1 INTRODUCTION

STRUCTURE OF NORMAL 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, 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 and connect with the . 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, , jaw, and pelvis) and the tubu- lar bones of the appendicular skeleton (9). Both types consist of cortical (or compact) bone and cancellous (or spongy) bone. In a typical such as the femur, the , or shaft, is composed of cortical bone surrounding a voluminous marrow, or medul- lary, 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 plates. The broad part of the long bone between the and the tubular diaphysis is termed the . The epiphys­eal cartilage and the metaphyseal portion form the growth apparatus. The cortex of the bone consists of compact osseous tissue and the contains cancellous bone. Cancellous bone is made up of plates and bars that form an interconnect- ing 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 , is the basic Figure 1-1 structural unit of cortical bone (fig. 1-3). It con- sists 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 , 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 . DEVELOPMENT OF BONE Bone develops either from preexisting car- tilage (endochondral ) 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 . 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 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). 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 com- mon 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. The biopsy Needle Biopsy sample should be examined before the material is immersed in formalin or decalcification solution. Percutaneous needle biopsy is an effective The soft material should be separated from the and safe technique (17) for obtaining diagnos- bony fragments before the sample is processed. tic material from bone lesions, especially from It is important to do this whether the material metastatic carcinoma (2,13). Various needles is used for frozen section or paraffin embedding have been used. The advantage over FNA is procedures. Almost without exception, bone tu- that a larger amount of tissue is obtained with mors can be processed without decalcification, a needle biopsy. Imprint cytologic preparations and microscopic sections should be available can also be made from the tissue. within 24 hours. Fine-Needle Aspiration Biopsy Frozen sections can be made with either a cryostat or freezing microtome. Hematoxylin The technique of FNA biopsy was pioneered and eosin (H&E) or toluidine blue is used to eight decades ago by Ewing, Coley, Martin, and stain the specimen (fig. 1-5). The nuclear details Ellis at Memorial Sloan-Kettering Cancer Center are excellent with the toluidine blue stain. in New York City. Despite the accumulation of

5 Tumors of the Bones and Joints

extensive experience with FNA worldwide, par- situ hybridization studies, and the polymerase ticularly in Scandinavia, many centers have not chain reaction as well as for tissue culture and adopted it as a standard part of the diagnostic karyotyping (provided the number of cells is work-up of bone lesions. adequate for the latter two studies). Also, aspi- The interpretation of FNA specimens of bone rated material can be used for traditional light has problems similar to those of a histologic and electron microscopic studies. diagnosis based on open biopsy. However, the scarcity of morphologic material, the loss of HANDLING OF SPECIMENS certain architectural features, and the introduc- A special laboratory is not needed to handle tion of artifacts unique to FNA probably account gross specimens of bone lesions. At Mayo Clinic, for some of the reluctance of many centers to the gross specimen is examined in the frozen incorporate it into their routine diagnostic rep- section laboratory, which is adjacent to the ertoire. Moreover, the accurate interpretation of surgical suites. The gross specimen may take FNA specimens of bone lesions requires a high the following forms. degree of expertise within the specialty area, but Incisional Biopsy. It is important for the this expertise is sparse because of the relative surgeon to take the biopsy specimen from the rarity of bone tumors, their wide morphologic soft regions of the lesion. In instances of osteo­ spectrum, and diagnostic pitfalls. FNA findings sarcoma, this usually involves the soft tissue must be interpreted in the context of the clini- extension. It rarely is necessary to take a biopsy cal and radiographic findings. Hence, FNA of specimen from the intraosseous component, bone lesions should be performed at medical which is usually more heavily mineralized. centers that have experience and expertise in Excisional Biopsy. In the case of bone tu- the diagnosis and treatment of musculoskeletal mors, excisional biopsy specimens usually are tumors. If FNA is performed in this setting, it is removed by curettage. If the specimen contains useful in most cases for determining whether a fragments of bone, the fragments should be bone lesion is primary or metastatic, benign or separated from the tumor before the specimen malignant, and a low-grade or high-grade neo- is sectioned. No hard and fast rules exist for plasm. In many cases, a specific diagnosis can be how many sections should be taken from any suggested. The technique is particularly useful tumor. Areas that grossly appear to be different for rapidly distinguishing among primary bone should be sampled. tumor, metastasis, myeloma, and lymphoma. Resection. Most patients who have high-grade The technical aspects of performing FNA on sarcomas have preoperative chemotherapy, and bone lesions has been described in detail else- the bone containing the tumor is resected. The where (4,10,16,19,20). specimen consists of the segment of bone with Palpable lesions that have cortical thinning the surrounding soft tissue. An ellipse of skin con­ or breakthrough are easily aspirated, in most taining the biopsy tract is also usually removed. instances, with a 0.7- to 0.9-mm needle (20–22 There are two ways to handle these speci- gauge). Nonpalpable lesions with an intact cortex mens. First, the dissection can be performed require a cutting needle or Tru-cut instrument immediately. All the soft tissue is dissected away, as a leader for the needle; these biopsies usually leaving the tumor with the involved bone. It is are performed under the guidance of computer- best to slice the bone open along the longitudinal ized tomography (CT) or other imaging tech- axis, through the middle of the marrow cavity. niques. Several aspirations are ideal to ensure The bone can be opened with either a band saw that representative material has been obtained. or butcher’s meat saw (fig. 1-6). If the latter is used, May-Grünwald-Giemsa and H&E stains are pref- the specimen has to be held in a vise. The cut sur- erable to the Papanicolaou stain for bone lesions face should be washed with a brush (e.g., surgical because they enhance the matrix component scrub brush) under running water. This removes of the lesion, which is critical in evaluating the the bone dust from the specimen, thus reducing lesion. Aspirates may be useful for performing artifact. The surgeon usually sends a separate routine histochemical stains, immunohisto- sample of bone marrow from the bony margin or chemistry, DNA ploidy studies, fluorescence in margins. These can be checked by frozen section

6 Introduction

which is made by mixing 400 ml of formic acid in 1,600 ml of 10 percent formalin. The specimen should be checked frequently with a pair of forceps to avoid overdecalcification. Specimens without cortical bone are ready for sectioning within 24 hours. Other specialized decalcification solutions, such as ethylenedia­ minetetraacetic acid (EDTA), are available but not necessary for routine work. The addition of caustic acids has no advantage. Assessment of Chemotherapy Effect Most patients with high-grade sarcomas, especially osteosarcoma, are treated routinely with neoadjuvant chemotherapy before surgi- cal removal of the neoplasm. Several studies (1,14) have shown a correlation between the effect of chemotherapy and survival. Hence, it Figure 1-6 is necessary to evaluate the extent of necrosis BAND SAW after chemotherapy. The gross specimen is dis- A band saw is used to cut longitudinally through a sected as described above, and the bone is cut resected femur. along its longitudinal axis. One thin slice of the entire bone with tumor is obtained. This slice is evaluation. It is not possible to use frozen sec- put in a clear plastic bag and “photographed” tions to check all the radial margins of a large on a photocopier. The photocopy image can be tumor. However, if the surgeon is concerned used as a template. The entire slice is decalcified. about a specific margin, such as the neurovas- Decalcification may take several days because of cular bundle, it can be checked separately. This cortical bone. When the bone is soft enough, it technique has several advantages: the margins is cut into several smaller blocks, which should can be checked grossly immediately; if neces- be numbered sequentially. These numbers are sary, tissue can be saved for special studies, such marked on the photocopy so that the location as cytogenetics; and gross photographs appear of each block can be identified. The number of more natural when the tissue is not frozen. blocks depends on the size of the tumor. The second method for handling resection The effect of chemotherapy can take several specimens is to freeze the entire specimen until forms. 1) The tumor is replaced with new bone it becomes hard enough that it can be sliced formation. The marrow spaces, where the tumor open in its entirety. This has the advantage of was present, are filled with new bone. Malignant keeping the gross contours of the tumor intact, cells may or may not be present in the sclerotic including the relationships with other struc- bone; this is the feature that determines whether tures. However, it has the disadvantage of delay. the tumor is viable. One problem is that os- teoblastic osteosarcomas can have the same Decalcification pattern, and it is impossible to decide whether Several techniques are available for decalcify- the sclerotic bone is a result of chemotherapy. ing bone specimens. Whatever method is used, 2) The ghost outlines of the original neoplasm it is important to saw the bone into thin slices to with infarct-like necrosis are present. 3) The part hasten decalcification. Thick cortical bone rarely of the bone marrow containing the tumor is needs to be decalcified for diagnostic purposes. De- replaced with a proliferation of loosely arranged calcifying it will only delay in making the sections. vessels and spindle cells. Frequently, there are The slice should be washed to remove bone dust. collections of hemosiderin-containing histio- A practical method is to use a solution of 20 cytes. It usually is possible to discern where the percent formic acid and 10 percent formalin, tumor was and where normal marrow is present.

7 Tumors of the Bones and Joints

The areas of viable tumor are identified with Sarcomas of bone are graded predominantly the microscope. Areas with viable tumor can on the basis of two features: cytologic atypia be mapped on the photocopy image of the (anaplasia) and cellularity. Mitotic figures usu- gross specimen and the amount of persistent ally are more common in high-grade tumors, as tumor calculated. It is not always possible to be is necrosis. Most sarcomas are diagnosed with certain about the viability of some areas of the a small biopsy sample; hence, necrosis and mi- tumor. In spite of this problem, many studies totic figures are hard to evaluate, but cytologic have shown (1,14) that evaluation of response atypia is not. Grading requires that tumors show to chemotherapy is prognostically important. histologic variability. For example, one of the As recent studies have shown (1,14), it is only distinguishing features of Ewing’s sarcoma is the necessary to establish whether 95 percent or uniformity of the cells in a tumor and between more of the tumor is viable. It has also been different tumors. Thus, Ewing’s sarcoma cannot suggested that any residual viable tumor is be graded. Studies have shown that histologic important prognostically and, hence, it is only grading is not useful for chordoma, adamanti- necessary to decide whether 99 percent or more noma, or myeloma. It is helpful to grade chon- of the tumor is necrotic. drosarcomas, malignant vascular tumors, and spindle cell sarcomas of all kinds. GRADING OF BONE TUMORS Grading is subjective, but this deficiency is Grading is an attempt to predict the biologic not unique to the system described by Brod- behavior of a tumor on the basis of its histologic ers. The same caveat applies to reproducibility. appearance. Many techniques of molecular Nevertheless, the results of each grading system biology are used to predict prognosis when a have been shown to correlate with prognosis. malignancy is diagnosed. Microscopic grading, however, is the basic attempt to describe the STAGING OF BONE TUMORS malignancy of a tumor. Interest has resurged in Although a radiologic staging system for be- the histologic grading of tumors, and grading nign bone tumors has been proposed (and may systems have proliferated which are unique to be helpful in planning surgical management) organs and even to specific tumors of an organ. (6), this section considers only the staging of The grading system used at Mayo Clinic is sarcomas. The system that is used almost uni- based on the technique first described by Brod- versally by musculoskeletal oncologists is that ers (5) while studying squamous cell carcinoma of Enneking et al. (8), which takes into account of the lip. He described four grades, depending the histologic grade and anatomic extent of the on the “differentiation” of the tumor cells. Tu- neoplasm. Tumors are considered to occur in mor cells were considered “differentiated” or anatomic compartments. A sarcoma confined to “undifferentiated” on the basis of how similar the bone is intracompartmental; it is extracom­ or dissimilar their appearance was to that of partmental if it extends into soft tissues. normal precursor cells. This concept was similar Sarcomas are graded as high-grade (grades 3 to “anaplasia” described by Von Hansemann and 4) and low-grade (grades 1 and 2) tumors. (18). The four grades were described as follows: The histologic grade and the anatomic descrip- grade 1, 0 to 25 percent of the cells are undif- tion of the tumor are combined to define the ferentiated; grade 2, 25 to 50 percent of the cells stage: stage 1A—low-grade, intracompart­mental; are undifferentiated; grade 3, 50 to 75 percent stage 1B—low-grade, extracompartmen­tal; stage of the cells are undifferentiated; and grade 4, 75 2A—high-grade, intracompartmental; stage to 100 percent of the cells are undifferentiated. 2B—high-grade, extracompartmental; and stage Broders showed a correlation between histologic 3—distant metastasis regardless of other factors. grade of the tumor and survival of the patient. This staging system also includes a descrip- Originally, Broders described this grading tion of surgical margins: 1) radical—the entire system for squamous cell carcinoma, but he compartment involved by the tumor is re- later applied it to other epithelial malignancies. moved; 2) wide—the tumor is removed with sur- There is no logical reason why the principles rounding normal tissue, and the “reactive zone” cannot be applied to grading sarcomas. (composed of the fibrovascular­pseudocapsule)

8 Introduction

Table 1-2 TNM CLINICAL CLASSIFICATION T Primary Tumor TX Primary tumor cannot be assessed T0 No evidence of primary tumor T1 Tumor 5 cm or less in greatest dimension T1a Superficial tumor T1b Deep tumor T2 Tumor more than 5 cm in greatest dimension T2a Superficial tumor T2b Deep tumor N Regional Lymph Nodes NX Regional lymph nodes cannot be assessed N0 No regional lymph node metastasis N1 Regional lymph node metastasis M Distant Metastasis MX Distant metastasis cannot be assessed M0 No distant metastasis M1 Distant metastasis G Histopathologic Grade GX Grade cannot be assessed G1 Well differentiated G2 Moderately differentiated G3 Poorly differentiated G4 Undifferentiated Stage Grouping Stage IA Low-grade, small, superficial, deep G1, T1a-b N0 M0 Stage IB Low-grade, large, superficial G1-2, T2a N0 M0 Stage IIA Low-grade, large, deep G1-2, T2b N0 M0 Stage IIB High-grade, small, superficial, deep G3-4, T1a-b N0 M0 Stage IIC High-grade, large, superficial G3-4, T2a N0 M0 Stage III High-grade, large, deep G3-4, T2b N0 M0 Stage IV Any metastasis Any G, any T N1 M0 Any G, any T N0 M1

is removed intact; 3) marginal—the tumor is tumor is not removed intact, and margins are removed entirely, but the incision goes through involved. the reactive zone; and 4) intra­lesional—the The TNM classification is given in Table 1-2.

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