Abstract
The foramen of Huschke (FH) is an aperture that is formed in the tympanic plate of the temporal bone at the age of about 1 year. The FH usually closes before the age of 5 years; but it occasionally persists throughout life. A persistent FH may result in complications such as temporomandibular joint (TMJ) herniation and salivary fistula formation, and facilitate ear injury during TMJ arthroscopy. In this study, the authors examined 1994 temporal bones from 997 Japanese dry skulls, in order to define age and gender specific features of the persistent FH after childhood. A persistent FH was found in 12% of men and in 20% of women, representing a female predominance ( P < 0.0001). The incidence of a persistent FH decreased with age in both genders, suggesting that a persistent FH can close over time.
Emil Huschke (1797–1858), in his 1844 publication ‘Sömmering’s Anatomie des Menschen’, described an aperture that was occluded by a fibrous membrane in the tympanic plate of an infant. Joseph Hyrtle (1810–1894), in his 1860 publication ‘Wiener Medicin. Wochenschrift’, described an aperture that was sometimes observed in the anteroinferior wall of the external auditory canal (EAC) within the temporal bone of an adult. He proposed this aperture resulted from a disorder of the osseous development of the tympanic bone. Emil Zuckerkandl (1849–1910), in his 1873 publication ‘Monatsschrift für Ohrenheilkunde’, concluded that the initial osseous EAC was constructed by the fusing of two prominences that arose from the anterior and posterior portions of the tympanic ring.
Based on these historical reports, it is thought that the tympanic plate develops from the following process. At birth, the tympanic ring is the only portion of the incompletely developed tympanic bone present ( Fig. 1 A ). During the first year of life, two prominences that arise from the tympanic ring grow towards each other ( Fig. 1 B). At the age of about 1 year, these two prominences fuse and an aperture persists medial to the point of fusion. This aperture, referred to as the foramen of Huschke (FH), becomes smaller as the tympanic plate grows through a membranous ossification process and usually closes before the age of 5 years ( Fig. 1 C), but it occasionally persists throughout life as a foramen that is occluded by a fibrous membrane . Today, the persistent FH is considered a normal variant in temporal bone anatomy. It is located at the anteroinferior aspect of the EAC, posteromedial to the mandibular head ( Fig. 2 A and B ). A persistent FH may result in complications such as temporomandibular joint (TMJ) herniation and salivary fistula formation, and increase the risk of ear injury during TMJ arthroscopy .
The previously reported incidence of a persistent FH has varied from 3 to 24% . One explanation of this variability is that it is due to differences in the lower size limit of the persistent FH used in each study. A persistent FH may range from the size of a pin hole to greater than 8 mm in diameter. Therefore, when describing the incidence of the persistent FH as a distinct entity, the definition of size is indispensable.
Of the pathologic cases of a persistent FH reported in the literature, the smallest FH was 1 mm in diameter . Based on this value, in this study the persistent FH was defined as any foramina in which the shortest diameter was 1 mm or greater, in order to detect foramina with a higher probability of pathological problems. Following this definition, the authors performed an osteological study of 1994 temporal bones from 997 dry skulls, in order to define age and gender specific features of a persistent FH after childhood.
Materials and methods
1994 temporal bones from 997 Japanese dry skulls (men, 681; women, 316) with known ages were examined. Skulls suspected to have damage to the EAC were excluded. The skulls were classified into one of five age bracket groups stratified by gender ( Tables 1 and 2 ). The number of skulls required in each age bracket group to achieve a confidence level of 95% with an absolute value of an accuracy of 10% or less was estimated using an expected ratio of 24% which was the highest previously reported incidence of the persistent FH .
| Age (mean, years) | Number of observed temporal bones | Number of persistent FH | Incidence of persistent FH (%) |
|---|---|---|---|
| 10–19 (16.2) | 116 | 31 | 26.7 |
| 20–29 (24.0) | 216 | 30 | 13.9 |
| 30–39 (34.8) | 198 | 20 | 10.1 |
| 40–49 (44.3) | 214 | 21 | 9.8 |
| 50– (62.5) | 618 | 58 | 9.4 |
| Overall: 10–90 (45.6) | 1362 | 160 | 11.7 |
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