Surgical anatomy of the chorda tympani: a micro-CT study

Purpose

Iatrogenic injury of the chorda tympani is a well-known complication of middle ear surgery, yet few studies have investigated the intraosseous course of the nerve. The aim of this study was to accurately delineate the posterior canaliculus in the temporal bone, particularly its relationship to the tympanic annulus, which is critical during the insertion of subannular ventilation tubes.

Methods

Forty temporal bones from 27 cadavers (15 male, mean age 75?years, 13 bilateral) were scanned using a micro-CT scanner, and standardised 3-D multiplanar reconstructions were generated using a software platform. The posterior canaliculus was measured in relation to reproducible bony landmarks.

Results

In 6 (15%) specimens, the chorda tympani originated from the facial nerve outside the skull and in 34 (85%) from within the facial canal at a mean of 3.2?±?1.8?mm above the stylomastoid foramen. The posterior canaliculus was 12.3?±?3.8?mm long and converged on the tympanic sulcus cranially. It entered the middle ear at 62?±?10% of the height of the tympanic membrane.

Conclusions

This novel micro-CT study defines the precise anatomy of the posterior canaliculus housing the chorda tympani and provides data that may help the otologic surgeon protect the nerve from iatrogenic injury.     

Posterior tympanotomy is a riskier procedure in chronic otitis media than in a normal mastoid: a high-resolution computed tomography study

Purpose

The aim of our study was to compare the difficulty in performing a posterior tympanotomy in chronic otitis media (COM) versus the same procedure in a normal mastoid.

Materials and methods

The study included 122 patients who underwent tympanomastoidectomy for unilateral chronic otitis media with contralateral normal mastoid pneumatization. We evaluated the anatomical relationships between the mastoid segment and neighboring structures by analyzing axial temporal bone computed tomography scans. A vertical line (line A) was drawn tangential to the most lateral end of the posterior semicircular canal (point A). Three distances were measured: the distance (D1) between the point A and the most lateral end of the mastoid segment of the facial nerve (point B), the distance (D2) between the line A and the point B, and the distance (D3) between the point B and the posterior end of the bony annulus of the external auditory canal.

Results

The average measurements of D1 and D3 were 3.79 ± 0.55 and 2.63 ± 0.51 mm, respectively, in the normal mastoid ears and 3.47 ± 0.59 and 2.35 ± 0.44 mm, respectively, in the COM ears. The measurements of D1 and D3 were statistically shorter in the COM ears than in the normal ears.

Conclusions

These findings suggest that the facial recess in COM may be narrower than in a normal mastoid and that performing a posterior tympanotomy may be riskier in COM than in a normal mastoid due to the potential for injury to the neighboring structures and the facial nerve.

     

后鼓室颞骨切片与CT对照研究

目的：为后鼓室及耳科病变的影像诊断和手术治疗提供解剖学基础。方法：l5例成人头部标本，以眦耳线（cML）为基线，获得间隔为1．00mm，厚度为1．00mm的CT图像，扫描后的头部标本按原定位截取以耳颞区为中心的组织块并将其制成厚为1．00mm的连续横断薄层切片。标本切片与CT图像对照，对颞骨内砧骨窝、鼓索隆起、茎突隆起、面神经隐窝、鼓室窦、岬小桥、外耳道上棘等结构进行观察。结果：砧骨窝深度为1．49mm，至面神经锥曲的距离为5．67mm。后鼓室窦内侧壁至面神经水平部的距离为3．14mm。外耳道上棘至面神经垂直段、鼓索神经、鼓岬的距离分别为16．76mm、15．94mm和21．81mm。结论：耳颞区断面标本与CT图像进行对照研究，其结果对耳科疾病的影像诊断及手术治疗具有参考价值。     

The distance of the sigmoid sinus and the middle fossa dura from the external auditory canal in chronic otitis media

Purpose

Mastoid pneumatization is reduced in most patients suffering from chronic otitis media (COM). In most studies, the relationship between the degree of pneumatization and the distance of the sigmoid sinus from the external auditory canal has been examined, yielding different results. This study addresses the relationship between COM and the distance of the sigmoid sinus and also middle fossa dura from the external auditory canal.

Methods

This was a case–control study on 15 adult COM patients, 12 traumatic facial palsy patients, and 15 cadaver temporal bones. After mastoidectomy, the distance between the spine of Henle and both the middle fossa dura and sigmoid sinus were measured, and the findings in each group was analyzed using Tukey’s and ANOVA tests.

Results

The average distance of the external auditory canal and the sigmoid sinus was 15.27 ± 3.3 mm in the COM group, 16.92 ± 3.23 mm in the traumatic facial palsy group, and 14.53 ± 2.92 mm in the cadaver temporal bones. There was no significant difference between the groups (p = 0.115). The average distance of the spine of Henle from the middle fossa dura was 6.73 ± 1.62 mm in the COM group, 11.4 ± 2.05 mm in the traumatic facial palsy group, and 8.93 ± 1.94 in the cadaver temporal bones. There was a significant difference between the groups (p < 0.001).

Conclusion

The distance of both the sigmoid sinus and the middle fossa dura from the external auditory canal (which indicates mastoid pneumatization) is reduced in COM patients.     

Morphometric analysis of the infraorbital groove, canal, and foramen on three-dimensional reconstruction of computed tomography scans

Purpose

This study aimed to investigate the anatomy of the infraorbital foramen (IOF), infraorbital canal (IOC), and infraorbital groove (IOG) with regard to surgical and invasive procedures using three-dimensional reconstruction of CT scans.

Methods

The CT scans of 100 patients were evaluated retrospectively. The morphology of the IOF, IOC, and IOG as well as their relationships to different anatomic landmarks was assessed in a three-dimensional model.

Results

The mean length of the IOC and IOG and the angle of the IOC relative to IOG were 11.7 ± 1.9, 16.7 ± 2.4 mm, and 145.5° ± 8.5°, respectively. The mean angles of the IOC relative to vertical and horizontal planes were 13.2° ± 6.4° and 46.7° ± 7.6°, respectively. In the relationships between the IOF and different anatomic landmarks, the mean distances from the IOF to supraorbital notch/foramen, facial midline, and infraorbital rim were 5.6 ± 3.1 mm laterally, 26.5 ± 1.9 mm laterally, and 9.6 ± 1.7 mm inferiorly, respectively. The mean distance from the IOF to anterior nasal spine (ANS) was 35.0 ± 2.6 mm, and the mean angle of the axis that passed the IOF and ANS relative to horizontal plane was 28.8° ± 4.1°. In addition, the mean soft tissue thickness overlying the IOF was 11.4 ± 1.9 mm.

Conclusions

These results provide detailed knowledge of the anatomical characteristics and clinical importance of the IOF. Such knowledge is of paramount importance for surgeons when performing maxillofacial surgery and regional block anesthesia.     

The gluteal sling: an anatomical study

Introduction

Sciatic nerve palsy is a devastating complication which may be seen after acetabular exposure in total hip resurfacing via a posterior approach. An anatomical structure termed as the “gluteal sling” was suggested to play a role in sciatic nerve palsies during this operation. “Gluteal sling” is formed by the attachment of the deep fibers of the inferior part of the gluteus maximus on the gluteal tuberosity of the femur and the lateral intermuscular septum. It is suggested to be released to avoid such compressive injuries. The purpose of this study is to demonstrate how much of the gluteal sling should be released to decrease the tension on sciatic nerve during posterior hip arthroplasties. We also aimed to study the anatomical structures at risk during releasing procedure.

Materials and methods

The gluteal sling was examined in 17 sides of 9 adult cadavers. Its relation with the sciatic nerve, first perforating artery, the tip of greater trochanter and the ischial tuberosity were evaluated.

Results

The closest distance between the gluteal sling and the sciatic nerve was measured as 1.9 ± 0.6 cm. This point was corresponding to the distal 2/3 part of the gluteal sling. The distance of the proximal edge of the gluteal sling to the first perforating artery was 3.7 ± 0.9 cm, while its ascending branch was closer, being 1.8 ± 0.8 cm.

Conclusions

Theoretically, it is enough to release the proximal 2/3 of the gluteal sling to avoid its compression on the sciatic nerve. However, further clinical studies would need to be undertaken to properly determine the effects of this procedure.     

A morphometric anatomical and comparative study of the foramen magnum region in a Greek population

Background

The foramen magnum (FM), a complex area in craniocervical surgery, poses a challenge for neurosurgeons. The knowledge of the detailed anatomy of the FM, occipital condyles (OC) and variations of the region is crucial for the safety of vital structures. This study focuses on the FM and OC morphometry, highlights anatomical variability and investigates correlations between the parameters studied.

Materials and methods

One hundred and forty-three Greek adult dry skulls were examined using a digital sliding calliper (accuracy, 0.01 mm).

Results

Mean FM width and length were found 30.31 ± 2.79 and 35.53 ± 3.06 mm, respectively. The commonest FM shape was two semicircles (25.9 %), whereas the most unusual was irregular (0.7 %). The OC minimum width, maximum width and length were 5.71 ± 1.61, 13.09 ± 1.99 and 25.60 ± 2.91 mm on the right, and 6.25 ± 1.76, 13.01 ± 1.98 and 25.60 ± 2.70 mm on the left side. The commonest OC shape was S-like and the most unusual was ring, bilaterally. The mean anterior and posterior intercondylar distances were 19.30 ± 3.25 and 51.61 ± 5.01 mm, respectively. The OC protruded into the FM in 86.7 % of the skulls. Variations such as a third OC existed in 5.6 % and basilar processes in 2.8 %. Posterior condylar foramina were present in 75.5 %. The gender was correlated with FM width and length, OC length, bilaterally, anterior intercondylar distance (AID) and posterior intercondylar distance (PID). The OC protrusion and existence of posterior condylar foramina were correlated. Bilateral asymmetry for OC shape was statistically significant.

Conclusion

Our results provide useful information that will enable effective and reliable surgical intervention in the FM region with the maximum safety and widest possible exposure.     

Implanting straight into cochlea risks the facial nerve: a Cartesian coordinate study

Purpose

To describe the straight-into-cochlea line that affords the best access for an electrode array to enter via the round window, and how this line relates to the facial nerve, the incus, and mastoid size. The straight-into-cochlea line is important to minimize the cochlear trauma and maximize the likelihood of placement into the scala tympani.

Methods

High-resolution CT scans were obtained for ten craniums with the extremes of large (N = 5) and small (N = 5) mastoid pneumatization; the specimens were from a series of 41 ear normal craniums. Using FIJI, a publicly available software program, the straight-into-cochlea insertion line was determined by defining the x–y–z coordinates of the middle of the round window and a point 6.0 mm into the cochlea on its centrifugal wall. Then, from the extended straight-into-cochlea insertion line, we determined the shortest perpendicular distance to the middle of the fallopian canal, and from that “fallopian point” to the apex of the posterior process of the incus.

Results

We found good repeatability of measurements. We found the extended straight-into-cochlea insertion lines routinely close to or in the midst of the fallopian canal (50 % ≤ 1.0 mm). We found the lines 4.7–7.8 mm from the apex of the posterior process of the incus. Line positions relative to “fallopian point” and incus showed no relation to mastoid pneumatization. For the distance “fallopian point” to incus, bilateral symmetry was suggested.

Conclusions

Using landmarks registered in an x–y–z coordinate system, straight-into-cochlea insertion via the round window puts the facial nerve at risk.

     

An anatomic study of the dorsal forearm perforator flaps

Purpose

The posterior forearm is an excellent donor site for the vascular pedicled cutaneous flaps; yet, there is surprisingly little detailed anatomical information based on clinical decision making. This study was undertaken to evaluate the anatomical basis of the dorsal forearm perforator flaps and to provide anatomical landmarks to facilitate flap elevation.

Methods

Thirty cadavers were available to perform this anatomical study after arterial injection. Twenty fresh cadavers were injected with a modified lead oxide–gelatin mixture, selected for 3-dimensional reconstruction using special software (MIMICS) and the arterial territory measured with Scion Image. Other ten were injected with red latex preparation, and perforators were identified through dissection.

Results

(1) The average number of posterior interosseous artery cutaneous perforators in the dorsal forearm was 5 ± 2, the average diameter was (0.5 ± 0.1) mm, and the pedicle length was (2.5 ± 0.2) cm. The average cutaneous vascular territory was (22 ± 15) cm². Cutaneous perforators could be found along the line extending from the lateral epicondyle to the radial border of the head of ulna. (2) Dorsal branch of anterior interosseous artery supplied blood to distal third of dorsal forearm; its average diameter was 0.8 mm.

Conclusion

The free transplantation of the posterior interosseous perforator artery flaps or rotary flap pedicled by dorsal branch of anterior interosseous artery for defect reconstruction is feasible.     

Surgical anatomy of the preauricular anteroparotid approach for mandibular condyle surgery

Purpose

The different surgical approaches used to treat mandibular condyle fractures are carried out in the periparotid skin area and can lead to facial nerve injury. We conducted a preauricular and anteroparotid surgical approach. Our main aim was to show the anatomical relationship between this approach site and the facial nerve branches, and to define cutaneous landmarks to locate the extraparotid facial nerve branches.

Method

A 2-step dissection of 13 fresh human cadaver semi-heads was performed: a preauricular approach followed by a superficial parotidectomy to visualize the facial nerve. Its course and ramifications were studied and compared to cutaneous landmarks. The proximity of the facial nerve branches with the surgical approach site was observed.

Results

The approach allowed systematically visualising the zygomatic and/or buccal branches. No facial nerve branches were sectioned. In three cases (23 %), a nerve branch was visualized during the approach. The buccal and zygomatic branches were ramified in 77 % of cases.

Conclusions

During our preauricular anteroparotid approach, the buccal and zygomatic branches were visualized but none was sectioned. Most often the approach was carried out between these two branches (46 % of cases). Cutaneous landmarks used were reliable to define a safe and nerve-free area for dissection. The buccal and zygomatic branches are very interesting because their high number of ramifications and anastomoses could serve as nerve relays in case of surgical lesion.     

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.     

Anatomical study of the medial patello-femoral ligament: landmarks for its surgical reconstruction

Purpose

The aim of this dissection study was to describe the anatomical insertions of the medial patello-femoral ligament (MPFL), and to assess its relationship with surrounding structures to improve its surgical reconstruction.

Methods

Twelve knees (7 cadavers) were included for the study. Measurements and general features of the MPFL were assessed: lengths, widths and insertions.

Results

The MPFL was found in all knees, presenting a triangular shape, and extending from the medial part of the patella to its femoral insertion (its length was of 59 ± 6.6 mm), distal to the adductor tubercle. The mean femoral insertion of the MPFL was 7.2 ± 2.7 mm proximal and 7.4 ± 4.0 mm posterior to the medial femoral epicondyle (MFE). It was also at a mean 11 ± 2.8 mm distal and 1.3 ± 2.1 mm posterior to the adductor tubercle, and 22 ± 6.4 mm anterior to the posterior condyle. We did not find any double-bundle organization on the patellar insertion. The width of the MPFL was 8.8 ± 2.9 mm at the femoral insertion, 27 ± 5.9 mm at the patellar insertion, and 12 ± 3.1 mm in the middle of the MPFL. The vastus medialis obliquus was found to be inserted on the superior part of the MPFL.

Conclusion

The adductor tubercle appeared to be a better landmark than the MFE for the femoral tunnel positioning during surgical reconstructions of the MPFL because it was easier to identify and its relationship with the femoral insertion of the MPFL was constant (10 mm below).     

Split temporalis muscle flap anatomy, vascularization and clinical applications

Introduction

For more than a century, the temporalis muscle has been used for facial reconstructions. More recently, a split temporalis muscle flap elevated on the superficial temporal pedicle has been described, for which the resulting gain of length makes crossing of the midline possible, as well as reconstruction of substance losses exceeding the midline.

Materials and methods

Fourteen fresh cadaveric dissections were performed to study the different techniques for splitting the temporalis muscle. Dissections with catheterization and injection of radio-opaque contrasting agent in the external carotid artery were then performed to specify the vascularization of the flap split on the superficial temporal pedicle.

Results

The duplication of the superficial temporal pedicle grants greater length compared to that of the deep pedicles, 57 mm versus 40 (p = 0.036). The middle temporal artery is capable of ensuring the vascularization, and therefore the viability, of the split flap. From these results, we spoke about the limitations of this study and we have inferred the main indications.     

Cycling time to failure is better maintained by cold than contrast or thermoneutral lower-body water immersion in normothermia

Purpose

To examine the effects of four commonly used recovery treatments applied between two bouts of intense endurance cycling on the performance of the second bout in normothermia (~21 °C).

Methods

Nine trained men completed two submaximal exhaustive cycling bouts (Ex1 and Ex2: 5 min at ~50 % ${\dot{\text{V}}\text{O}}_{2}$ peak, followed by 5 min at ~60 % ${\dot{\text{V}}\text{O}}_{2}$ peak and then ~80 % ${\dot{\text{V}}\text{O}}_{2}$ peak to failure) separated by 30 min of (a) cold water immersion at 15 °C (C15), (b) contrast water therapy alternating 2.5 min at 8 °C and 2.5 min at 40 °C (CT), (c) thermoneutral water immersion at 34 °C (T34) and (d) cycling at ~40 % ${\dot{\text{V}}\text{O}}_{2}$ peak (AR).

Results

Exercise performance, cardiovascular and metabolic responses during Ex1 were similar among all trials. However, time to failure (~80 % ${\dot{\text{V}}\text{O}}_{2}$ peak bout) during Ex2 was significantly (P < 0.05) longer in C15 (18.0 ± 1.6) than in CT (14.5 ± 1.5), T34 (12.4 ± 1.4) and AR (10.6 ± 1.0); and it was also longer (P < 0.05) in CT than AR. Core temperature and heart rate were significantly (P < 0.05) lower during the initial ~15 min of Ex2 during C15 compared with all other conditions but they reached similar levels at the end of Ex2.

Conclusions

A 30 min period of C15 was more beneficial in maintaining intense submaximal cycling performance than CT, T34 and AR; and CT was also more beneficial than T34 and AR. These effects were not mediated by the effect of water immersion per se, but by the continuous (C15) or intermittent (CT) temperature stimulus (cold) applied throughout the recovery.     

Usefulness of the radiological planning for hearing preservation surgery in vestibular schwannoma

Purpose

During vestibular schwannoma surgery there is a risk of endolymphatic duct and sac injury, which may cause a loss or a deterioration of hearing. The goal of the study was to evaluate the empirical utility of presurgical planning using CT with the bone window for the hearing preservation surgery.

Methods

The study was performed on 14 human temporal bones. CT scans with the bone window were obtained in the standard position. Safe drilling line was evaluated and after that drilling distances were analysed: the lateral drilling distance, total length of internal acoustic meatus, drilled length of internal acoustic meatus. After this, a surgical exposure was performed, using size of a drill tip as measuring scale. The dura was excised and endolymphatic duct was injected with a latex. Revision of the internal acoustic meatus was performed with the use of a microscope.

Results

Mean results of safe drilling coefficients were: lateral drilling distance: 10 ± 2 mm, total length of internal acoustic meatus: 9 ± 2 mm, drilled length of internal acoustic meatus: 7 ± 2 mm. In all cases, no endolymphatic duct injury was observed.

Conclusions

Preoperative radiological planning using the safe drilling coefficients is of value for the hearing preservation surgery in vestibular schwannoma. The size of the drilling tip may be used as an intraoperative measuring scale during this procedure. However, CT with a bone window is a necessary tool for the purposes of this procedure.

     

Relationship of cochlea with surrounding neurovascular structures and their implication in cochlear implantation

Purpose

The purpose of this investigation was to evaluate the topographic relations of cochlea with vital neurovascular structures and their implications for cochlear implantation (CI).

Methods

Sixty cadaveric human temporal bones were microdissected to expose the basal turn (BT) of cochlea, the carotid canal, the facial canal (FC) and the jugular fossa (JF). The minimum distances of BT of the cochlea from the carotid canal, the FC and roof of the JF were measured.

Results

The mean minimum distances of BT of the cochlea from the carotid canal, the FC and roof of the JF were found to be 1.38 ± 0.82, 1.06 ± 0.46 and 4.68 ± 2.21 mm, respectively. The abutment and impingement of carotid canal on anterior cochlear wall was found in three (5 %) and six (10 %) cases, respectively. Thin bone separation was observed between cochlea and FC (0.1 mm) in one case (1.67 %).

Conclusions

The preoperative knowledge of the variant anatomy of BT of cochlea in relation to adjacent vital structures like abutment and impingement of carotid canal and thin bone separation of the BT of cochlea from FC and JF is of immense importance in CI, which may otherwise lead to disastrous consequences during surgery.

     

The posterior groove as a landmark for location of the palatovaginal canal in axial computed tomography

Purpose

To investigate use of posterior groove of palatovaginal (PV) canal as an anatomic landmark in determining the location of PV canal in axial computed tomography (CT) images of pterygopalatine fossa (PPF).

Methods

A total of 20 skull specimens were examined in this analysis. Each skull was scanned by CT with and without a probe inserted through PV canal to measure the anatomic structures. CT images of 70 patients were used for comparing the rate of correct location of PV canal between the conventional method (using the vidian canal as a landmark) and the method of using the posterior groove as a landmark. Two skulls were dissected using endoscopy to further reveal the advantage of the posterior groove as a landmark.

Results

In all 20 skull specimens, the groove showed the morphology of a narrow groove and elliptical fossa in 24 and 16 sides, respectively. In CT images, the angle from PV canal and the posterior groove to the hard palate was 53.14° ± 5.48° and 20.93° ± 6.28°, respectively, which was significantly different (P ≤ 0.05). The rate of correct location of PV canal was statistically significantly higher with the method of posterior groove as a landmark than the conventional method (70.7 vs 49.3 %, P < 0.05). The endoscopic anatomy of the posterior groove and its use in locating the PV canal were described.

Conclusion

The posterior groove can be used as an anatomic landmark in correctly locating PV canal in the axial CT image of the PPF.

     

Three‐Dimensional Study of the Facial Canal Using Microcomputed Tomography for Improved Anatomical Comprehension

The aims of this study were to determine the various dimensions of the normal facial canal and to identify the spatial relationships between the facial canal and its adjacent structures using microcomputed tomography (micro‐CT) imaging and three‐dimensional (3D) reconstruction. The petrous parts of 54 temporal bones were scanned using micro‐CT with a slice thickness of 35 μm. The serial micro‐CT images were used to reconstruct 3D volumes of the facial canal and the bony labyrinth with the aid of computer software. These volumes were used to measure 31 dimensions of the facial canal and its spatial relationships with adjacent structures. The length of the meatal segment, the tympanic segment, and the mastoid segment were significantly larger in males than in females (p < 0.05). The narrowest portions of the facial canal were immediately lateral to the meatal foramen in the labyrinthine segment and the midpoint of the tympanic segment. The distance between the origin of the canal for the chorda tympani nerve and midpoint of the stylomastoid foramen was 35.3% of the length of the mastoid segment, and the angle between the tympanic segment and the lateral semicircular canal was 16.3°. The angle between the mastoid segment and the canal for the chorda tympani nerve could be classified into two groups: <180° and >180°. These findings represent supplemental data for improving the detailed understanding of the facial canal anatomy. Anat Rec, 297:1808–1816, 2014. © 2014 Wiley Periodicals, Inc.