Background: Skull base tumors can extend into the temporal bone and occasionally even be visible through the tympanic membrane (TM) if they grow into the middle ear cavity. The differential diagnosis of a skull base mass is extensive and ranges from non-tumorous lesions like cholesteatoma to benign tumors like schwannoma and to malignant lesions like metastatic cancer. Optical coherence tomography (OCT) is a noninvasive imaging technique that can image tissue with high resolution in three dimensions, including through structures such as the TM and bone. OCT angiography is also able to assess tissue vascularity. We hypothesized that OCT could help shrink the differential diagnosis in clinic on the day of initial presentation. Specifically, we thought that OCT angiography could help distinguish between highly vascular skull base tumors such as glomus jugulare and other less vascular tumors and middle ear pathologies such as cholesteatoma and schwannoma. Objectives: We sought to determine whether OCT can image through the TM in clinic to distinguish a normal ear from an ear with a mass behind the tympanic membrane. Furthermore, we sought to assess whether OCT angiography can detect vascularity in these masses to help inform the diagnosis. Methods: We designed and built a custom handheld OCT system that can be used like an otoscope in clinic. It is based off a 200 kHz swept-source laser with a center wavelength of 1310 nm and a bandwidth of 39 nm. It provides a 33.4 μm axial and 38 μm lateral resolution. Cross-sectional images of the middle ear space, including OCT angiography, were captured in an academic neurotology clinic. Patients with normal ear exams, glomus tumors, cholesteatomas, and facial nerve schwannoma were imaged. Results: OCT images revealed key structures within the middle ear space, including the TM, ossicles (malleus and incudostapedial joint), chorda tympani, and cochlear promontory. OCT also identified middle ear pathology (using pixel intensity ratio in the middle ear normalized to the TM) when compared with patients with normal ear exams (mean 0.082, n = 6), in all patients with a glomus tumor (mean 0.620, n = 6, p < 0.001), cholesteatoma (mean 0.153, n = 4, p < 0.01), and facial nerve schwannoma (0.573, n = 1). OCT angiography revealed significant vascularity within glomus tumors (mean 1.881, n = 3), but minimal vascularity was found in normal ears (mean 0.615, n = 3, p < 0.05) and ears with cholesteatoma (mean 0.709, n = 3, p < 0.01), as expected. Conclusions: OCT is able to image through the TM and detect middle ear masses. OCT angiography correctly assesses the vascularity within these masses. Thus, OCT permits the clinician to have additional point-of-care data that can help make the correct diagnosis.

SignificanceEarly detection of ear pathology is essential for preventing hearing loss, yet the sensitivity of otoscopic examinations by primary care providers during annual physicals remains low. Optical coherence tomography (OCT) offers a promising alternative for detailed imaging of the tympanic membrane (TM) and middle ear (ME), providing the potential for early identification of ear disease.AimWe aim to develop a quantitative method for assessing symmetry between the right and left ears and to establish a baseline for this approach in normal subjects.ApproachVolumetric OCT images were acquired from 12 normal subjects using a custom hand-held OCT otoscope. A volume registration and fusion method was applied to expand the TM field of view, followed by TM thickness measurement and generation of 3D thickness maps. The symmetry between left and right TMs was quantitatively analyzed using the Dice similarity coefficient.ResultsThe average TM thickness was measured as 73.89±14.79 μm for left ears and 70.72±11.58 μm for right ears, with no statistically significant difference at the 0.05 level. The symmetry analysis revealed a mean similarity coefficient of 0.79±0.02 between left and right ears among the 12 normal subjects.ConclusionsOCT imaging enables quantitative assessment of TM thickness and symmetry, offering a baseline for identifying early ear pathologies.

Hearing loss and vertigo occur when there is an imbalance between the two inner ear fluids, endolymph and perilymph. The inner ear is a small delicate structure encased in dense bone deep in the base of the skull, making it challenging to image with high resolution. Because the fluid chambers are so small, there is no reliable way to measure their balance in a living patient to guide therapy. Here, we translated the technology of optical coherence tomography (OCT) for use in the human inner ear. Peering through the otic capsule bone during mastoid surgery, we imaged the lateral and posterior semicircular canals of patients with Ménière’s disease or vestibular schwannoma and measured the endolymph-to-perilymph ratio. Compared with normal controls, both patient groups demonstrated increased endolymph and reduced perilymph, a disorder termed endolymphatic hydrops. OCT imaging demonstrated good repeatability for measuring the endolymph-to-perilymph ratio. Our data indicate that increased endolymph-to-perilymph ratios correlated with the degree of hearing loss. Thus, small yet meaningful changes in inner ear fluid balance are detectable with this approach with better resolution than gadolinium-enhanced 3 Tesla magnetic resonance imaging, the current gold standard clinical imaging modality. Our findings support the feasibility of imaging the human inner ear during surgical procedures with OCT and demonstrate the ability to detect endolymphatic hydrops. Moreover, this technique permits the measurement of the fluid chambers within the inner ear in real time during surgical procedures with adequate sensitivity to guide the management of complex but common ear diseases.