Three-dimensional imaging of the human internal acoustic canal and arachnoid cistern: a synchrotron study with clinical implications

Anatomy and embryology of the middle ear, labyrinth and intracranial vestibular pathways

The intricate anatomy and embryology of the middle ear, labyrinth, and vertigo-related intracranial pathways involve complex developmental processes and contributions from multiple germ layers. The middle ear, comprised of the tympanic cavity, ossicles, and Eustachian tube, develops from the first and second branchial arches and clefts. In contrast, the inner ear originates from the otic vesicle, forming the bony and membranous labyrinths. The embryological timeline spans from the 40th day of gestation to the 24th week. The vestibulocochlear nerve (cranial nerve VIII) emerges with the inner ear structures and is essential for auditory and vestibular functions. The brainstem integrates sensory inputs from the labyrinth through various nuclei and pathways, contributing to balance and spatial awareness. This review highlights the critical developmental stages and anatomical details relevant to understanding auditory and vestibular system disorders.

Morphologic Analysis of the Scala Tympani Using Synchrotron: Implications for Cochlear Implantation

OBJECTIVES

To use synchrotron radiation phase-contrast imaging (SR-PCI) to visualize and measure the morphology of the entire cochlear scala tympani (ST) and assess cochlear implant (CI) electrode trajectories.

METHODS

SR-PCI images were used to obtain geometric measurements of the cochlear scalar diameter and area at 5-degree increments in 35 unimplanted and three implanted fixed human cadaveric cochleae.

RESULTS

The cross-sectional diameter and area of the cochlea were found to decrease from the base to the apex. This study represents a wide variability in cochlear morphology and suggests that even in the smallest cochlea, the ST can accommodate a 0.4 mm diameter electrode up to 720°. Additionally, all lateral wall array trajectories were within the anatomically accommodating insertion zone.

CONCLUSION

This is the first study to use SR-PCI to visualize and quantify the entire ST morphology, from the round window to the apical tip, and assess the post-operative trajectory of electrodes. These high-resolution anatomical measurements can be used to inform the angular insertion depth that can be accommodated in CI patients, accounting for anatomical variability.

LEVEL OF EVIDENCE

N/A. Laryngoscope, 134:2889-2897, 2024.

High-Resolution Phase-Contrast Tomography on Human Collagenous Tissues: A Comprehensive Review

Phase-contrast X-ray imaging is becoming increasingly considered since its first applications, which occurred almost 30 years ago. Particular emphasis was placed on studies that use this technique to investigate soft tissues, which cannot otherwise be investigated at a high resolution and in a three-dimensional manner, using conventional absorption-based settings. Indeed, its consistency and discrimination power in low absorbing samples, unified to being a not destructive analysis, are pushing interests on its utilization from researchers of different specializations, from botany, through zoology, to human physio-pathology research. In this regard, a challenging method for 3D imaging and quantitative analysis of collagenous tissues has spread in recent years: it is based on the unique characteristics of synchrotron radiation phase-contrast microTomography (PhC-microCT). In this review, the focus has been placed on the research based on the exploitation of synchrotron PhC-microCT for the investigation of collagenous tissue physio-pathologies from solely human samples. Collagen tissues' elasto-mechanic role bonds it to the morphology of the site it is extracted from, which could weaken the results coming from animal experimentations. Encouraging outcomes proved this technique to be suitable to access and quantify human collagenous tissues and persuaded different researchers to approach it. A brief mention was also dedicated to the results obtained on collagenous tissues using new and promising high-resolution phase-contrast tomographic laboratory-based setups, which will certainly represent the real step forward in the diffusion of this relatively young imaging technique.

Length of the Narrow Bony Channels May Not be the Sole Cause of Differential Involvement of the Nerves in Vestibular Neuritis

OBJECTIVE

To measure the vestibular nerve bony channels, applying a 3D measurement to account for the oblique trajectory of the singular nerve.

BACKGROUND

The clinical syndrome vestibular neuritis affects structures innervated by the superior vestibular nerve more commonly than the inferior vestibular nerve. Anatomical differences such as a longer, narrower bony channel of the superior vestibular nerve may increase its susceptibility to entrapment.

MAIN OUTCOME MEASURES

Length of the narrow segment of each vestibular nerve in which the nerve occupies more than 80% of the bony channel was measured.

RESULTS

Forty six normal ears sectioned in the axial plane were measured. The narrow channel for the lateral semicircular canal (SCC, mean [SD] 2.94 ± 0.54) mm was longer than that of the singular nerve innervating the posterior SCC (1.95 ± 0.58 mm [p < 0.0001]), which also exceeded that of the utricular nerve (1.45 ± 0.36 mm [p < 0.0001]). The nerve to the superior part of the saccule (i.e., Voit's nerve) was 1.14 ± 0.48 mm and that of the inferior saccule was 0.52 ± 0.37 mm.

CONCLUSIONS

The length of the narrow bony channel for the singular nerve is longer than previously reported and exceeds the utricular nerve. Comparing these data with the frequency of clinical lesions in recent literature suggests that, although bony channel length may contribute to differential involvement of the vestibular nerves, other factors may increase susceptibility of the superior vestibular nerve, including redundancy in innervation of the saccule and posterior SCC and anastomoses between the facial nerve and the superior vestibular nerve through which reactivated herpes virus may spread.

High resolution imaging in bone tissue research-review

This review article focuses on imaging of bone tissue to understand skeletal health with regards to bone quality. Skeletal fragility fractures are due to bone diseases such as osteoporosis which result in low bone mass and bone mineral density (BMD) leading to high risk of fragility fractures. Recent advances in imaging and analysis technologies have highly benefitted the field of biological sciences. In particular, their application in skeletal health has been of significant importance in understanding bone mechanical behavior (structure and properties) at the tissue level. While synchrotron based microCT technique has remained the gold standard for non-destructive evaluation of structure in material and biological sciences, several lab based microCT systems have been developed to provide high resolution imaging of specimens with greater access, and ease of use in laboratory settings. Lab based microCT scanners are widely used in the bone field as a standard tool to evaluate three-dimensional (3D) morphologies of bone structure at image resolutions appropriate for bone samples from small animals to bone biopsy specimens from humans. Both synchrotron and standard lab based microCT systems provide high resolution imaging ex vivo for a small sized specimen. A few X-ray based systems are also commercially available for in vivo scanning at relatively low image resolutions. Synchrotron-based CT microscopy is being used for various ultra-high-resolution image analyses using complex 3D software. However, the synchrotron-based CT technology is in high demand, allows only limited numbers of specimens, expensive, requires complex additional instrumentation, and is not easily available to researchers as it requires access to a synchrotron source which is always limited. Therefore, desktop laboratory scanners (microXCT, Zeiss/Xradia, Scanco, SkyScan. etc.), mimicking the synchrotron based CT technology or image resolution, have been developed to solve the accessibility issues. These lab based scanners have helped both material science, and the bone field to investigate bone tissue morphologies at submicron mage resolutions. Considerable progress has been made in both in vivo and ex vivo imaging towards providing high resolution images of bone tissue. Both clinical and research imaging technologies will continue to improve and help understand osteoporosis and other related skeletal issues in order to develop targeted treatments for bone fragility. This review summarizes the high resolution imaging work in bone research.

Enhancement patterns of the normal facial nerve on three-dimensional T1W fast spin echo MRI

Objectives:

With increasing neuroimaging applications of contemporary three-dimensional T₁W fast spin echo (3D T1W FSE) sequences, it was aimed to reappraise the normal patterns of skull base facial nerve gadolinium enhancement.

Methods:

Pre- and post-gadolinium 3D T1W fast spin echo imaging studies (n = 64) were retrospectively analysed in patients without suspected facial nerve pathology. Two independent observers scored the signal at each of six skull base facial nerve segments. Wilcoxon signed-rank test was used to compare changes in signal between pre- and post-gadolinium sequences at each location, and how this differed between proprietary sequences or between the pairs of facial nerves.

Results:

There was significant enhancement at the fundal canalicular (16%), geniculate ganglion (96%), tympanic (45%) and mastoid (38%) facial nerve segments (p < 0.05). Two different proprietary sequences demonstrated similar patterns of enhancement and there was symmetry between the two sides.

Conclusions:

There is a differing pattern of normal facial nerve enhancement on contemporary 3D T1W FSE sequences compared to previous studies of 2D T1W SE imaging and fundal canalicular enhancement may be physiological.

Advances in knowledge:

This is the first study to evaluate patterns of normal facial nerve enhancement using contemporary 3D T1W FSE MRI sequences.

A Micro-CT and Synchrotron Imaging Study of the Human Endolymphatic Duct with Special Reference to Endolymph Outflow and Meniere's Disease

Meniere’s disease remains enigmatic, and has no treatment with sufficient evidence. The characteristic histopathological finding is endolymphatic hydrops, suggesting either an overproduction or decreased reabsorption of endolymph in the human inner ear. This study presents the first analysis of the vascular plexus around the human endolymphatic duct using micro computed tomography and coherent synchrotron radiation with phase contrast imaging. Using a software program, data were processed by volume-rendering with scalar opacity mapping to create transparent three-dimensional reconstructions. A rich vascular plexus was discovered around the endolymphatic duct that drained into collecting channels, linked to the vestibular venous outflow system. This network is believed to make up the principal route for endolymph outflow, and its associated malfunction may result in endolymphatic hydrops and Meniere’s disease.

Clinical outcomes of resecting scarpa's ganglion during vestibular schwannoma surgery

Vestibular schwannomas are slow-growing tumors arising from the Schwann cells of the vestibular nerve. Scarpa's ganglion, the vestibular nerve ganglion, is located within the internal auditory meatus. Surgical treatment of vestibular schwannomas carries the potential of resecting Scarpa's ganglion along with the tumor. No prior studies have evaluated outcomes based on the presence of Scarpa's ganglion within tumor specimens. The neurosurgery patient records were queried for patients who underwent surgical resection of vestibular schwannomas at the University of Missouri Healthcare between January 1, 2008 and December 31, 2018. Inclusion criteria consisted of minimum age of 18, imaging demonstrating an eighth nerve tumor, surgical resection thereof, and a final pathological diagnosis of WHO grade I schwannoma. Data were collected retrospectively. The histological slides of the tumors were reviewed, and the presence or absence of the ganglion was noted. Outcomes analyzed included postoperative dizziness, hearing, and facial nerve function. Fifty-two patients met inclusion criteria. Ten (19%) resected tumors contained portions of the ganglion. No difference in risk of resection of ganglion occurred based on the surgical approach (p = 0.2454). Mean follow-up duration was 24.6 months ± 26.2 standard deviation. No differences in postoperative hearing or dizziness (p = 0.8483 and p = 0.3190 respectively) were present if Scarpa's ganglion was resected. House-Brackmann classification of facial nerve function at last follow-up was similar (p = 0.9190). Resection of Scarpa's ganglion with vestibular schwannomas does not increase risk of post-operative dizziness, facial nerve weakness, or hearing loss.