Cartilage

Biomedical Aspects

Brian K. Hall, Brian K. Hall

• Publisher: Academic Press
• Year: 2013
• ISBN:
  9781483266909
• Topic: Sciences biologiques
• Subtopic: Zoologie

Cartilage, Volume 3: Biomedical Aspects is a compilation of articles that covers the various aspects of age-related cartilage deterioration, bone disease, and genetic mutation. The book is composed of 10 chapters that highlight different subjects related to the diseases and malformations of cartilage. Relevant topics that are discussed in each chapter include the formation of cartilage outside the confines of the skeleton; aspects of age-related changes in cartilage; tumors that invade cartilage; molecular and biochemical bases of cartilage mutations; and the immunological and bioelectrical properties of cartilage. Physicians, pathologists, orthopedic surgeons, and those working on the human skeletal system will find this text a very good reference material.

1

Ectopic Cartilage, Neoplasia, and Metaplasia

William A. Beresford

Publisher Summary

This chapter discusses ectopic cartilage, neoplasia, and metaplasia. To pronounce a tissue of an individual as out of its rightful place requires a thorough knowledge of anatomy and its variations. Thus, cartilage is expected in the tongue of a dog but not in that of a human. Cartilage occurring separately from the principal skeleton, ear, and airway and as a normal part in a particular species is called extraskeletal, in distinction to ectopic (EC) cartilage, which is not usually found at the site in any member of that species. The formation of EC cartilage in an already formed and functioning soft connective tissue implies the conversion of one differentiated tissue into another, that is, a metaplasia. Metaplasia also happens were EC cartilage to experience a direct conversion to bone. In its unexpected late development, the cartilage is a new growth, but when it is normal cartilage, limited in its growth, it is scarcely a neoplasm. Many cartilage-bearing soft-tissue lesions are neoplastic. The chapter also discusses the concepts of metaplasia and neoplasia to pathological and experimental EC cartilage. Most EC cartilage apparently forms by metaplasia of specialized cells. Its variety and rarity in pathology and limitations in the scope of experimentation have hampered the exact elucidation of its genesis. Remedies will come from more chemical and immunologic identification of cells, products, receptors, and agents; the use of agents to block induction of the cell; attention to the many potentially chondrogenic cells and circumstances pointed to by human medicine and comparative anatomy; and guidance from veterinary pathology on suitable animals to better exploit the presently bewildering species differences.

I. Introduction

II. Extraskeletal versus Ectopic Cartilage

III. Specious Ectopic Cartilages

IV. Tumors and Tumor-Like Conditions with Ectopic Cartilage

A. Osseous Tumors

B. Benign Extraosseous Tumors

C. Malignant Extraosseous Tumors

D. Composite Extraosseous Tumors

E. Miscellaneous Extraosseous Tumors

F. Tumor-Like Conditions

G. Cartilage in Malformations

H. Veterinary Examples of Ectopic Cartilage

V. Experimental Ectopic Cartilage

A. Embryonic Cartilage

B. Extraosseous Cartilage in “Maturity”

VI. Discussion and Summary

A. Matrix Synthesis and Variety

B. Precursor Cells

C. Stimuli

References

I INTRODUCTION

To pronounce a tissue of an individual as out of its rightful place requires a thorough knowledge of anatomy and its variations. Thus, cartilage is expected in the tongue of a dog, but not in that of a human. Cartilages occurring separately from the principal skeleton, ear, and airway, and as a normal part in a particular species, will here be called extraskeletal, in distinction to ectopic (EC) cartilage, which is not usually found at the site in any member of that species. This convention is necessary here, but contradicts (1) the common practice of clinicians to use extraskeletal in the sense of ectopic and (2) the skeletal role of the extraskeletal cartilages in the heart, tongue, eye, and elsewhere. Cartilage also arises on or within the skeleton and will be named osseous ectopic. For the EC cartilage of soft tissues, extraosseous will be used. Difficulties and points of interest between the extraskeletal and ectopic categories will be explored.

How easy is it to claim a material in a soft-tissue or bony site as cartilage? Chondroid, pseudocartilage, myxoid, chondroosteoid, and other entities have been hard to distinguish from cartilage, and in some instances the terms may have been misnomers for proper cartilage (see Volume 1, Chapters 1 and 2). True cartilage, of course, has a wide range of forms. How well the ectopic instances meet the morphological and histochemical criteria for cartilage, and the better criteria becoming available will be discussed.

Most EC cartilage falls into Schaffer’s (1930) class of secondary cartilage, appearing after the establishment of the primary cartilaginous skeleton, and frequently much later in life. The formation of EC cartilage in an already formed and functioning soft connective tissue implies the conversion of one differentiated tissue into another, that is, a metaplasia (Virchow, 1884; Willis, 1962). Metaplasia might also happen, were EC cartilage to experience a direct conversion to bone, as is sometimes claimed. In its unexpected late development, the cartilage is a new growth, but when it is normal cartilage, limited in its growth, it is scarcely a neoplasm. However, many cartilage-bearing soft-tissue lesions are without question neoplastic in the modern sense. Consideration will be given to the fit of the concepts of metaplasia and neoplasia to pathological and experimental EC cartilage.

II EXTRASKELETAL VERSUS ECTOPIC CARTILAGE

Schaffer (1930), Willis (1962), and Beresford (1981) list the many sites of extraskeletal cartilage in various species. Examples are still coming to light, thus the fibrocartilaginous reinforcements in the urethral process of the goat’s penis (Ghoshal and Bal, 1976) and the submandibular ventral pouch of rorqual whales (Pivorunas, 1977). The latter cartilage is closely bound to the mylohyoid muscle. A similarly intimate relation to muscle exists for a previously undescribed anterior element of the hyoid skeleton of the finch, Passer: the preglossale (Bock and Morony, 1978). This forms late via cartilage, articulates with another bone, and is definitely skeletal. The interest in the preglossale with regard to EC cartilage lies in its absence in all other birds and their possible reptilian ancestors, making it a skeletal neomorph. Bock and Morony suggest that it might have originated phylogenetically as an ectopic splint for its muscle, which developed a joint with the paraglossale and somehow became a constant skeletal element.

This hypothesis of a skeletal element being a genetically incorporated manifestation of an earlier EC cartilage contrasts with the more common, but ill-founded, view of EC mammalian abdominal-wound and scleral cartilages as atavistic expressions of crocodilian abdominal ribs and reptilian scleral cartilage. But atavism cannot be cast out altogether. The human os paracuneiforme, accessory to the tarsus, presumably forms in a cartilage, which by its sporadic presence might (but should not) be considered ectopic. Conroy (1978) argues that this element is the vestigial homolog of the primate prehallux.

Returning to the hyoid apparatus, Gentscheff (1934) saw small islands of hyaline cartilage in around 30% of human tongues (including those of newborns) near the tip where the genioglossal muscle inserts into the septum. The position of the cartilage matches that of the carnivores’ lyssa, which led Gentscheff to conclude that both instances constitute a relic of the rod in ancestral reptilian tongues. This inconstant extraskeletal cartilage has not confused the categorization of other lingual nodules in man as ectopic (see Section IV,B,1), because its existence is virtually unknown, and the chondromas are off the midline and not so anterior.

Misconceptions have arisen because of ignorance of the partly cartilaginous nature of the cardiac skeleton in m...