Features and management of a schwannoma of the chorda tympani and review of the literature

Intrinsic facial nerve tumors are rare lesions. Among the different histology types, schwannomas is the most frequently reported in literature. Other histological types of facial nerve tumors are hemangiomas, meningiomas, and neurofibromas. Chorda tympani schwannomas (CTSs) are extremely rare entities and are considered as an independent subgroup of facial nerve schwannomas because of their clinical characteristics. The aim of this report is to present the clinical and radiological features and the management of a CTS in a 27-year-old male presenting with conductive hearing loss.

Salivary glands regenerate after radiation injury through SOX2-mediated secretory cell replacement

Salivary gland acinar cells are routinely destroyed during radiation treatment for head and neck cancer that results in a lifetime of hyposalivation and co-morbidities. A potential regenerative strategy for replacing injured tissue is the reactivation of endogenous stem cells by targeted therapeutics. However, the identity of these cells, whether they are capable of regenerating the tissue, and the mechanisms by which they are regulated are unknown. Using in vivo and ex vivo models, in combination with genetic lineage tracing and human tissue, we discover a SOX2+ stem cell population essential to acinar cell maintenance that is capable of replenishing acini after radiation. Furthermore, we show that acinar cell replacement is nerve dependent and that addition of a muscarinic mimetic is sufficient to drive regeneration. Moreover, we show that SOX2 is diminished in irradiated human salivary gland, along with parasympathetic nerves, suggesting that tissue degeneration is due to loss of progenitors and their regulators. Thus, we establish a new paradigm that salivary glands can regenerate after genotoxic shock and do so through a SOX2 nerve-dependent mechanism.

Successful treatment of dysgeusia after middle-ear surgery with amitriptyline: Case report

INTRODUCTION

The chorda tympani branches off of the facial nerve within the petrous portion of the temporal bone, and is responsible for controlling the taste in the anterior two-thirds of the tongue on each side. Due to its location, it is commonly injured during middle-ear surgery resulting in dysgeusia.

METHOD

A case of a 59-year-old male had recurrent otitis media resulting in tympanic membrane perforation. Patient subsequently underwent lateral graft tympanoplasty. Shortly after surgery patient reported onset of dysgeusia consisting of metallic taste at the tip of the tongue and salty taste on the left side of the tongue.

RESULTS

Treatment with Amitriptyline 50mg each night significantly improved the patient's symptoms of dysgeusia.

CONCLUSIONS

Amitriptyline may be an effective treatment for dysgeusia occurring after middle-ear surgery.

Impact of chorda tympani nerve injury on cell survival, axon maintenance, and morphology of the chorda tympani nerve terminal field in the nucleus of the solitary tract

Chorda tympani nerve transection (CTX) has been useful to study the relationship between nerve and taste buds in fungiform papillae. This work demonstrated that the morphological integrity of taste buds depends on their innervation. Considerable research focused on the effects of CTX on peripheral gustatory structures, but much less research has focused on the central effects. Here, we explored how CTX affects ganglion cell survival, maintenance of injured peripheral axons, and the chorda tympani nerve terminal field organization in the nucleus of the solitary tract (NTS). After CTX in adult rats, the chorda tympani nerve was labeled with biotinylated dextran amine at 3, 7, 14, 30, and 60 days post-CTX to allow visualization of the terminal field associated with peripheral processes. There was a significant and persistent reduction of the labeled chorda tympani nerve terminal field volume and density in the NTS following CTX. Compared with controls, the volume of the labeled terminal field was not altered at 3 or 7 days post-CTX; however, it was significantly reduced by 44% and by 63% at 30 and 60 days post-CTX, respectively. Changes in the density of labeled terminal field in the NTS paralleled the terminal field volume results. The dramatic decrease in labeled terminal field size post-CTX cannot be explained by a loss of geniculate ganglion neurons or degeneration of central axons. Instead, the function and/or maintenance of the peripheral axonal process appear to be affected. These new results have implications for long-term functional and behavioral alterations.

Functional role for interleukin-1 in the injured peripheral taste system

The peripheral taste system presents an excellent model for studying the consequences of neural injury, for the damaged nerve and sensory cells and the neighboring, intact neural cells. Sectioning a primary afferent nerve, the chorda tympani (CT), rapidly recruits neutrophils to both sides of the tongue. The bilateral neutrophil response induces transient functional deficits in the intact CT. Normal function is subsequently restored as macrophages respond to injury. We hypothesized that macrophages produce the proinflammatory cytokine interleukin (IL)-1, which contributes to the maintenance of normal taste function after nearby injury. We demonstrate that IL-1β protein levels are significantly increased on the injured side of the tongue at day 2 after injury. Dietary sodium deficiency, a manipulation that prevents macrophage recruitment, inhibits the elevation in IL-1β. IL-1β was expressed in several cell populations, including taste receptor cells and infiltrating neutrophils and macrophages. To test whether IL-1 modulates taste function after injury, we blocked signaling with an IL-1 receptor antagonist (IL-1 RA) and recorded taste responses from the intact CT. This treatment inhibited the bilateral macrophage response to injury and impaired taste responses in the intact CT. Cytokine actions in the taste system are largely unstudied. These results demonstrate that IL-1 has a beneficial effect on taste function after nearby injury, in contrast to its detrimental role in the injured central nervous system.

Dysgeusia and cholesteatoma

OBJECTIVE

To describe an individual with cholesteatoma whose sole presenting symptom was dysgeusia.

STUDY DESIGN

Case report.

METHOD

A retrospective review of an individual presenting with dysgeusia without any hearing loss, otorrhea, or imbalance who was found to have chronic otitis media with cholesteatoma.

RESULT

Surgical exploration confirmed the presence of cholesteatoma and identified an intact but attenuated chorda tympani nerve. The dysgeusia persisted after surgery.

CONCLUSION

The anatomical course of the chorda tympani and the usual routes of expansion of cholesteatoma sacs indicates a higher incidence of dysgeusia with cholesteatoma. Further elucidation is necessary to determine the true incidence of this complaint with cholesteatoma.

Ultrastructural Analysis of the Chorda Tympani Nerve in Chronic Suppurative Otitis Media

OBJECTIVE

To compare ultrastructure of the chorda tympani nerve by light and electron microscopy in patients with otosclerosis and chronic suppurative otitis media.

STUDY DESIGN

Comparative prospective study.

SETTING

Tertiary care, referral medical center.

PATIENTS

The tympanic segments of chorda tympani nerves were collected for ultrastructural investigation in 20 cases with chronic suppurative otitis media and 10 cases with otosclerosis that underwent middle ear surgery.

RESULTS

Histopathologic examinations of the suppurative group showed that unmyelinated fibers were almost totally lost and replaced by collagen fibers. The thickness of the myelin sheaths was very slender, whereas some of them were atrophic. A substantial increase was encountered in the endoneural collagen substance and connective tissue, whereas inflammatory elements and edema were present occasionally. Degenerative alterations of the myelinated fibers mainly occurred in the form of adaxonal vacuoles. There was disorganization and separation of parallel lamellae of Schmidt-Lanterman clefts.

CONCLUSION

The chorda tympani nerve should be preserved in otologic surgery. However, inadvertent dissection of the chorda tympani nerve in chronic suppurative otitis media surgery will not possibly cause a postoperative disturbance in light of ultrastructural changes that occur in the nerve.

Fallopian canal dehiscences: a survey of clinical and anatomical findings

This survey investigates fallopian canal dehiscences in order to assess the risk of encountering an unprotected facial nerve during routine ear surgery. In a prospective non-randomized study, the intraoperative appearance of the facial canal in 357 routine ear operations was compared with 300 temporal bone specimens from 150 autopsies. Intraoperatively, a dehiscence was detected in 6.4% (23/357) of the operations, most frequently at the oval niche region (16/23 cases). The incidence increased with the number of operations (P<0.0002). Cholesteatoma surgery had the highest relative risk (RR 4.6) of exposing an unprotected facial nerve. Postoperatively, no persistent facial paralysis was observed. In four of five cases with a transient facial palsy due to local anesthetics, a bony dehiscence could be found. The anatomical study revealed fallopian canal dehiscences in 29.3% (44/150) of the autopsies. One-third (15/44) of the individuals affected displayed bilateral findings, thus resulting in 19.7% (59/300) of temporal bones affected. A total of 17/59 bones showed microdehiscences, and most (55/59) were located at the oval niche. The actual prevalence of fallopian canal dehiscences is significantly higher than intraoperative findings suggest. The oval niche is the most affected region. High-resolution computed tomography is of diagnostic value only in selected cases. Facial paralysis following local anesthesia is the most significant clinical sign. Vigilance in acute facial palsy after local anesthetics and in cholesteatoma surgery and adequate intraoperative exposure help to prevent iatrogenic injury of the uncovered nerve. In unclear cases, nerve monitoring can facilitate a safe outcome.

Taste function in elderly patients with unilateral middle ear disease

OBJECTIVE

It is generally said that taste function deteriorates naturally with age. Taste function after middle ear surgery in elderly patients has not been clarified.

MATERIAL AND METHODS

The taste function of the chorda tympani nerve on the normal and diseased sides was examined before and after middle ear surgery using electrogustometry in 79 patients aged>60 years, and the findings were compared with those in 228 young and middle-aged patients.

RESULTS

The threshold of electrogustometry on the normal side increased significantly with increasing age (p<0.0001). The rate of thresholds that were off the scale was highest in the>70 years age group. The preoperative threshold on the diseased side increased significantly with increasing age in patients with chronic otitis media (p=0.0029) and cholesteatoma (p<0.0001). In patients with chronic otitis media, the postoperative threshold of the>60 years age group tended to be higher than that of the<60 years age group.

CONCLUSIONS

These findings suggest that the taste function of the chorda tympani nerve deteriorated on the diseased side as much as on the normal side in elderly patients. Therefore, in most cases, we do not have to pay as much attention to the chorda tymapani nerve when performing surgery in elderly patients compared to young and middle-aged patients.

Histopathological basis of hearing impairment in Wolf-Hirschhorn syndrome

OBJECTIVES/HYPOTHESIS

To perform histological examination of temporal bones acquired from an infant with Wolf-Hirschhorn syndrome with an emphasis on identifying abnormalities that might be responsible for hearing impairment in this disorder.

STUDY DESIGN

Retrospective case review.

METHODS

Temporal bones were taken at autopsy from a 10-month-old infant with Wolf-Hirschhorn syndrome. The right-side temporal bone was studied by microdissection. The middle ear was examined, and the inner ear sensory organs dissected for study by light microscopy. The left-side temporal bone was embedded in celloidin, and sections were cut for microscopic examination.

RESULTS

Chronic otitis media was observed in both ears. Inflammation, effusion, and adhesions were present in the middle ear space. The malleus was malformed, and the chorda tympani nerve was found to pass through the bone of the malleus bilaterally. There was an area of sharply defined outer hair cell loss in the lower basal turn of the right-side organ of Corti, and defects were noted in the bone of the apical osseous spiral lamina in both cochleae.

CONCLUSION

In addition to the presence of otitis media, the likelihood of congenital abnormalities of the middle and inner ear should be considered in the assessment of patients with Wolf-Hirschhorn syndrome with hearing impairment.

[Taste disorder caused by carotid artery dissection]

There exist only a few reports on loss of taste sensation caused by dissection of the internal carotid artery. We describe a patient with carotid dissection and ipsilateral ageusia in the anterior two thirds of the tongue, presumably from a lesion of the chorda tympani. Ageusia in carotid dissection is explained by the close anatomic relation of the internal carotid artery and the chorda tympani in the short petrous bone. However, since extension of the space-occupying, dissecting intramural hematoma into the carotid channel as in our patient occurs infrequently--a probable precondition for the chorda tympani lesion--loss of taste is accordingly very rare. Reduced perfusion of the vasa nervorum can be excluded as another cause, because the chorda tympani is supplied only from branches of the external carotid artery.

Histopathological changes of chorda tympani in chronic otitis media

OBJECTIVE

To investigate whether histopathological changes of chorda tympani might exist in patients with chronic otitis media without facial paralysis.

STUDY DESIGN

The study was designed as a prospective trial.

METHODS

Twenty of 107 patients with chronic otitis media, in whom the chorda tympani were injured inadvertently during middle ear surgery, were enrolled into the study. The cases were divided into two groups based on the activity of chronic infection at the time of surgery. Twelve cases with suppurative disease were included in group I, and 8 cases with dry ear in group II.

RESULTS

Histopathological examinations of the specimens revealed findings such as thickening of perineural and epineural connective tissue, vacuolar degeneration of Schwann cells, and proliferation of fibroblasts in endoneurium. Disorganization of the axons of some nerve fibers was also determined.

CONCLUSION

Based on the histopathological changes of chorda tympani in chronic middle ear disease, it is postulated that chronic otitis media may give rise to functional loss of the nerve.

Schwannoma of the chorda tympani

The authors present a rare clinical entity in a schwannoma of the chorda tympani. The case is discussed including the difficulty in making the diagnosis and management.

Schwannoma of the chorda tympani nerve

We report a case of schwannoma of the chorda tympani. This is a very rare benign tumour and only five other cases have been found in the literature. This is the first case to mimic a cholesteatoma presenting as a pearly tumour in the postero-superior segment of the drum with aural discharge and conductive deafness. Diagnosis is usually by biopsy and treatment is surgical with preservation of facial and auditory function. A summary of the other presentations of this tumour together with a review of the histopathology of the disease is presented.

A quantitative morphological study of the recovery of cat lingual nerves after transection or crushing

The morphological changes were examined proximal and distal to crush and transection injuries of the lingual/chorda tympani nerve. Under general anaesthesia the nerve was transected unilaterally in 6 adult cats and crushed with watchmakers forceps in 6 others. After 12 wk, again under general anaesthesia, the injured and contralateral (control) nerves were removed, fixed and embedded for histological examination. Sections were cut from sites proximal and distal to the injury and from a site equivalent to that of the injury on the control side. Using systematic randomised sampling techniques the number of nonmyelinated axons and the number and size of myelinated axons in each nerve at each location was estimated. In addition, the mean number of nonmyelinated axons in each Schwann cell unit was determined. The only significant difference between control and injured nerves proximal to either injury was a reduction in the number of myelinated axons in the chorda tympani after transection, and an increase in their mean size. This indicates a selective loss of smaller fibres and is consistent with the poor recovery of gustatory and thermosensitive fibres previously reported (Robinson, 1989). Distal to both types of injury there was an increase in the number of fascicles. The mean number of myelinated axons was reduced distal to a crush injury but unchanged distal to transection. The number of nonmyelinated axons distal to a transection injury was 5 times control counts and after a crush injury double. These findings suggest that sprouting persists 12 wk after both injuries but is much greater after transection.

[Studies on total nerve fivers of chorda tympani nerve in man]

An analysis of nerve fibers of the chorda tympani taken from six patients with otitis media cholesteatoma in whom the nerve could not be spared during tympanoplasty was performed. This study was designed to measure the diameter and the number of nerve fibers by making a full reconstruction of human chorda tympani in order to clarify the composition of myelinated and unmyelinated fibers, and to estimate the total number of fibers based on the results of the compartment measuring method. The following results were obtained: 1) The area of cross-section of the nerve ranged from 0.059mm2 to 0.110mm2, mean 0.081mm2. The sectional area was related to the patients age. 2) The total number of myelinated nerve fibers ranged from 3,305 to 4,668, with a mean of 3,829. The distribution of diameters of myelinated fibers had a peak at 2 to 3 microns and fibers of 1 to 4 microns accounted for 93.4% of the total. The number of myelinated fibers reduced with an increase in the patients age. 3) The total number of unmyelinated nerve fibers ranged from 2,044 to 4,334, with a mean of 3,306. The number of Schwann cell units was distributed between 791 and 1,937, with a mean of 1,386. The number of unmyelinated fibers per one Schwann cell unit ranged between 1 and 5 in 93.6% of cases. There was no age-related reduction in the number of fibers. 4) Comparing the actual measurements and the result of the compartment measuring method, the distribution of the diameter of myelinated fibers could be approximated by sampling three compartments, which area was 0.0048mm2. The total number of nerve fibers could be estimated by sampling three compartments for myelinated fibers and four compartments, one of which contained unmyelinated fibers, for unmyelinated fibers. 5) The measurement of the number of nerve fibers by the compartment measuring method and the microscopic observation indicated the locality of unmyelinated fibers. These localized fibers were speculated to be secretory fibers to hypoglossal and submandibular glands.

Necrosis of the incus by the chorda tympani nerve

Ossicular necrosis is often associated with chronic adhesive otitis media. An unusual abnormality discovered in an incus removed during tympanoplasty is reported. The long process appears to have been grooved by pressure from the chorda tympani. An alternative theory to explain the vulnerability of the long process of the incus is suggested.

Facial nerve biopsy for etiologic clarification of Bell's palsy

Electron microscopic findings of biopsy specimens of the intratemporal facial nerve from four selected patients with Bell's palsy are described, and the results of clinical examinations and surgical findings are presented. In all specimens, wallerian degeneration of various degrees was demonstrated. In one specimen, extravascular erythrocytes, and in another, lymphatic infiltrations were noted. On the basis of the present investigation and reported temporal bone histopathologic evidence, the causes of Bell's palsy are concluded to be multiple and to be vascular, inflammatory, or degenerative.

Epidermal cyst attached to the chorda tympani nerve

The incidental post-mortem finding of a small epidermal cyst in the middle ear of a 78-year-old female is presented. The epidermal cyst was attached to the chorda tympani nerve adjacent to the body of the incus, but was not associated with bony erosion or any other suggestion of enlargement or invasive growth. The pathological relationship of this lesion to previously reported "congenital cholesteatomas" of the middle ear is discussed.

Metastatic squamous cell carcinoma in the neck invading the facial canal--a case report

The results of histopathologic examination of the temporal bone of a 71-year-old woman with squamous cell carcinoma of the tonsil and ipsilateral facial palsy are presented. The right temporal bone was directly involved by metastatic spread of the primary lesion to the right upper cervical lymph nodes. Tumor cells had invaded the canal of the facial nerve, the chorda tympani nerve, and the stapedius muscle, as well as the air cells in the mastoid region. However, although tumor cells had infiltrated the facial canal to a considerable distance from the metastatic tumor mass, the facial nerve had not been infiltrated. Slight degeneration of the facial nerve, however, was observed and appeared to have been caused by compression by the tumor.

Stapedectomy. Postmortem findings

Histological studies were made of 16 temporal bones of 13 subjects who had stapedectomy operations. Photographs of the prostheses in situ are a special feature of the studies. It was found that prostheses which overlap the margins of the oval window cause incomplete closure of the air-bone gaps. Fibrous adhesions were a common consequence of trauma to the mucous membrane of the middle ear. Gelfoam implantation promotes the formation of thin oval window membranes which tend to bulge out of the oval window. Most incudes show small areas of cortical bone resorption. In at least half the cases the surgical technique of stapedectomy, as judged from these studies, was less than ideal. Surgeons who perform stapedectomy should be cognizant of the relevant surgical pathology and adopt methods which will optimize functional results and minimize complications.

Pathogenesis of Bell's palsy. Retrograde epineurial edema and postedematous fibrous compression neuropathy of the facial nerve

The pathogenesis of Bell's palsy is presented as retrograde epineurial compression edema with ischemia of the facial nerve. Although the etiology is unknown, an attractive theory is vasospasm, from any cause, along any facial nerve branch, with the chorda tympani, perhaps, the usual primary involvement. Retrograde vascular distension and edema, within the epineurium of the bony facial canal, compresses the nerve from outside its perineurial sheath. The compression force may be mild or severe, resulting in varying degrees of reversible or irreversible ischemic degeneration of myelin sheaths and axons, with varying degrees of cellular reaction to myelin breakdown. The edema may be resorbed, leaving reversible or irreversible nerve damage, or may stimulate collagen formation within the epineurium, with persisting fibrous compression (entrapment) neuropathy of the facial nerve. This concept is consistent with the varying results of Bell's palsy, and depends on the severity and duration of edema, and whether fibrosis occurs within the epineurium of the facial canal. Epineurial fibrosis also results in disturbance of metabolic exchange through the epineurial-perineurial-endoneurial tissues, and may ultimately result in obliteration of vascular drainage. Two temporal bone cases of Bell's palsy, one occurring ten years before death, with residual paralysis, and one two years before death, with clinical recovery, are added to the previously described four cases in the literature, three of early Bell's palsy, and one of remote palsy with almost complete recovery.

Macroscopic and ultrastructural findings in some diseases of the facial nerve

The authors describe the findings observed in: 10 cases of Bell's palsy, 1 case of traumatic facial paralysis, 1 case of congenital facial paralysis, and 1 case of Melkersson-Rosenthal syndrome. The chorda tympani nerve of these patients was studied, employing the electron microscope, comparing it with that of 5 patients having otosclerosis. Our ultrastructural findings appear to confirm that the chorda tympani nerve presents a similar degenerative behaviour in those diseases studied by us. The degenerative stages range from a lesser to greater degree in the following order: Bell's palsy, traumatic facial paralysis, congenital facial paralysis, Melkersson-Rosenthal syndrome.