Sex Estimation From Measurements of the Mastoid Triangle and Volume of the Mastoid Air Cell System Using Classical and Machine Learning Methods: A Comparative Analysis.

ABSTRACT: Previous studies on the sexual dimorphism of the mastoid triangle have typically focused on linear and area measurements. No studies in the literature have used mastoid air cell system volume measurements for direct anthropological or forensic sex determination. The aims of this study were to investigate the applicability of mastoid air cell system volume measurements and mastoid triangle measurements separately and combined for sex estimation, and to determine the accuracy of sex estimation rates using machine learning algorithms and discriminant function analysis of these data. On 200 computed tomography images, the distances constituting the edges of the mastoid triangle were measured, and the area was calculated using these measurements. A region-growing algorithm was used to determine the volume of the mastoid air cell system. The univariate sex determination accuracy was calculated for all parameters. Stepwise discriminant function analysis was performed for sex estimation. Multiple machine learning methods have also been used. All measurements of the mastoid triangle and volumes of the mastoid air cell system were higher in males than in females. The accurate sex estimation rate was determined to be 79.5% using stepwise discriminant function analysis and 88.5% using machine learning methods.

An anatomical study of the sigmoid sinus artery: Application to the transmastoid approach.

INTRODUCTION: We aimed to investigate the morphological features of the artery that traverse the sigmoid sinus's lateral surface and to discuss this structure's clinical relevance. METHODS: Ten sides from five cadaveric Caucasian heads were used for gross anatomical dissection to investigate the morphological features of the sigmoid sinus artery (SSA), and additional five sides were used for histological observation. RESULTS: The SSA was found on eight out of ten sides (80%). The mean diameter of the SSA was 0.3 mm. The mean distance from the tip of the mastoid process to the artery was 20.3 mm. Histological observation identified extradural and intradural courses of SSA. The intradural course was further categorized into protruding and non-protruding types. In the protruding type, the SSA traveled within the dura but indented into the bone, making it more or less an intraosseous artery. In the non-protruding type, the SSA traveled within the dura but did not protrude into the bone but rather indented into the lumen of the SS. In all sections, both intradural and extradural courses were identified simultaneously. CONCLUSIONS: When the mastoid foramen is observed, it does not always only carry an emissary vein but also an artery. The SSA could be considered a "warning landmark" during bone drilling for the transmastoid approach.

Clinical applications of the mastoid emissary vein.

PURPOSE: During retrosigmoid craniotomy, the mastoid emissary vein (MEV) can be a source of considerable bleeding during the operation, especially when the larger diameter MEV or sigmoid sinus is torn. In this study, we evaluated the relevant structure of the MEV for their anatomy and applied the data in surgery to summarize their clinical significance. METHODS: The posterior craniocervical regions of 15 silicon-injected Chinese human cadaver specimens were dissected to expose the MEV and adjacent structures. Fifty-one patients who were scheduled to undergo retrosigmoid craniotomy were selected. All patients underwent preoperative routine CT of the head. The relevant data were collected on cadaveric anatomy and CT. Eventually, all patients underwent retrosigmoid craniotomy and the MEV was observed during the operation. RESULTS: In cadaver specimens, the prevalence of the MEV was 90.0%. It originated from the middle and lower parts of the posterior wall of the sigmoid sinus and extended in the posterior direction in the mastoid process, usually having 1-2 external openings (86.7%) and only 1 internal opening. The intraosseous courses of the MEV were classified as straight and curved. The straight type accounted for 57.9%, and the curved type for 42.1%. The mean diameter of the MEV was 1.84 ± 0.85 mm, and the straight length of the MEV inside the mastoid process was 11.93 ± 3.58 mm. In 16.7% and 6.7% of all cadaver specimens, the MEV diameter was greater than 2.5 and 4 mm, respectively. In 51 patients (bilateral), routine head CT scan showed the MEV in 49.0% of the patients, and the MEV diameter was greater than 2.5 and 4 mm, respectively, in 17.6% (18/102) and 3.9% (4/102) of the cases. During surgery (unilateral) in the 51 patients, 48 had the MEV and 3 had no MEV. None of the patients had sigmoid sinus tears or massive bleeding. CONCLUSION: In the process of retrosigmoid craniotomy, detailed anatomical knowledge of the MEV, well-planned CT scan, and meticulous microsurgical techniques are key for successful operation, which can reduce the occurrence of complications.

Anatomy of the mastoid triangle and morphometric sex differences.

OBJECTIVE OF THE STUDY: This study aimed to quantify the area of the mastoid triangle (MT) and assess potential morphometric differences between males and females. PATIENTS: The sample consisted of 244 dry human skulls, with biological sex known based on genetic analysis, collected from a medicolegal osteological database from Central-Western Brazil. MATERIALS AND METHODS: The study was observational, analytical, and cross-sectional. The skulls were analyzed using Heron's equation to calculate the area of the MT. The landmarks connecting each of the sides of the triangle were: Porion (Po)>Mastoidale (Ma)>Asterion (Ast). Morphometric references were calculated and compared based on sex. RESULTS: The area of the MT was nearly 14% larger in males compared to females (p<0.05). The mean MT area for the right and left sides of males were 684.11±93.25mm2 and 668.94±111.95mm2, respectively. In females, the mean MT for the right and left sides were 588.93±91.09mm2 and 582.88±102.98mm2, respectively. Right and left side measurements were significantly different (p<0.05), except for Po-Ast (p=0.232). CONCLUSION: Morphometric features regarding the MT were slightly different between males and females. Application of the MT as a dimorphic tool should be adjuvant. Moreover, this tool should be considered carefully, especially because the sex-based differences were statistically significant, but discrete between males and females.

Comprehensive review of the mastoid foramen.

Anatomical variations of the mastoid foramen have been observed to vary in a number of qualities including size, number, and location. These variants have the potential to become problematic during surgical approaches to the posterior cranial fossa and mastoid part of the temporal bone, and should thus be appreciated by the surgeon. Herein, we discuss the mastoid foramen in detail including issues with such foramina that should be known to the neurosurgeon.

Evaluation of the relationship of chronic otitis media with the Körner's septum, auditory tube angle, and tubotympanic angle.

PURPOSE: This study aimed to evaluate the relationships between chronic otitis media (COM) and the characteristics of Auditory tube (Eustachian) angle (ATa), tubotympanic angle (TTa), and Körner's septum (KS). METHODS: A retrospective research was conducted between January 2019 and October 2019. The computed tomography (CT) results and medical files of 210 patients were evaluated. According to CT results and medical files, the patients were evaluated regarding the presence of COM, KS, ATa, and TTa. RESULTS: There were 113 (53.81%) males and 97 (46.19%) females in the study group, and the mean age of the patients was 42.05 ± 10.77 years. The frequency of the KS was significantly higher in patients who were diagnosed with COM (35.66% vs. 7.41%, p < 0.001). The patients diagnosed with COM were found to have a narrower ATa and a wider TTa than the patients who were not diagnosed with COM. ATa was narrower and TTa was wider in patients with KS. The presence of KS and higher TTa value were considered as risk factors for COM (p < 0.001, p < 0.001, respectively) CONCLUSION:  Our findings indicate that ATa was narrower, TTa was wider and KS was more frequent in patients with COM. Analysis of risk factors demonstrated that increased TTa and the presence of KS were associated with increased risk for COM.

Anatomo-sonographic identification of the longissimus capitis and splenius cervicis muscles: principles for possible application to ultrasound-guided botulinum toxin injections in cervical dystonia.

OBJECTIVE: The main objective of this study was to define and verify anatomo-sonographic landmarks for ultrasound-guided injection of botulinum toxin into the longissimus capitis (LC) and splenius cervicis (SC) muscles. METHODS AND RESULTS: After a preliminary work of anatomical description of the LC and SC muscles, we identified these muscles on two cadavers and then on a healthy volunteer using ultrasound and magnetic resonance imaging (MRI) to establish a radio-anatomical correlation. We defined an anatomo-sonographic landmark for the injection of each of these muscles. The correct positioning of vascular glue into the LC muscle and a metal clip into the SC muscle of a fresh cadaver as verified by dissection confirmed the utility of the selected landmarks. DISCUSSION: For the LC muscle, the intramuscular tendon of the cranial part of the muscle appears to be a reliable anatomical landmark. The ultrasound-guided injection can be performed within the cranial portion of the muscle, between the intra-muscular tendon and insertion into the mastoid process at dens of the axis level. For the SC muscle, the surface topographic landmarks of the spinous processes of the C4-C5 vertebrae and the muscle body of the levator scapulae muscle seem to be reliable landmarks. From these, the ultrasound-guided injection can be carried out laterally by transfixing the body of the levator scapulae. CONCLUSION: The study defined two cervical anatomo-sonographic landmarks for injecting the LC and SC muscles.

Mastoid notch as a landmark for localization of the transverse-sigmoid sinus junction.

BACKGROUND: The top of the mastoid notch (TMN) is close to the transverse-sigmoid sinus junction. The spatial position relationship between the TMN and the key points (the anterosuperior and inferomedial points of the transverse-sigmoid sinus junction, ASTS and IMTS) can be used as a novel method to precisely locate the sinus junction during lateral skull base craniotomy. METHODS: Forty-three dried adult skull samples (21 from males and 22 from females) were included in the study. A rectangular coordinate system on the lateral surface of the skull was defined to assist the analysis. According to sex and skull side, the data were divided into 4 groups: male&left, male&right, female&left and female&right. The distances from the ASTS and IMTS to the TMN were evaluated on the X-axis and Y-axis, symbolized as ASTS&TMN_x, ASTS&TMN_y, IMTS&TMN_x and IMTS&TMN_y. RESULTS: Among the four groups, there was no significant difference in ASTS&TMN_x (p = 0.05) and ASTS&TMN_y (p = 0.3059), but there were significant differences in IMTS&TMN_x (p < 0.001) and IMTS&TMN_y (p = 0.01), and multiple comparisons indicated that there were significant differences between male&left and female&left both in IMTS&TMN_x (p = 0.0006) and in IMTS&TMN_y (p = 0.0081). In general, the ASTS was located 1.92 mm anterior to the TMN on the X-axis and 27.01 mm superior to the TMN on the Y-axis. For the male skulls, the IMTS was located 3.60 mm posterior to the TMN on the X-axis and 14.40 mm superior to the TMN on the Y-axis; for the female skulls, the IMTS was located 7.84 mm posterior to the TMN on the X-axis and 19.70 mm superior to the TMN on the Y-axis. CONCLUSIONS: The TMN is a useful landmark for accurately locating the ASTS and IMTS.

Does Mastoid Pneumatization Affect Facial Canal Dimensions and Distances of Facial Tympanic Segment-Scutum and Lateral Semicircular Canal-Scutum?

OBJECTIVES: In the present study, we investigated whether mastoid pneumatization affects facial canal dimensions and distances of facial tympanic segment and scutum, and lateral semicircular (LSS) canal and scutum. METHODS: One hundred sixty-one temporal multidetector computed tomography scans were reviewed. Patients with unilateral sclerotic mastoid pneumatization (no aeration) (group 1, n = 81) and unilateral total mastoid pneumatization (100.0% aeration) (group 2, n = 80) were included. Facial canal dimensions at the labrythine, tympanic, and mastoid segments; facial canal dehiscence and length; and facial tympanic segment-scutum and LSS canal-scutum distances were evaluated. RESULTS: In the present study, facial canal dimensions of labyrinthine, tympanic, and mastoid segments in total pneumatized mastoid group were significantly lower than sclerotic mastoids on axial and coronal images (P < 0.05). Facial tympanic segment and scutum distance of the sclerotic mastoid group was significantly lower than those of the total pneumatized mastoid group (P < 0.05). However, LSS canal-scutum distance was not different between both groups (P > 0.05). The LSS canal-scutum distance of the females was lower than those of the males (P < 0.05). Facial canal dehiscence ratio was 11.3% and 11.1% in sclerotic and total pneumatized mastoids, respectively. The mean ± SD length of the dehiscence was 2.46 ± 1.29 mm in pneumatized mastoids and 1.92 ± 0.68 mm in sclerotic mastoids. CONCLUSIONS: In cholesteatoma cases, scutum erosion may occur. Because facial tympanic segment and scutum distance decreased in sclerotic mastoids compared with completely pneumatized ones, maximum care must be taken in the operations for avoiding to damage facial canal and nerve. Revision cases may be more difficult because of distorted anatomy. However, in pneumatized mastoids, the mean length of the facial canal was more than 2 mm, which must be kept in mind during operations.

Morphology of asterion and its proximity to deep vein sinuses in Iranian adult skull.

Background: The asterion is located at the posterior lateral side of the skull at the junction of the parietal, temporal and occipital bones.Methods: We examined the morphology of the asterion, its association with deep vein elements, the mastoid apex and inion in 105 adult cadavas (210 hemicraniums) including 146 males and 64 females at the anatomy lab of the Legal Medicine Organization.Results: Two types of asterion were observed. Type I was found in 14.7%, and type II in 85.3% of cases. In 70% of cases, the asterion was at or above the venous sinus. The distance between the asterion and the mastoid appendage on the right side was 47.03 mm and on the left side was 46.5 mm. The distance between the asterion and the inion at the right side was 70.55 mm and on the left side was 70.2 mm.Conclusion: The asterion in 70% of cases was at or above the level of the transverse sinus. For this reason, in posterior fossa surgical approaches, the first burr hole is preferred to start in the lower parts of the asterion.

Anatomical Study of the Posterior Auricular Branch of the Facial Nerve: Application to Parotid Surgery.

The posterior auricular nerve (PAN) is the first branch of the facial nerve after it leaves the stylomastoid foramen. The literature describing the anatomy of the PAN is very sparse. Therefore, the purpose of this study was to clarify the detailed anatomical features of the PAN and consider its clinical and surgical applications. The authors examined 10 sides from 6 fresh frozen adult cadaveric Caucasian heads. The PAN was observed as the first branch of the facial nerve in all specimens. During the dissection of the PAN, the posterior auricular artery was constantly near the PAN. Moreover, the PAN was located under the investing layer of deep cervical facia covering the sternocleidomastoid and mastoid process in all specimens. The diameter of the PAN was 0.82 ±â€Š0.21 mm (range from 0.55 to 1.21). The distance from the stylomastoid foramen to where the PAN branched from the facial nerve was 0.40 ±â€Š1.25 mm (range from 0 to 4.35). The distance from the location of this branching point of the PAN to the entering point of the PAN to any muscles was 28.03 ±â€Š5.51 mm (range from 19.71 to 38.75). Understanding the anatomical features of the PAN is essential for performing surgical procedures in this region.

Surgical "Safe Zone": Rapid Anatomical Identification of the Lesser Occipital Nerve.

BACKGROUND: Surgical intervention has established a vital role in the management of chronic headaches. The lesser occipital nerve (LON) is a common target in patients suffering from occipital neuralgia and is often resected as a first-line option. We endeavored to define the relationships of the LON in the posterolateral neck to facilitate its safe and rapid intraoperative identification. METHODS: Seven fresh cadavers (14 nerves) were dissected, and their relationships to the mastoid prominence and nearby spinal accessory nerve (SAN) and greater auricular nerve were noted. RESULTS: The distance from the mastoid to the emergence of the LON along the posterior sternocleidomastoid ranged from 36 to 51 mm (mean: 45.2 mm), with relative symmetry between the two nerves in the same cadaver. The SAN emerged an average of 54 mm from the mastoid prominence. CONCLUSION: Exploration for the LON should begin at a point 40 mm from the mastoid prominence along the posterior border of the sternocleidomastoid muscle. If the point of exit of the LON is not identified within 10 mm of this exposure, our dissection continues cranially along the posterior border of the sternocleidomastoid, anterior to the trapezius. In rare cases the nerve may pierce the fibers of the muscle and ascend directly on top of the muscle belly. By limiting the caudal extend of the dissection, we can avoid exposure of the SAN and minimize the risk of iatrogenic nerve injury.

Bilateral supernumerary clavicular heads of sternocleidomastoid muscle in a Korean female cadaver.

Many anatomical variants on the sternocleidomastoid muscle have been reported. In this study, supernumerary clavicular heads of sternocleidomastoid muscle in a Korean female cadaver were bilaterally displayed. The observed supernumerary heads were classified as follows: one sterno-mastoid, one cleido-occipital and one cleido-mastoid on the right side, and one sterno-mastoid-occipital, four cleido-occipitals, and one cleido-mastoid on the left side. The sterno-mastoid and sterno-mastoid-occipital and the cleido-occipital made the superficial layer of the sternocleidomastoid muscle, while others made deep layer. We discussed clinical relevance and developmental basis of these muscular variations important for clinicians and anatomists.

The radioanatomical assessment of the Körner's septum.

PURPOSE OF THE STUDY: Körner's septum (KS) is a developmental remnant formed at the junction of mastoid and temporal squama, representing the persistence of the petrosquamosal suture. During mastoid surgery, it could be taken as a false medial wall of the antrum so that the deeper cells might not be explored. The aim of the study was to assess a Körner's septum prevalence and to analyze its topography. METHODS: The study was performed on 80 sets of cone-beam computed tomography (CBCT) images of temporal bone (41 male, 39 female, 160 temporal bones). Körner's septum was identified and its thickness was measured on axial sections at three points: at the level of superior semicircular canal (SCC), at the level of head of malleus (HM) and at the level of tympanic sinus (TS). RESULTS: KS was encountered at least in one point of measurements in 50 out of 80 sets of CBCT images (62.5%). The average thickness at the level of SCC was 0.87 ± 0.34 mm, at the level of HM was 0.99 ± 0.37 mm and at the level of TS was 0.52 ± 0.17 mm. CONCLUSIONS: Körner's septum is a common structure in the temporal bone-air cell complex. It is more often encountered in men. In half of the patients, it occurs bilaterally. However, in most of the cases it is incomplete with anterior and superior portions being the most constant.

Effect of mastoid bone pneumatization on the conformation and depth of the sinus tympani, a high-resolution computed tomography study.

PURPOSE: To investigate the relationship between mastoid pneumatization and the conformation and depth of the sinus tympani (ST) in patients with chronic otitis media (COM), based on the high-resolution computed tomography (HRCT) scans. METHODS: Two hundred and two patients affected by COM were included in the study. The patients were divided into three groups according to the extent of mastoid pneumatization on HRCT scans; pneumatized (group 1), diploic (group 2) or sclerotic (group 3). The variation in the ST area (types A, B, C) was assessed using a radiomorphological classification based on the relationship between the medial boundary of the ST and the third portion of the facial nerve. Depth of the ST was calculated by measuring the distance between the medial boundary of the ST and medial boundary of the third portion of the facial nerve RESULTS: There was a statistically significant difference between the groups in terms of the type of ST (p < 0.001). The mean depths of the ST were 1.59 ± 0.82 mm (0.00-2.80 mm) in group 1, 1.10 ± 0.79 mm (0.00-3.00 mm) in group 2 and 0.53 ± 0.63 mm (0.00-2.60 mm) in group 3. The groups were significantly different in terms of the depth of the ST (p < 0.001). CONCLUSION: A well-pneumatized mastoid is highly associated with a deep and posteriorly positioned ST with respect to the facial nerve. The preoperative HRCT scans of patients with cholesteatoma should be carefully evaluated to determine the conformation and depth of the ST.

Mastoid foramen, mastoid emissary vein and clinical implications in neurosurgery.

BACKGROUND: Mastoid emissary vein is especially important from the neurosurgical point of view, because it is located in variable number in the area of the occipitomastoid suture and it can become a source of significant bleeding in surgical approaches through the mastoid process, especially in retrosigmoid craniotomy, which is used for approaches to pathologies localized in the cerebellopontine angle. Ideal imaging method for diagnosis of these neglected structures when planning a surgical approach is high-resolution computed tomography. The aim of this work was to provide detailed information about this issue. METHODS: We studied a group of 295 skulls obtained from collections of five anatomy departments and the National Museum. Both quantitative and qualitative parameters of the mastoid foramen were evaluated depending on side of appearance and gender. Individual distances of the mastoid foramen from clearly defined surface landmarks (asterion, apex of mastoid process, foramen magnum) and other anatomical structures closely related to this issue (width of groove for sigmoid sinus, diameters of internal and external openings of mastoid foramen) were statistically processed. RESULTS: The most frequently represented type of the mastoid foramen is type II by Louis (41.2%). The differences between right and left sides were not statistically significant. In men there was a higher number of openings on the right side and in qualitative parameters the type III and IV predominated, whereas in women the types I and II were more frequent. In men, greater distances from the mastoid foramen were observed when evaluating qualitative parameters for defined surface landmarks. Mean size of the external opening diameter was 1.3 mm; however, several openings measured up to 7 mm. CONCLUSIONS: Despite excellent knowledge of anatomy, however, good pre-operative examination using imaging methods and mastering of microsurgical techniques create the base for successful treatment of pathological structures in these anatomically complex areas.

Endoscopic Anatomic Study Via Grinding Partial Petrous Ridge to the Middle Fossa in Retromastoid Keyhole Approach.

OBJECTIVE: This study aimed to observe the range of exposure, indications, and feasibility of the retromastoid keyhole approach via grinding partial petrous ridge to the middle fossa. METHODS: Simulated endoscopic surgeries via grinding suprameatal tubercle and petrous ridge to expose the middle fossa in retromastoid keyhole approach were performed on 8 adult cadaver heads (16 sides) fixed by formalin. The maximum exposure range in endoscope was observed. The boundaries of Parkinson triangle and the anatomic structures contained by Meckel cave and cavernous sinus (CS) lateral wall were revealed. The distances from midpoint of sigmoid sinus posterior border to every important anatomic structures in the middle fossa and the length of all sides of Parkinson triangle were measured. RESULTS: By using endoscope, the exposure of the cerebellopontine angle, ventrolateral brainstem, incisure of tentorium, petroclival region, and CS lateral wall were satisfactory. Many important anatomic structures in middle fossa were exposed well. The distances from midpoint of posterior border of sigmoid sinus to suprameatal tubercle, trigeminal semilunar ganglion, posterior curve segment of internal carotid artery were 34.42 ± 2.14, 54.52 ±â€Š2.87, and 65.15 ±â€Š3.13 mm. The lengths of all sides of Parkinson triangle were 18.97 ±â€Š2.93, 16.23 ±â€Š2.02, and 8.04 ±â€Š2.34 mm. CONCLUSION: The retromastoid keyhole approach via grinding partial petrous ridge to the middle fossa by using endoscope can increase the exposure of middle fossa effectively, which is proper for most lesions in posterior cranial fossa while some parts extend to middle fossa.

Preoperative Exposure of Sigmoid Sinus Trajectory in Posterolateral Cranial Base Approaches Using a New Landmark Through a Neurosurgical Perspective.

The location of burr holes in posterolateral cranial base approaches should be appropriate to provide an adequate operative field, and surgical freedom is crucial for bone window opening. The aim of this study was to search for more convenient and easily detectable landmarks in comparison with current landmarks in posterolateral cranial base surgery. Twenty 3-dimensional reconstructed head and neck computed tomography angiography images (group 1) and 20 cadaver heads (group 2) were evaluated. An imaginary line connecting the angle of the mandible and the mastoid tip was extended upward. A second line passing through the lateral edge of the zygomatic arch was also extended posteriorly. The authors examined if the first line met with the sigmoid sinus throughout its course and determined the location of the intersection point of these 2 lines relative to the sigmoid-transverse sinus junction. The intersection point did not correspond to the sinus region in 3 images from group 1 and 4 specimens from group 2. The matching of the mandibula-mastoid line trajectory with the sigmoid sinus course was unacceptable in 4 images and 5 cadavers. For venous anatomy preservation and anatomic skull base fossa orientation during posterolateral cranial base approaches, upward extension of the mandibula-mastoid line can be a proper landmark for surgical planning in this region. The authors' proposed superficial anatomical line and intersection point over the skull could be used as a reliable indicator for the external projection of the sigmoid sinus and an appropriate initial burr-hole location.

Jugular Bulb Anatomy for Lateral Skull Base Approaches.

BACKGROUND: This study was designed to define the detailed anatomical relations of the jugular bulb with the facial nerve, sigmoid sinus, otic capsule, and internal acoustic canal allowing the safe management of the jugular bulb. METHODS: Thirty-five formalin-perfused cadaveric temporal bones that had well mastoid and petrous pneumatization without any neurovascular variations on computed tomography scan were selected for the study. The bones were dissected via translabyrinthine approach. RESULTS: The dome of the jugular bulb was located under the facial nerve in 21 of the cases (60%), in the mastoid cavity in 8 of the cases (22.9%), and in the tympanic cavity in 6 of the cases (17.1%). Significant difference was observed only between the temporal bones in which the dome of the jugular bulb was located in the mastoid cavity and under the facial nerve with regard to the mastoid cortex-lateral semicircular canal measurement (P = 0.04). CONCLUSION: Because of the high variability of the position of the dome of the jugular bulb, the precise knowledge of the relations of the jugular bulb and the preoperative radiologic verification of possible variations are essential to avoid the problems associated with its position and to decide the approach individually.

Spatial orientation of the adult cochlea: rotation, tilt, and angle theta 3.

OBJECTIVE: Quantitative description in adult crania of (1) angular orientation of the basal turn of the cochlea relative to the sagittal (termed "rotation") and Frankfort horizontal (termed "tilt") planes, and angle theta 3 [angular relationship of the line defined by the cochlea's spiral center and cochlear (round) window, to the cochlear window]; (2) orientation of the cochlea relative to the plane defined by the horizontal and vertical portions of the facial nerve; (3) orientation of the basal turn of the cochlea relative to the plane of the posterior semicircular canal; and (4) the association of these orientations with the extent of mastoid pneumatization. METHODS: Postmortem material analysis. From 41 bequeathed anatomical ear-normal cadaveric cranial, high-resolution CT scans were performed of the five crania with the largest and the five with the smallest mastoids. Eleven points in three-dimensional Cartesian space were appointed and studied with the software program FIJI. RESULTS: The median angle values (and ranges) for right ears were: "rotation" 52° (range 47-61); and, "tilt" 84° (79-89). The planes of the cochlear basal turn and facial nerve approximated superimposition: median 15° (2-19). Angle theta 3 for right ears was median 40° (28-44). Bilateral symmetry was found for the relationships between the planes. However, no association of any planar relationship with mastoid pneumatization was suggested. CONCLUSION: Considering the range of angles found in clinically normal adult specimens, spatial orientation of the cochlea may explain some of the difficulties in implantation.