Anatomic Study on the Retrolabyrinthine Region through Presigmoid Approach

Objective:To provide anatomic data for clinical operations in retrolabyrinthine region through presigmoid approach. Methods:15 cadaveric specimens immersed in 10% formaldehyde solution were used in this study. Stripping the sclerotin among the posterosuperior spine of auricular canal, supramastoid crest and mastoidale to expose sigmoid sinus,superior petrosal sinus, junct of petrosal sinus and sigmoid sinus,dura mater of middle cranial fossa, dura mater of posterior cranial fossa in front of sigmoid sinus. The posterior semicircular canal, lateral semicircular canal, superior semicircular canal, vertical part of facial nerve, and jugular bulb were showed up after the superficial bone of mastoid tip was drilled away. To measure and record the related data. Results:The sclerotin in the retrolabyrinthine region was consisted of three layers, namely the superficial cortical substance, mastoidal honeycomb-like sclerotin and rigid substantiae covering the below structures. The distance from the posterosuperior spine of auricular canal to the posterior semicircular canal was (17.88±1.27)mm.The vertical part of facial nerve made its way from the inferior part of horizontal semicircular canal and the anterior part of posterior semicircular canal to the costalanteriomedialis of digastric ridge. The length of vertical part of facial nerve was (7.58～14.02)mm. The shortest distance from the Helen’s spine to sigmoid sinus was (13.84 ±2.74)mm.Conclusions:The anatomic characteristics in retrolabyrinthine region and findings from this study could provide a favourable guidance and important anatomic data for the operation via presigmoid approach, in order to avoid damaging some important structures.