Clin Exp Otorhinolaryngol.  2020 May;13(2):106-112. 10.21053/ceo.2019.00766.

Extratympanic Observation of Middle and Inner Ear Structures in Rodents Using Optical Coherence Tomography

• Oh SJ
• Lee IW
• Wang SG
• Kong SK
• Kim HK
• Goh EK

• KMID: 2500282
• DOI: http://doi.org/10.21053/ceo.2019.00766

Abstract

Objectives
. This study aimed to investigate whether optical coherence tomography (OCT) provides useful information about the microstructures of the middle and inner ear via extratympanic approach and thereby could be utilized as an alternative diagnostic technology in ear imaging.
Methods
. Five rats and mice were included, and the swept-source OCT system was applied to confirm the extent of visibility of the middle and inner ear and measure the length or thickness of the microstructures in the ear. The cochlea was subsequently dissected following OCT and histologically evaluated to compare with the OCT images.
Results
. The middle ear microstructures such as ossicles, stapedial artery and oval window through the tympanic membrane with the OCT could be confirmed in both rats and mice. It was also possible to obtain the inner ear images such as each compartment of the cochlea in the mice, but the bone covering bulla needed to be removed to visualize the inner ear structures in the rats which had thicker bulla. The bony thickness covering the cochlea could be measured, which showed no significant differences between OCT and histologic image at all turns of cochlea.
Conclusion
. OCT has been shown a promising technology to assess real-time middle and inner ear microstructures noninvasively with a high-resolution in the animal model. Therefore, OCT could be utilized to provide additional diagnostic information about the diseases of the middle and inner ear.

Keyword

Optical Coherence Tomography; Otolaryngology; Optical Imaging; Cochlea; Middle Ear

Figure

• 

  Fig. 1. Schematic diagram of the real-time swept-source optical coherence tomography (OCT) imaging system. PD, photodiode; DAQ, data acquisition board.

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  Fig. 2. Swept-source optical coherence tomography (OCT) system that was used in this experiment. The objective lens had an outer diameter of 34 mm and a working distance of 7.5 mm. A mouse is placed on the scanning stage of the OCT system. The head of the mouse is grasped by the holder to keep it steady. The white arrow indicates the head holder.

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  Fig. 3. Endoscopic findings in the right ear of the mouse. (A) Tympanic membrane (TM) viewed extra-tympanically. (B) Middle ear of mouse after removal of the TM and the cartilaginous and bony external auditory canal. M, malleus; I, incus; S, stapes; SA, stapedial artery; R, round window; P, promontory.

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  Fig. 4. In vivo middle ear and inner ear structure images of a mouse using optical coherence tomography. (A) Two-dimensional image at the apex of the cochlear structures. (B) Three-dimensional image of the same structure in (A). (C) Two-dimensional image of the ossicles in the middle ear cavity. Scale bars (white) represent 500 μm in length. TM, tympanic membrane; M, manubrium of malleus; BM, basilar membrane; SM, scala media; RM, Reissner's membrane; SV, scala vestibuli; ST, scala tympani; P, promontory; I, incus; S, stapes; TC, tympanic cavity; C, cochlea.

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  Fig. 5. Two-dimensional (2D) images of rat TM, middle ear, and inner ear structures. (A) TM and M with the bulla removed. (B) Apical, middle, basal turn of C and round window with TM with the bulla removed. (C) SA passing on the C and OW. The white arrow indicates the diameter of the SA. (D) Two-dimensional en face image at the apex of the cochlear structures. Scale bars (white) represent 500 μm in length. TM, tympanic membrane; M, malleus; P, promontory; C, cochlea; MO, modiolus; RW, round window; OW, oval window; HS, head of stapes; SA, stapedial artery; ST, scala tympani; SM, scala media; SV, scala vestibuli; BM, basilar membrane; RWN, round window niche.

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  Fig. 6. The comparison between the optical coherence tomography (OCT) image and histologic view in rats. (A) Apical, middle, basal turn of cochlea and round window with tympanic membrane with the bulla removed. The white arrows indicate the thickness of the bone at each turn of cochlea. Scale bars represent 500 μm in length. (B) Histology of the cochlea, sections were stained with H&E (×40). (C) The comparison of bony thickness covering the cochlea measured by OCT and histology, which shows no significant differences between two methods. MO, modiolus; RW, round window.

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