Preoperative Identification Of Cranial Nerves Near CPA Schwannomas Using Superselectivc Diffusion Tensor Tractography

Objective. The goals of surgical treatment of vestibular schwannomas (VSs) areto eliminate the tumor and preserve facial nerve (FN) and acoustic function. These arechallenging goals with large VSs due to uncertainties in the locations of cranial nervecourses and significant deviations in their morphology. Preoperative diffusion tensortractography (DTT) of the FN has been proposed to predict its location. This studywas conductedto evaluate the effectiveness of this technique for anatomical andfunctional preservation of the FN, cochlear nerve (CN) and trigeminal nerve (TN)during the surgical removal of large VSs.Methods. The study included23consecutive patients with VSs of Hannoverclassification T3b to T4b from November2013throughMay2014. Diffusion tensorimages and anatomical images (contrasted constructive interference in steady state)were generated, and the DTT was extracted using a Brainlab iPlan3.03workstation.The cranial nerves were constructedfrom the DTT before surgery for each patient todeterminethe relationships of these nerves with the tumor. The results were thenvalidated during the tumorectomy.Results. In21(91.30%) patients, the locations of the FNson DTT images agreedwith intraoperative findings, including in2patientsin whom the FNs passed throughthe interface between the parenchyma and cystic changes and in3patients withmembranoid FNs. In addition, CNs were observed on DTT images in2patients withfunctional hearing. Moreover, one penetrating fiber of cranial nerve VIIIwaseffectivelyconstructed using the technique. The locations of the TNs on DTTimages were accurate in all patients.Conclusion.The DTT effectively located the FNs, including membranoid FNsadjacent to large VSs and FNs that passed through the interface between an areaexhibiting cystic changes and the tumor nodule. The CN in patients who still have functional hearing was revealed by DTT. Penetrating fibers were also found usingDTT.This technique can be useful during VS resection. Background: Trigeminal schwannomas (TS) are the second common intracranialschwannomas. Surgery induced cranial neuropathies are prevalent during themicrosurgical treatment. As the location of cranial nerves (CN) around the TSs variedgreatly, the arrangement of surround CNs could be different largely. However,Literature of large series demonstrate the nerves’ location was limit since the lowincidence of the disease. This restricted the surgeons’ pre-judge of the tumor beforethe surgery.Method: The study included3consecutive patients with TSs of CPA area fromJan.2014throughNov.2014. Diffusion tensor images and anatomical images (contrastedconstructive interference in steady state) were generated, and the DTT was extractedusing a Brainlab iPlan3.03workstation. The cranial nerves were constructedusingsuperselective DTT before surgery for each patient to determinethe relationships ofthese nerves with the tumor. The results were then verified during the surgery.Results.During the operation, the arrangement of CNs V-VIII around the tumor werefound of great different. However, the superselective DTT results were able toforecast all the differences of CNs V-VIII of these patients but CN VI of case3.Conclusion.Via the reconstruction of CN V-VIII, superselective DTT effectivelyrevealed the arrangement of cranial nerves around TSs. This could provide an reliableoverall impression to the surgeons, and would be beneficial for the preservation ofcranial nerves.