. While the literature supports the role of intraoperative neurophysiological monitoring (INM) in intramedullary spinal cord tumor (ISCT) surgery, it remains unclear whether different histotypes of ISCT benefit of INM to a different extend. We therefore retrospectively analyzed the functional and neurooncological outcome in a series of spinal cord astrocytomas operated on under INM assistance.

Methods:

Between 2001 and 2008 32 patients underwent 34 surgeries for SCA. The extend of surgical resection was judged by the surgeon's intraoperative impression and by postoperative magnetic resonance imaging (MRI). Multimodal INM included Somatosensory Evoked Potentials (SEPs) and transcranially elicited spinal (D-wave) and muscle (mMEPs) motor evoked potentials. Functional status was assessed preoperatively, postoperatively and at follow-up using the McCormick scale.

Results:

Six patients are lost to follow up. At a mean follow-up of 61 months (9–109 months) 14 patients are alive and all but one are progression free after groß total (n=3), subtotal (n=6) and partial (n=4) tumor removal. One patient was operated twice for symptomatic tumor recurrence.

Twelve patients that harboured high grade astrocytomas (WHO grade III and IV) deceased during the follow-up period with a mean postoperative survival of 13.3 months (7–25 months).

Monitorability in 34 surgeries was 94% for mMEPs, 91% for SEPs and 59% for D-wave.

In 6 patients neurophysiological data (MEP deterioration) either alone or in combination with intraoperative findings (hard tumor texture, neurovegetative disorders, absence of a clear cleavage plane) prompted to stop surgery. At the follow-up 79% of the patients showed either unchanged or improved McCormick grade compared to preoperatively.

Conclusions:

In SCA, the neurooncological outcome mainly depends on tumor grade. Long term progression free survival can be obtained in the vast majority of patients with low-grade astrocytomas even after subtotal tumor removal. Long term functional outcome depends mainly on the preoperative neurological status, emphasizing the need of an early diagnosis and therapy. When surgery is tailored according to INM data preoperative neurological functions can be preserved in most patients. INM for SCA surgery appeared to be especially useful for this histologic entity.