TOTAL ENDOSCOPIC STAPES SURGERY. OUR TECHNIQUE AND EXPERIENCE OF 45 CASES

Objective: To assess the hearing results of transcanal endoscopic stapedotomy Study Design: Descriptive study. Place and Duration of Study: Pakistan Naval Ship Hafeez Islamabad Pakistan, from Jun 2016 to Jun 2020. Methodology: All patients with surgically confirmed otosclerosis were included in the study. All patients were operated with 0-degree 3mm, 14cm rigid endoscope under general anesthesia. Preoperative and post operative air bone gap was noted along with demographic data, middle ear anomalies (persistent stapedial artery, dehiscent facial nerve, anteriorly placed facial nerve, floating foot plate) and injury to chorda tympani. Postoperative air bone gap (A-B Gap) was documented 12 weeks after surgery. All patients were followed up for 6-12 months Results: Mean age of patients was, 37 years and standard deviation was 12.34 (range 27-52 years). Out of total 45 cases 13 were males (29%) and 32 females (71.%). Four (8.8%) patients had dehiscent facial canal and 1 (2.2%) patient had persistent stapedial artery. Average preoperative A-B gap was 35 db and Average Postoperative A-B Gap was 7 db. Chorda tympani was preserved in all cases. One patient (2.2%) complained of altered taste which resolved after 3 months. Four patients had Postoperative vertigo that lasted 2 days on average. Conclusion: Endoscopic trans canal Stapes surgery is scarless safe effective procedure demonstrable hearing benefits in all patients with minimum complications. The Technique is single handed and has steep learning curve.

Probing the multimodal fungiform papilla: complex peripheral nerve endings of chorda tympani taste and mechanosensitive fibers before and after Hedgehog pathway inhibition

The fungiform papilla (FP) is a gustatory and somatosensory structure incorporating chorda tympani (CT) nerve fibers that innervate taste buds (TB) and also contain somatosensory endings for touch and temperature. Hedgehog (HH) pathway inhibition eliminates TB, but CT innervation remains in the FP. Importantly, after HH inhibition, CT neurophysiological responses to taste stimuli are eliminated, but tactile responses remain. To examine CT fibers that respond to tactile stimuli in the absence of TB, we used Phox2b-Cre; Rosa26LSL−TdTomato reporter mice to selectively label CT fibers with TdTomato. Normally CT fibers project in a compact bundle directly into TB, but after HH pathway inhibition, CT fibers reorganize and expand just under the FP epithelium where TB were. This widened expanse of CT fibers coexpresses Synapsin-1, β-tubulin, S100, and neurofilaments. Further, GAP43 expression in these fibers suggests they are actively remodeling. Interestingly, CT fibers have complex terminals within the apical FP epithelium and in perigemmal locations in the FP apex. These extragemmal fibers remain after HH pathway inhibition. To identify tactile end organs in FP, we used a K20 antibody to label Merkel cells. In control mice, K20 was expressed in TB cells and at the base of epithelial ridges outside of FP. After HH pathway inhibition, K20 + cells remained in epithelial ridges but were eliminated in the apical FP without TB. These data suggest that the complex, extragemmal nerve endings within and disbursed under the apical FP are the mechanosensitive nerve endings of the CT that remain after HH pathway inhibition.

Improved visualization of the chorda tympani nerve using ultra‐high-resolution computed tomography

Background Recognition of the anatomical course of the chorda tympani nerve (CTN) is important for preventing iatrogenic injuries during middle-ear surgery. Purpose This study aims to compare visualization of the CTN using two computed tomography (CT) methods: conventional high-resolution CT (C-HRCT) and ultra‐high-resolution CT (U-HRCT). Materials and methods We performed a retrospective visual assessment of 59 CTNs in normal temporal bones of 54 consecutive patients who underwent both C-HRCT and U-HRCT. After dividing CTN into three anatomical segments (posterior canaliculus, tympanic segment, and anterior canaliculus), two neuroradiologists scored the visualizations on a four-point scale. Results On C-HRCT, the visual scores of the posterior canaliculus, tympanic segment, and anterior canaliculus were 3.5 ± 0.7, 1.6 ± 0.6, and 3.1 ± 0.7, respectively. The respective values were significantly higher in all segments on U-HRCT: 3.9 ± 0.2, 2.4 ± 0.6, 3.5 ± 0.6 ( p < 0.01). Although the difference in scores between methods was greatest for the tympanic segment, the visual score on U-HRCT was lower for the tympanic segment than for the anterior and posterior segments ( p < 0.01). Conclusion Ultra‐high-resolution CT provides superior visualization of the CTN, especially the tympanic segment.

“Cone Beam Imaging of Cochlear Implants “

Objectives to assess the role of Cone Beam CT (CBCT) in the postoperative cochlear implant (CI) imaging in determining details about the electrode position, insertion depth, angle and other fine anatomical details. Methods This retrospective study included 32 patients (34 ears) with post-CI CBCT imaging. All images were anonymized and reviewed by two experienced head and neck radiologists in consensus for the measurements of the implant insertion depth, facial canal (vertical part) diameter, wall thickness and distance between it and the electrode cable, then assessment of the quality of visualization of fine structures as the facial nerve canal, chorda tympani, separate electrode contacts and scalar position of electrodes were done using 4-point scale. Results The insertion angles for the electrodes were measured in all the ears with a mean ± SD = 430.24 ± 121.43, the facial canal diameters were measured in 97.1% (33 ears) with a mean ± SD = 1.54 ± 0.33, the facial wall thickness was measured in 79.4% (27 ears) with a mean ± SD = 0.62 ± 0.32, the facial canalelectrode cable distances were measured in 97.1% (33 ears) with a mean ± SD = 1.64 ± 0.50 and the chorda tympani was visualized in 88.2% (30 ears). Perfect visualization of the scalar position of electrodes were encountered in 76.5% (26 ears), separate electrode contacts in 20.6% (7 ears), facial canal in 35.3% (12 ears), facial canal wall in 26.5% (9 ears), and chorda tympani in 41.2% (14 ears). Conclusion CBCT is a valuable tool in the postoperative assessment of cochlear implants

Postoperative radiological assessment of the mastoid facial canal in cochlear implant patients in correlation with facial nerve stimulation

Objectives To correlate the radiological assessment of the mastoid facial canal in postoperative cochlear implant (CI) cone-beam CT (CBCT) and other possible contributing clinical or implant-related factors with postoperative facial nerve stimulation (FNS) occurrence. Methods Two experienced radiologists evaluated retrospectively 215 postoperative post-CI CBCT examinations. The mastoid facial canal diameter, wall thickness, distance between the electrode cable and mastoid facial canal, and facial-chorda tympani angle were assessed. Additionally, the intracochlear position and the insertion angle and depth of electrodes were evaluated. Clinical data were analyzed for postoperative FNS within 1.5-year follow-up, CI type, onset, and causes for hearing loss such as otosclerosis, meningitis, and history of previous ear surgeries. Postoperative FNS was correlated with the measurements and clinical data using logistic regression. Results Within the study population (mean age: 56 ± 18 years), ten patients presented with FNS. The correlations between FNS and facial canal diameter (p = 0.09), wall thickness (p = 0.27), distance to CI cable (p = 0.44), and angle with chorda tympani (p = 0.75) were statistically non-significant. There were statistical significances for previous history of meningitis/encephalitis (p = 0.001), extracochlear-electrode-contacts (p = 0.002), scala-vestibuli position (p = 0.02), younger patients’ age (p = 0.03), lateral-wall-electrode type (p = 0.04), and early/childhood onset hearing loss (p = 0.04). Histories of meningitis/encephalitis and extracochlear-electrode-contacts were included in the first two steps of the multivariate logistic regression. Conclusion The mastoid-facial canal radiological assessment and the positional relationship with the CI electrode provide no predictor of postoperative FNS. Histories of meningitis/encephalitis and extracochlear-electrode-contacts are important risk factors. Key Points • Post-operative radiological assessment of the mastoid facial canal and the positional relationship with the CI electrode provide no predictor of post-cochlear implant facial nerve stimulation. • Radiological detection of extracochlear electrode contacts and the previous clinical history of meningitis/encephalitis are two important risk factors for postoperative facial nerve stimulation in cochlear implant patients. • The presence of scala vestibuli electrode insertion as well as the lateral wall electrode type, the younger patient’s age, and early onset of SNHL can play important role in the prediction of post-cochlear implant facial nerve stimulation.

Taste activity in the parabrachial region in adult rats following neonatal chorda tympani transection

The chorda tympani is a gustatory nerve that nerve fails to regenerate if sectioned in rats 10 days of age or younger. This early denervation causes an abnormally high preference for NH4Cl in adult rats, but the impact of neonatal chorda tympani transection on the development of the gustatory hindbrain is unclear. Here, we tested the effect of neonatal chorda tympani transection (CTX) on gustatory responses in the parabrachial nucleus (PbN). We recorded in vivo extracellular spikes in single PbN units of urethane-anesthetized adult rats following CTX at P5 (chronic CTX group) or immediately prior to recording (acute CTX group). Thus, all sampled PbN neurons received indirect input from taste nerves other than the CT. Compared to acute CTX rats, chronic CTX animals had significantly higher responses to stimulation with 0.1 and 0.5 M NH4Cl, 0.1 NaCl, and 0.01 M citric acid. Activity to 0.5 M sucrose and 0.01 M quinine stimulation was not significantly different between groups. Neurons from chronic CTX animals also had larger interstimulus correlations and significantly higher entropy, suggesting that neurons in this group were more likely to be activated by stimulation with multiple tastants. Although neural responses were higher in the PbN of chronic CTX rats compared to acute-sectioned controls, taste-evoked activity was much lower than observed in previous reports, suggesting permanent deficits in taste signaling. These findings demonstrate that the developing gustatory hindbrain exhibits high functional plasticity following early nerve injury.