Anatomical features of the mandibular canal and their clinical significance - review of literature

The clinical issues related to the anatomical variation of the mandibular canal have been extensively analyzed since the 19th century. Evolving dentistry techniques and advancements in the prosthetics forced to collect detailed information about anatomical variations of the mandibular canal due to its neurovascular content. Therefore, its radiographic imaging became an essential part of the oral surgery, in order to avoid complications resulted from an accidental damage of the mandibular canal.

A micro-computed tomography study of the sinus tympani variation in humans

BACKGROUND

The posterior part of the tympanic cavity comprises a depression called the sinus tympani (ST). The said structure is of outmost importance, e.g. in surgical procedures involving the middle ear, as a pathology (microbial biofilm or cholesteatoma) present in this difficult to access location might hinder its effective treatment. The aim of the study was to evaluate anatomical variants of the ST in human adult petrous bones. For this purpose, three-dimensional (3D) models of the ST were recreated from micro-computed tomography (CT) scans of 44 dry petrous bone samples (19 female, 25 male), applying 3D Slicer, Meshmixer and MeshLab software.

MATERIALS AND METHODS

Anatomical variants of the ST were classified in terms of both shape and surface configuration. The internal configuration of the ST was classified as heterogeneous - containing small bony trabeculae and crests up to 1.0 mm in size, contrasting to homogeneous ST that characterizes a relatively smooth interior, or mere presence of minor depressions and mild folds. Female STs were more bowl-shaped (57.9%) than saccular (42.1%), and had heterogeneous surface configuration (52.6%) compared to homogeneous (47.4%). On the contrary, male STs were more saccular (52.0%) rather than bowl-shaped (48.0%), and predominantly had a heterogeneous surface (84.0%) over homogeneous (16.0%).

RESULTS AND CONCLUSIONS

A complex combination of ST features comprised of a saccular shape and heterogeneous surface occurred in 52.0% of males and in 15.8% of females (a statistically significant difference; p = 0.0254, Fisher's exact test) seems to be clinically important because of its potential negative implication on health outcomes after surgery in the case of, for example, cholesteatoma, and it may also favour chronic pathological processes.

Visual perception of the osseous labyrinth rendered from micro-CT scans of the petrous bone

Grayscale images comparing to the color images may have less of visual information necessary for easy recognition of the anatomical structures. Although micro-CT scanners deliver images of ultra-high resolution, application of false-colors to the rendered structures enhance their visual perception and allow for quick delineation between them and surrounding bony matrix. This paper presents differences of imaging of the osseous structures of the inner ear labyrinth using pseudo-color volume rendering in contrast to grayscale volume rendering of the micro-CT data. Applied procedures of image processing improved significantly delineation between the bony matrix surrounding the cochlea and vestibule rendered in the pseudo-colors than in grayscale.

Micro-CT study of the dehiscences of the tympanic segment of the facial canal

PURPOSE

To depict the anatomy of the tympanic segment of the facial canal using a 3D visualization technique, to detect dehiscences, and to evaluate their frequency, location, shape, and size.

METHODS

Research included 36 human temporal bones (18 infant and 18 adult samples) which were scanned using a Nanotom 180N device. The final resolution of the reconstructed object was 18 µm. Obtained micro-CT data were subsequently processed by the volume rendering software.

RESULTS

The micro-CT study allowed for the 3D visualization of the tympanic segment of the facial canal and detects dehiscences in the studied material in both infants and adults. Most of the dehiscences (66.7 %) involved the inferior wall of the tympanic segment in infants as well as in adults, and were located above and backward to the oval window. The most frequent dehiscence shape was elliptic (66.7 % in infants; 50 % in adults). Furthermore, we observed dehiscences of fusiform and trapezoidal shape in infants. Length of the dehiscences in most cases ranged from 0.5 to 1.4 mm (50 % in infants; 75 % in adults).

CONCLUSIONS

Volumetric reconstructions demonstrated the course of the tympanic segment of the facial canal and its relationship with the tympanic cavity. Knowledge about the size and location of any dehiscence within the tympanic segment of the facial canal is necessary due to the surgical significance of this region. If a dehiscence occurs, there is an increased risk of injury to the facial nerve during the operations or spread of inflammation from the middle ear.

3D visualization of the intratemporal course of the facial canal using computed micro-tomography

The current study presents high resolution reconstructions showing the course of the facial canal within the temporal bone and visualizes the spatial orientation of the subsequent segments of the facial canal. 3D reconstructions of the facial canal were created from micro-CT data obtained from the right and left human temporal bones of an adult individual of the male sex. For this purpose, volume and surface rendering was applied. 3D models of the facial canal and adjacent osseous structures comprehensively revealed its intricate course and depicted the spatial orientation of its subsequent segments: labyrinthine, tympanic and mastoid. The labyrinthine segment of the facial canal was clearly displayed in the horizontal plane whereas the tympanic and mastoid segments were entirely visible in the sagittal plane, which lines up along the long axis of the petrous part of the temporal bone.

Anatomy of the fundus of the internal acoustic meatus - micro-computed tomography study

The aim of this paper was to present micro-computed tomography (micro-CT) high resolution images of the fundus of internal acoustic meatus (FIAM) and characterise the normal appearance of its singular areas which are places of passage of numerous anatomical structures. By using micro-CT we obtain detailed volume rendering images presenting topography of the FIAM in 3-dimensional (3D) space. We figured out that 3D reconstructions obtained from micro-CT scans can precisely demonstrate all areas of the FIAM (facial nerve area, cochlear area, superior and inferior vestibular areas, singular foramen). Application of this technique allows finding out new anatomical structures like the foramen of the transverse crest, which is not described in literature. Hence, we estimated the size of each area of the FIAM by measuring their minimal and maximal diameter. In the studied material we did not find out any statistically significant difference between mean diameters calculated for infant and adult individuals.

Improved reliability for fractal dimension calculation of the vascular imprints on the cranial vault mapped with topographical correction

We presented a novel approach to studies of the vascular grooves located on the inner surface of the cranial vault. A three-dimensional vision system that acquired the endocranial surface topography was used for this purpose. The acquired data were used to generate images showing the branching pattern of the middle meningeal artery. Fractal dimension was used to characterize and analyze branching pattern complexity. We discussed the usefulness of the latter method and indicated difficulties and potential errors connected to the fractal dimension application. The technique introduced for recording traits of the object surface appears to be helpful in anatomical study of morphological variation of dural vascularization. It may also be applicable in paleoneurological research based on analysis of the cranial remnants. Fractal dimension should be used carefully as a method sensitive to many aspects of data acquisition and processing.

Application of the temporal bone for sex determination from the skeletal remains

This paper presents state of current knowledge on possibilities and accuracy of sex determination from the temporal bone. Experimental and comparative studies performed on temporal bones derived from different human populations allowed to verify to what extend this bone is valuable source of information on sex of individual. It was figured out that the temporal bone can be used for this purpose and the size of the mastoid process is considered to be one of the best sex discriminator.

Volume rendering of the tympanic cavity from micro-CT data

The current study presents volumetric reconstruction of the tympanic cavity obtained from micro-CT scans which pixel size was 18 μm. Thanks to this, osseous components of the tympanic cavity were shown in high optical resolution, causing that their morphological appearance was clearly demonstrated. Particular attention was paid on imaging the medial wall of the tympanic cavity, because its structures are of clinical importance. In this respect we showed spatial relationship between the promontory, the oval window, the round window and other minute structures like the pyramidal eminence, subiculum and ponticulus. Hence, application of the microcomputed tomography allowed to visualize abnormal osseous formation located within the tympanic cavity, which potentially could interrupt normal movement of the auditory ossicles.

Micro-computed tomography study of the abnormal osseous extensions of sella turcica

The paper presents anatomical considerations on the abnormal ossification, which occurred around the dorsum of the sella turcica in the human skull of the female individual. Probably the morphological alterations of the sellar region were associated with extensive heterotopic ossification of the dura mater attached to the dorsum of the sella turcica and the posterior clinoid processes. The analysis of gray values of the voxels representing the areas of abnormal ossification indicated on variation in bone density in the entire sample. We have established that the highest mineralisation of bony tissue occurred in the marginal parts of the osseous extensions deriving from the posterior clinoid processes. The ossified parts of dura mater attached to the posterior clinoid processes showed significantly higher content of the hydroxyapatite (1.9 g/cm3) than the dorsum of the sella turcica (1.0 g/cm3).

Trans-foramen magnum examination of the sella turcica region in the macerated human skulls

This report presents a method of quick and accurate imaging of the sellar region by means of the laryngological mirror equipped with a light pipe and followed by taking digital photograph as the mirror image visible through the foramen magnum. A technique of the intracranial imaging of the osseous structures was tested on the macerated human skulls. Images of the sellar region were presented as the example of quality of the employed technique, which can be regarded as a simplified version of the endoscopic examination.

Morphological features of the macerated cranial bones registered by the 3D vision system for potential use in forensic anthropology

In this paper we present potential usage of the 3D vision system for registering features of the macerated cranial bones. Applied 3D vision system collects height profiles of the object surface and from that data builds a three-dimensional image of the surface. This method appeared to be accurate enough to capture anatomical details of the macerated bones. With the aid of the 3D vision system we generated images of the surface of the human calvaria which was used for testing the system. Performed reconstruction visualized the imprints of the dural vascular system, cranial sutures, and the three-layer structure of the cranial bones observed in the cross-section. We figure out that the 3D vision system may deliver data which can enhance estimation of sex from the osteological material.

Imaging of the Wormian bones using microcomputed tomography

Wormian bones are irregular ossicles of small size and reveal fractal pattern of their edges. Their anatomy was visualized in volumetric reconstructions obtained from a series of micro-CT scans. In visual evaluation Wormian bones showed typical anatomy for the calvarial bones. They revealed three-layer composition: the outer and the inner table of the compact bone intervening with the table of the spongy bone. Microcomputed tomography captured all details of the interdigitation of the edge being incorporated into the lambdoid suture and interlocked between opposing edges of the occipital and parietal bones. This modality provided accurate images which allowed delineating morphological differences between the compact bone and the diploe, including vascular channels.