THE JUGULAR DURAL FOLD - A HELPFUL SKULL BASE LANDMARK TO THE CRANIALNERVES

During a retrosigmoid (or combined retrolabyrinthine-retrosigmoid) app roach to the posterior fossa for vestibular neurectomy or removal of s mall acoustic neuromas, a white dural fold is a consistent landmark to cranial nerves VII through XII. This fold of dura appears as a white linear structure extending from the foramen magnum across the sigmoid sinus, attaching to the posterior aspect of the temporal bone, anterio r to the vestibular aqueduct. The name ''jugular dural fold'' is sugge sted for this landmark. The jugular dural fold overlies the junction o f the sigmoid sinus and the jugular foramen. As measured in formalin-f ixed cadaver heads, the overall length of the jugular dural fold is 20 .8 mm (+/- 2.9 mm). The cochleovestibular nerve lies 9.9 mm (+/- 1.5 m m) anterior to the superior aspect of the jugular dural fold, the glos sopharyngeal nerve lies 9.5 mm (+/- 1.6 mm) anterior to the midpoint o f the jugular dural fold, and the operculum of the vestibular aqueduct lies 6.6 mm (+/- 0.7 mm) posterior to the jugular dural fold. Intraop erative measurements in patients undergoing combined retrolabyrinthine -retrosigmoid vestibular neurectomy show an overall length of the jugu lar dural fold of 16.3 mm (+/- 1.9 mm). the cochleovestibular nerve li es 8.6 mm (+/- 1.3 mm) anterior to the superior aspect of the jugular dural fold, the glossopharyngeal nerve lies 8.6 mm (+/- 1.3 mm) anteri or to the midpoint of the jugular dural fold, and the operculum lies 7 .5 mm (+/- 0.8 mm) posterior to the jugular dural fold. The jugular du ral fold can be used as a reliable landmark for rapidly locating crani al nerves in the posterior fossa.