Osteoma

OSTEOMA (from Greek osteon-bone and oma - particle added to denote a tumor), a bone tumor; represents a circumscribed, originating from bone and consisting of bone tissue benign tumor. Previously, all bone formations were included in the concept of O., regardless of their origin (inflammatory, traumatic, neuropathic, blastomatous, etc.), although even at present the distinction between a true tumor and hyperplastic growths is a poorly illuminated and extremely difficult question. The difficulty of such a distinction depends partly on the ability of bone tissue to respond to irritation (inflammatory, traumatic) by forming tumor-like circumscribed growths (see Osteophytes); in addition, metaplastic processes, as well as processes of secondary ossification and finally the appearance of tumor-like formations in a number of systemic diseases of unknown etiology, belonging to the group of hypertrophic osteopathies [ostitis deformans Paget, leontiasis ossea (see), melorheostosis Leri (eburning hyperostosis affecting one limb-Putti)] and others, significantly complicate the above distinction. The site of formation of O. are the bones of the skeleton. Of the long tubular bones, the femur and humerus are most frequently affected; of the flat bones-the frontal and temporal; in addition, O. are often localized in the orbit and cavities of the facial skeleton. A tumor protruding above the surface of the bone is called an exostosis, one enclosed in spongy substance-an enostosis. According to their structure, O. are divided into 1) osteoma eburneum, consisting of compact substance with complete absence of bone marrow and almost complete absence of Haversian canals; 2) osteoma spongiosum, consisting of porous, spongy substance, and 3) osteoma medullare with large wide bone marrow cavities. Microscopically, the structure of O. resembles normal bone tissue. The tumor consists of bone plates with bone cells lying among them. The plates surround Haversian canals and bone marrow spaces. Bone marrow retains its normal properties. The size of bone marrow spaces and the number of Haversian channels vary considerably depending on the different forms of osteoma. Cartilaginous islands are often found among the bone tissue, which are embedded either in the spongy substance or in the subcortical layer. According to genesis, 1) epiphyseal exostoses (of cartilaginous origin) and 2) periosteal exostoses (of connective tissue origin) are distinguished. Epiphyseal exostoses occur only where bone is preformed from cartilage, and primarily in the area of the epiphyseal cartilage, spreading to the metaphysis. In structure, they belong to the spongy and medullary O., usually have the shape of a half-dome, often with the formation of a wide, correct pedicle, more rarely resemble stalactites in shape. Having a long, slow growth, they are subsequently displaced to the side of the diaphysis of the bone. The histological picture of O. preserves the correct shape of the bone structure, and the break of the cortical layer with the formation of the so-called cap (French authors), so characteristic of malignant tumors, is never observed. True O. are usually solitary. The so-called multiple exostoses represent a systemic, often familial disease. Reinecke collected 30 cases where the heredity of the disease was traced once in five generations, 15 times in three generations and 12 times in two generations. Multiple exostoses actually belong to enchondromas with subsequent normal ossification of cartilage and are closely related to multiple chondromas, with which they are often combined, which is why Kienbock proposed the name "chondral dysplasia" for this condition. According to Virchow, the essence of the disease consists in a violation of the bone development process. Appearing in the first years of life, sometimes in very large numbers, at the border of the epiphyses of long tubular bones, mostly with symmetrical arrangement, exostoses grow slowly and become stationary at the time of completion of the general growth of the skeleton bones, which approximates this disease to a hyperplastic process. The appearance of exostoses very often leads to shortening and deformation of bones; at the same time, congenital defects of tubular bones are also often observed. Periosteal tumor-like formations develop on the basis of traumatic irritation, the so-called traumatic osteoma of König and callus luxuriens, when significant protrusions form at the site of the bone callus, penetrating between muscles. A special form is the so-called exostosis bursata Volkmann's, in which the bony protrusion is surrounded by a connective tissue membrane closely resembling in structure to the joint capsule and secreting a synovial-type fluid. Such exostoses are found mainly at the border of the lower epiphysis of the femur. They owe their origin either to the proliferation of articular cartilage with subsequent eversion of the joint capsule or arise on the basis of external irritation with subsequent preformation of the surrounding connective tissue. True periosteal exostoses or cortical O. usually belong to the osteoma eburneum type, rarely consist of spongy substance and are most often found in the area of the cranial covering in the form of single or multiple tumors, sitting on the inner or outer cortical layer of the bone. O. occurring in the cavities of the frontal and sphenoid bones do not always have a periosteal origin; often they originate from embryonic cartilaginous remnants. Slowly increasing, they can cause erosion of the walls of the cavities, penetrating into the orbit or into the cranial cavity. With secondary inflammation and necrosis of their base, O. may become detached from the wall, forming a "dead O." (tote Osteome; Tillmans). In the sinus maxillaris, periosteal exostoses and central O. surrounding tooth rudiments are found, the so-called dental O. Of these latter, only part has a bone origin, others consist of dentin and are therefore odontomas. Periosteal O. is often observed on the nail phalanx of the thumb, directly under the nail or at its edge, and forms a small spongy tumor, the so-called osteoma subunguale. The nail disappears from the pressure of the tumor, and a very painful ulcer forms. Parosteal O. is called bone neoplasms arising near the bone or as a result of separation of an exostosis or originating from an isolated area of the periosteum due to trauma. True enostoses usually have their formation site in the diploe of cranial bones and are difficult to distinguish from periosteal exostoses. In long tubular bones, enostoses are extremely rare (Virchow, Benecke).-If there is a formation of bone where bone tissue is not normally found, one speaks of heterotopic O. Its occurrence in some cases depends on the ossification of the cartilaginous rudiment, in others it represents a metaplastic formation of bone from connective tissue (Myositis ossificans, see Myositis). Such heterotopic formations are found in the meninges, in the lungs, trachea, in the parotid gland, sclera, in muscles, in the skin of old people and cannot be considered true O. A particularly rare form of bone tumor is the one originating from osteoblasts-osteoblastoma, standing on the border between benign and malignant neoplasms (sarcomas). The tumor consists of groups of osteoblasts enclosed in osteoid and bone tissue as intermediate substance, which gives it a lattice-like structure and resembles the picture of adenomatous tumors (Herxheimer). The possibility of malignant degeneration of O. is not excluded; this especially applies to the "cartilaginous" exostoses (Ribbert, Chiari). Clari observed a case where there were more than 1,000 exostoses, with subsequent degeneration of one of them into a spindle cell sarcoma. Bramann, 7 years after removal of a solitary "cartilaginous" exostosis of the humerus, observed the occurrence of osteochondrosarcoma. Clinically, O. often develops asymptomatically, causing painful phenomena only when there is pressure on a nerve or when the tumor at a certain localization is a mechanical obstacle to movements. In the presence of exostoses having a pointed shape, damage to large vessels-arteries and veins-with the formation of traumatic aneurysm has been observed, as for example in the case described by Kuster, where there was an aneurysm of the a. popliteae. The differential diagnosis of O. is based on clinical and X-ray data: long course, slow growth of the tumor, its certain localization and form, the correct structure of the newly formed tissue with sharply limited contours and with the surrounding normal, non-atrophied bone tissue and absence of bone defects. In differential radiodiagnosis, in addition to malignant neoplasms, ossifying myositis and subperiosteal hematoma should be taken into account.-Treatment consists in radical removal of the tumor. Indications for surgical intervention are 1) violation of organ function or pain, 2) change in shape or retardation of bone growth, leading to limitation of mobility or violation of the statics of the limb.