Cerebrospinal Fluid Leak in Cochlear Implantation: Enlarged Cochlear versus Enlarged Vestibular Aqueduct (Common Cavity Excluded)

Hindawi Publishing Corporation International Journal of Otolaryngology Volume 2016, Article ID 6591684, 9 pages http://dx.doi.org/10.1155/2016/6591684 Research Article Cerebrospinal Fluid Leak in Cochlear Implantation: Enlarged Cochlear versus Enlarged Vestibular Aqueduct (Common Cavity Excluded) Giovanni Bianchin, Valeria Polizzi, Patrizia Formigoni, Carmela Russo, and Lorenzo Tribi Otorhinolaryngology and Audiology Department, ASMN-IRCCS Hospital, Reggio Emilia, Italy Correspondence should be addressed to Giovanni Bianchin; Received 26 July 2016; Accepted 3 October 2016 Academic Editor: Srdjan M. Vlajkovic Copyright © 2016 Giovanni Bianchin et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Objective. To share our experience of cerebrospinal fluid gusher in cochlear implantation in patients with enlarged cochlear or vestibular aqueduct. Study Design. Case series with comparison and a review of the literature. Methods. A retrospective study was performed. Demographic and radiological results of patients with enlarged cochlear aqueduct or enlarged vestibular aqueduct in 278 consecutive cochlear implant recipients, including children and adults, were evaluated between January 2000 and December 2015. Results. Six patients with enlarged cochlear aqueduct and eight patients with enlarged vestibular aqueduct were identified. Cerebrospinal fluid gusher occurs in five subjects with enlarged cochlear aqueduct and in only one case of enlarged vestibular aqueduct. Conclusion. Based on these findings, enlarged cochlear aqueduct may be the best risk predictor of cerebrospinal fluid gusher at cochleostomy during cochlear implant surgery despite enlarged vestibular aqueduct. 1. Introduction In the last few decades, advances in cochlear implant (CI) technology and technique have resulted in improved surgical outcomes in subjects with cochlear malformations [1]. Knowledge of the fine structures of the temporal bone using high resolution CT is essential for correct planning of surgery, preventing surgical complications, and predicting the outcome of the procedure. A minimum anatomical requirement for CI is the presence of an implantable cavity near stimulable elements whose projections connect to the auditory cortex [2]. The reported prevalence of inner ear malformation in individuals with congenital deafness or sensorineural hearing loss varies widely from 2.3% to 28.4% depending on patient selection criteria [3]. According to the literature, all cochlear dysplasias can be implanted, with the exception of cochlear aplasia. Another absolute contraindication is the absence of the acoustic nerve [4]. Recent reports of experience with implantation of children and adults with cochlear abnormalities have demonstrated that implantation results in levels of performance not unlike that seen in patients with normal anatomy. Nevertheless cochlear malformations may occur with a higher percentage of surgical complications [5]. Intraoperative cerebrospinal fluid (CSF) leakages from the cochleostomy site are a serious complication of cochlear implantations. They occur as a result of abnormal communication between CSF and perilymph in the cochlea with possibility of residual CSF fistula and a hypothetic increased risk for developing meningitis postoperatively [6]. The incidence of CSF leak in cochlear implantation is reported to be between 1 and 5% in large case series [7– 10]. In 1987, Jackler et al. classified cochlear malformations into five types: complete labyrinthine aplasia, cochlear aplasia, cochlear hypoplasia, incomplete partition, and common cavity [11]. Sennaroglu and Saatci proposed a new classification system in 2002 that distinguished incomplete partition 2 into two types: cystic cochleovestibular malformation (IP-I) and the classic Mondini deformity (IP-II) [4]. However, the degree of dysplasia is not necessarily correlated to the risk of CSF leakage [12, 13]. The pathogenesis of perilymph fistulas is thought to be the result of direct communication between the subarachnoid space and inner ear caused by a defect in the bony partition of the fundus of the internal auditory canal (IAC) [13, 14]; enlargement of the cochlear aqueduct (ECA) and vestibular aqueduct (EVA) has also been suggested as a cause of sensorineural hearing loss and perilymph fistula [15]. The preoperative CT and MRI of the internal auditory canal do not make it currently possible to check the conditions of the fundus of the internal auditory canal and, in particular, an abnormal connection between the arachnoid space and inner ear. This condition can only be suspected, there are no dedicated studies, and the aetiological hypothesis is made after other possible causes have been ruled out. It is, however, different for the ECA and EVA studies; these can easily be conducted radiologically by means of current CT methods. Evaluating the conditions of these aqueducts which can provoke CSF leak may be particularly useful in planning cochlear implantation surgery, stapedectomy, and others (Figure 1) [16]. Anatomy and Physiology of Cochlear Aqueduct. The CA is a small bony canal in the temporal bone that connects the subarachnoid space of the posterior fossa to the basal turn of the cochlea [17]. Generally, it is located 7 mm below the internal acoustic meatus and at the upper edge of the jugular foramen [18]. The lumen of the CA is elliptic, and its largest diameter lies in the horizontal plane [19]. It contains the perilymphatic duct, which connects the subarachnoid space with the scala tympani and is filled with a loose mesh of connective tissue that, although permeable to fluid, limits the patency of the CA [13]. For the most part, it is filled by loose fibrous connective tissue, which is similar to that surrounding the endolymphatic sac. This layer of connective tissue is continuous laterally with the endosteal covering of the scala tympani and medially with the dura and arachnoid, which extends into the canal to a variable length. Therefore, unlike the vestibular aqueduct, the cochlear aqueduct does not contain a true epithelium-lined duct [20]. The CA runs a downward oblique course between the cochlea and the subarachnoid space. Thanks to the CT the course of the CA is divided into four segments [13]. The lateral orifice is the narrow opening of the bony aqueduct into the basal turn of the cochlea. It is located along the anteroinferior edge of the scala tympani immediately anterior to the crest of the attachment of the round window [21, 22]. The lateral orifice opens into the otic capsule segment, which runs medially through the labyrinthine bone. The otic capsule segment becomes continuous with the petrous apex segment, medially. The petrous apex segment runs through bone, which may be either pneumatized or filled with marrow. The petrous ape (...truncated)