The cochlear aqueduct in pediatric temporal bones

Abstract

The cochlear aqueduct is a bony channel which contains the fibrous periotic duct and connects the perilymphatic space of the basal turn of the cochlea with the subarachnoid space of the posterior cranial cavity. Previous histological studies suggested that patency depended on age, whereas a more recent study showed no statistical correlation between age and patency. To clarify patency in pediatric cochlear aqueducts, we selected 21 temporal bones from 12 infants and children, varying in age from birth to 9 years, in which the cochlear aqueduct was fully visible on one histological section. Photographs were taken for documentation and the length and width of the orifice of the external aperture of the aqueduct at the scala tympani were measured and followed to the internal aperture at the subarachnoid space. The lumen of the duct was examined for mononucleated cells, blood cells and fibrous tissue. Measurements revealed that the mean length of the cochlear aqueduct was 4.6 mm (range, 2.4-10.7 mm), mean width of the external aperture was 484 microm (range, 225-869 microm), and mean width of the internal aperture was 1293 microm (range, 699-2344 microm). The mean diameter of the narrowest part (isthmus) was 151 microm (range, 75-244 microm). In all temporal bones the cochlear aqueduct was patent, with one exception. This latter temporal bone was from a 2-month-old girl with multiple intralabyrinthine anomalies, with the missing cochlear aqueduct believed to be due to an aplasia. Our results support prior measurements of the cochlear aqueduct and demonstrate a short and patent cochlear aqueduct in newborns. With growth, a significant increasing length of the duct was found.

Enlargement of the cochlear aqueduct: does it exist?

“…no age related changes. Bacher et al made histologic sections of the CA in paediatric temporal bones, they found a short and patent CA in newborns and a significant increasing length with growth [13]. In the same year, Gopen et al [3] stated that there was no correlation between age and narrowest diameter or between age and category and of patency, also using histologic sections.…”

“…Even in newborns, the CA is continuously detectable and increases in length during the growth period [10].…”

The External Opening of the Cochlear Aqueduct in Infants and Adults

“…In the sample studied, there was no evidence of pathology, since all CA were pervious. In spite of the description of variability [2,12] the measurements depend on the technique. The infundibular form of the CA opening and its anatomical variations may give rise to problems in the determination of the depth of reference points [2,8,9].…”

“…Measures of width of adult dissected bone were obtained within the opening of the funnel with values from 0.5 to 3.0 mm [1,4]. Using histological techniques the diameter in adults varied from 0.7 to 2.1 mm [10,11] with similar values from newborns and infants from 0.7 to 2.3 mm [12,13]. Image studies showed values from 2.0 to 6.7 mm in infants [2,7,9,14] and from 0 to 11 mm in adults [8].…”

“…The external opening of the CA can be identified in the posterior fossa as an infundibuliform structure, which extends from the posterior surface of the petrous part of the temporal bone to the anterior division of the jugular foramen, above the passage of the glossopharyngeal nerve [1,6]. Previous studies used different techniques to investigate the external opening of the CA, among them temporal bone dissection [1,4], imaging techniques [7,8] associated with molds and dissections [2,9] as well as histological techniques [10][11][12]. These studies presented variable measurements of width and diameter.…”