Histopathology and ultrastructural examination of optic nerve sheath biopsies after optic nerve sheath decompression with and without mitomycin

Purpose: We chose to compare histologically and ultrastructurally changes i n the optic nerve sheath after optic nerve sheath decompression, initially after a second surgery and after treatment with mitomycin-C. The mechanism by which optic nerve sheath decompression alleviates papilledema can be fur ther understood in consideration of the results. Methods: Tissue was obtained by biopsy from 3 first-time surgical and 4 reo perative cases with and without mitomycin-C in patients with idiopathic int racranial hypertension. The sheaths were fixed in a mixture of 2% paraforma ldehyde and 2% glutaraldehyde. osmicated and dehydrated in a series of etha nol, and finally embedded in epon. Tissue blocks were sectioned at I Am and stained with both PPD and toluidine blue. Thin sections were examined by t ransmission electron microscopy. Results: Normal meningeal tissue obtained at the time at optic nerve sheath decompression consisted mainly of collagen, closely packed and roughly par allel to the axis of the optic nerve. Collagen deposition seen in scar tiss ue after secondary optic nerve sheath decompression was extremely disorgani zed and irregular, with the individual fibers laid down seen-tingly at rand om. There was little sense of layering or of parallel arrays. Mitomycin-C a ppeared to influence collagen deposition in such a way that the collagen wa s more regularly packed and more closely resembled unoperated tissue. Conclusions. The regular well-organized collagen packing seen in normal she ath tissue is disrupted and replaced by less organized but compact scar tis sue after optic nerve sheath decompression. With mitomycin use, more regula r collagen packing closely approximating that found in unoperated sheath oc curs. This configuration of fibers lends support for the filtration mechani sm of optic nerve sheath decompression in treating papilledema.