Function preservation for resection of vagal schwannoma of the head and neck: Are we talking about the same technique?

Dear Editor, We read with interest the paper “Vagal schwannomas of the head and neck: A comprehensive review and a novel approach to preserving vocal cord innervation and function”and congratulate the authors on their manuscript. However, there appears to be an element of confusion or variation in the terminology relating to function preserving vagal schwannoma surgery, highlighted by the paper, which we believe would benefit from clarification. The surgical treatment of cervical schwannoma has historically involved excision of the whole tumor with the nerve from which is arises. As the majority arise from the vagus nerve, treatment has been associated with significant morbidity, and many of these benign tumors have been managed conservatively. Conservative management may however be associated with ongoing gradual tumor growth and progressive loss of function in both the involved and adjacent cranial nerves. Disease progression may also be associated with significant mass effect, obstruction of the jugular foramen, and potentially intracranial extension with associated brainstem compression. Intracapsular enucleation as a surgical technique offers the prospect of surgical treatment addressing the tumor mass without imposing neurological deficit. The technique was popularized by Netterville, who described a surgical approach that involved incising the nerve at an electrically “silent” area, to find an “obvious and often very superficial” plane between the tumor and the capsule. However, it is unclear to what extent surgeons adopting this technique are in fact doing the same thing. The recent paper by Sandler et al groups surgical approaches into two categories, the first is gross total resection, the traditional surgical approach excising the tumor with associated nerve fascicles, and nerve function sacrificed. The second is tumor enucleation, the technique for which they describe as “the nerve fibers are pushed aside, and the capsule of the schwannoma is cut open allowing for the removal of the schwannoma leaving the capsule and most of the nerve fibers uncut.” This they classify as subtotal resection, the implication being that a capsule of tumor is left in situ. The description therefore differs significantly from Nettervilles. We take issue with this interpretation of the intracapsular enucleation technique. Histologically, a schwannoma has a capsule, which is a thin boundary layer between the tumor and the normal nerve, which is itself displaced rather than invaded or infiltrated (in contrast to the behavior of a neurofibroma). The displaced but otherwise normal tissue of the surrounding nerve forms a layer surrounding the tumor, which may be relatively uniform in the case of a tumor arising centrally within the nerve, or concentrated on one side of the tumor. We describe this displaced normal tissue as forming a “pseudocapsule” around the tumor, and believe the plane in which an intracapsular enucleation is ideally performed is the plane between this displaced tissue and the tumor itself. The tumor may therefore be excised intact, with its true capsule intact (Figure 1) with what seems more appropriately called extracapsular enucleation. The implication of this is that the resection of the tumor via “intracapsular enucleation” is not by definition subtotal. Complete tumor resection is possible and generally achieved, particularly in those tumors located lower in the neck. We acknowledge that the risk of residual disease remaining is higher than if the tumor is excised within the relatively robust capsule which the nerve forms; however, the clinical significance of residual disease is likely to be minimal. We would therefore advocate the use of this technique for all patients with head and neck schwannomas, not just the subgroup of “the elderly, or patients who would not be able to tolerate prolonged surgery with significant postoperative morbidity and potential mortality” as suggested by Sandler et al. We strongly feel that all patient undergoing surgical treatment for cervical schwannoma should be treated in a way which both preserves neurological function and offers complete tumor resection, that is, intracapsular enucleation in the appropriate plane. Received: 22 June 2020 Accepted: 18 August 2020