Morphological Study of Surgically Obtained Human Cochlear Specimens - Technical Aspects

ObjectTo explore the procedures in per-operative harvesting and management of fresh human cochlear specimens for research.MethodsDuring trans-cochlear surgery to remove large petro-clival meningiomas causing life-threatening compression on the brainstem, cochleae are normally destroyed and drilled away in order to reach the apical petrous and clivus region. Instead the cochlea can be dissected out after ethical permission was obtained from the local ethical committee (EPN) and allowance gained from the patients. Surgery is performed by a team consisting of oto- and neurosurgeons as a two-day procedure with total petrosectomy in combination with an inferior re-routing of the facial nerve. Fixation of the cochleae was done in the operating room as soon as the specimens had been separated from the temporal bones. Decalcification began after hours’ to overnight’s fixation for 4 weeks. Sectioning parallel to the modiolus (mid-modiolus) was performed with a cryostat microtome. The sections were subjected to immunofluorescence (IF).ResultsUsing freshly prepared 4% paraformaldehyde (PFD) solution, adequate fixation of fine inner ear structures was achieved with hours’ immersion of the cochlear specimens. Decalcification in 6.2% ethylene diamine-tetracetic acid (EDTA) solution for 4 weeks yielded a thoroughly decalcified cochlea. Experiences in processing 14 human cochleae and analysing main landmarks in five human inner ear plastic/silicone casts showed that the oval window/stapes footplate are backward tilted, at an angle about 15 degrees, from the plane perpendicular to the modiolar axis. The distance from the modiolar apex to the anterior border of the oval window/footplate in these inner ear casts measured between 4 and 5 mm. High quality IF staining was obtained.ConclusionSurgically obtained human cochlear specimen, when properly processed, contains ideally preserved antigenicity for immunohistochemical study. Adequate orientation during sectioning helps obtain optimal mid-modiolar sections showing fine structures of the cochlea.