Imaging of the calvarium

Apical expansion of calvarial osteoblasts and suture patency is dependent on fibronectin cues

The skull roof, or calvaria, is comprised of interlocking plates of bones that encase the brain. Separating these bones are fibrous sutures that permit growth. Currently, we do not understand the instructions for directional growth of the calvaria, a process which is error-prone and can lead to skeletal deficiencies or premature suture fusion (craniosynostosis, CS). Here, we identify graded expression of fibronectin (FN1) in the mouse embryonic cranial mesenchyme (CM) that precedes the apical expansion of calvaria. Conditional deletion of Fn1 or Wasl leads to diminished frontal bone expansion by altering cell shape and focal actin enrichment, respectively, suggesting defective migration of calvarial progenitors. Interestingly, Fn1 mutants have premature fusion of coronal sutures. Consistently, syndromic forms of CS in humans exhibit dysregulated FN1 expression, and we also find FN1 expression altered in a mouse CS model of Apert syndrome. These data support a model of FN1 as a directional substrate for calvarial osteoblast migration that may be a common mechanism underlying many cranial disorders of disparate genetic etiologies.

Apical expansion of calvarial osteoblasts and suture patency is dependent on graded fibronectin cues

The skull roof, or calvaria, is comprised of interlocking plates of bone. Premature suture fusion (craniosynostosis, CS) or persistent fontanelles are common defects in calvarial development. Although some of the genetic causes of these disorders are known, we lack an understanding of the instructions directing the growth and migration of progenitors of these bones, which may affect the suture patency. Here, we identify graded expression of Fibronectin (FN1) protein in the mouse embryonic cranial mesenchyme (CM) that precedes the apical expansion of calvarial osteoblasts. Syndromic forms of CS exhibit dysregulated FN1 expression, and we find FN1 expression is altered in a mouse CS model as well. Conditional deletion of Fn1 in CM causes diminished frontal bone expansion by altering cell polarity and shape. To address how osteoprogenitors interact with the observed FN1 prepattern, we conditionally ablate Wasl/N-Wasp to disrupt F-actin junctions in migrating cells, impacting lamellipodia and cell-matrix interaction. Neural crest-targeted deletion of Wasl results in a diminished actin network and reduced expansion of frontal bone primordia similar to conditional Fn1 mutants. Interestingly, defective calvaria formation in both the Fn1 and Wasl mutants occurs without a significant change in proliferation, survival, or osteogenesis. Finally, we find that CM-restricted Fn1 deletion leads to premature fusion of coronal sutures. These data support a model of FN1 as a directional substrate for calvarial osteoblast migration that may be a common mechanism underlying many cranial disorders of disparate genetic etiologies.

Cranium growth, patterning and homeostasis

Craniofacial development requires precise spatiotemporal regulation of multiple signaling pathways that crosstalk to coordinate the growth and patterning of the skull with surrounding tissues. Recent insights into these signaling pathways and previously uncharacterized progenitor cell populations have refined our understanding of skull patterning, bone mineralization and tissue homeostasis. Here, we touch upon classical studies and recent advances with an emphasis on developmental and signaling mechanisms that regulate the osteoblast lineage for the calvaria, which forms the roof of the skull. We highlight studies that illustrate the roles of osteoprogenitor cells and cranial suture-derived stem cells for proper calvarial growth and homeostasis. We also discuss genes and signaling pathways that control suture patency and highlight how perturbing the molecular regulation of these pathways leads to craniosynostosis. Finally, we discuss the recently discovered tissue and signaling interactions that integrate skull and cerebrovascular development, and the potential implications for both cerebrospinal fluid hydrodynamics and brain waste clearance in craniosynostosis.

Musculoskeletal imaging manifestations of beta-thalassemia

Beta-thalassemia is a heterogeneous group of anemic disorders caused by the absence or defective production of beta-globin chains. Their clinical manifestations vary from asymptomatic to severe symptoms leading to a transfusion-dependent anemic state. The genes that cause thalassemia are prevalent in Asian and African populations, particularly concentrated in the Middle East, Mediterranean region, parts of India, and South East Asia. Over time, the disease causes various musculoskeletal abnormalities with complex pathophysiology secondary to chronic anemia. The compensatory mechanisms result in diffuse marrow hyperplasia, yellow to red marrow reconversion, osteopenia, and pathologic fractures. Inability to remove excess iron and inevitable iron overload as a result of multiple blood transfusions in patients with thalassemia major and intermedia is another face of the disease. Musculoskeletal manifestations include osteopenia, coarse trabeculae, bone expansion, synovitis, joint effusion, and metaphyseal dysplasia. These complications have long-lasting effects on the skeletal growth pattern resulting in bone deformity, short stature, premature closure of physes, and predisposition to infection. Additionally, there are radiologic features of iron-chelator therapy, which are unique and unrelated to the disease process itself. Familiarity of radiologists with the imaging features of beta-thalassemia is crucial in both diagnosis and timely management of the disease and its complications.

Posterior Cranial Vault Manifestations in Nonsyndromic Sagittal Craniosynostosis

ABSTRACT

Sagittal synostosis is the most common type of craniosynostosis. Sagittal suture fusion causes restriction of biparietal cranial vault growth, with expansion of the growing brain causing frontal bossing, an occipital bullet, and an elongated head shape. Due to the absence of studies focusing on the posterior cranial vault pattern in isolated sagittal craniosynostosis, we organized this study to characterize the posterior part of the cranial vault and its association with sagittal craniosynostosis. A retrospective study was conducted of isolated sagittal craniosynostosis patients who had undergone total cranial vault remodeling at the Cleft and Craniofacial South Australia (formerly known as the Australian Craniofacial Unit) between January 2018 and February 2020. Preoperative three-dimensional computed tomography (3D-CT) images were reviewed. The following parameters were evaluated: the cephalic index, lambdoid suture shape, lambdoid suture line pattern, presence of wormian bones along the lambdoid sutures and occipital fontanelle, presence of the mendosal suture, and angle at the tip of the join between the 2 lambdoid sutures. Thirty-nine 3D-CT scans of 32 males and 7 females were evaluated. The mean age when the patients underwent the 3D-CT imaging was 6.72 ± 7.9 months. A high prevalence of mendosal sutures (74.4%) was significantly found in sagittal craniosynostosis. Adult-like types of lambdoid suture interdigitating patterns were also significantly associated with young patients with sagittal craniosynostosis. No associations between the remaining parameters and particular synostoses were revealed.

Imaging of focal calvarial lesions

Focal calvarial lesions may present as a visible, palpable, or symptomatic lump; however, with increasing use of cross-sectional imaging they are often encountered as an incidental finding. Knowledge of the possible disease entities along with a structured approach to imaging is required to suggest an appropriate diagnosis and assist in management planning. Abnormalities range from common neoplastic lesions to rarer congenital conditions, benign pathologies, and calvarial defects that can mimic lesions. The aim of this article is to demonstrate the salient imaging features that may help to limit the differential diagnosis of a focal calvarial lesion.

The current state of imaging pediatric hemoglobinopathies

The hemoglobinopathies are a group of genetic disorders with a broad spectrum of clinical manifestations and radiologic findings. The imaging of pediatric hemoglobinopathies, which is influenced by concomitant hemosiderosis and the sequela of chelation therapy, has evolved over the years along with ever-improving technology. This article reviews and illustrates the most common radiographic and cross-sectional imaging findings of the 2 best known and clinically relevant hemoglobinopathies in pediatric patients, sickle cell disease and β-thalassemia.

Functional craniology and brain evolution: from paleontology to biomedicine

Anatomical systems are organized through a network of structural and functional relationships among their elements. This network of relationships is the result of evolution, it represents the actual target of selection, and it generates the set of rules orienting and constraining the morphogenetic processes. Understanding the relationship among cranial and cerebral components is necessary to investigate the factors that have influenced and characterized our neuroanatomy, and possible drawbacks associated with the evolution of large brains. The study of the spatial relationships between skull and brain in the human genus has direct relevance in cranial surgery. Geometrical modeling can provide functional perspectives in evolution and brain physiology, like in simulations to investigate metabolic heat production and dissipation in the endocranial form. Analysis of the evolutionary constraints between facial and neural blocks can provide new information on visual impairment. The study of brain form variation in fossil humans can supply a different perspective for interpreting the processes behind neurodegeneration and Alzheimer’s disease. Following these examples, it is apparent that paleontology and biomedicine can exchange relevant information and contribute at the same time to the development of robust evolutionary hypotheses on brain evolution, while offering more comprehensive biological perspectives with regard to the interpretation of pathological processes.