Surgical Pathology of Spinal Schwannomas: A Light and Electron Microscopic Analysis of Tumor Capsules

Abstract

ABSTRACT OBJECTIVE Although spinal schwannomas are often encountered, the pathology of the tumor capsule has not been reported. In this study, we describe the ultrastructural pathology of the tumor capsule of spinal schwannomas. METHODS In 18 patients who underwent total removal of spinal schwannomas (C2–conus), the tumor capsule was collected and examined by light and electron microscopy. RESULTS The thickness of the tumor capsule ranged from 15 to 800 μm (mostly 30–100 μm) and was composed of three layers from the surface to the center: 1) a thinly stretched nerve tissue layer; 2) a fibrous layer of fibrocytes, abundant collagen fibers, and tumor vessels; and 3) a thin transitional layer intermingled with fibrous components and tumor cells. The thickness of each layer varied in different regions of the surface. There was no clear separation between the tumor capsule and the neoplastic tissue, even on the electron microscopic level. A number of nerve fibers ran through the fibrous layer and beneath the capsule as well as in the nerve tissue layer. CONCLUSION Compared with vestibular schwannomas, which have been reported to be covered by an extremely thin layer (3–5 μm) of connective tissue, spinal schwannomas were well encapsulated. The capsule was composed of three distinct components; however, the cleavage between thin capsule and tumor cells was indistinct, and the thickness of the axon-containing capsule varied from site to site. Therefore, resection of the nerve of tumor origin, rather than enucleation, would be justified to avoid tumor recurrence. Surgeons should be aware of this pathology when performing the procedure.