Anatomic features of the fetal round and oval windows, and their relations with the tympanic nerve.

OBJECTIVE: The study aimed to examine morphometric properties of the round window (RW) and oval window (OW) and to show their relation with the tympanic nerve (the Jacobson's nerve, JN) in human fetuses from the otologic surgeon's perspective. METHODS: Thirty temporal bones of 15 fetal cadavers (8 males, 7 females) aged with 24.40 ± 3.71 weeks were included in the study. The height, width and surface area of the RW and OW and also distance from the JN to the OW and RW were measured. RESULTS: The height, width and surface area of the RW in this work were measured as 1.48 ± 0.25 mm, 1.57 ± 0.37 mm, and 2.05 ± 0.69 mm2, respectively. The RW was detected as round-shaped (8 cases, 26.7%), oval-shaped (15 cases, 50%), and dome-shaped (7 cases, 23.3%). The height, width and surface area of the OW were measured as 1.42 ± 0.26 mm, 2.90 ± 0.44 mm, and 3.63 ± 0.74 mm2, respectively. The OW was observed as oval-shaped (15 cases, 50%), kidney-shaped (10 cases, 33.3%), D-shaped (4 cases, 13.3%), and trapezoid-shaped (1 case, 3.3%). The JN was found 1.21 ± 0.60 and 1.18 ± 0.54 mm away from the RW and OW, respectively. CONCLUSION: This study containing morphological data about the shapes, diameters and area of the RW and OW may be useful to predict surgical difficulty, and to select implants of suitable size preoperatively for the windows. Knowing the relationship between the JN and the windows can be helpful to avoid iatrogenic injuries of the nerve.

New insight into the bony labyrinth: a microcomputed tomography study.

OBJECTIVES: To visualize and quantify the morphology and mineralization of the developing fetal human bony labyrinth, using 3D-microcomputed tomography (3D-microCT) imaging. METHODS: Eleven right temporal bones from late second and third trimester fetuses were used in this prospective pilot study. After fixation in 10% formalin solution, all samples underwent a microcomputed tomography (microCT) scan, permitting the 3D imaging of the bony labyrinth as well as the quantitative assessment of mineral density, angular distances and dimensions of inner ear components the progression of ossification was precised with histological observations. RESULTS: Our findings show different rates of growth among the semicircular canals, the vestibular aqueduct, the oval window, the round window and the cochlea. The final sizes of the cochlea and round window are achieved at 23 weeks of gestation, with heights of 5mm and 2mm, respectively. The oval window reaches adult size at 35 weeks, whereas the vestibular aqueduct will attain adult size after birth. An increasing degree of torsion of each semicircular canal is observed during fetal development. The superior semicircular canal achieves adult size at 24 weeks, before the posterior and the lateral canals (25 weeks). The time-course of ossification and mineralization observed in structures and confirmed by histology. CONCLUSIONS: During this developmental period poorly studied until now, our findings suggest that each part of the bony labyrinth follows distinct growth and ossification kinetics trajectories, some of these reaching their adult size only after birth.

Development and surgical anatomy of the round window niche.

The round window niche is a bony pouch of the tympanic cavity and clinically frequently explored, therefore its topography has fundamental impact on microsurgery. A total of 783 macerated and formalin-fixed temporal bones were used to study the normal anatomy of the round window and its development. The ossification of the niche starts in the 16th fetal week and is complete at birth. A process of the otic capsule, called the cartilage bar, forms the inferior wall of the round window niche. The anterior and superior walls of the niche form by intramembranous ossification, whereas the posterior and inferior walls predominantly form by enchondral ossification. The uneven growth of different walls of the round window niche can alter the shape of the entrance, which results in eight different types of niches: extremely narrow, descending tegmen, anterior septum, bony membrane, open fundus, exostosis, jugular dome and trabeculae.

Developmental study of the round window region.

A silicone impression method to study the anatomy of the round window region was used in 102 temporal bones belonging to individuals aged from 4 months of fetal life to 3-year-old children as well as adults. A total of 2,142 measurements of the round window, oval window and round window fossula was made in the molds. The data demonstrate that the round window shows a diameter from 1.21 mm (average for the short axis) to 1.74 mm (average for the long axis) and the circular shape was present in 55% of the adult temporal bones and in 18.18% of the fetal and infantile ones. The adult dimensions of the measured structures are reached during fetal development.

Anatomy of the round window niche.

The contributing elements to boundaries of the round window niche are superiorly the tegmen fossula fenestra rotunda (roof support), inferiorly the fustis (depth) and area concamerata, anteriorly the sustentaculum (support) and postis anterior (anterior pillar), and posteriorly the postis posterior (posterior pillar) and the subiculum (underlying supporting structure). Variations in their size and orientation can give rise to significant variability in the overall size and shape of the round window niche.