Category Archives: Anatomy

Blood and bone

Superficial_blood_vessels_of_the_head_and_neckHematopoiesis is the process by which blood cellular components are formed, and takes place especially within the bone marrow. The haematopoietic cells produce all types of blood cells and tissues including red blood cells (erythrocytes), lymphocytes (T-cells, B-cells and natural killer cells), and the myeloid types of cells (granulocytes, megakaryocytes, macrophages). The haematopoietic cells are self-renewing and in adults are present in the vertebrae, pelvis, ribs, sternum, skull, proximal end of long bones and scapulae, being the main components of the red marrow. The red marrow is gradually changing with age into yellow marrow (tissue rich in adipose cells) following a specific pattern, when the process starts at the distal phalanges and continues towards the axial skeleton. However, in some cases, yellow marrow can also be converted again into a hematopoietically active tissue. The skeleton plays a crucial role in the normal hematopoiesis and both systems (bone and blood) interact and influence each other. In their recent paper Valderrábano and Wu (2019) reviewed the effect of various diseases of the circulatory system on the skeleton. The authors mention chronic disorders of hematopoiesis (thalassemia and sickle cell anemia) which are connected to the bone loss and increased fracture risk. Then they further discuss anemia and its association with the bone fragility in older adults. In anemia, the hemoglobin in the blood decreases (by decreasing the number of healthy red blood cells) which results in lower ability of the blood to carry oxygen. Anemia is most commonly caused by a nutritional deficiency (frequently the iron deficiency) or by the inflammation of chronic disease. Bone fragility and fracture risk are usually estimated based on the bone mineral density (BMD) test. Several authors have studied the association of BMD and amount of hemoglobin in the blood but with different results and methodology. The mechanisms behind the bone fragility in anemia and other circulatory diseases are unclear. The role of increased erythropoiesis (producing red blood cells) and its demands on the bone tissue was considered as a possible factor of impairment of bone cells. Possibly, a change in the mechanical and loading properties of bone marrow due to anemia could be also affecting the strenght of the bone. Nevertheless, more studies are needed to fully understand the interactions between the bone tissue and hematopoietic cells, and to discuss potential clinical implications.

Stáňa Eisová

 

 

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Carotid foramen and brain metabolism

2019-03-15 14_28_31-Harrington 2019 - Carotid foramen kopie kopieMetabolic cost of the human brain is known to be higher than any other organ of the body. The adult brain consumes up to 20% of the whole body energy, and the energetic cost is even higher during early ontogeny. It peaks at the age of  4 – 5 years with the cost of 66% (Kuzawa et al. 2014). It has been also hypothesized that such high brain energy requirements are compensated by the slow somatic growth in preadolescent humans. In the context of evolutionary anthropology, shape, size and various traits of the endocranial cavity are used to study human brain development during the phylogeny. The metabolic processes associated with brain development are directly relevant to the study of human evolution. The brain metabolic rate can be estimated from the rate of cerebral blood flow through which the supply of glucose and oxygen is provided to the cerebral tissues. The dimensions of the cranial foramina that transmit blood vessels into and out of the brain can be used as proxies of blood flow within the cranium. Specifically, carotid canals which allow passages to the internal carotid arteries (ICAs) are considered in the case of cerebral vasculature. However, there is a debate about the actual correspondence between foramina radius, blood flow, and energetic cost. In their new study, Harrington and her colleagues (2019) tested whether the radius of carotid foramen can be used as a reliable predictor of the blood flow rate in the ICA. They analyzed data sampled on 98 infant and juvenile crania by Lang et al. (1983) and applied formulas based on the method designed by Seymour et al. (2015). Importantly, they also evaluated age changes in the radius size of the carotid canal. The estimated blood flow rate within the ICAs based on the radius size of the carotid canal was calculated and compared to the previously reported values, describing age changes in the metabolic rate of the developing human brain. The results suggest the general correspondence of predicted values and known developmental changes in human brain metabolism, although the predicted ICA blood flow rate reaches a maximum between ages 5 and 8. As the authors also highlighted, further analyses on bigger samples with higher age variability should be performed to verify the relationship between cranial foramina, cerebral vessels, and human brain metabolism. The role of vertebral arteries in brain metabolism was also discussed. Boyer and Harrington (2018) showed that the vertebral artery is significantly involved in both cerebral and cerebellar blood flow; however, the amount of the blood contribution is not constant across species and might change during ontogeny of individuals. Nevertheless, these findings suggest that studies of metabolic changes on osteological material and even in the fossil record are possible.

Stáňa Eisová


Cranial foramina

2019-03-13-14_55_57-mcgonnell-2019-cranial-foramina-in-press-kopie-1.jpgCranial foramina are small openings of the cranial bones that allow the passage of nerves and blood vessels. During ontogeny, they develop in specific locations and usually remain open throughout the whole life of an individual. Recently McGonnell and Akbareian (2018) published a review on what is currently known about these anatomical elements. The authors observed the development of the foramina in chick embryos. They discuss the possible influence of different origins of the bone tissue (mesoderm or neural crest) and type of ossification (endochondral or intramembranous) in the formation and maintenance of the foramina. They also discuss the role of nerves and blood vessels in the formation of “zones of inhibition” which probably direct the foramen development. The authors also considered the impact of some diseases and syndromes on malformation or closing of the foramina. Specifically, they mention craniosynostosis, achondroplasia, hyperostosis, sclerosis, Chiari malformation, and osteopetrosis as conditions which may lead to significant alteration of their functions. Malformation can negatively affect the functions of major nerves or blood vessels, and even cause blindness, deafness and high intracranial pressure which can be fatal. In anthropology, cranial foramina together with other intracranial traits are considered in research of biological distances, population studies, paleoanthropology, paleopathology and forensic sciences (Píšová et al. 2017). Size and location of cranial foramina are used as proxies for their respective nerves and blood vessels. However, McGonnell and Akbareian also question the reliability and validity of this approach in case of fossil samples, considering our limited knowledge on the foramina development, and the fact that they might contain more than just one element (nerve or vessel). More comprehensive studies exploring human cranial foramina and their association with vascular and neural structures are needed, as well as better understanding of their interaction within the cephalic system.

Stáňa Eisová


Nicolas Henri-Jacob, 1844

[Antique Anatomy]


Primate brain folding

A recent work, analyzing the development and evolution of the primate cortical folding, evidences two separate folding processes of the neocortex. Namba and colleagues examine two subtypes of neocortex, the dorsal isocortex, defined as the portion of neocortex limited laterally by the lateral fissure (LF) and medially by the cingulate sulcus (CiS), and the proisocortex within these same boundaries, comprising the insular cortex and the cingulate cortex, respectively. Their sample was composed by three to five specimens from 13 different primate species, including two great apes (humans and chimpanzees), two Old World monkeys, four New World monkeys, one tarsier, one galago, and three lemurs. For each specimen they analyzed five comparable coronal sections. They measured the gyrencephalic index (GI) as the ratio of the length of the inner to outer cortex contours, and calculated the LF score as the ratio of the LF greatest depth to the maximum width of the hemisphere. Then they analyze the relationships between LF score, and the GI values for the dorsal isocortex, the cingulate and insular cortices, and the neocortex, which included the three cortices and the temporal isocortex. To provide an evolutionary perspective, they reconstruct GI and LF score values for the primate ancestors. Furthermore, they examine the timing of folding in a longitudinal sample of humans and long-tailed macaques, and the folding differences in human lissencephalic patients, for a developmental and genetic overview. The proisocortex showed a similar GI across the sample, and the reconstructed ancestor LF scores were in the same magnitude as those of the 13 present-day primates. Conversely, the degree of folding of the dorsal isocortex differs across the species, and between the ancestors and the extant species, increasing with increasing folding of the neocortex. Furthermore, their analyses also revealed that  LF and CiS appear earlier in development, while the dorsal isocortex starts to fold later. This portion of the cortex is also the most affected in human lissencephaly, as the LF, and CiS to a lesser degree, are still detectable in all grades of malformation. Hence, the authors conceptualize the folding of the neocortex as two distinct and sequential processes. The conserved folding occurs earlier in development, at the boundaries between the proisocortex and the dorsal isocortex, and involves the formation of the LF and CiS. The evolved folding occurs within the isocortex, after the onset of the conserved folding. Moreover, the authors suggest these two processes might be influenced by different cellular mechanisms, with neuron production contributing more to the conserved folding, and neuron migration to the evolved folding, a matter deserving further investigation.

 

Sofia Pedro


Mouse Lemur Brain

The gray mouse lemur (Microcebus murinus) is a small Madagascan primate, averaging 12 cm length and weighing between 60-120 grams. Despite the diminutive size, mouse lemurs are increasingly used in medical studies of Alzheimer’s disease and similar neurological disease processes found in humans. Mouse lemurs often live to 12 years or more in the wild, which combined with torpor (a form of short-term hibernation) may be associated with the longer lifespans. Considering mouse lemurs have prolonged lifespans, it is probably not surprising that they also experience age-related brain atrophy. Nadkarni et al. (2019) address the absence of a dedicated mouse lemur brain atlas through in-vivo MRI scanning 34 mouse lemurs, investigating age-related brain atrophy and the neuroanatomy of Microcebus murinus in a comparative context. Results showed that most of the cerebral cortex was affected with age-related brain atrophy including the primary visual cortex and, although the remainder of the primary sensory areas were unaffected by atrophy, an even higher amount of atrophy was found in the sub-cortical brain regions including the thalamus, hippocampus and amygdala. All previous studies of mouse lemur neuroanatomy have been conducted with histological atlases. However, Nadkarni and colleagues compared mouse lemur cerebral to cortical volumes using high-quality MRI, finding that contrary to histology studies, mouse lemurs had similar cortical to cerebral volume indices to other primate species and were not to be considered a “lesser primate” species as has been previously argued. The proportion of cerebral white matter was the highest in humans, before a continual decrease in macaques and smaller monkeys with the lowest white matter volumes observed in mouse lemurs. The trend for increasing white matter volumes in primates, culminating with the highest values in humans, has often been argued as necessary for reinforcing intra-cerebral connectivity, hypothesized as an important process in primate brain evolution.

Included with this study of mouse lemurs, Nadkarni and colleagues also produced an accompanying MRI in-vivo brain atlas which includes 120 labelled brain structures specific to Microcebus murinus which to-date, has been unavailable. The accessibility of a brain atlas specific for mouse lemurs removes the time-consuming process of manual MRI segmentation, allowing quick and direct comparison of brain regions with other primates for a comparative evolutionary context and in medical research for Alzheimer’s disease.

Alannah Pearson


Forgotten boneyard

 

Medusa’s skull

[archive]


Donor vessels

2

The traces of the middle meningeal artery (MMA) can be observed on dry skulls. For this reasons, it is often investigated in paleoneurology. The vessels run between the two layers of dura mater, along with the endosteal (periosteal) layer which is adherent to the inner surface of the skull. The MMA display connections with other vascular networks, but it is largely independent of the cerebral vascular system. Apparently, in adults there is only scarce or absent blood flow in MMA at rest, and activation may be triggered by thermal stress or other emergency responses (see Bruner et al. 2011). In a recent paper, Niknejad and colleagues (2018) test the possibility of using the MMA as a donor vessel in cerebrovascular bypass procedures, as an alternative to the superficial temporal artery (STA) which is standardly used for this purpose. The authors performed cadaveric dissections on 12 specimens and compared size, diameter and feasibility of both the MMA and the STA for the bypass to the middle cerebral artery. Their results confirmed that the MMA can be a suitable donor vessel. The premise of the donor potential of the MMA is based on its dispensability. Nevertheless, the authors note that the MMA may play an important role in case of the moyamoya disease, in which conditions MMA forms an important collateral network. In addition, this study provides valuable empirical data on the MMA morphology. Authors were able to identify three main branches in all specimens, with the dominant anterior petrosquamosal branch in all the cases. The diameter of the MMA was measured at its ostium and was 2.4 mm in average.

Stáňa Eisová


Automated digital tools

Since the early 2000s, the expansion of digital anatomy tools has been aided by advances in computational power and accessibility of medical imaging such as Computed Tomography (CT). The greater accessibility to digital imaging of fossil material has allowed the reconstructions of inner cranial cavities (endocasts), sinuses cavities, and dental reconstructions of the enamel-dentine junctions (EDJ) of fossilized teeth. Despite great accessibility, the segmentation processes used to generate digital reconstructions of inner cavities remain time-consuming and require specific expertise in computer analysis, anatomy, digital imaging.

Profico et al. (2018) provide two fully-automated digital methods to minimize these time-consuming digital segmentation tasks. Both of these methods rely on point-of-views (POVs) to delineate a region-of-interest (ROI). In the CA-LSE method, POVs were located outside a ROI and all areas beyond are subtracted from the final reconstruction. In contrast, the AST-3D method relies on a ROI defined by POVs placed inside a cavity and all external areas, subtracted from the final reconstruction. While both methods are similar and can be used to generate reconstructions of the inner cavities, each method has slightly different benefits. Profico and colleagues conducted a comparison of both methods to determine strengths and weaknesses of each approach. While both of these methods are available through the Cran R network, two different R packages were tested: Morpho and Arothron.

Results indicated that in the Morpho package, CA-LSE had no restrictions on where POVs could be placed, but using AST-3D method in Morpho, POVs had to be manually placed inside the internal cavity for successful reconstruction. In the Arothron package, CA-LSE method allowed fully-automated placement of POVs outside the ROI surface, however, the AST-3D method a ROI must be defined by manually placed POVs within the inner cavity. In general, accuracy of the AST-3D and CA-LSE methods were determined by each method, with AST-3D more reliable generating reconstructions of inner cavities (such as endocasts), while the CA-LSE was more suited to reconstructions of outer structures (such as skulls).

Although, automatic approaches offer time-efficiency and often allow larger sample sizes to be more quickly processed, many fossilized skulls are highly fragmentary and automated methods remain limited when fossilized remains are partially or entirely matrix-filled with anatomical and digital expertise still requiring manual segmentation. In these complex scenarios, further fine-tuning of automated methods would be invaluable with inclusion of fully-automated, semi-automatic and manual options.

Alannah Pearson


Neonate folding patterns

Duan and colleagues developed a new computational method for automatic detection of patterns of cortical folding in large datasets. This method extracts multiple features that characterize the folding patterns, such as sulcal bottoms and gyral crest curvatures. Then, an overall similarity matrix is calculated that contains information on shared patterns and individual variation. Finally, the subjects are clustered on groups that represent a common folding pattern. The authors show their method is more efficient than previous ones in detecting folding patterns and clustering subjects into affinity groups. They validate its reproducibility and reliability in two main samples. They demonstrate the application of their methodology on a large sample of 595 healthy neonate brains, to characterize folding patterns in newborns. Then, they compare their results to a dataset of adult brains from the Human Connectome Project. They focus on four cortical regions, the superior temporal gyrus (STG), the inferior frontal gyrus (IFG), the cingulate cortex, and the precuneus, considering both sex differences and hemispheric asymmetries. Overall, the typical folding patterns of infants were consistent with those of adults, evidencing that cortical folds are largely established from an early age. On the other hand, some differences were also identified. For instance, four folding patterns were recognized in infant STG, while adults have an extra pattern. In contrast, one of the neonates’ IFG pattern is absent in adults. In both samples, there are sex differences in the proportions of some of the folding patterns of STG, IFG, and cingulate cortex. Hemispheric asymmetries were observed in the cingulate and STG, being more significant in the latter, which the authors suggest might reflect language lateralization. Considering the precuneus, their method revealed three main gyral patterns which were not associated with sex differences or hemispheric asymmetries. These gyral patterns appear to be mainly grouped based on the presence of either a gyral structure (patterns 1 and 2, more frequent) or a deep sulcus (pattern 3) in the middle of the precuneus. According to the authors, these groups are similar to the ones described in a previous study by our lab on a sample of adult healthy brains.

Sofia Pedro