Topographic Changes in Petrous Bone Anatomy in the Presence of a Vestibular Schwannoma and Implications for the Retrosigmoid Transmeatal Approach

Abstract

Vestibular schwannomas cause significant distortion of the petrous bone anatomy. Detailed preoperative knowledge of the topography is necessary for the preservation of function.

Image-guided, microsurgical topographic anatomy of the endolymphatic sac and vestibular aqueduct via a suboccipital retrosigmoid approach

“…Its malfunction, may determine the symptoms of Meniere disease (endolymphatic hydrops). It is generally believed that while injury to the ES may or may not be associated with hearing or vestibular problems injury to the ED are linked to significant hearing compromise [2,3,5,14].…”

“…Other authors have advised to gain an optimized working angle on the internal acoustic meatus through a medial extension of the classic retrosigmoid craniectomy in order to expose the intrameatal portion of the tumor while at the same time preserving the VA [5].…”

“…While the ES is identifiable, being contained in a dural duplication, the ED is not, as it is embedded in the temporal bone. Though there is no consensus on whether or not manipulation or damage to the ES can cause inner ear malfunction, damage to the ED is associated with hearing compromise [2,5,14]. Several papers have given anatomical topographical landmarks that are useful to preserve these two structures [1,2,4,[6][7][8]14].…”

Improved CT Imaging for Mastoid Emissary Vein Visualization Prior to Posterior Fossa Approaches

“…Through thin-slice CT scans, a minimal radiation dose not exceeding the dose of a standard routine CT scan is applied to the patient and a large amount of information is gained, not only about the EV locations, but also regarding the amount of pneumatization of the petrous bone, the exit of the endolymphatic sac, the displacement of the internal auditory canal in the presence of acoustic schwannomas, the presence of a high jugular bulb, and bony changes of the posterior petrous bone surface in erosive tumors (e.g., meningiomas/chondrosarcomas). 19 The question remains whether the MEV could be depicted on magnetic resonance imaging (MRI) with the same accuracy as on the proposed helical CT scans. With three-dimensional (3D) phase-contrast MR venography, small MEVs are visible; however, the resolution is not comparable.…”

“…EVs may serve as supplementary landmarks for the deeper lying venous sinuses during operative approaches, including the condylar EVs in the transcondylar far-lateral approach and the MEV in retrosigmoid approaches. 14,19,21,22 In this context, reports on landmarks in the retrosigmoid area identified with the aid of neuronavigation described a decrease in EV laceration and/or air embolism or sinus injury due to a navigated approach. 3,23 However, the inconsistent presence of the EVs does not favor a landmark approach in every case, although with the knowledge gained from thin-slice CT scans, the exit and entry points may be followed and identified.…”