[Applied anatomy of facial recess and posterior tympanum related to cochlear implantation]

OBJECTIVE

To investigate the related parameters of temporal bone structure in the surgery of cochlear implantation through facial recess approach so as to offer a theoretical reference for the avoidance of facial nerve injury and the accurate localization.

METHOD

In a surgical simulation experiment, twenty human temporal bones were studied. The correlation parameters were measured under surgical microscope.

RESULT

Distance between suprameatal spine and short process of incus was (12.44 +/- 0.51) mm. Width from crotch of chorda tympani nerve to stylomastoid foramen was (2.67 +/- 0.51) mm. Distance between short process of incus and crotch of chorda tympani nerve was (15.22 +/- 0.83) mm. The location of maximal width of the facial recess into short process of incus, crotch of chorda tympani nerve were (6.28 +/- 0.41) mm, (9.81 +/- 0.71) mm, respectively. The maximal width of the facial recess was (2.73 +/- 0.20) mm. The value at level of stapes and round window were (2.48 +/- 0.20 mm) and (2.24 +/- 0.18) mm, respectively. Distance between pyramidalis eminence and anterior round window was (2.22 +/- 0.21) mm. Width from stapes to underneath round window was (2.16 +/- 0.14) mm.

CONCLUSION

These parameters provide a reference value to determine the position of cochlear inserting the electrode array into the scale tympani and opening facial recess firstly to avoid potential damage to facial nerve in surgery.

Measurements of the facial recess anatomy: implications for sparing the facial nerve and chorda tympani during posterior tympanotomy

Posterior tympanotomy is commonly performed through the facial recess to facilitate cochlear implantation. A rare but serious complication of this procedure is paralysis of the facial nerve and/or the chorda tympani. These complications generally occur because of a limited understanding of the anatomy of the facial recess. To help further define this area, we used computer-aided design software to measure (1) the angle between the facial nerve and the chorda tympani nerve and (2) the distance between the takeoff point of the chorda tympani and the posteriormost prominent point of the short process of the incus in 30 cadaveric adult temporal bones. The mean angle was 23.58° (±6.84), and the mean distance was 7.78 mm (±2.68). Our most important finding was that there was a correlation between the two measurements in that the distance tended to be greater when the angle was less than the mean and vice versa. This trend approached but did not quite reach statistical significance (r = -0.248, p = 0.059).

Anatomical variations of the mandibular nerve and its branches correlated to clinical situations

AIM

The mandibular division of the trigeminal nerve is the largest of the three major divisions of the trigeminal nerve (fifth cranial nerve). In this way, many health professionals belonged to different fields are commonly evaluating patients suffering with orofacial pain and stomatognatic dysfunction associated to this structure. But, in the most cases, it is difficult to establish a correct diagnosis due to the anatomical complexity of the head and neck surfaces, especially when the focus is the trigeminal nerve. Thus, the objective of this research was to present the anatomical variations of the mandibular nerve and its branches correlated to more common clinical situations.

METHODS

For this purpose, 20 human heads were anatomically dissected, so to study their structures, an external, medial and endocranial view.

RESULTS

No significant variations related to ophthalmic and maxillary nerves were observed. Anatomical variations were observed in 20% of the total human heads dissected, all related to mandibular nerve and its branches: masseter, temporal, auriculotemporal and lingual. Variations in three to seven, on the number of the following nerves ramus, masseter and temporal were described.

CONCLUSIONS

According to the present data using the described methodology, it was possible to conclude that anatomical variations are present in many subjects and they can explain many clinical situations that involve the stomatognathic structures.

[Applied anatomy of operation through posterior tympanum approach]

OBJECTIVE

To provide the anatomic data for operation on the middle ear through the observation and measurement of related anatomic structure.

METHOD

Forty human temporal bones of 20 voluntary bone donors were dissected, relative anatomical data of operation were observed and measured under operating microscope through posterior tympanum approach entering posterior tympanum.

RESULT

The average distances from suprameatal spine to short crus of incus, pyramid segment of facial canal were 19.14 mm, 16.30 mm, respectively. The average distances from pyramid segment of facial canal to the surface of mastoid, crotch of chorda tympani nerve, posterior wall of auditory meatus were 20.84 mm, 11.28 mm, 4.40 mm, respectively. The average length of facial nerve in the horizontal segment, the perpendicular paragraph was about 11.60 mm, 15.30 mm, respectively. The average distance from pyramidal eminence to the anterior lip of round window niche, from oval window to round window niche, from incudostapedial joint to round window niche was 4.46 mm, 3.74 mm, 3.80 mm, respectively. The included angle of facial nerve in the horizontal segment and chorda tympani nerve with facial nerve in the perpendicular paragraph was 110.4 degrees, 24.8 degrees, respectively. Horizontal semicircular canal and facial nerve in the level paragraph was 17.5 degrees, long process of incus and incus buttress was 46.0 degrees.

CONCLUSION

The position of anatomic structure in middle ear was constant and the relationship including distance and angle between anatomic structures changed in limited region. The anatomical parameters provide a reference value for avoiding the injury during the operation.

[Surgical approaches and related microsurgical anatomy about suprameatal approach: new surgical approach for cochlear implantation]

OBJECTIVE

To study a new surgical approach for cochlear implantation.

METHOD

We operated on 8 cadaver heads (16 side) use Suprameatal approach for cochlear implantation, describe related anatomic mark.

RESULT

The electrode is passed through the suprameatal tunnel, the EAC groove, the space underneath the chorda tympani between the malleal and the long process of the incus, and the cochleostomy. Angle between tunnel and temporal imaginary line is 28.0 degrees +/- 1.3 degrees in adult, 29.0 degrees +/- 1.7 degrees in children, the location of inserting electrode into cochleostomy is (1.31 +/- 0.13) mm to round window in adult, (1.19 +/- 0.12) mm in child.

CONCLUSION

The SMA approach is a safe technique, maintaining a safe distance to facial nerve and chorda tympani. So We should make right decision in clinic.

Refinement of innervation accuracy following initial targeting of peripheral gustatory fibers

During development, axons of the chorda tympani nerve navigate to fungiform papillae where they penetrate the lingual epithelium, forming a neural bud. It is not known whether or not all chorda tympani axons initially innervate fungiform papillae correctly or if mistakes are made. Using a novel approach, we quantified the accuracy with which gustatory fibers successfully innervate fungiform papillae. Immediately following initial targeting (E14.5), innervation was found to be incredibly accurate: specifically, 94% of the fungiform papillae on the tongue are innervated. A mean of five papillae per tongue were uninnervated at E14.5, and the lingual tongue surface was innervated in 17 places that lack fungiform papillae. To determine if these initial errors in papillae innervation were later refined, innervation accuracy was quantified at E16.5 and E18.5. By E16.5 only two papillae per tongue remained uninnervated. Innervation to inappropriate regions was also removed, but not until later, between E16.5 and E18.5 of development. Therefore, even though gustatory fibers initially innervate fungiform papillae accurately, some errors in targeting do occur that are then refined during later embryonic periods. It is likely that trophic interactions between gustatory neurons and developing taste epithelium allow appropriate connections to be maintained and inappropriate ones to be eliminated.

Development of the anterior chordal canal

Resent advances have led to the reexamination of the intraosseous pathway of the chorda tympani a few years ago and they stated that the nerve never enters the mandibular fossa and its exit the skull base in the sphenopetrosal fissure. In our report, 58 temporal bones were investigated after maceration and formalin fixation in order to understand the development of the anterior chordal canal. Our study revealed that the chorda tympani leaves the tympanic cavity through the tympanosquamosal fissure before formation of the anterior chordal canal of Huguier. This canal is situated parallel to and in front of the musculotubal canal and formed by the processus inferior tegminis tympani and the sphenoid bone between the second and fifth years of age. Prior to the age of 2, only the exit of the bony canal exists which is gradually followed by the appearance of a groove in the growing processus inferior tegminis tympani. The borders of the groove elevate and develop to upper and lower plates which lengthen with similar plates of the sphenoid bone, completing the anterior chordal canal by the fifth postnatal year. The entrance of the canal develops above the petrotympanic fissure and similar to the canal itself, it is also completely formed in the fifth year. In case of an incomplete development the anterior chordal canal remains partially opened laterally which might allow the head of the mandibula to effect the chorda tympani mechanically causing Costen's syndrome.

Cochlear orientation and dimensions of the facial recess in cochlear implantation

OBJECTIVE

To study the dimensions of the facial recess and the spatial relationship between the facial recess and the cochlea, using CT scanning in cochlear implantees.

METHOD

In 29 cochlear implantees, preoperative CT scans of the temporal bone were compared with findings done at surgery. The dimensions of the facial recess and the relationship between the facial recess and the cochlea were both measured on a viewing station and classified on printed films by 3 blinded and independent reviewers.

RESULTS

No significant relations could be found between either intuitive classification of facial recess width or electrode array insertion feasibility and the measurements with the viewing station. The 3 reviewers had large interobserver variability. In 5 cases, neither intuitive review of the CT scans nor viewing station measurements could predict any of the problems encountered during surgery.

CONCLUSION

Our findings show that intuitive review was not reliable in classifying facial recess width. Viewing station measurements, in classifying the spatial relation between the facial recess and the cochlear basal turn, need a more detailed review in terms of the relationship with the operation direction and the orientation of the basal turn of the cochlea. Advanced imaging techniques, specifically multislice CT, might improve the diagnostic capabilities.

Clinical use of electrogustometry: strengths and limitations

Electrogustometry (EGM) has a number of strengths and a few limitations in clinical use. The strengths of EGM are: (i) the range of measurements can be kept constant; (ii) quantitative control of the intensity of the stimulation is possible; (iii) only a short period of time is required for testing; (iv) it is possible to detect even slight taste disorders for which the patient has no subjective symptoms; (v) it is useful for topognosis of lesions of taste pathways and for determining prognosis; and (vi) it is the only quantitative method for diagnosing disorders of the glosssopharyngeal nerve. The limitations of EGM are: (i) it is not useful for determining or diagnosing some of the symptoms often complained of by patients with taste disorder, namely dissociated taste disorder, heterogeusia and spontaneous dysgeusia; and (ii) it is not useful for following the progress of taste disorder. The many strengths and few limitations of EGM make it the first choice among taste examinations. This paper describes the clinical use of EGM as well as discussing other taste examinations used in our taste clinic and, in particular, the advantages and disadvantages of filter paper disk testing with taste solutions.

Structure of the middle ear and auditory tube in the house musk shrew, Suncus murinus

Anatomical features of the middle ear and auditory tube (AT) in the house musk shrew, Suncus murinus, were examined by dissection and light microscopy. The tensor veli palatini (TVP) and tensor tympani (TT) have no connections with the wall or cartilage of the AT although they are connected by the intermediate tendon. None of the levator veli palatini (LVP) muscle bundles are attached to the AT. The salpingopharyngeus (SA) alone has its origin on the caudal edge of the tubal cartilage. The origin extends to the pharyngeal two thirds of the cartilage. The SA originates perpendicular to the AT and runs caudomedialward. Some SA muscle bundles intermingle with those of the palatopharyngeus to end on the dorsal wall of the pharynx. The observations provide no evidence that the TVP, LVP and TT have any role in AT function. The only muscle affecting the AT function in S. murinus is the SA, and it would be the AT dilator.

Topographical relationships among the facial nerve, chorda tympani nerve and round window with special reference to the approach route for cochlear implant surgery

The topographical relationships among the facial nerve (FN), chorda tympani nerve (CT), and round window (RW) in 22 temporal bone specimens were analyzed morphometrically in order to examine which route is widest through the facial recess between the FN and CT during cochlear implant surgery and in order to establish some criteria to assist in the evaluation of the best surgical approach. Two lines, i.e., the FN-RW line and CT-RW line, were speculated as limitations of a visual field for this surgery. According to the relative position of these structures, including the posterior wall of the external auditory canal (EAC) and an inserted pin-gage that indicates the hypothetical widest approach route, the relationships were classified into five types. Most frequently, the widest approach route through the facial recess did not point directly at the RW, but at the basal turn at the promontory. Moreover, this approach route crossed the FN-RW line in a posterior to anterior direction and the CT-RW line frequently crossed the posterior wall of the EAC. The latter seemed to provide a critical landmark for avoiding damage to the CT during cochlear implant surgery. Therefore, we recommend inserting the electrode into the basal turn.

Cross-sectional anatomy of the facial nerve

The length and complexity of the anatomical course of the facial nerve explains the difficulty of its accurate morphologic evaluation. CT and MR appear to be complementary techniques to precisely depict the nerve from its pontine origin to the parotid gland. Anatomical variations exist in length or thickness of all intrapetrous segments or as frequent dehiscences which can lead to false positive results or at the opposite falsely negative diagnoses. Close relations with the antero-inferior cerebellar artery in the intracisternal and intracanalicular segments must be known. Gadolinium enhancement is usual in the fallopian canal with variable intensity and thickness and should be differentiated from pathological enhancement. Finally the intrapetrous course of the chorda tympani can be precisely displayed on CT in the intra-osseous canal and in the middle ear near the ossicles.

[Surgical anatomy of the facial nerve and chorda tympani with special reference to cochlear implantation]

The surgical anatomy of the facial nerve (FN), chorda tympani nerve (CT) and round window (RW) in 26 Japanese temporal bone specimens was analyzed. The relationships were classified according to the relative position of these structures and the posterior wall of the external auditory canal (EAC). Most frequently, the widest approach route through the facial recess did not point directly at the RW, but rather at the basal turn. Moreover, the approach route crossed the FN-RW line in a posterior to anterior direction (76.9%) and the CT-RW line frequently crossed the posterior wall of the EAC (92.3%). The latter seemed to provide a critical landmark for avoiding damage to the CT during cochlear implant surgery. Therefore, we recommend inserting the electrode into the basal turn at the promontory. Several other anatomical indices were measured and we extracted the index which was related to the maximum approach amplitude and direction. Preoperative diagnosis may be possible using these indices.

High-resolution computed tomography of the canals of the temporal bone: anatomic correlations

The aim of this study was to define precisely the imaging of the canals of the temporal bone by means of high-resolution computed tomography (HR CT). Based on 24 temporal bones removed from embalmed cadavers and investigated with HR CT, several canals were studied: the canal of the chorda tympani (CdT), the canal of the auricular branch of the vagus nerve (ABV), the canal of the tympanic nerve, the canal of the carotico-tympanic nerve and that of the lesser petrosal nerve. Anatomic correlations for six temporal bones were made to confirm the validity of our radiologic hypotheses. In CT, in axial sections OM 0 degree, the posterior canal of the CdT was visualized in 71% of cases, the ABV canal in 4%, the inferior tympanic canal in 12.5%, the carotico-tympanic canal in no cases and the canal of the lesser petrosal nerve in 50% (and in 75% with an incidence of OM + 10 degrees). In coronal incidence, the posterior canal of the CdT was seen in 20% of cases, the ABV canal in 25%, the inferior tympanic canal in 85%, the caroticotympanic canal in 65% and that of the lesser petrosal nerve in 15%. The six anatomic comparisons confirmed the radiologic hypotheses in every case. These different structures are easy to identify in HR CT and are important to define so that any lesion (tumoral or vascular) developing in their vicinity may not be overlooked.

Facial nerve parasympathetic preganglionic afferents to the accessory otic ganglia by way of the chorda tympani nerve in the cat

The distribution of accessory otic ganglia and connections between the ganglia and the chorda tympani nerve were investigated in the cat in order to determine the parasympathetic preganglionic facial nerve afferents to the otic ganglia using whole mount acetylthiocholinesterase (WATChE) histochemistry. The otic ganglia consist of a single main prominent ganglion and many small accessory ganglia lying on a plexus around the origins of the branches of the mandibular nerve and near the junction of the chorda tympani nerve and lingual nerve. In cell analysis of Nissl-stained preparations, the neurons composing the accessory otic ganglia were morphologically similar to the main otic ganglion neurons. Connecting branches from the chorda tympani nerve to the peripherally located accessory otic ganglia were found and they were not stained by WATChE histochemistry. WATChE-positive connecting branches from the ganglia to the inferior alveolar, lingual, and mylohyoid nerves were also found in the same preparations. The WATChE histochemistry on various autonomic nervous tissues revealed that autonomic postganglionic nerve fibers are selectively stained darkly and that preganglionic fibers remain unstained. Therefore, it is considered that the WATChE-negative connections from the chorda tympani nerve consist chiefly of autonomic preganglionic fibers, whereas the WATChE-positive connections to the branches of the mandibular nerve are mainly postganglionic fibers. This suggests that some of the facial nerve parasympathetic preganglionic fibers in the chorda tympani nerve are mediated in the accessory otic ganglia and then join the branches of the mandibular nerve to supply the target mandibular tissues.

Convergence of afferent inputs from the chorda tympani, lingual-tonsillar and pharyngeal branches of the glossopharyngeal nerve, and superior laryngeal nerve on the neurons in the insular cortex in rats

The responses of single neurons in the insular cortex to electrical stimulation of the chorda tympani (CT), lingual-tonsillar branch of the glossopharyngeal (LT-IXth) nerve, pharyngeal branch of the glossopharyngeal (PH-IXth) nerve, and superior laryngeal (SL) nerve were recorded in anaesthetized and paralyzed rats. Ninety-four neurons responding to stimulation of at least one of the four nerves were identified from the insular cortex. Most of the neurons were located in the posterior portion of the insular cortex; the mean location was 0.8 mm anterior to the anterior edge of the joining of the anterior commissure (AC) and was 1.4 mm dorsal to the rhinal fissure (RF). Of the 94 neurons, 84 (89%) received convergent inputs from two or more nerves, and the remaining 10 (11%) received inputs from one nerve. The neurons responding to the CT stimulation were distributed more anteriorly than those responding to other three nerves in the anterior-posterior dimension. Our results indicate that the neurons recorded mainly from the posterior portion of the insular cortex receive convergent inputs from the oropharyngolaryngeal regions.

[Morphometric study of chorda tympani-derived fibers along their course in the lingual nerve]

The topographical organization of chorda tympani-derived fibers (Ch-fibers) was investigated macroscopically and histologically along their entire course through the lingual nerve in 81 adult Japanese cadavers (113 sides), in order to obtain basic data to explain the taste disturbance occurring after oral anesthesia. Ch-fibers frequently (approx. 80%) merged and intermingled with nerve bundles composed of fibers of the lingual nerve proper (L-fibers) above the level of the mandibular foramen (intermingled type). However, on 23 sides (20.4%) the Ch-fibers could be separated under a stereomicroscope from the L-fiber bundles during their course behind the oral cavity (separated type). Moreover, on 12 of the 23 sides, the Ch-fibers were clearly separated from the L-fibers, since the Ch-fibers formed an independent nerve bundle attached to the surface of the L-fiber bundles throughout almost their entire course to the tongue. Irrespective of whether they were intermingled or separated, however, the Ch-fibers traveled downward, maintaining their superficial and posterolateral topographical organization in the lingual nerve. In 8 of the 12 clearly separated cases, the perimeter of the myelinated fibers was analyzed at three levels: the hard palate, the mandibular foramen and immediately above the angle of the mandible. At each level, the perimeter spectrum of Ch-fibers was significantly smaller (mean: 16.6 +/- 5.4 microns, e.q. at the level of the mandibular foramen) than that of the L-fibers (mean: 20.2 +/- 6.2 microns, at the same level) (p < 0.01). Moreover, the lingual nerve consistently had 2-3 buccal branches supplying the lining of the oral cavity posterior to the internal oblique line of the mandibular ramus. These buccal branches did not contain Ch-fibers, but were composed of only L-fibers, possibly including pain fibers. These observations suggest that physicians performing nerve block to and around the mandibular foramen tend to regard the inferior alveolar nerve and the lingual nerve as targets of the block, irrespective of whether or not this is intended, since the buccal branch of the lingual nerve should also be anesthetized in such cases. Moreover, local anesthetics seem to have a rapid effect on Ch-fibers, because of their superficial position in the lingual nerve and their smaller diameter than L-fibers. Consequently, Ch-fibers along the lingual nerve seem to be easily damaged by local anesthesia of the oral region. Greater care should therefore be exercised to avoid producing a taste disturbance when performing oral anesthesia in clinical practice.

Postnatal developmental changes in facial nerve morphology. Computer-aided 3-D reconstruction and measurement

Accurate measurements of the lengths and angles of the facial nerve were obtained in eight normal human temporal bones of varying ages from 7 days to 76 years. Measurements were made on serial histological sections, using computer-aided three-dimensional (3-D) reconstruction. The most noteworthy of the findings demonstrated that both the mastoid portion of the facial nerve and the segment of the facial nerve between the second genu and the divergence of the chorda tympani nerve lengthened with age. The mastoid segment lengthened more significantly than the latter, indicating the facial canal grows more than the facial nerve in its mastoid portion. This difference in growth rates results in the site of the chorda tympani nerve divergence shifting with age relative to the stylomastoid foramen.

Gustatory responsiveness of chorda tympani fibers in the cynomolgus monkey

Responses of chorda tympani (CT) fibers of cynomolgus monkeys to various gustatory stimuli were analysed to obtain quantitative data on their response properties and to reveal the coding of gustatory information. Based on responses of 66 fibers to the four basic gustatory stimuli, they were classified into 16 sucrose-best, 28 NaCl-best, 11 HCl-best and 11 QHCl (quinine hydrochloride)-best fibers. Sucrose-best fibers were narrowly tuned to sucrose, while HCl-best fibers were broadly tuned to the four stimuli. The average breadth of response measure. H for all the 66 fibers was 0.375. The average value of H for sucrose-, NaCl-, HCl- and QHCl-best fibers was 0.276, 0.348, 0.634 and 0.384, respectively. Hierarchical cluster analysis performed on responses of 25 fibers to 14 gustatory stimuli revealed that all the stimuli except for 0.3 M Na-saccharin were grouped into four clusters; sucrose and 0.01 M Na-saccharin, NaCl and LiCl, acids, and non-sodium and -lithium salts, and QHCl. It is concluded that in the monkey CT each of the four classes of fibers predominantly contributes to mediate gustatory information for sweet, salty, sour and bitter stimuli.

Facial nerve near the external auditory meatus in man: computer reconstruction study--preliminary report

The anatomy of the facial nerve relative to its intratemporal and extratemporal courses varies over time with developmental changes. Otologic and parotid surgery in infants and children demands detailed knowledge of the precise anatomy of the facial nerve with respect to the tympanic ring and external auditory canal. The authors analyzed this area using our three-dimensional (3-D) computer-aided reconstruction and measurement method studying the spatial relations of the facial nerve to the tympanic ring and stylomastoid foramen. Temporal bones from five normal individuals aged 36 gestational weeks, 3 months, 8 months, 4 years, and 17 years were retrieved from the temporal bone collection stored at the Elizabeth McCullough Knowles Otopathology Laboratory in Pittsburgh. Three-dimensional reconstruction of the facial nerve comparing the developmental anatomy across the various age groups provides the surgeon with the technical information necessary to address problems in this area.

Anatomic variations of the chorda tympani canal

The anatomic variations of the facial recess are of interest in certain otosurgical procedures. The medial border of the recess is the mastoid portion of the facial nerve canal, and the lateral border is the bony canal of the chorda tympani. These two structures were investigated in 64 polyester casts of temporal bone specimens. The point of exit of the chorda tympani canal from the facial canal was assessed together with the angle, formed between these two nerve channels. As a further way of describing the spaciousness at the facial recess, the distance between the sulcus of the stapedius muscle and the chorda tympani canal was evaluated.

Computer-aided 3-D temporal bone anatomy for cochlear implant surgery

To define anatomical relationships important in cochlear implantation, computer-aided three-dimensional reconstruction and measurement of middle and inner ear structures in six normal temporal bones were performed. Our findings were as follows: 1. When viewed from the posterior hypotympanotomy (facial recess) approach, the inferior 10% to 30% of the round window (RW) membrane was visible in only half the cases. 2. The most inferior portion of the basal turn of the scala tympani was not only inferior but also slightly anteriorly behind the RW membrane in more than half the cases. 3. The shortest distances from the aperture of the RW niche and from the margin of the RW to the stapes head were 2.38 +/- 0.33 and 2.15 +/- 0.22 mm, respectively. 4. The distance between the RW and the most inferior portion of the basal turn scala tympani was 5.15 +/- 0.34 mm. 5. The direction of the electrode advancement lay at a sharp angle to the inferior part of the RW (mean 31.9 +/- 3.6 degrees). 6. The direction from the RW to the most inferior portion of the basal turn scala tympani lay 16.0 +/- 5.3 degrees anteroinferior to the direction of the advancement of the electrode to the RW. 7. The distance between the margin of the RW and the basilar membrane of the cochlea was 0.58 +/- 0.10 mm at the superior aspect of the RW, and was 1.23 +/- 0.12 mm at the lateral aspect of the RW. 8. Dissecting away less than 1 mm (mean 0.7 +/- 0.27 mm) of the RW margin inferiorly or inferolaterally was enough to permit straight insertion of the electrode in most cases.

Three-dimensional reconstruction of the temporal bone

Study of the complex anatomy and pathology of the temporal bone has traditionally used microscopy which permits analysis in only two dimensions. Recent advances in bioimaging technology have permitted visualization and reconstruction of computed tomography images in three dimensions. We have developed a technique that applies this technology in the imaging and reconstruction of human temporal bones. Data taken from serial histologic sections of the temporal bone are entered into a computer. The sections are edited and, through the use of specially developed software, a realistic three-dimensional reconstruction is produced. The reconstructed image can be rotated along any of three axes, and structures within the temporal bone can be isolated for more detailed analysis. Applications for the study of pathologic conditions of the temporal bone will be discussed.

[Anatomical study on the facial nerve innervating the floor of the mouth in chondrichthyes. Homology of the chorda tympani]

This paper deals with the results of the investigation of the facial nerves of chondrichthyes in order to consider the phylogenetic origin of the Chorda tympani in human. Six species of elasmobranchs (Chlamydoselachus anguineus, Cephaloscyllium umbratile, Squalus acanthias, Dasyatis akajei, Raja kwangtungensis and Mobura diabolus) were dissected under a stereoscopic microscope for this purpose, and the following results were obtained. Ramus palatinus and R. pre-spiracularis were observed as pre-trematic branches, while R. mandibularis externus, R. mandibularis internus and R. hyoideus originating from R. hyomandibularis were observed as post-trematicus of the facial proper in chondrichtyes. The rami intermedii indicated by Tanaka and Nakao (1979) were observed only in Dasyatis akajei. The R. hyomandibularis of Squalus acanthias had cutaneous branches, and the same branches were described in Chimaera by Takahashi and Kobayashi (1988). R. pre-spiracularis and R. mandibularis internus supply the floor of mouth in Squalus acanthias. As for the other chondrichthyes, R. mandibularis internus was only the one that could be found at the floor of mouth cavity under a stereoscopic microscope. From the observations described above and from previous studies, it may be concluded that the problem of whether the Chorda tympani is homologous with whether the pre- or post-trematicus of branchial nerves seems to depend on the animal species.

The fascicular structure of the lingual nerve and the chorda tympani: an anatomic study

Damage of the lingual nerve is one of the most common problems in oral surgery, especially during removal of the third molar. After microsurgery of the lingual nerve, there is a lack of regeneration of the gustatory fibers in comparison with the sensory fibers. The histologic investigation of ten human lingual nerve preparations showed that the chorda tympani fibers distribute widely in the fascicles of the lingual nerve. Therefore, after microsurgical reconstruction of the lingual nerve in the third molar region, the chance of the gustatory fibers meeting and regenerating is very low.

Early development of the facial nerve in the chick embryo with special reference to the development of the chorda tympani

The development of the facial nerve from Hamburger and Hamilton stage 17 to stage 28 is described in chick embryos by means of a new immunochemical nerve staining method that uses an antineurofilament protein (NFP) antibody. A postspiracular branch and an unknown transient posterior branch beneath the ostocyst were observed at stage 17. At stage 19, the primordia of the r. palatinus were observed. A prespiracular branch appeared at stage 21, and with the postspiracular nerve, it made a loop encircling the spiracle (spiracular loop). The first primordium of the ramus (r) hyoideus and transient rami (rr) dorsales appeared around stage 23. At stage 25, the chorda tympani was first observed to arise from the ventral end of the spiracular loop. At stage 26, a communicating branch, connexus cum nervo glossopharyngeo, was found along with the vena (v) capitis lateralis. The rr. dorsales seemed to represent the r. supratemporalis in lower animals. The communicating branches around the v. capitis lateralis seemed to correspond to the cutaneous nerve communications between the branchial nerves frequently encountered in Amphibia. It was found that the chorda tympani becomes a prespiracular nerve for the most part in the chick by the reduction of the postspiracular component of the spiracular loop. Thus, the nerve differs markedly from that in other animals, which is postspiracular. This difference explains the different passage of this nerve in the chick as compared with other amniotes.

Surgical dimensions of the facial recess in adults and children

The facial recess approach permits surgical access to the round window area. This route is used in patients who are undergoing cochlear implantation. To evaluate the feasibility of this procedure in children as compared with adults, serial sections of temporal bones were used to measure the surgical dimensions of the facial recess. No statistically significant differences in the dimensions of the facial recess or the extended facial recess approaches were found between children and adults. The relationship of the facial and chorda tympani nerves to the annular plane exhibited no change with postnatal growth. These structures translate posteriorly and laterally toward the annular plane as they descend within the temporal bone. Therefore, the facial recess approach represents no greater hazard in a child than in an adult.

[Characteristics of the topographic anatomical correlations of the chorda tympani, auriculotemporal nerve and anterior tympanic artery with the temporomandibular joint]

The aim of the investigation was to reveal the possibility to draw into the pathological process known as the "Costen syndrome" the formations mentioned in the title. The investigation performed by means of the craniometry method on 150 mature person skulls, that are rather evenly distributed according to their sex, age and form, and simultaneous investigation of 70 heads of corpses of persons of both sex, gave the data denying the possibility of mechanical damage of the chorda tympani, when the mandibular head is shifted backward or medially. This phenomenon can be observed at a loss of teeth and lowered bite. When the mandibular head is shifted backward, it does not involve the chorda tympani, since the nerve gets out of the osseous canal more medially to the spine of the sphenoid bone. The medial shift of the mandibular head also cannot damage the chorda tympani, since the nerve is separated from the joint by a marked osseous protrusion. At the same time the data are obtained on variations in topography of the chorda tympani at various form of the intratemporal fossa. It has been stated that when a pathological process occurs around the temporomandibular joint, the auriculotemporal nerve and the anterior tympanic artery can be involved into this process. This can produce appearance of the "Costen syndrome" components.

Chorda tympani innervation of anterior mandibular taste buds in the chicken (Gallus gallus domesticus)

While the mammalian chorda tympani innervates taste buds on the anterior two-thirds of the tongue, the chorda tympani of chickens does not enter the tongue, but rather is reported to supply the oral epithelium of the lower beak subjacent to the tongue. This study in the chicken investigated whether the integrity of taste buds in the lower beak is normally dependent upon innervation by the chorda tympani. Following unilateral ligation and removal of a large section of the chorda tympani, animals were sacrificed at 11, 14, and 21 days postoperatively. Oral tissue between the lingual frenulum and beak tip was serially examined, and the presence of each bud was recorded, noting the point at which the bud opened into the oral cavity. No buds were observed on the operated side in any of the cases, while the average bud count on the unoperated side was 33 +/- 10 (SD). On the unoperated side, taste buds were generally associated with anterior mandibular salivary gland ducts that reached surface epithelium and opened into the oral cavity. On the operated side, the cellular organization adjacent to gland ducts and in duct-free epithelium appeared as in control (i.e., bud-free) epithelium. The number of salivary gland duct openings into the oral cavity was equivalent on the operated and control sides. It is concluded that the chorda tympani of chickens innervates taste buds in the anterior lower beak epithelium and that it functions to maintain the structural integrity of these buds.

The fibre spectrum of the chorda nerve in the chicken (Gallus gallus var. domesticus)

Using transmission electron microscopy, the numbers and diameters of all nerve fibres were studied in the chorda tympani nerve of the domestic fowl. The mean diameter of the whole nerve was 64.6 micron and contained 203-407 (mean 302) myelinated and 205-345 (mean 265.6) unmyelinated fibres. Of the myelinated fibres (including sheath) 95% were in the range 0.5-3 micron in diameter and 94% of the unmyelinated fibres ranged from 0.2 to 0.9 micron in diameter. After section of the facial nerve within the facial canal, there was a marked reduction in the number of myelinated fibres present in the chorda tympani nerve (range 12-160, mean 103) but a less marked reduction in the unmyelinated fibres (range 94-362, mean 223). The loss of myelinated fibres was not confined to any one fibre size whereas the loss of unmyelinated fibres was mainly in the smaller fibres (range 0.1-0.5 micron). Since facial nerve section results in degeneration of efferent fibres it would seem that a large proportion of the afferent fibres are unmyelinated.

Central distribution of afferent fibers in the intermediate nerve: a transganglionic HRP study in the cat

Afferent fibers in the two components of the intermediate nerve of the cat, i.e. the chorda tympani (CTN) and greater petrosal (GPN) nerves, were traced into the lower brainstem transganglionically after applying horseradish peroxidase (HRP) to the central cut end of the CTN or GPN. CTN fibers ended in the trigeminal (principal sensory and spinal trigeminal nuclei) and solitary (medial, interstitial and dorsal solitary nuclei) nuclei, whereas GPN fibers ended only in the solitary nucleus.

Anatomy of the gustatory system in the hamster: central projections of the chorda tympani and the lingual nerve

The sensory modalities of taste and touch, for the anterior tongue, are relegated to separate cranial nerves. The lingual branch of the trigeminal nerve mediates touch: the chorda tympani branch of the facial nerve mediates taste. The chorda tympani also contains efferent axons which originate in the superior salivatory nucleus. The central projections of these two nerves have been visualized in the hamster by anterograde labelling with horseradish peroxidase (HRP). Afferent fibers of the chorda tympani distribute to all rostral-caudal levels of the solitary nucleus. They synapse heavily in the dorsal half of the nucleus at its rostral extreme; synaptic endings are sparser and located laterally in caudal regions. These taste afferents travel caudally in the solitary tract and reach different levels by a series of collateral branches which extend medially in the the solitary nucleus, where they exhibit preterminal and terminal swellings. Taste afferent axons range in diameter from 0.2 micrometer to 1.5 micrometers. The thickest axons project exclusively to the rostral and intermediate subdivisions of the solitary nucleus; the find ones may distribute predominantly to the caudal subdivision. Afferent fibers of the lingual nerve terminate heavily in the dorsal one-third of the spinal nucleus of the trigeminal nerve and also as a dense patch in the lateral solitary nucleus at the midpoint between its rostral and caudal poles. This latter projection overlaps that of the chorda tympani. Thus the two sensory nerves which subserve taste and touch from coincident peripheral fields on the tongue converge centrally on the intermediate subdivision of the solitary nucleus. Efferent neurons of the superior salivatory nucleus were labelled retrogradely following application of HRP to the chorda tympani. These cells are located ipsilaterally in the medullary reticular formation ventral to the rostral pole of the solitary nucleus; their dendrites are oriented dorsoventrally. The efferent axons course dorsally, form a genu lateral to the facial somatomotor genu, and course ventrolaterally through the spinal nucleus of the trigeminal nerve to exit the brain ventral to the entering facial afferents.

Central distribution of efferent components in the greater petrosal nerve of the cat

Central distribution of efferent components in the greater petrosal nerve (GPN) of the cat was examined by applying HRP to the central cut end of the GPN in the pterygopalatine fossa. Efferent neurons of the GPN are located in the lateral reticular formation from the levels of the exiting root of the facial nerve to the most caudal level of the facial nucleus. The axons of these neurons follow bent courses in the tegmental region of the lower brainstem to form a small genu medially to the genu of the axons of the facial motoneurons.

The motor nuclei and primary projections of the facial nerve in the monitor lizard Varanus exanthematicus

The location of the motor nuclei and the projection of the primary afferent fibers of the facial nerve of the reptile Varanus exanthematicus were studied by means of the HRP method and the anterograde degeneration technique. The motor nuclei are located ventrolaterally in the rhombencephalon and are constituted by a medial cell group consisting of large, polygonal cells and a lateral cell group consisting of medium-sized, spindle-shaped, and multipolar cells. From HRP applications to the various branches of the facial nerve it could be concluded that the medial cell group represents the branchiomotor nucleus and the lateral cell group the superior salivatory nucleus. The efferent axons from the motor nuclei course dorsomedially toward the fourth ventricle, where they form a genu, and exit from the brainstem in the ventral fiber bundle of the facial nerve. The primary afferent fibers enter the brainstem in the dorsal bundle of the facial nerve. This bundle courses medially, enters the solitary tract, and diverges into rostrally and caudally running fibers. Part of the caudally directed fibers leave the solitary tract and course laterally toward the descending trigeminal tract. Some fibers enter the nucleus of this tract. There was no noticeable terminal degeneration in the solitary tract or in the descending trigeminal tract or its nucleus.

Motor fibre organization in the intratemporal portion of cat and rat facial nerve studied with the horseradish peroxidase technique

The intra-axonal transport of horseradish peroxidase (HRP) was used to label fibres in the intratemporal facial nerve portion (ITFN) in the rat and cat. HRP was applied to the proximal cut end of facial nerve branches innervating different facial muscles. Following appropriate survival periods, the animals were fixed by perfusion. The ITFN was processed histochemically for demonstration of intra-axonal HRP, using tetramethylbenzidine as substrate. The distribution of labelled fibres was analyzed in serial longitudinal sections and in photographic transverse-like reconstructions from three selected levels. HRP-labelled fibres from all examined motor branches were found to be diffusely distributed almost throughout the entire ITFN, leaving only a narrow zone free of label. By applying HRP to the chorda tympani nerve, it was shown that this zoe harbours fibres of this nerve. The findings support the conclusion that the motor fibres to the facial muscles are diffusely organized in the ITFN.

Central distribution of afferent and efferent components of the chorda tympani in the cat as revealed by the horseradish peroxidase method

Central distribution of afferent and efferent components of the chorda tympani (CT) in the cat was examined by using the anterograde and retrograde tracing techniques of horseradish peroxidase (HRP). HRP was applied to the CT in the tympanic cavity. HRP-labeled CT fibers were traced to the brain stem along the ventral surface of the vestibular nerve. The afferent CT fibers were divided into ascending and descending components. The rostrally directed ascending fibers ended within and around the dorsomedial portions of the principal sensory trigeminal nucleus. The descending fibers entered the solitary tract to run caudally as far as the levels slightly rostral to the obex, giving terminals to the solitary nucleus. A cluster of HRP-labeled neurons were seen ipsilaterally in the lateral reticular formation medial to the spinal trigeminal nucleus; it was observed from the caudalmost levels of the exiting root of the facial nerve to the caudal levels of the facial nucleus. HRP-labeled axons arising from the HRP-labeled neurons firstly ran dorsomedially and then medially under the genu of the facial nerve to form a small genu at the region medial to the genu of the facial nerve. Subsequently the labeled axons ran laterally and ventrolaterally to join other CT fibers at the dorsomedial aspect of the spinal trigeminal tract.

Tympanic neurectomy and chorda tympani section

Tympanic neurectomy with or without chorda tympani section is a surgical procedure which can play a role in the treatment of diseases for which more extensive procedures have in the past been performed. The surgical approach is familiar to most ear, nose and throat surgeons, and the operation, which can be satisfactorily performed under local anaesthesia, is associated with very little, if any, discomfort to the patient.

Central origins of cranial nerve parasympathetic neurons in the rat

The location of central neurons that contribute preganglionic parasympathetic axons to cranial nerves VII, IX, and X in rats has been identified using horseradish peroxidase (HRP) tracing methods. Collectively, these neurons form an uninterrupted dorsal column that extends over the entire length of the medulla. The cephalic end of this column turns ventrally with neurons scattered in the parvicellular reticular formation between the rostral pole of the nucleus of the solitary tract (NST) and the facial motor nucleus. Applying HRP crystals to the cut cervical vagus labels neurons in the classically defined dorsal motor nucleus. Rostrally, this distribution continues along the medial edge of NST, ending just caudal to neurons exiting in the lingual-tonsilar branch of IX. At the rostral pole of the NST and ventral to it, neurons occur that serve the lingual-tonsilar and tympanic branches of IX, as well as the chorda tympani and greater superficial petrosal (GSP) branches of VII. Central neurons of the chorda tympani and tympanic nerves spread ventrally from NST into a sparse but largely coextensive distribution in the reticular formation lateral to the ascending radiations of the facial motor nucleus. Immediately ventral to this distribution, a dense accumulation of GSP efferent neurons appears rostrolateral to the facial motor nucleus. Although they vary considerably in number and packing density, the neurons of the dorsal efferent column and those extending from it into the reticular formation have similar morphological characteristics. The somata are medium-sized, fusiform, or multipolar, but with usually no more than five or six major processes.

The nucleus of the solitary tract in the monkey: projections to the thalamus and brain stem nuclei

The projections of the nucleus of the solitary tract (NST) were studied by autoradiographic anterograde fiber-tracing and horseradish peroxidase (HRP) retrograde cell-labeling. Tritiated proline and leucine were deposited in electrophysiologically identified regions of NST. Injections of NST at levels caudal to where the vagus enters the nucleus, from which responses were evoked by stimulation of cranial nerves IX and X, revealed topographically organized bilateral projections to, most prominently, the ventrolateral medullary reticular formation which contains neurons of the ambiguus complex, and to the lateral and medial parabrachial nuclei, including a small portion of the medially adjacent central gray substance. Labeled fibers in the ventrolateral reticular formation were present from the nucleus retroambigualis rostralward to the retrofacial nucleus, with the densest concentration located over the nucleus ambiguus proper. The parabrachial projection was confirmed using HRP and shown to originate from cells in the medial subdivision of NST. Due to the problem of fibers en passant, it was not possible to interpret conclusively the cell-labeling seen around the solitary tract after HRP injections made in the region of the nucleus ambiguus. Labeled fibers were also traced from caudal NST to the dorsal motor nucleus of the vagus, but their origin could not be determined with certainty. Other labeled axons, traced to circumscribed parts of the inferior olivary complex and via the contralateral medial lemniscus to VPL of the thalamus, were shown in HRP experiments to originate from the dorsal column nuclei rather than NST. No labeled fibers were traced into the spinal cord, nor were any cells labeled in NST after large HRP deposits in upper cervical segments. Isotope deposits at levels of NST rostral to the entrance of the vagus, from which responses were evoked by rapid stimulation of the tongue, revealed an ipsilateral projection which ascends as a component of the central tegmental tract to the parvicellular part of the ventral posteromedial thalamic nucleus (VPMpc). After small HRP deposits in VPMpc, labeled cells in NST were restricted to the rostral part of the lateral subdivision. No labeled axons were traced from rostral NST to the ambiguus complex or parabrachial area. Injections of 3H-amino acids at intermediate levels of NST resulted in fiber-labeling in VPMpc, the parabrachial area, and the ambiguus complex.

Quantitative and histomorphological studies on the geniculate ganglion of the facial nerve in man

The human geniculate ganglion was studied histologically and quantitatively. It appeared pyramidal in shape. The mean diameter of the side of the triangle constituting its base was 1,050 micrometer and its mean height 1,800 micrometer; the volume of the ganglion was 26 X 10(7) micrometer 3. The ganglionic cells were arranged in clusters with longitudinally extending bundles of nerve fibres in between. At the apex of the ganglion compact neurons were delineated from those in the rest of the ganglion by a bundle of nerve fibres. Moreover, scattered solitary nerve cells were met with between fibres of the greater petrosal and the chorda tympani nerves. The mean neuronal population was 1,070, the mean cell volume 11,913 micrometer 3, the cell territory 242,990 micrometer 3 and the volume of the intercellular space 231,077 micrometer 3. Extraganglionic vessels approximated the ganglion perpendicular to its long axis, while further intraganglionic vessels extended in a direction parallel to the long axis of the ganglion and vertical terminal ramifications formed dense vascular channels around the capsule of the nerve cells. The significance of that pattern of blood supply was discussed.

Surgical anatomy of the submandibular triangle

The topographic anatomy of the submandibular triangle and its contents are described in terms of four surgical planes, with considerations of the anatomic complications during surgery. Attention is called to the importance of identifying and sparing five nerves in this triangle--the mandibular and cervical branches of the facial nerve, the hypoglossal nerve, the lingual nerve, and the chorda tympani.

Surgical procedure for exposure of the chorda tympani in dogs: a ventral approach

An experimental neuroanatomic investigation of the innervation of the dog's tongue by the method of retrograde axonal transport of horseradish peroxidase required that chorda tympani neurectomy be performed in neonatal pups. Surgical exposure and transection of the chorda tympani proximal to its union with the lingual branch of the mandibular nerve in the past has been accomplished by radical lateral approach which is suited only for acute experimentation. This report describes a ventral surgical exposure of the extracranial portion of the chorda tympani in the dog. This surgical procedure permits long-term survival and is considered especially useful for the chronic neuroanatomic and neurophysiologic investigations on the role of the chorda tympany in taste, salivation and lingual vasodilation in the dog.

Tympanic neurectomy and chorda tympanectomy for the control of drooling

Seventeen patients suffered from drooling that either occurred as a sequelae of extensive head and neck cancer resections or was due to neurological disorders. In these patients, a tympanic neurectomy and/or chorda tympanectomy was performed in an attempt to eliminate the drooling. The conditions in five of 12 (41%) patients with head and neck cancer were improved following such surgery. Two of four children with cerebral palsy initially had a good result. However, the long-term follow-up of the patients demonstrated that the drooling recurred. An additional patient suffering from bulbar weakness and drooling owing to a cerevrobascular accident had less problems with salivary secretions. The results were relatively disappointing; there are several possible explanations for this.

[Applied anatomy of the facial nerve. I. Nuclei, supranuclear connectiions and peripheral nerve (author's transl)]

The clinically important anatomy and morphology of the facial nerve is reviewed. The nuclei, and the supranuclear and internuclear connections are described, and the facial canal, its dehiscences and its relation with the nerve are discussed in detail.

Auditory systems of Heteromyidae: functional morphology and evolution of the middle ear

Middle ears (515) from 26 species of the rodent family Heteromyidae - genera Dipodomys, Microdipodops, Perognathus, and Liomys - were studied both grossly and histologically, for qualitative and quantitative comparisons. Middle ear modifications characteristic of each genus are qualitatively described. Quantitative comparisons are made among the 26 species in the study. Some correlations between middle ear size and other measurements are discussed. The middle ear is an acoustical transformer that for best efficiency must match the impedance of the cochlea to the impedance of the air in the external auditory meatus. It accomplishes this by a pressure increase and a velocity decrease through the combined effects of the lever and areal ratios; however, because the important consideration is a matching of two impedances rather than an absolute pressure increase, the pressure transformer ratio is a less informative measure of the middle ear's efficiency than is the impedance transform ratio. The impedance transformer mechanism is explained (from a morphological point of view), and equations are presented. Dipodomys, Microdipodops, and Perognathus have a theoretical transmission (at the resonant frequency) of 94-100% of the incident acoustical energy; Liomys, 78-80%. The areal ratio of stapes footplate to 2/3 tympanic membrane is remarkably constant among the species, varying only from 0.04 to 0.07: in Dipodomys and Microdipodops this small ratio is due to the very large tympanic membrane; in Perognathus and Liomys it is due to the extremely small stapes footplate. The lever ratio of incus to malleus varies from 0.28 to 0.33 in Dipodpmys and Microdipodops, from 0.37 to 0.46 in Perognathus, and from 0.55 to 0.60 in Liomys. In addition, the middle ear volumes and the morphology of tympanic membrane, ossicles, ligaments, and muscles, all combine to minimize both mass and stiffness. All these data suggest middle ear mechanisms which are very efficient over a broad frequency range. The middle ear modifications found in heteromyids are adaptive in predator avoidance, especially in areas of little natural cover; nevertheless, contrary to expectations, there is no firm relationship between habitat and the extent of these modifications in the 26 species. However, environment did apparently plan an important role in the evolution of the family, and this is discussed.