Antoine Dhem

haversian bone remodelling in human fetus

Haversian bone remodelling used to be considered an attribute of adult bone. In the present paper, typical haversian remodelling was observed in the humerus, ulna, radius, femur, tibia, fibula and 6th and 7th ribs as soon as the 24th week. Its aspect suggests an already ancient occurrence. Remodelling was found in the same bone pieces of the neonate as well as in the clavicle and the other ribs. Mechanical factors may be responsible for starting the remodelling but their effects could be modulated by metabolic needs. Other still unknown factors might play a role too.

Presence of Chondroid Tissue in the Symphyseal Region of the Growing Human Mandible

The mandibular symphysis studied by histology and microradiography in the fetus and in the newborn shows a mineralized tissue different from the calcified cartilage observed in endochondral ossificati

Craniofacial abnormalities induced by retinoic acid: a preliminary histological and scanning electron microscopic (SEM) study

Exogenous retinoic acid has been found to be teratogenic in animals and man. Craniofacial defects induced by retinoic acid have stimulated considerable research interest. The present report deals with scanning electron microscopical observations of the craniofacial region concurrent with histological examination of craniofacial dysmorphism induced in rat embryos following maternal treatment treated with varying dosages of all-trans-retinoic acid (tretinoin). Two groups of pregnant rats were treated with rat embryos exposed to retinoic acid suspended in corn oil (100 mg/kg b.w. on gestational day 11.5 and 50 mg/kg b.w. on gestational day 10, 11 and 12 respectively). A third group was treated with corn oil (vehicle) while a fourth group remained untreated. A wide spectrum of congenital abnormalities, including exophthalmos, microphthalmia and anophthalmia, maxillo-mandibular dysostosis, micrognathia of both maxilla and mandible, cleft palate, subdevelopment of ear lobe, preauricular tags and macroglossia, were observed in the offspring of retinoic acid treated animals. The abnormalities were both time and dosage dependent, and characteristic of Treacher Collins syndrome when retinoic-acid was administered on gestational day 11.5. In contrast, when retinoic acid was administered were on gestational days 10-12, the defects were similar to those seen in the first and second pharyngeal arch syndrome, as well as in the oculo-auriculo-vertebral spectrum. Whereas our data support the hypothesis that all-trans retinoic-acid disturbs growth and differentiation of several embryonic cell types essential for normal craniofacial development, its mechanism of action remains unclear.

Ossification of the Human Fetal Ilium

Ossification of the ilium is similar to that of a long bone. It possesses three cartilaginous epiphyses and one cartilaginous process. Moreover, it undergoes peculiar osteoclastic resorption, comparable with that of the cranium bones. Asymmetrical ossification of the ilium, haversian bone remodelling and apposition of chondroid tissue posterosuperiorly to the acetabulum most probably emphasize the importance of mechanical factors in the morphogenesis of the hip bone during fetal life.

Chondroid tissue in the early facial morphogenesis of the chick embryo

The calcified tissues involved in the early morphogenesis of the so-called intramembranous bones of the facial skeleton were studied by microradiographic and histological techniques in 22 chick embryos at the 9th, 12th and 14 th days of incubation. On the 9th day, the bones of the upper face and palatal vault are made up of thin sheets of chondroid tissue, deposited in their respective mesenchymal condensations. Woven and lamellar bone formation subsequently takes place in each of them from the 12th day of incubation, mainly on the external side of their chondroid primordia. The same phenomena occur in the lower facial and mandibular bones. These facts indicate that the primitive facial desmocranium of the chick embryo, which is classically considered to be formed by intramembranous ossification, first consists of chondroid tissue. As in the cranial vault, this tissue thus represents the initial modality of the skeletogenic differentiation within the avian facial mesenchyme.

Electron-microscopic Study of Chondroid Tissue in the Cat Mandible

SummaryThis paper deals with electron microscopic appearance of chondroid tissue. Samples from eight cat mandibles were studied without decalcification. The ultrastructural characteristics of the chondroid tissue cells are common with young osteocytes. The interterritorial matrix of chondroid tissue is mineralized, being constituted of large collagen fibrils and calcospherites. The compositions of these parts of the chondroid tissue matrix and of bony matrix are similar but they are two different tissues. The pericellular matrix of the chondroid tissue consists of finely branched filaments, thin collagen fibrils, and an abundant ground substance. It resembles a cartilage matrix and contains type II collagen which is not present in bony matrix.

Embryonic origin and fate of chondroid tissue and secondary cartilages in the avian skull

Chondroid tissue is an intermediate calcified tissue, mainly involved in desmocranial morphogenesis. Often associated with secondary cartilages, it remained of unprecise embryonic origin.

Histological observations of palatal malformations in rat embryos induced by retinoic acid treatment

Malformations of the palate were induced in white rat embryos following maternal exposure to retinoic acid (tretinoin). Five experimental groups and the controls were treated by the following protocol: Group 1: pregnant rats received 100 mg retinoic acid (RA)/kg b.w. suspended in corn oil on gestational day (GD) 11.5; Group 2: 20 mg RA/kg b.w. from GD 8-12; Group 3: 20 mg RA/kg b.w. from GD 7.5-11.5; Group 4: 100 mg RA/kg b.w. on GD 10-11; Group 5: 100 mg RA/kg b.w. on GD 10 and 12; Group 6 received corn oil vehicle from GD 7-14.5; and Group 6: served as non-injected controls. In all retinoic acid treated groups, varying degrees of clefts with occasional attempts of fusion were noted. The severity and frequency of the malformations were dependent on dosage or gestational day of drug treatment. Our results indicate that RA, even at the lowest dose tested (20 mg/kg b.w.) severely affects the various tissues constituting the embryonic palatal shelves by altering cell interaction and possibly programmed cell death. These events would then result in lack of or inadequate differentiation with subsequent formation of aberrant craniofacial architecture.

Microradiographic and histological study of the styloid process of the temporal bone

In order to establish the mechanisms underlying the morphogenesis of the so-called elongated styloid process, a comparative microradiographic and histological study was performed on 19 long and short processes. Some morphological differences between short and long processes are noticed. Numerous partially calcified cartilaginous islets are observed within the trabecular bone of very long styloid processes or covering their tip. Calcified fibrous tissue or calcified fibrocartilage sometimes contributes to the thickening of enlarged styloid processes. But the growth of the process does not seem to be due either to calcification or to ossification of the stylohyoid ligament, as thought in the past. Mechanical stresses stretching the second branchial arch during the fetal development probably induce a variable involvement of the different parts of Reicherts cartilage in the morphogenesis of the styloid process. The so-called elongated styloid process should thus be congenital. However, a further growth is still possible through the activity of the cartilaginous cap of the tip.

Calcified tissues involved in the ontogenesis of the human cranial vault.

SummaryThe cranial vault of fifteen human subjects varying in age from 20th week of gestational life to 9th month post-matum were submitted to microradiographic and histological analysis.Different phenomena such as cortical drift, bone cavitation and progressive substitution of different calcified tissues by lamellar bone are illustrated.Moreover, this study reveals in several areas the presence of chondroid tissue; it constitutes the edges of the sutures and is responsible for their growth till the post-natal period. Therefore, it can be supported that the role of chondroid tissue is essential for the harmonious development of the cranial vault.