A Novel Classification And Its Clinical Significance In Spinal Schwannoma Based On The Membranous Hierarchy

Background and purpose:Schwannoma is the most common spinal benign tumor.1,2 Unlike neurofibroma,they are often solitary and lack an obvious genetic predisposition.Surgery is the preferred treatment method,and patients should undergo 1-stage surgical gross total resection(GTR)as far as possible without causing injury to important structures,such as the spinal cord and nerve roots.3 However,these tumors can grow in a variety of ways and lie adjacent to or even adhere to important structures,such as the spinal cord and the vertebral artery etc.Additionally,the way to deal with the tumor capsule and the nerve root of the tumor origin is still controversial:this often leads to difficultly achieving total resection and makes it easy for paravertebral structures to be damaged during surgery.The classification of spinal schwannoma is of great significance for its surgical treatment.Previous classification schemes are mainly according to size,volume and number of vertebral segments,which have solved two important issues in the management of schwannomas:(1)which approach to use;(2)how much bone to resect—supplement with spinal fixation or not.However,one issue that has been neglected in these existing classification systems is the hierarchical relationship between schwannomas and surrounding membranous structures.However,the tumor-membrane relationship is very important for intraoperative safety and significantly improve the GTR rate.The shortcomings of previous classifications prompted us to devise a novel classification for spinal schwannomas and to put forward a new concept for the surgical treatment of spinal schwannoma.Contents and methods:Data from 101 patients who presented with spinal schwannoma from Jan 2016-June 2019 and underwent standard microsurgery were collected for clinical analysis.Based on intraoperative findings and tumor-membrane relationships,a novel classification of spinal schwannoma is proposed.Clinical manifestations,functional scores and follow-up data were analyzed to evaluate the utility of this classification.ResultsThe spinal nerve root was artificially divided into three segments according to folds in the arachnoid:subarachnoid,intra-arachnoid,and extra-arachnoid.Spinal schwannomas were divided into four types based on membranous structure:intrapial(type Ⅰ),subarachnoidal(type Ⅱ),intra-and extradural(type Ⅲ),and extradural growth(type Ⅳ).Type Ⅱ and Ⅲ was further subdivided into two subtypes.Type Ⅱa was completely subarachnoidal;Type Ⅱb,subarachnoidal and intra-arachnoidal.Type Ⅲa were localized both inside and outside the arachnoid,while type Ⅲb tumors were localized outside the arachnoid.100 patients were treated using only a posterior approach,while 1 patient with type Ⅳ tumor underwent surgery via a combined anterior and posterior approach.GTR was achieved in all patients,and postoperative pathology confirmed schwannoma.The mean postoperative follow-up time was 20.2 months(range,2-44 months).Postoperatively,a total of 89(88%)patients had better follow-up McCormick grades,while 12(12%)were unchanged,and the postoperative grade of none was increased..The McCormick scale significantly improved(P<0.001).The VAS score decreased from 5.16±0.366 before surgery to 0.27±0.081 after surgery(P=0.000).The JOA-Cervix score improved from 11.15 ± 0.619 before surgery to 16.15 ± 0.175 after surgery(P=0.000);The JOA-Thorax score improved from 5.94±0.84 before surgery to 9.63±0.694 after surgery(P=0.001);The JOA-Lumbar score improved from 17.72±0.991 before surgery to 26.92±0.584 after surgery(P=0.000).The overall improvement rate was 92%,and there was no significant difference in surgical outcomes according to tumor classification(P=0.618).Although five patients(5%)developed intracranial infection and two patient(2%)developed postoperative impaired wound healing after surgery,no intraoperative vertebral artery injuries or postoperative cerebrospinal fluid fistula occurred.No tumor recurrence and spinal instability were observed during follow-up.ConclusionSpinal schwannoma classification based on a membranous hierarchy facilitated the selection of optimal surgical methods for tumor resection,thereby significantly improving the GTR rate and reducing the incidence of surgical complications.