Micro‐CT of the human ossicular chain: Statistical shape modeling and implications for otologic surgery

Abstract

The ossicular chain is a middle ear structure consisting of the small incus, malleus and stapes bones, which transmit tympanic membrane vibrations caused by sound to the inner ear. Despite being shown to be highly variable in shape, there are very few morphological studies of the ossicles. The objective of this study was to use a large sample of cadaveric ossicles to create a set of three‐dimensional models and study their statistical variance. Thirty‐three cadaveric temporal bone samples were scanned using micro‐computed tomography (μCT) and segmented. Statistical shape models (SSMs) were then made for each ossicle to demonstrate the divergence of morphological features. Results revealed that ossicles were most likely to vary in overall size, but that more specific feature variability was found at the manubrium of the malleus, the long process and lenticular process of the incus, and the crura and footplate of the stapes. By analyzing samples as whole ossicular chains, it was revealed that when fixed at the malleus, changes along the chain resulted in a wide variety of final stapes positions. This is the first known study to create high‐quality, three‐dimensional SSMs of the human ossicles. This information can be used to guide otological surgical training and planning, inform ossicular prosthesis development, and assist with other ossicular studies and applications by improving automated segmentation algorithms. All models have been made publicly available.

Automated Extraction of Anatomical Measurements From Temporal Bone CT Imaging

“…The accuracy of this pipeline is further corroborated by comparing its findings to published findings of manual measurements of similar metrics. Reported anatomical measurements for malleus manubrium length, 6,11‐13 incus interprocess angle, 13 facial nerve first and second genu angles, 14‐16 facial nerve–cochlea distance, 17 and superior EAC‐tegmen distance 18 in this study have been consistent with measurements reported in previous literature. However, our methodology for calculating incus short and long process lengths varies from previous definitions.…”

“…This is the first study, to our knowledge, to validate a method for automated anatomical measurement extraction with reliable accuracy. Prior methods for calculating clinically relevant anatomical measurements typically involve manual segmentation of structures on CT imaging with placement of fiducials on visualization software [6][7][8] or meticulous harvesting of cadaveric structures with direct manual measurements. [9][10][11] By manually segmenting a single average bone template along with clinical relevant landmarks, this image registration-based method is able to automatically propagate template labels to other temporal bone scans with reliable accuracy.…”

“…However, our methodology for calculating incus short and long process lengths varies from previous definitions. While other studies have defined short and process lengths as the distance between the tip of each process to the head of the incus, 6,12,13 we instead calculated the centroid of the incus as a common endpoint. This is because the centroid of the incus can be objectively calculated from its 3D mesh, rather than subjectively identifying a point at the head of the incus.…”

Statistical Shape Model of the Temporal Bone Using Segmentation Propagation

“…The temporal bone and lateral skull base contain a complex three-dimensional (3D) geometry of nerves, arteries, veins, as well as the organs for both hearing and balance (1). Due to this complex anatomy, multiple efforts over the years have aimed at defining the anatomical norms and variations of specific temporal bone structures, such as the ossicles, sigmoid sinus, and cochlea (2)(3)(4). These efforts have sought to better understand surgical landmarks and to investigate the biological significance of these anatomical variations.…”

Shape modelling of the oropharynx distinguishes associations with body morphology but not whiplash‐associated disorder

“…By understanding the way shapes vary and whether separate cohorts vary differently, subtle changes can be uncovered. This technique has been used to quantify the variability in boney and soft tissue structures such as the lumbar spine, hip, knee, ankle, orbit, ossicles and levator ani (Bartling et al, 2021 ; Gass et al, 2022 ; Pavlova et al, 2017 ; Vafaeian et al, 2022 ; Vrancken et al, 2014 ). However, SSM has not been used to examine a hollow cavity such as the oropharynx in vivo.…”