Cochlear Aqueduct Post-Natal Growth: A Computed Tomography Study

Abstract

The cochlear aqueduct (CA) is a bony canal located at the base of the scala tympani of the cochlea. It connects the inner ear perilymph fluid to the cerebrospinal fluid of the posterior cerebral fossa. Its function is not well understood, as it seems to be patent in only a fraction of adult patients. Indirect observations argue in favor of the CA being more patent in children. To study the CA morphology in children, we performed a retrospective single-center study of 85 high-resolution temporal bone computed tomography (hrCT) scans of children with a mean age of 3.23 ± 3.07 years (13 days of life up to 18 years), and compared them with a group of 22 adult hrCT (mean age of 24.01 ± 3.58 years). The CA morphology measurements included its total length, its funnel (wider intracranial portion) length and width and its type (indicating its radiological patency), according to a previously published classification. The dimensions of the CA were significantly smaller in children compared with adults for the axial length (10.37 ± 2.58 versus 14.63 ± 2.40 mm, respectively, p < 0,001) and the funnel length (3.94 ± 1.59 versus 6.01 ± 1.77 mm, respectively, p < 0,001). The funnel width tended to be smaller but the difference was not significant: 3.49 ± 1,33 versus 3.89 ± 1.07 mm, p = 0,22. The repartition of types of CA was also statistically different. The CA appeared to be more identifiable in the children population. Type 1 (CA visible along its entire course) accounted for 42% (36/85) of children and only 5% (1/22) of adults, type 2 (visible in the medial two thirds) for 30% (25/85) versus 31% (7/22), type 3 (not visible completely along the medial two thirds) for 27% (23/85) versus 50% (11/22). Finally, type 4 (undetectable) was found in only 1% (1/85) of children and 14% (3/22) of adults (p < 0,001). Our study showed significant postnatal growth of the length of the CA, which was more rapid before the age of 2, and slowed after 6 years of age. Its width increased less, with children older than 2 years presenting a similar width to adults. The CA was more identifiable in hrCT in children, arguing for a more permeable tract. The number of completely ossified CA was significantly lower in the children population. These findings highlight the differences between the CA morphology in adults and children and raise the question of differences in function. Moreover, these differences may impact the pharmacodynamics of drugs or vectors delivered into the pediatric inner ear. Further studies are required, both on the anatomy of temporal bones and on the function of the CA in children.