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.

Complications of cochlear implantation surgery in Zagazig University Hospitals

Background Cochlear implantation (CI) has been established worldwide as the surgical treatment for individuals with bilateral severe to profound hearing loss. Complications due to surgery are minimal and are often encountered in cases with congenital anomalies of the temporal bone and inner ear. Complications in CI are related to malfunctioning of the device or the process of wound healing. In most cochlear implant centers, as the surgeon’s skill and clinical expertise in managing various cochlear implant cases improve with years of experience, the complication rates ideally come down over time. This article is intended to describe the most common surgical complications of cochlear implantation in Zagazig University Hospitals. This retrospective study included 130 patients who underwent cochlear implantation in Zagazig University Hospitals from 2016 to 2018. The patients were 61 males and 69 females; their ages ranged between 2 and 6 years old with a mean age of 4.3. This study aims to provide feedback on the common complications of CI surgery at our institution to help the reduction of its incidence in the future. Results One hundred thirty cases of cochlear implants were performed in our department between 2016 and 2018. Sixty complications were recorded, including 27 cases of minor and 21 cases of major complications. Minor complications were flap wound infection in 4 cases (3.1%), chorda tympani nerve injury in 7 cases (5.4%), postoperative vertigo and vomiting in 3 cases (2.3%), injury of EAC in 7 cases (5.4%), wound seroma/hematoma in 4 cases (3.1%), and facial nerve twitching in 2 cases (1.5%). Major complications were electrode extrusion in 2 cases (1.5%), CSOM in 1 case (0.8%), CSF leak in 8 cases (6.1%), magnet migration in 3 cases (2.3%), total facial nerve paralysis in 5 cases (3.8%), and device failure in 2 cases (1.5%). Conclusion The overall incidence of major complications is low. The majority of minor complications can be effectively managed with conservative measures. Cochlear implantation remains a safe and effective surgical procedure.

In Vivo Monitoring of Acetylcholine Release from Nerve Endings in Salivary Gland

A microdialysis technique was used to monitor acetylcholine levels in the local interstitial fluid in rat submandibular glands, with the aim of determining parasympathetic nerve activity in vivo. The dialysis probe housed a 10 × 0.22 mm semipermeable membrane (molecular weight cutoffs: 50,000 Da). When the probe was perfused at 2 μL/min in vitro, the mean relative recovery of acetylcholine was 41.7% ± 2.5%. The dialysis probes were implanted in the submandibular glands of anesthetized rats and perfusion with Ringer’s solution, at 2 μL/min, was performed. Acetylcholine concentrations in the dialysate were measured by high-performance liquid chromatography and electrochemical detection. The results revealed the following: (1) that mixing Eserine with Ringer’s solution allowed acetylcholine in the salivary glands to be quantified; (2) that acetylcholine concentrations in the dialysate were highly variable and unstable over the first 120 min after probe implantation, but reached a nearly stable level (4.8 ± 2.7 nM) thereafter in the presence of 100 µM of Eserine; and (3) that electrical stimulation of the chorda tympani nerve, or perfusion with high potassium Ringer’s solution, significantly increased acetylcholine concentrations in the dialysate. These results indicate that the present microdialysis technique offers a powerful tool for detecting changes in parasympathetic activity within the salivary glands.

Carotid Sympathetic Plexus Schwannoma Presenting as Middle Ear and External Auditory Canal Mass

Schwannomas in the middle ear and external auditory canal are exceedingly rare. The facial nerve, chorda tympani nerve, and Jacobson’s nerve have rarely been reported as the origins of primary schwannomas in the middle ear cavity. We experienced a case of carotid sympathetic plexus (CSP) schwannoma that arose from the carotid canal and extended into the middle ear and external auditory canal. The tumor presented bone erosion of the carotid canal, and it adhered tightly to the internal carotid artery. This report represents the first documented case of a CSP schwannoma, which involved the middle ear and external auditory canal.

Systematic Review and Meta-analysis of Endoscopic vs Microscopic Stapes Surgery for Stapes Fixation

Objective To systematically review the current literature regarding the operative outcomes of stapes surgery for stapes fixation via the endoscopic and microscopic approaches. Data Sources PubMed, Embase, and Web of Science. Review Methods An electronic search was conducted with the keywords “endoscop* or microscop*” and “stapes surgery or stapedectomy or stapedotomy or otosclerosis or stapes fixation.” Studies were included if they compared endoscopy with microscopy for stapes surgery performed for stapes fixation and evaluated hearing outcomes and postoperative complications. Articles focusing on stapes surgery other than for stapes fixation were excluded. Results The database search yielded 1317 studies; 12 remained after dual-investigator screening for quantitative analysis. The mean MINORS score was 18 of 24, indicating a low risk of bias. A meta-analysis demonstrated no statistically significant difference between the groups with regard to operative time, chorda tympani nerve manipulation or sacrifice, or postoperative vertigo. There was a 2.6-dB mean improvement in the change in air-bone gap in favor of endoscopic stapes surgery and a 15.2% increased incidence in postoperative dysgeusia in the microscopic group, but the studies are heterogeneous. Conclusions Endoscopic stapes surgery appears to be a reasonable alternative to microscopic stapes surgery, with similar operative times, complications, and hearing outcomes. Superior visibility with the endoscope was consistently reported in all the studies. Future studies should have standardized methods of reporting visibility, hearing outcomes, and postoperative complications to truly establish if endoscopic stapes surgery is equivalent or superior to microscopic stapes surgery.

Radiological and surgical aspects of round window visibility during cochlear implantation: a retrospective analysis

Purpose The round window approach has become the most preferred option for cochlear implant (CI) insertion, however, sometimes it may not be possible due to the (in)visibility of the round window membrane (RWM). We addressed the prevalence, consequences and indicators of difficult detection of the RWM in cochlear implant surgery. Methods This study retrospectively analysed the operative reports and preoperative high resolution axial-computed tomography (CT) scans of a consecutive cohort of patients who underwent a CI insertion. The main outcomes were surgical outcomes of the RW approach, and assessment of radiological markers. Results The operative reports showed that RWM insertion was feasible in 151 out of 153 patients. In 18% of the patients the RWM was difficult to visualize. All these patients had at least one intraoperative event. The chorda tympani nerve (CTN) or posterior canal wall was affected in 8% of the 153 patients and the fallopian canal in 6%. These patients had a facial-chorda tympani nerve distance on the CT scan that was considerably smaller than normal patients (1.5 mm vs 2.3 mm). In addition, a prediction line towards the anterolateral side of the RWM was found to be more prevalent in these patients’ CT scans (sensitivity 81%, specificity 63%). Conclusion The RW approach is feasible in almost all patients undergoing CI surgery. Difficult visualisation of the RWM seems to lead to at least one intraoperative event. Radiological measures showed that these patients had a smaller facial recess and a more anteriorly placed facial nerve, which can be used to better plan a safe insertion approach.

Cell non-autonomous requirement of p75 in the development of geniculate oral sensory neurons

During development of the peripheral taste system, oral sensory neurons of the geniculate ganglion project via the chorda tympani nerve to innervate taste buds in fungiform papillae. Germline deletion of the p75 neurotrophin receptor causes dramatic axon guidance and branching deficits, leading to a loss of geniculate neurons. To determine whether the developmental functions of p75 in geniculate neurons are cell autonomous, we deleted p75 specifically in Phox2b + oral sensory neurons (Phox2b-Cre; p75fx/fx) or in neural crest-derived cells (P0-Cre; p75fx/fx) and examined geniculate neuron development. In germline p75−/− mice half of all geniculate neurons were lost. The proportion of Phox2b + neurons, as compared to Phox2b-pinna-projecting neurons, was not altered, indicating that both populations were affected similarly. Chorda tympani nerve recordings demonstrated that p75−/− mice exhibit profound deficits in responses to taste and tactile stimuli. In contrast to p75−/− mice, there was no loss of geniculate neurons in either Phox2b-Cre; p75fx/fx or P0-Cre; p75fx/fx mice. Electrophysiological analyses demonstrated that Phox2b-Cre; p75fx/fx mice had normal taste and oral tactile responses. There was a modest but significant loss of fungiform taste buds in Phox2b-Cre; p75fx/fx mice, although there was not a loss of chemosensory innervation of the remaining fungiform taste buds. Overall, these data suggest that the developmental functions of p75 are largely cell non-autonomous and require p75 expression in other cell types of the chorda tympani circuit.

VARIATIONS OF INFERIOR ALVEOLAR NERVE AND ITS RELATION WITH MAXILLARY ARTERY IN INFRA TEMPORAL FOSSA

Infra temporal fossa (ITF) is a difficult area to access both in anatomical dissection and surgery. Thorough knowledge on the anatomy of infra temporal fossa is a prerequisite for maxillofacial, ENT and neurosurgeons since it is in close relation with oral & nasal cavities, maxillary antrum, orbit & pharynx and has direct access to skull base & cranial cavity. Moreover it is a difficult area to describe because of lack of well defined boundary. It contains mandibular nerve (MN), maxillary artery (MA), otic ganglion, chorda tympani nerve and venous plexus apart from pterygoid muscles for mastication. Some variations of the structures in the fossa were noted during routine dissection. This study focuses on such variations of the Inferior Alveolar Nerve and its relation with the maxillary artery in the infra temporal fossa. Present study was done in 60 ITF from 30 cadavers. Variations were observed in 9 specimens – 2 bilaterally, 3 on right side and 2 on left side – in connection with their mode of origin and communication with other nerves. Variations were also observed in their length, thickness and relation with MA. A peculiar branching pattern of MA has been described. Possible embryological basis of such variations has been discussed.