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

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.

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.

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.

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.