Three-dimensional geometric morphometric studies of modern human occipital variation

Origin coordinate influence on performance of temporally extended signal space separation in magnetoencephalography

OBJECTIVE

Temporally extended signal space separation (tSSS) is a powerful method for artifact suppression in magnetoencephalography (MEG). Because tSSS first separates MEG signals coming from inside and outside a certain sphere, definition of the sphere origin is important. For this study, we explored the influence of origin choice on tSSS performance in spontaneous and evoked activity from epilepsy patients.

METHODS

Interictal epileptiform discharges (IEDs) and somatosensory evoked fields (SEFs) were processed with two tSSSs: one with the default origin of (0, 0, 40 mm) in the head coordinate, and the other with an individual origin estimated using each patient's anatomical magnetic resonance imaging (MRI). Equivalent current dipoles (ECDs) were calculated for the data. The ECD location and quality of estimation were compared across conditions.

RESULTS

MEG data from 21 patients revealed marginal differences in ECD location, but the estimation quality inferred from goodness of fit (GOF) and confidence volume (CV) was better for the tSSS with individual origins. This choice affected IEDs more than it affected SEFs.

CONCLUSIONS

Individual sphere model resulted in better GOF and CV.

SIGNIFICANCE

Application of tSSS using an individual origin would be more desirable when available. This parameter might influence spontaneous activity more strongly.

The Frequency of Occipital Spurs in Relation to the Cephalic Index: An Anatomorphometric Cone Beam CT Study

BACKGROUND

The occipital spur (OS) can be described as an abnormal elongation of the external occipital protuberance (EOP). The cephalic index (CI) refers to the ratio of width to length in any skull.

AIM

The aim of the present study was to evaluate the frequency and types of OS. It also aimed to determine the mean CI and the distribution of skull types using cone beam computed tomography (CBCT). And to determine if there was a relationship between the cephalic index and the presence and types of OS.

METHODS

CBCT scans from 523 patients were included in the study. OSs were classified as type 1 (flat), type 2 (crest), and type 3 (spine). Skull length and width were measured on axial sections and the CI was calculated. Based on the cephalic index (CI), skull types were classified as dolichocephalic (CI < 75), mesocephalic (75 < CI < 80), brachycephalic (80 < CI < 85), and hyperbrachycephalic (CI > 85).

RESULTS

The most common cranial types in the study group were brachycephalic (44.7%), mesocephalic (28.3%), hyperbrachycephalic (21.2%), and dolichocephalic (5.7%). Regarding the presence of OS, 54.3% of the participants had no OS, 23.1% had flat type, 15.3% had crest type, and 7.2% had spin type OS. There was a statistically significant difference (P < 0.05) in the frequency of OS according to skull type.

CONCLUSION

This study, the first to evaluate CI and OS using CBCT, concludes that brachycephaly is the most common cranial type. OS is more common in mesocephalic and dolichocephalic skulls, at older ages, and in males.

An Anatomorphometric Study of Occipital Spurs and Their Association With Dental Occlusion

Background and objective The occipital spur (OS) can be described as an abnormal elongation of the external occipital protuberance (EOP); its etiology is multifactorial and may involve biomechanical, immunological, and/or genetic factors. This study aimed to determine the frequency and characteristics of elongated EOP or OS as well as the relationship of OS with occlusion in a group of Turkish dental patients. Materials and methods Lateral cephalometric radiographs of 1925 patients taken in 2022 were retrospectively analyzed. The frequency, types, and dimensions of OS were determined based on gender and age groups. Molar occlusion and incisal bite were also evaluated. Results Of the 1925 patients, 679 were males and 1246 were females. The mean age of the cohort was 18.17 ±5.03 years (range: 4-61). OS was detected in 483 (25.1%) patients and was more common in males (p<0.001); 133 (27.5%) of the OSs were flat, 247 (51.1%) crest, and 103 (21.3%) spin type. The incidence of OS increased depending on age groups (p<0.001). There was no statistically significant association between OS presence and molar occlusion (p>0.05). However, a statistically significant association was observed between anterior incisal bite (p=0.001) and OS presence. There was a statistically significant difference in terms of OS sizes in males and females; the sizes of OS were larger in males than in females (length: p<0.05, base and thickness: p<0.001). Conclusions The frequency of OS was quite high in our cohort; it was more common and of larger size in males and older age groups. The most common type was the crest type. While there was no statistically significant association between OS frequency and molar occlusion, there was a significant relationship with incisal bite. The frequency of OS was highest in people with anterior crossbite.

Comparative morpho-functional analysis of the humerus and ulna in three Western European moles species of the genus Talpa, including the newly described T. aquitania

The forelimb is involved in many behaviours including locomotion. Notably, the humero-ulnar articulation, implicated in the elbow joint, is of particular importance for both mobility and stability. Functional constraints, induced in part by environmental plasticity, are thought to drive an important part of the bone shape as bone directly responds and remodels in response to both muscle and external forces. In this context, the study of subterranean moles is of particular interest. These moles occupy a hard and heavy medium in comparison with air or water, requiring a powerful body structure to shear and shift the soil. Their general morphology is therefore adapted to digging and to their subterranean lifestyle. The various morpho-functional patterns, which drive diverse abilities according to the environment, are likely targets of natural selection and it is, therefore, useful to understand the relationships between the bone shape and their function. Here, we quantify, through 3D geometric morphometric methods, the interspecific variability in the morphology of the ulna and humerus of three Talpa species, including the new species Talpa aquitania, to infer their potential consequence in species digging performance. We also quantify shape covariation and morphological integration between the humerus and the ulna to test whether these bones evolve as a uniform functional unit or as more or less independent modules. Our results show that interspecific anatomical differences in the humerus and ulna exist among the three species. Shape changes are mostly located at the level of joints and muscle attachments. As the species tend to live in allopatry and the fossorial lifestyle induces strong ecological constraints, interspecific variations could be explained by the properties of the environment in which they live, such as the compactness of the soil. Our results also show that the humerus and ulna are highly integrated. The covariation between the humerus and ulna in moles is dominated by variation in the attachment areas and particularly of the attachment areas of shoulder muscles concerning the humerus, which affect the mechanical force deployed during locomotion and digging. This study also highlights that in the new species, T. aquitania, variations in anatomical structure (general shape and joints) exist and are related to the locality of collect of the individuals.

Surgical Management of Chiari Malformation Type I and Instability of the Craniocervical Junction Based on Its Pathogenesis and Classification

We investigated the mechanism underlying Chiari malformation type I (CM-I) and classified it according to the morphometric analyses of posterior cranial fossa (PCF) and craniocervical junction (CCJ). Three independent subtypes of CM-I were confirmed (CM-I types A, B, and C) for 484 cases and 150 normal volunteers by multiple analyses. CM-I type A had normal volume of PCF (VPCF) and occipital bone size. Type B had normal VPCF and small volume of the area surrounding the foramen magnum (VAFM) and occipital bone size. Type C had small VPCF, VAFM, and occipital bone size. Morphometric analyses during craniocervical traction test demonstrated instability of CCJ. Foramen magnum decompression (FMD) was performed in 302 cases. Expansive suboccipital cranioplasty (ESCP) was performed in 102 cases. Craniocervical posterolateral fixation (CCF) was performed for CCJ instability in 70 cases. Both ESCP and FMD showed a high improvement rate of neurological symptoms and signs (84.4%) and a high recovery rate of the Japanese Orthopaedic Association (JOA) score (58.5%). CCF also showed a high recovery rate of the JOA score (69.7%), with successful joint stabilization (84.3%). CM-I type A was associated with other mechanisms that caused ptosis of the brainstem and cerebellum (CCJ instability and traction and pressure dissociation between the intracranial cavity and spinal canal cavity), whereas CM-I types B and C demonstrated underdevelopment of the occipital bone. For CM-I types B and C, PCF decompression should be performed, whereas for small VPCF, ESCP should be performed. CCF for CCJ instability (including CM-I type A) was safe and effective.

Global patterns of the cranial form of modern human populations described by analysis of a 3D surface homologous model

This study assessed the regional diversity of the human cranial form by using geometric homologous models based on scanned data from 148 ethnic groups worldwide. This method adopted a template-fitting technique for a nonrigid transformation via the iterative closest point algorithm to generate the homologous meshes. Through the application of principal component analysis to 342 sampled homologous models, the largest variation was detected in overall size, and small South Asian crania were clearly verified. The next greatest diversity was found in the length/breadth proportion of the neurocranium, which showed the contrast between the elongated crania of Africans and the globular crania of Northeast Asians. Notably, this component was slightly correlated with the facial profile. Well-known facial features, such as the forward projection of the cheek among Northeast Asians and compaction of the European maxilla, were reconfirmed. These facial variations were highly correlated with the calvarial outline, particularly the degree of frontal and occipital inclines. An allometric pattern was detected in facial proportions in relation to overall cranial size; in larger crania, the facial profiles tend to be longer and narrower, as demonstrated among many American natives and Northeast Asians. Although our study did not include data on environmental variables that are likely to affect cranial morphology, such as climate or dietary conditions, the large datasets of homologous cranial models will be usefully available for seeking various attributions to phenotypic skeletal characteristics.

Correlation of the external occipital protuberance with venous sinuses: a magnetic resonance imaging study

PURPOSE

To date, no study has explored the external occipital protuberance (EOP) using neuroimaging modalities. This study aims to characterize them using magnetic resonance imaging (MRI).

METHODS

A total of 96 patients underwent thin-sliced, post-contrast MRI. The sagittal images were analyzed.

RESULTS

In 97%, the EOPs were delineated as a focal external protrusion of the midline region of the occiput with varying morphologies. In 89% of 93 patients with identifiable EOPs, parts of the intracranial dural sinuses were found to lie just below the inion, the most prominent point of the EOP. The most frequently targeted dural sinus was the confluence of sinuses that was found in 57%, followed by the superior sagittal sinus. In 16%, a bony foramen and transmitting vessel were detected in the EOP, connecting between the diploic channels and the subcutaneous veins. Furthermore, in 33%, bony foramina and transmitting venous structures were identified in the region just below the EOPs, connecting between the diploic channels and the subcutaneous veins.

CONCLUSIONS

The intracranial dural venous sinus is located just below the EOP with a high probability. Most bony foramina in the EOP and midline suboccipital region may transmit veinous structures connecting to the diploic channel.

Evans index among adult Ghanaians on normal head computerized tomography scan

Introduction

Normal-Pressure Hydrocephalus (NPH) is a neurological condition which is made up of a clinical triad of gait disturbance, dementia and urinary incontinence and can be reversed by ventricular shunting. Currently, some guidelines suggest the use of Evans' index (EI) for diagnosis of hydrocephalus radiologically. Most of the studies are based on the Western population data. None of these studies have been performed in the Ghanaian population setting yet. The aim of this study was to quantitatively establish normal borderline value for Evans Index in the Ghanaian adult population with respect to age and sex.

Methods

This study was retrospectively conducted on normal enhanced head CT scan images of 266 males and 241 females. EI was calculated as the linear ratio of Maximum Anterior Horn Width (MAHW) of the frontal horns of the lateral ventricles at the level of foramina of Monroe and the Maximum Intracranial Diameter (MICD) of the inner skull. Student T-test, ANOVA and Pearson's correlation were used to analyze the data. A test for a relationship was performed with a scatter plot and a linear regression was performed based on age, sex and different EI of ventricular size.

Results

The mean and median value of EI was 0.24 ± 0.02. There was no statistically significant difference in the EI values between males and females, (p-value = 0.61). A steady increase in EI with age was observed. There was a strong correlation coefficient r = 0.89 of EI and age, which suggested a strong linear relationship between EI and Age. The overall linear relationship model was EI = 0.1879 + 0.0011∗Age.

Conclusions

The mean EI of 0.24 ± 0.02 in our study agrees with adapted international guidelines cut-off value for normal adult patients of (<0.30) and can be a useful tool in determining ventricular enlargement particularly in resource limited settings.