Page 551 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 25 Tumors of the Skeletal System 529

changes may be seen, depending on the size, histologic subtype, needle biopsy has an accuracy rate of 91.9% for detecting tumor
location, and duration of the lesion. versus other disorders and an 82.3% accuracy rate for diagnosis
Accuracy of diagnoses from needle
140
of specific tumor subtype.
Differential diagnoses of lytic, proliferative, or mixed pattern
VetBooks.ir aggressive bone lesions identified on radiographs include: other core samples can be dependent on the experience of the patholo-
primary bone tumors (chondrosarcoma [CSA], fibrosarcoma
gist and comfort level with examination of small samples. Histol-
[FSA], hemangiosarcoma [HSA]); metastatic bone cancer; mul- ogy reports indicating the presence of reactive bone should not
tiple myeloma or lymphoma of bone; fungal osteomyelitis; bac- rule out the presence of a primary bone tumor or other pathol-
terial osteomyelitis; and, albeit rare, bone cysts. Other primary ogy, especially if the radiographic changes suggest tumor. In some
bone tumors are far less common than OSA but may be suspected, cases, it can be very difficult to get the diagnosis by preoperative
especially in dogs with unusual signalment or tumor location. biopsy (i.e., repeated biopsy attempts yield “reactive bone”), and
The radiographic appearance of primary bone tumors is similar yet the pathologist has no trouble identifying tumor when the
to osteomyelitis, specifically fungal osteomyelitis. 131 In cases in entire specimen is available for histopathologic analysis. This is
which the travel or clinical history might support the possibil- likely because of the heterogeneity of the tumor tissue itself and
ity of osteomyelitis, a biopsy with submission for histology and the large amount of reactive bone present within the tumor.
culture may be warranted. Metastatic cancer can spread to bone The biopsy site is selected carefully. Radiographs (two projec-
from almost any malignancy, but is most commonly encountered tions) are reviewed and the center of the lesion chosen for biopsy.
from genitourinary carcinomas. 132 A careful physical examina- Biopsy at the lesion periphery will often result in sampling the
tion is important, including a rectal examination, with special reactive bone surrounding the tumor without a resulting diag-
attention paid to the genitourinary system to help rule out the nosis. 140 The skin incision is made so the biopsy tract and any
presence of a primary cancer. Common sites for metastatic bone potentially seeded tumor cells can be completely removed at the
cancer are lumbar and sacral vertebrae, pelvis, ribs, and diaphyses time of definitive surgery. Care is used to avoid major nerves,
of long bones. 132 There are usually other clues for the diagnosis vessels, and joint spaces. A 4-inch, 8- or 11-gauge needle is used.
of multiple myeloma, such as hyperproteinemia, and both mul- With the dog anesthetized, prepared, and draped for surgery, a
tiple myeloma and lymphoma of bone are usually associated with small stab incision (2–3 mm) is made in the skin with a #11
radiographic lesions that are almost entirely lytic. scalpel blade. The bone needle cannula, with the stylet locked
in place, is pushed through the soft tissue to the bone cortex.
Tissue Biopsy The stylet is removed and the cannula is advanced through the
A diagnosis of primary malignant bone tumor may be suggested bone cortex into the medullary cavity using a gentle twisting
by signalment, history, physical examination, and radiographic motion and firm pressure. The opposite cortex is not penetrated.
findings. Cytology has not been thought to be definitive for diag- The needle is removed and the specimen is gently pushed out of
nosis; however, recent evidence indicates a high accuracy for diag- the base of the cannula by inserting the probe into the cannula
nosis of sarcoma and, in combination with alkaline phosphatase tip. One or two more samples can be obtained by redirecting the
staining, high specificity to support the diagnosis of OSA. Con- needle through the same skin incision so that samples of the tran-
sistent cytologic criteria of OSA has recently been described; with sition zone may also be obtained. Ideal specimens should be 1 or
repeated evaluations and dependent on experience, cytopatholo- 2 cm in length and not fragmented. Biopsy is repeated until solid
gists may be more definitive in making a diagnosis from cytology tissue cores are obtained. Material for culture and cytology may
alone. 133,134 Alkaline phosphatase staining of cytologic samples be taken from the samples before fixation in 10% neutral buff-
has been shown to differentiate OSA from other vimentin-positive ered formalin. Diagnostic accuracy is improved when samples are
tumors; 101 however, in cases in which cytology is equivocal, a evaluated by a pathologist thoroughly familiar with bone cancer.
definitive diagnosis requires histopathologic assessment of a tissue Fluoroscopy or advanced imaging (CT) can assist in obtaining
sample. It is crucial that the biopsy procedure is planned and per- needle-core biopsy samples of suspected bone lesions, especially
formed carefully with close attention to asepsis, hemostasis, and for axial sites. 141
wound closure. 135 The skin incision for the biopsy must be small After tumor removal (amputation or limb sparing), histology
and placed such that it can be completely excised or included with should be performed on a larger specimen to confirm the preoper-
the tumor if limb salvage surgery (LSS) or SRT is chosen. Poorly ative diagnosis. If the clinical and radiographic features are typical
placed biopsy tracts can result in excessive normal tissue exposure for a primary bone tumor, especially when there is little possi-
(radiation) or difficulties in closure (LSS). Transverse or large inci- bility of fungal or bacterial infection, confirmation of histologic
sions must be avoided. Ideally, the surgeon who is to perform the diagnosis after surgical treatment of local disease (amputation or
definitive surgical procedure (especially if this is LSS) should be limb sparing) can be considered. Few diseases causing advanced
the person to perform the preoperative bone biopsy. 136 destruction of the bone can be effectively treated without removal
Bone biopsy may be performed as an open incisional, closed of the local disease. If the owners are willing to treat aggressively,
needle, or trephine biopsy (Fig. 25.2). The advantage of the open surgical removal of local disease with biopsy submission after sur-
techniques is that a large sample of tissue is procured, which pre- gery may be acceptable.
sumably improves the likelihood of establishing an accurate histo-
logic diagnosis. Unfortunately, this advantage may be outweighed Staging and Patient Assessment
by the disadvantages of an involved operative procedure and risk of Systemic Staging
postsurgical complications such as hematoma formation, wound Examination for evidence of apparent spread of the disease is
breakdown, infection, local seeding of tumor, and pathologic frac- important. Regional LNs, although rarely involved, should be pal-
ture. 137,138 Although biopsy with a trephine yields a diagnostic pated and fine needle cytology performed on any enlarged LN. 113
accuracy rate of 93.8%, there is increased risk of creating patho- Sites of bone metastasis may be detected by a careful orthopedic
logic fracture than with a smaller gauge needle. 139 This under- examination with palpation of long bones and the accessible axial
scores some of the advantages of a closed biopsy using a Jamshidi skeleton. Organomegaly may be detected by abdominal palpa-
bone marrow biopsy needle or similar type of needle. Jamshidi tion. Usually pulmonary metastases are undetectable by clinical