This study involved cadaveric dissection using transmastoid approach in cadaveric embalmed five half heads and posterior fossa approach in fourteen. The sac was identified by electron microscopy. The relatively consistent measurements were the relationship of the operculum to the internal auditory meatus (10mm) and the width of the operculum varied only slightly more. Marked variations were noted in the distance from superior petrosal sinus to the operculum (6-14mm), width of the sac (7-16mm), length of sac borders- lateral (5-15mm), medial (4-17mm) and the distance from the operculum to the sigmoid sinus – lateral (7-17mm), medial (8-15mm). In eight cases the endolymphatic sac extended beyond the medial margin of the sigmoid sinus. No appreciable lumen was identified in two. The most consistent finding was dural thickening in the region of the endolymphatic sac. Results are compared with previous studies and appear largely similar. Emphasis is laid on adequate removal of bone from superior petrosal sinus to the jugular bulb and from a point medial to the posterior semicircular canal to the sigmoid sinus, remembering that the sac can extend a bit further and decompression of this sinus may be required. A previously described method of measuring from the short process of the incus to the lower limit of the posterior semicircular canal in transmastoid approach is considered unreliable as it pertains to the intradural part of the sac where it is most variable.
Anatomic guidelines to endolymphatic sac in transmastoid approach – a cadaveric study
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