Introduction

1 INTRODUCTION STRUCTURE OF NORMAL BONE concentrically around the central canal. The The skeleton serves several important func- haversian canals form an anastomosing system tions, for which its structure is ideally suited. of canals arranged along the long axis of the First, it performs a mechanical function by bone; thus, in cross section, bones appear as supporting the body and providing attachment round openings surrounded by rings of bone. sites for muscles and tendons that provide mo- The lamellae have a large number of lacunae, tion. Second, it protects vital organs and houses which contain osteocytes and connect with the bone marrow. Third, it serves as a reservoir one another through a series of canaliculi. The for various minerals, especially calcium, and has haversian canals are connected to the external a role in meeting the immediate needs of the organism for calcium (3). Bones are divided into two main types: the flat bones of the axial skeleton (skull, scapula, clavicle, vertebra, jaw, and pelvis) and the tubular bones of the appendicular skeleton (9). Both types consist of cortical (or compact) bone and cancellous (or spongy) bone. In a typical long bone such as the femur, the diaphysis, or shaft, is composed of cortical bone surrounding a voluminous marrow, or medullary, cavity (fig. 1-1). The epiphyses at the ends of long bones consist mostly of cancellous bone and a thin peripheral rim of cortical bone. In an immature skeleton, the epiphyses are separated from the diaphysis by the epiphyseal cartilage plates. The broad part of the long bone between the epiphyseal plate and the tubular diaphysis is termed the metaphysis. The epiphys eal cartilage and the metaphyseal portion form the growth apparatus. The cortex of the bone consists of compact osseous tissue and the medullary cavity contains cancellous bone. Cancellous bone is made up of plates and bars that form an interconnecting network (fig. 1-2). These plates and bars are composed of varying numbers of contiguous thin layers (lamellae). The bony trabeculae are arranged along the lines of maximal pressure or tension. The haversian system, or osteon, is the basic Figure 1-1 structural unit of cortical bone (fig. 1-3). It consists of a central haversian canal, which contains LONG BONE blood vessels, and lamellae of bone arranged The normal tibia and fibula of a 7-year-old boy illustrate the anatomy of a long bone. 1 Tumors of the Bones and Joints Figure 1-2 CANCELLOUS BONE Left: An interconnecting network is created by plates and bars of lamellar bone. Right: Higher-power view shows cancellous trabeculae surrounded by the marrow cavity containing fat and hematopoietic elements. surface of bone and the marrow cavity through the canals of Volkmann. Bone is covered by a connective tissue layer, the periosteum, except where it is in contact with the articular cartilage. The attachment between bone and periosteum is tight where bundles of collagen (Sharpey fibers) from the periosteum penetrate cortical bone. Large blood vessels and nerves enter the bone at these points. The periosteum has two layers: an outer layer composed of dense connective tissue and an inner cambium layer composed of loosely arranged collagen and elastic fibers and a few spindle cells. The inner aspect of the cortex is separated from the marrow space by a thin layer of connective tissue called the endosteum. DEVELOPMENT OF BONE Bone develops either from preexisting cartilage (endochondral ossification) or in mem- branous connective tissue (intramembranous ossification). Intramembranous Ossification The first signs of bone development are thin bars of a dense intercellular substance. The cells that remain in this meshwork are large, assume Figure 1-3 a polyhedral shape, and become osteoblasts. CORTICAL BONE The cells are surrounded by a dense interstitial Dense compact cortical bone with haversian canals is substance that undergoes calcification and be- surrounded by concentric lamellar bone. comes bone. 2 Introduction Figure 1-4 ENDOCHONDRAL OSSIFICATION Left: Low-power appearance of an epiphyseal plate, with bone formation seen in the lower portion of the panel. Right: Columns of cartilage cells in the zone of provisional calcification just before osteoid production. Endochondral Ossification CLASSIFICATION OF BONE TUMORS Endochondral ossification is the mechanism The classification of bone tumors is based by which long tubular bones grow in length, on either the cytologic features of the tumor and is also is the process in fracture callus. The cells or the matrix produced by them (11,15). chondrocytes of the epiphyseal plate are ar- The classification system that follows is a slight ranged in columns, and near the metaphyseal modification of these two schemes. Malignant end, they undergo hypertrophy and vacuoliza- tumors rarely arise from benign ones, although tion of the cytoplasm and eventually become it is convenient to divide tumors into benign calcified (fig. 1-4). Loops of blood vessels and and malignant counterparts (Table 1-1). Neo- connective tissue invade the hypertrophic plasm simulators are discussed in chapter 14. cartilage cells, which are then removed. The connective tissue cells are transformed into INCIDENCE OF BONE TUMORS osteoblasts. Between the cartilage cells and Primary tumors of bone are extremely rare, osteoblasts, connective tissue becomes calci- and no reliable statistics are available for the fied, giving rise to columns of bone. With the whole group. In the SEER (Surveillance, Epi- cessation of longitudinal growth of bone, the demiology, and End Results) program, during epiphyseal plate disappears. 1973 to 1987, only 0.2 percent of all cancers 3 Tumors of the Bones and Joints Table 1-1 CLASSIFICATION OF BONE TUMORSa Benign Malignant Histologic Total Class No. of No. of Type No. % Tumor Cases Tumor Cases Hematopoietic 1,788 18.8 Myeloma 986 Lymphoma 802 Chondrogenic 2,914 30.6 Osteochondroma 946 Chondrosarcoma 1,023 Chondroma 469 Secondary chondrosarcoma 128 Chondroblastoma 138 Dedifferentiated chondrosarcoma 130 Chondromyxoid 48 Mesenchymal chondrosarcoma 32 fibroma Osteogenic 2,480 26.0 Osteoid osteoma 369 Osteosarcoma 1,941 Osteoblastoma 97 Parosteal osteosarcoma 73 Unknown 1,281 13.4 Giant cell tumor 627 Ewing’s sarcoma 578 Malignancy in giant cell tumor 36 Adamantinoma 40 Histiocytic 99 1.0 Fibrous histiocytoma 9 Malignant fibrous histiocytoma 90 Fibrogenic 285 3.0 Desmoplastic fibroma 14 Fibrosarcoma 271 Notochordal 411 4.3 Chordoma 411 Vascular 244 2.6 Hemangioma 131 Hemangioendothelioma 98 Hemangiopericytoma 15 Lipogenic 10 0.1 Lipoma 8 Liposarcoma 2 Neurogenic 18 0.2 Neurilemmoma 18 Total 9,530 100.0 Total 2,860 Total 6,670 aThe number of cases in the Mayo Clinic files. METHODS OF BIOPSY were bone sarcomas (7). It has been estimated Diagnostic material from a bone tumor may that 93,000 new cases of lung cancer and 88,000 be obtained in one of three ways: open biopsy, cases of breast cancer occur annually in the needle biopsy, or fine-needle aspiration (FNA). United States, compared with only 1,500 cases Open Biopsy of sarcoma of bone. Myeloma is the most common primary bone tumor, although one may ar- Open biopsy is still the most common gue that myelomas are tumors of bone marrow; method for diagnosing bone tumors. It has most of them are diagnosed by biopsy of the the great advantage of obtaining the maximal bone marrow. In the SEER program, 35 percent amount of tissue. It is important to plan the of all sarcomas were osteosarcoma (however, biopsy so that the tract could be removed at myelomas and lymphomas were not included the time of definitive surgical procedure. It is in that study). Chondrosarcoma and Ewing’s preferable for the surgeon who would perform sarcoma are the next most common types. There the surgical procedure to perform the biopsy. is a bimodal distribution, with osteosarcoma An ill-conceived biopsy may preclude a limb and Ewing’s sarcoma occurring in the first and salvage procedure (12). The biopsy should be second decades of life and chondrosarcoma and planned with consultation among the radiolo- myeloma in the older age groups. gist, pathologist, and orthopedic surgeon. 4 Introduction Figure 1-5 FROZEN SECTION A hematoxylin and eosin– stained frozen section of syno- vial chondromatosis shows the characteristic clustering pattern of the chondrocytes. It is important to examine the biopsy speci- Frozen sections have several advantages over men before the wound is closed. Frozen sections other diagnostic techniques. Perhaps the most are convenient for confirming that diagnostic important reason for making frozen sections material has been obtained. is to check the adequacy of the specimen. If Role of Frozen Sections in Diagnosis of diagnostic tissue is received, part of it can be Bone Tumors. The common misconception is reserved for special studies such as microbio- that bone tumors are too hard (literally and figu- logic cultures, cytogenetics, and flow cytometry. ratively) for frozen section diagnosis. However, Margins can be checked on frozen sections. It is if a few simple rules are followed, frozen sections not possible to check all the margins on large tu- can be made successfully. As with any diagnostic mors, but those that are closest, such as the bone method (such as paraffin-embedded tissue and marrow margin, can be examined. In benign FNA), it is important to have good communica- and low-grade malignant lesions, a definitive tion between the pathologist and the clinicians diagnosis can be made and immediate treatment involved in caring for the patient. It is convenient instituted. With experience, a diagnosis can be to have the frozen section laboratory close to the based on frozen section specimens just as well surgical suites. Most bone tumors have soft mate- as it can with paraffin sections. rial that can be used for frozen sections.

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