Histopathological Patterns of Otosclerosis Progression: Exploring Otic Capsule and Round Window Involvement

Abstract

Objectives: Obliteration of the round window (RW) in cases of otosclerosis presents a significant clinical challenge due to its association with more severe hearing loss and a poorer prognosis for functional recovery after stapes surgery. The objective is to assess and characterize the occurrence of RW involvement in otosclerosis cases and to identify patterns of disease progression that may indicate a potential for RW obliteration.

Methods: We selected archival temporal bones from donors with otosclerosis. We evaluated the degree of RW obliteration using a semi-quantitative scale and the location of the foci within the temporal bone, and whether the foci were continuous or isolated.

Results: Most of the foci were located anteriorly to the oval window (89.2%), while RW area involvement was seen in 26.9% of the ears. In cases with fenestral foci, 68.1% directly involved and/or fixed the footplate. Among donors with bilateral otosclerosis, foci affected both ears in a similar pattern in 64.2%. Among donors with RW involvement, ones with continuous, large lesions that extended from the oval window associated with complete RW obliteration, while ones with smaller degrees of obliteration had solitary foci scattered within the otic capsule.

Conclusion: Our results demonstrate a high rate of RW involvement in cases of otosclerosis. Ears with continuous lesions extending from the oval window region to the RW area were more likely to present with complete RW obliteration. These results provide insights that could lead to better prognostic assessment of patients with otosclerosis in the future.

Level of evidence: NA Laryngoscope, 135:324-330, 2025.

Keywords: otopathology; otosclerosis; oval window; round window.

Fig. 1

(A) Arrow head: crista semilunaris. Arrow: opening of cochlear aqueduct. Star: round window membrane. Parameter a: length of a parallel line to crista semilunaris which is drawn from the opening cochlear aqueduct to the outer edge of the contralateral bone wall. Parameter b: length of a line from the outer edge of the bone wall to inside line of otosclerosis foci (Line a and line b are also parallel). In this case, the ratio of b/a is less than 50%. (B) Arrow head: crista semilunaris. Arrow: opening of cochlear aqueduct. Star: round window membrane. Parameter a: length of a parallel line to crista semilunaris which is drawn from the opening cochlear aqueduct to the outer edge of the contralateral bone wall. Parameter b: length of a line from the outer edge of the bone wall to inside line of otosclerosis foci (Line a and line b are also parallel). In this case, the ratio of b/a is more than 50% but not complete occlusion. Arrow: cochlear aqueduct. Star: round window membrane. This case is an example of complete RW occlusion and diffuse/massive otosclerosis case. In this case, the opening of the cochlear aqueduct and the crista meniscus were engulfed by the otosclerotic lesion and obscured.

Fig 2

A–F Arrow: these arrows indicate the outline of the otosclerosis foci. This is an example of a case in which aOW lesion and RW area lesion have continuity through the “boundary legion.” The specimens in Figures A to F are sections at intervals of about 20 slices (~400um).

Fig 3

A–F Arrow: these arrows indicate the outline of the otosclerosis foci. This is an example of a case in which the aOW and RW area lesion does not have continuity through the “boundary legion.” The specimens in Figures A to F are sections at intervals of about 20 slices, proceeding from the head to the tail direction. From section D to section E, continuity from the aOW lesion is interrupted, and from section F onward, the independent (isolated from the aOW foci) RW area lesion is observed.