The following section provides some basic information about the different imaging modalities commonly used in the work-up of a patient with a bone tumor.

Successful therapy for malignant disease requires that treatment be accomplished before systemic dissemination has occurred. It is axiomatic, therefore, that when the treatment of choice is ablative surgery, the procedure should be done at the earliest practical moment in an attempt to remove the tumor before neoplastic embolization leads to death of the patient.

At least 90% of bone tumors have soft portions that can be sectioned and examined for immediate diagnosis. In most cases, these soft portions afford the best material for diagnosis. For example, a sclerosing osteosarcoma almost invariably has noncalcified zones at its periphery. Study of the radiograph guides the surgeon to these zones, from which biopsy specimens can be obtained for early diagnosis. Protracted decalcification of densely sclerotic portions of the tumor or adjacent cortical bone only delays therapy.

Fresh frozen sections allow an immediate, accurate, definitive diagnosis of more than 90% of bone tumors. The rare lesion that is too difficult or too ossified for rapid interpretation can also be easily recognized. As with fixed sections of various types, good histologic preparations and sound basic understanding of the pathologic features are requisites for successful interpretation of frozen sections. Deficiency in either requisite tends to make one deprecate this diagnostic medium.

At Mayo Clinic, the frozen-section laboratory is adjacent to the surgical suites. The surgeon frequently comes to the frozen-section laboratory carrying the biopsy specimen and the corresponding radiograph. It is important to examine the biopsy specimen grossly to separate fragments of bone from the soft, fleshy
material that almost all bone tumors have. This step is important even if frozen sections are not obtained. Some neoplasms, such as lymphoma, may be associated with a sclerotic reaction. It may be necessary to tease out small fragments of fleshy tumor with the tip of a scalpel blade. This material can be processed separately and does not require decalcification.

At our institution, a freezing microtome, rather than a cryostat, is used for making frozen sections. The biopsy material is placed on the stage, which is then cooled. The tissue freezes from the bottom toward the top. When about half of the material is frozen, the unfrozen material from the top is cut off with a microtome; this material usually does not have many frozen-section artifacts and can be used for permanent sections. A section is obtained from the frozen tissue, and the section is rolled off the blade with a glass rod. The tissue is stained with methylene blue, and excess stain is washed off. The stained section is mounted with water. The whole process should take no more than 30 to 45 seconds.

This method has several advantages. First and most important perhaps is the identification of viable and diagnostic material. Even if a specific diagnosis is not made on the frozen section, the surgeon can be reassured that diagnostic material has been obtained and it is not necessary to obtain better material. Second, if the lesion under consideration is deemed to be infectious, cultures can be done. Third, a definite diagnosis can be made with assurance in most tumors. Many malignant neoplasms are no longer treated surgically immediately after diagnosis is made. However, many of the benign and low-grade malignant tumors can be treated immediately. This has the advantages of not subjecting the patient to a second anesthetic procedure and reducing hospital stay. Fresh frozen sections can also be used for checking the adequacy of margins. Obviously, it is impossible to check all margins on a large sarcoma of bone or soft tissue. However, at least margins deemed “close” by the surgeon can be checked microscopically. A margin that is free only microscopically may be too close.

If a diagnosis cannot be made immediately, it should still be possible to make one within 24 hours. As mentioned above, almost all bone tumors have soft portions. It is very important to separate the material from the bony fragments with which it may be admixed. This material should be processed without decalcification. However, decalcification may be necessary in some rare instances, even for diagnostic material. Decalcification is certainly necessary for larger specimens, such as resections for osteosarcoma after chemotherapy. Several different decalcification methods are available. At Mayo Clinic, 20% formic acid and 10% formalin are routinely used. The solution is made by mixing 400 mL of formic acid in 1,600 mL of 10% formalin. It is important to make thin slices of tissue so that decalcification is rapid. Examining the specimen periodically to make sure that overdecalcification does not occur is important.

Core needle biopsy and fine-needle aspiration are also popular methods for diagnosing bone lesions; the latter has more or less replaced the former. At our institution, we use a method that combines the two. The biopsy is performed by a radiologist under computed tomographic guidance with a 14- to 16-gauge needle. Smears are made and stained with a Papanicolaou technique. If they yield diagnostic material, the radiologist is so informed, and the small core of tissue that is always obtained is used to make permanent sections. We occasionally make a frozen section from the core if the smears are negative. The biopsy may be repeated if both are negative.

We reviewed our experience with fine-needle aspirations for the period from April 1993 to April 2003. The number of procedures performed each year has changed little (about 84 per year). It was disappointing that the number of nondiagnostic biopsies has not diminished with increasing experience. Part of the explanation may be that aspirations are done in lesions, such as cysts, with little hope of obtaining diagnostic material. As with any “new” technique, there is a temptation to overutilize it. Next to “nondiagnostic” (39%), metastatic carcinoma was the most common diagnosis made. Myeloma, lymphoma, and osteosarcoma were the most common “primary” neoplasms diagnosed.

Performing fine-needle aspirations clearly has advantages. The most obvious is the avoidance of using an operating room. The chance for contamination of the biopsy site is also reduced. Fine-needle aspiration is often said to be cost-effective; however, a negative biopsy adds to the cost. Increasingly, oncologists are demanding special studies, such as cytogenetics and molecular studies, before a patient is admitted to a protocol. Radiologists are responding by taking multiple cores for this purpose. It must be remembered that we do not examine the tissue that is used for special studies; hence, we cannot be sure that the material being studied is representative.

A special laboratory for handling specimens of bone is not necessary. The gross dissection is similar whether the specimen is a major resection or an amputation. Comparing the gross specimen with the radiograph is important to determine the exact location of the neoplasm. The soft tissue surrounding the bone and the attached neoplasm are dissected away, so that only the bone and the attached neoplasm are left behind. The specimen is cut in half with a band saw or a butcher’s meat saw. The specimen is washed gently with running water and bone dust is removed with a brush. Cleaning the specimen avoids artifacts in the
microscopic sections caused by bone dust. An alternate method is to freeze the entire specimen and bisect it. Although this method has the advantage of preserving the gross anatomy, it has the disadvantages of delay and freezing and thawing artifacts.

The grading system used at Mayo Clinic essentially follows the grading system that Dr. A. C. Broders proposed for epithelial malignant tumors. The grade of the neoplasm depends on the cellularity of the lesion and the cytologic features of the neoplastic cells. Low-grade neoplasms simulate the appearance of the putative cell of origin of the neoplasm. High-grade malignant lesions have such undifferentiated malignant cells that their cell of origin is, at best, conjectural. Although more common in higher grade neoplasms, necrosis is not used as a criterion for grading. Similarly, mitotic figures are more common in higher grade malignant lesions, but mitotic count is not used for grading tumors. Most bone tumors are graded 1 to 4, with the exception of cartilage tumors and vascular neoplasms, which have only three grades. Grading of a neoplasm demands a morphologic variation within a given entity. For example, because Ewing sarcoma has little variation from tumor to tumor, there is no practical way to grade Ewing sarcoma. This is true also of some low-grade neoplasms, such as adamantinoma. In some neoplasms, such as chordomas, experience has shown that variation in cytologic features is not correlated with clinical prognosis. Hence, there is no point in grading chordomas.

This grading system is admittedly subjective, but no more so than other grading systems. Orthopedic oncologists demand that tumors be graded because the grade of the neoplasm is an important part of staging. Fortunately, it is only necessary to say whether the neoplasm is low grade or high grade.

The staging system used by the Musculoskeletal Tumor Society is a distinct advance in the management of patients with bone tumors. Tumors are staged primarily on the grade of the neoplasm and the extent of involvement. When no distant metastases are present, all low-grade tumors are stage I and all high-grade tumors are stage II. If the neoplasm is confined to the bone, it is considered stage A, and if the tumor has also involved the soft tissues, it is considered stage B. Hence low-grade tumors can be divided into stages IA and IB, depending on the anatomic extent of the neoplasm. Similarly, high-grade tumors, that is, stage II, can also be divided into A and B on the basis of the anatomic extent of the tumor. All tumors with distant metastasis are considered stage III regardless of other considerations. This staging system promotes the use of uniform criteria for comparison of results of treatment from different institutions around the world. It also affords prognostic information.

It is useful to know the terminology orthopedic oncologists use in referring to surgical margins. When the entire compartment in which the neoplasm is situated is removed completely, radical margin is the term used. In a tumor involving the distal femur, a radical margin requires that the entire femur be removed. When the tumor is removed completely with surrounding normal tissue, wide margin is the term used. This surrounding tissue should also include the so-called reactive zone around the neoplasm. The reactive zone is an area composed of capillary proliferation apparently surrounding a tumor as it grows. When the tumor is removed completely but the resection margin does not remove the entire reactive zone, the term marginal margin is used. The resection is considered to be intralesional when the tumor is removed but no attempt is made to obtain normal tissues around it.