Morphological Relation of Peripheral Nerve Sheath Tumors and Nerve Fascicles: Prospective Study and Classification

Removal of benign peripheral nerve sheath tumors (bPNST) represents a surgical challenge. The morphological relation of bPNST and healthy nerve fascicles are of utmost importance for achieving both removal of the entire tumor and preservation of functional integrity of the peripheral nerve. Thus, we intraoperatively assessed the morphological patterns between bPNST and nerve fascicles using photo documentation obtained between January 2009 and September 2021. In 31 patients (20 women and 11 men) with a mean age of 48 ± 18 years a total of 34 bPNST were removed. Four constant morphological patterns between bPNST relatively to nerve fascicles were detected: (1) bPNST is located peripherally (n = 16), (2) it splits the nerve into two main fascicles (n = 5), (3) it totally splits up the nerve out of the nerve's center (n = 8) und (4) it encloses the nerve and its fascicles (n = 5) without any detectable boundary layer. Histology revealed 28 schwannomas, five neurofibromas, and one perineurioma. The proposed classification reflects the increasing complexity of tumor removal with a higher type number. This might be beneficial for preoperative diagnostics, i.e., high-resolution ultrasound or MRI-tractography, as well as for planning the bPNST's surgical resection and the possible need for nerve reconstruction.