Pectus carinatum--first ultrastructural findings of a potential metabolic lesion.

The histological and ultrastructural findings of rib specimens after two re-interventions in the case of recurrence of pectus carinatum (PC) are presented in this report. A 15-year-old boy developed recurrences of mild PC after re-chondroplasties using the Ravitch technique. Histological study of the resected cartilage showed markedly degenerative changes of the sternocostal cartilage. For the first time, intracellular crystalline inclusions in some of the chondrocytes were found. These findings indicate metabolic changes as a possible pathogenetic parameter in PC.

Aspectos histológicos de la articulación manubrioesternal / Histologic aspects of the manubriosternal joint

La articulación manubrioesternal ha sido comúnmente un tema de discusión anatómico e histológico debido a sus diversas clasificaciones. Ha sido descrita como sínfisis, como cartilaginosa primaria o sincondrosis e incluso sinovial. El objetivo del trabajo fue examinar meso y microscópicamente la articulación manubrioesternal, con la finalidad de determinar el tipo de tejido que la constituye y de este modo definir el tipo de articulación, contribuyendo de esta manera al mejor conocimiento anatómico. Se extrajeron 10 esternones: 7 cadáveres frescos y 3 de cadáveres formolizados, cuya edades fluctuaban entre 40 y 60 años, de sexo masculino, todos de origen chilenos. En cada esternón se identificó la articulación manubrioesternal y se seccionó el hueso a 1 cm por arriba y 1 cm por abajo de la interlínea articular. Posteriormente, los segmentos fueron descalcificados para luego obtener 9 cortes en sentido anteroposterior: 3 de la parte mediana de la articulación y 3 de cada parte lateral próxima a la articulación esternocostal, los cuales fueron teñidos con hematoxilina-eosina y van Giesson. La observación microscópica permitió determinar que en 5 casos (50 por ciento) una fina capa de tejido hialino periférico cubría las superficies articulares del manubrio y cuerpo esternal, encontrándose entre las dos superficies una moderada capa (+++) de tejido fibrocartilaginoso. En 3 casos (30 por ciento), encontramos una fina capa de tejido hialino entre las superficies articulares y abundante tejido fibrocartilaginoso (++++) y en 2 casos (20 por ciento), el tejido cartilaginoso que recubría las superficies articulares eran muy abundante, con escasas presencia de fibrocartílago (++) en la región central. En 6 casos (60 por ciento) existía en el interior del fibrocartilago una pequeña cavidad. La articulación manubrioesternal presentó sus superficies articulares cubiertas con tejidos cartilaginoso del tipo hialino en relación con el tejido fribrocartilaginoso. Este último, un verdadero disco interpuesto entre las superficies articulares, en la mayoría de los casos con una pequeña cavidad, debido tal vez a la absorción que sufre la parte central de él, se aproxima más a una articulación sinovial que a una sincondrosis, producto de una calcificación periférica o de una sinostosis manubrioesternal

An ultrastructural study of the perichondrium in cartilages of the chick embryo.

The ultrastructure of perichondrial tissue of cartilage rudiments (metatarsus, tibiotarsus and sternum) of the chick embryo at various stages of development (H.H. stages 28-45) was investigated by transmission electron microscopy. Previous microscopic and submicroscopic data were generally confirmed, but new findings indicated: (a) the existence of a temporary syncytial state of perichondroblasts during the earliest developmental stages, (b) the existence of a perichondrial cambial layer of stem cells, (c) involvement of perichondroblasts in the appositional growth of cartilage. Electron microscopy revealed clear temporal relations between cell differentiation, perichondrial growth and the structure and production of perichondrial ECM. In addition, the boundaries between cartilage and perichondrial tissue were demonstrated unambiguously. Perichondrial structure varied specifically with each cartilage segment; in particular the perichondrium in long bone rudiments (where ossification starts early) contrasted with that in the permanent cartilage medial process of the sternum.

The ultrastructure of the connective tissue matrix of skin and cartilage after high-pressure freezing and freeze-substitution.

Studies designed to investigate the ultrastructure of the connective tissue matrix have historically relied on chemical fixatives to stabilize tissue microarchitecture. However, conventional fixatives are not completely effective in retaining many matrix constituents, including proteoglycans. Fixative recipes have been modified to include agents that retain proteoglycans, but they precipitate the glycosaminoglycan moiety into electron-dense granules and therefore do not preserve native microstructure. To avoid the structural artifacts introduced by aqueous fixatives, we prepared cartilage and skin by a cryostabilization procedure that included high-pressure freezing and freeze-substitution. Although similar approaches have been applied previously for study of connective tissue, our results and interpretation of matrix structure are significantly dissimilar. In optimally preserved areas of cartilage, collagen fibrils are continually surrounded by a densely staining sol. Empty fluid spaces are absent. In less optimally preserved areas, artifacts are noted and described, including a network that mimics the expected structure of proteoglycan. Similarly, the dermal matrix of human skin contains a preponderance of densely staining material that almost fills the voids commonly seen after aqueous fixation. Decorin, immunolocalized to the surface of dermal collagen fibrils, appears to be retained after this procedure.

Electron microscopic study of proteoglycan aggregates synthesized by embryonic chick sternal chondrocytes in vitro.

Proteoglycan(PG)-aggregates are known to play an important role in the inhibition of matrix calcification. PG extracted from future calcifying cartilage are smaller than those extracted from non-calcifying cartilage. The present study investigates if alterations in aggregate size are also observed in chrondrocyte cultures. Agarose cultures from chondrocytes derived from the non-calcifying (caudalic) and the future calcifying (cephalic) region of embryonic chick sterna are used. An average aggregate of the caudalic culture contained 27 monomers, an average aggregate of the cephalic culture 20. These data are in accordance with in vivo observation. Since the agarose culture creates the possibility to observe the whole population of de novo synthesized PG, this culture system can be helpful to investigate the role of PG-aggregates in matrix calcification.

Spontaneous fibro-osseous proliferative lesions in the sternums and femurs of B6C3F1 mice.

Bone morphology associated with fibro-osseous proliferation in the femurs and sternums of 98 female B6C3F1 mice were compared morphologically and quantitatively to femurs and sternums from 100 male B6C3F1 and 79 CF1 mice (48 female and 31 male). In addition, sternal samples from five B6C3F1 mice per sex were collected and processed for electron microscopy. Fibro-osseous proliferation was present in female B6C3F1 mice, but not male B6C3F1 or female CF1 mice. In female B6C3F1 mice at 32 weeks of age, the marrow spaces in the region of the proximal and distal epiphyseal plate were lined by large osteoblasts and had large vascularized centers. At 58 weeks, metaphyseal fibrovascular proliferative areas containing multinucleated cells and new cancellous bone delineating the lesion were seen. At 84 weeks, fibro-osseous tissue occupied the outer third of the sternal marrow cavity and by 110 weeks, more than two thirds of the marrow cavity. Fibro-osseous proliferation was present in 100 and 94% of the examined sternums and femurs, respectively, of female B6C3F1 mice at 110 weeks of age, but not in male B6C3F1 or female CF1 mice. Ultrastructural examination of the sternal changes at 110 weeks showed numerous osteoblasts, irregular bony spicules, and fibrocyte-like cells. By morphometry, the normal marrow cavity in B6C3F1 females occupied 35% of a longitudinal section of the whole sternebra compared with 70% and 75% of the whole sternebra in B6C3F1 males and CF1 female, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone lining cells and hematopoiesis: an electron microscopic study of canine bone marrow.

Hematopoietic bone marrow in the dog is enclosed by a nearly complete and rather complex layer of endosteum, consisting of a diverse group of cells collectively called bone lining cells (BLC). Cell types comprising BLC include osteoblasts and osteoclasts, and other cell types, among which are elongated, flat cells with a spindle-shaped nucleus, and small cytoplasmic vesicles. The composition and thickness of the layer of BLC varies along the perimeter of the marrow. The layer may be simple or stratified. Occasionally a zone of tightly packed regularly arranged collagenous fibers lies between the bone lining cells and bone. Hematopoiesis, particularly neutrophilic, often occurs in the bone marrow next to the BLC. Cytoplasmic processes of BLC occasionally extend into the hematopoietic spaces and stromal cells in the hematopoietic compartment may extend processes to the layer of BLC. Occasionally cells of the BLC are similar in appearance to stromal cells within the marrow. Our observations together with the experimental findings of others (that fibroblastic stromal cells contribute to the hematopoietic inductive microenvironment, that hematopoietic stem cells are concentrated subosteally, that cells responsible for regeneration of the marrow stroma are derived from the endosteal layer, and that high concentrations of hematopoietic colony-stimulating factors are produced there) indicate that the hematopoietic capacities of bone marrow may be regulated by BLC.

Analysis of the morphology and function of primary cilia in connective tissues: a cellular cybernetic probe?

More than 300 primary cilia have been identified electronmicroscopically in a variety of embryonic and mature connective tissue cells. To further define the enigmatic function of these cilia, we examined the interrelationships between the basal apparatus and cytoplasmic organelles and the ciliary shaft and the extracellular matrix. The basal diplosome was consistently associated with the secretory organelles including the maturing face of the Golgi complex, Golgi vacuoles and vesicles, the microtubular network, the plasma membrane, and coated pits and vesicles. Small vesicles and amorphous granules were also observed within the ciliary lumen and adjacent to the ciliary membrane. Microtubule-membrane bridges linked axonemal tubules to the ciliary membrane. The position, projection, and orientation of the axoneme were influenced by the structural organisation and mechanical properties of the matrix and frequently caused angulation of the ciliary shaft relative to the basal body. Located midway between the secretory apparatus and the extracellular matrix, primary cilia would appear ideally situated to mediate the necessary interaction between the cell and its surrounding environment prerequisite to the formation and maintenance of a functionally effective matrix. We propose that primary cilia in connective tissue cells could act as multifunctional, cellular cybernetic probes, receiving, transducing, and conducting a variety of extrinsic stimuli to the intracellular organelles responsible for effecting the appropriate homeostatic feedback response to changes in the extracellular micro-environment.