ACCURACY OF MAGNETIC RESONANCE IMAGING FOR ESTIMATING INTRAMEDULLARY OSTEOSARCOMA EXTENT IN PRE-OPERATIVE PLANNING OF CANINE LIMB-SALVAGE PROCEDURES

The objective of this work was to compare the accuracy of radiographs and magnetic resonance imaging (MRI) for estimating appendicular osteosarcoma margins. The accuracy of computed tomography (CT) and bone scintigraphy was also assessed when these studies were available. Eight dogs with appendicular osteosarcoma underwent radiographic and MRI of affected limbs. In addition, bone scintigraphy was performed in six dogs and CT examination was performed in five dogs. Two observers jointly measured tumor length on all imaging studies. Correlative gross and histologic evaluation of all affected limbs was performed to determine tumor extent as measured from the nearest articular surface. Results from imaging studies were compared to gross and microscopic morphometry findings to determine the accuracy of each modality for determining tumor boundaries. MRI images were accurate with a mean overestimation of actual tumor length of 3 +/- 13%. T1-weighted non-contrast images were superior in identifying intramedullary tumor margins in most instances whereas contrast-enhanced images provided supplemental information in two dogs. Lateromedial and craniocaudal radiographs overestimated tumor length by 17 +/- 28% and 4 +/- 26%, respectively. Scintigraphy and CT overestimated tumor margins by 14 +/- 28% and 27 +/- 36%, respectively. MRI appears to be an accurate diagnostic imaging modality in determining intramedullary osteosarcoma boundaries. MRI should be considered as part of a pre-operative assessment of appendicular osteosarcoma, particularly when a limb-sparing procedure is contemplated.     

Comparison of radiography, computed tomography, and magnetic resonance imaging for evaluation of appendicular osteosarcoma in dogs

OBJECTIVE: To determine which imaging modality best determines the microscopic extent of primary appendicular osteosarcoma in amputated limbs in dogs. DESIGN: Case series. ANIMALS: 10 dogs with appendicular osteosarcoma. PROCEDURE: 10 dogs with appendicular osteosarcoma that did not receive neoadjuvent chemotherapy were treated by use of limb amputation. Amputated limbs were imaged by use of radiography, computed tomography (CT), and magnetic resonance imaging (MRI) and examined microscopically to determine longitudinal extent of neoplastic cell involvement and length of associated intramedullary fibrosis. Changes detected by use of the various imaging studies were compared with the actual tumor length determined microscopically. Data were analyzed to determine which imaging technique most closely predicted tumor length. RESULTS: Measurements obtained by use of craniocaudal radiographic views were most accurate at predicting tumor length but underestimated tumor length substantially in 1 limb and slightly in another limb. Measurements made by use of CT were most accurate at predicting tumor length when intramedullary fibrosis was taken into account but underestimated tumor length in 1 limb. Measurements made by use of MRI were least accurate but did not underestimate tumor length in any of the limbs. CONCLUSIONS AND CLINICAL RELEVANCE: Although radiography is used in diagnosis of osteosarcoma in dogs, additional imaging studies to confirm the extent of neoplasia prior to limb-sparing ostectomy may be beneficial. Underestimation of tumor length would be associated with higher incidence of incomplete excision and local tumor recurrence.     

Preoperative measurement of canine primary bone tumors, using radiography and bone scintigraphy

Specimens of 20 canine primary bone tumors (18 osteosarcoma, 2 fibrosarcoma) were examined to compare the maximal axial length of gross tumor with the length of the lesion seen on preoperative radiographs and 99mTc methylene diphosphonate bone scintigraphic images. Radiographs defined the length of the tumor to within +/- 10% of the gross measurement for 6 (30%), underestimated it for 12 (60%), and overestimated it for 2 (10%) specimens. Bone scintigraphy defined tumor length within +/- 10% for 8 (40%), underestimated it for 1 (5%), and overestimated it for the remaining 11 (55%) specimens. Use of radiographic evaluation alone could result in underestimation of the diaphyseal extent of a primary bone tumor, with risk of incomplete resection. Bone scan images tend to overestimate tumor length and, therefore, may provide safer resection guidelines.     

Proximal radial and distal humeral osteosarcoma in 12 dogs

Twelve dogs were diagnosed with osteosarcoma of the proximal radius or distal humerus from 1990 to 2002, representing 1.0% of all dogs diagnosed with appendicular osteosarcoma. The median body weight (29.8 kg) was significantly less than that of dogs with appendicular osteosarcoma at other sites. Ten dogs were treated with amputation and chemotherapy. These dogs had a metastatic rate of 60%, a median metastasis-free interval of 356 days, and a median survival time of 824 days. There were no significant differences in metastasis-free interval or survival time between dogs with osteosarcoma of the proximal radius or distal humerus and dogs with appendicular osteosarcoma at other sites.     

Ipsilateral vascularised ulnar transposition autograft for limb-sparing surgery of the distal radius in 2 dogs with osteosarcoma

Canine osteosarcoma is the most commonly diagnosed primary bone tumour in the dog, affecting mainly large and giant breed dogs with the predilection site being the metaphysis of long bones, specifically the distal radius, proximal humerus, distal femur and proximal tibia and fibula. Treatment options are either palliative or curative intent therapy, the latter limb amputation or limb-sparing surgery together with chemotherapy. This article describes the use of an ipsilateral vascularised ulnar transposition autograft as well as chemotherapy in 2 dogs with osteosarcoma of the distal radius. Both dogs showed minimal complications with the technique and both survived over 381 days following the surgery. Complications seen were loosening of the screws and osteomyelitis. The procedure was well tolerated with excellent limb use. This technique is indicated for use in cases with small tumour size that have not broken through the bone cortex.     

Cortical allograft and endoprosthesis for limb-sparing surgery in dogs with distal radial osteosarcoma: a prospective clinical comparison of two different limb-sparing techniques

OBJECTIVE: To compare surgical and oncologic outcome in dogs with osteosarcoma (OSA) of the distal aspect of the radius treated with limb-sparing surgery, using either a cortical allograft or endoprosthesis, and postoperative chemotherapy; and to evaluate predictive factors for outcome. STUDY DESIGN: Prospective cohort study. ANIMALS: Dogs (n = 20) with spontaneous, non-metastatic OSA of the distal aspect of the radius. METHODS: Dogs were prospectively randomized for limb-sparing surgery with either a cortical allograft (n = 10) or endoprosthesis (10) and full-course adjuvant chemotherapy using single or dual agent protocols of cisplatin, carboplatin, and/or doxorubicin. Surgical (intraoperative findings, postoperative infection, construct failure) and oncologic (local tumor recurrence, metastasis, survival) outcomes were compared. The influence of intraoperative and postoperative variables on surgical and oncologic outcome were evaluated. RESULTS: No clinically significant differences in surgical and oncologic outcome were detected between groups. The percentage of radius replaced by the implant was significantly greater in the endoprosthesis group (60.9% compared with 48.6%, P = .008). Median survival time (MST) for dogs with construct failure, regardless of implant type, was 685 days and significantly greater than MST of dogs without construct failure (322 days, P = .042; hazard ratio [HR] 16.82). Median metastasis-free interval and MST (685 days versus 289 days; P = .034, HR 24.58) were significantly greater in dogs with postoperative infection. Disease-free and overall limb-salvage rates were 70% and 85%, respectively. Overall MST was 430 days. CONCLUSIONS: For dogs with OSA of the distal aspect of the radius, a cortical allograft or endoprosthesis can be used for limb-sparing surgery. Construct failure and postoperative infection significantly improve survival time regardless of implant type. CLINICAL RELEVANCE: An endoprosthesis is an attractive alternative to cortical allografts for limb-salvage of the distal aspect of the radius in dogs because surgical and oncologic outcomes are similar, but the endoprosthesis is an immediately available off-the-shelf implant which is not complicated by the bone harvesting and banking requirements associated with cortical allografts. Mechanisms whereby postoperative infection improves survival time requires further investigation and, if elucidated, may provide the opportunity to improve the outcome of dogs and humans with OSA.     

Microcrack density and length in the proximal and distal metaphyses of the humerus and radius in dogs

OBJECTIVE: To compare microcrack density and length in the proximal and distal metaphyses of the humerus and radius in dogs. SAMPLE POPULATION: Left humerus and radius from each of 10 dogs of medium to large size. PROCEDURE: Metaphyseal specimens were bulk stained in 1% basic fuchsin in graded alcohols and embedded in methylmethacrylate. For quantification of fatigue-induced microscopic damage, transverse sections were prepared from proximal and distal metaphyseal regions, and length and density of microcracks were determined, using light microscopy. RESULTS: Bone region, age, and body weight were not significantly associated with microcrack density or length. CONCLUSIONS AND CLINICAL RELEVANCE: The hypothesis that fatigue-induced injury (increased microcrack density and length) caused by cyclic loading associated with daily activity is greater in bone regions prone to development of osteosarcoma was not supported by data from this study.     

Single-phase methylene diphosphate bone scintigraphy in the diagnostic evaluation of dogs with osteosarcoma

In this study, 25 dogs each with a histopathologically diagnosed appendicular or axial osteosarcoma were prospectively and consecutively examined by methylene diphosphate nuclear scintigraphy. Scannings that revealed scintigraphically enhanced focal increased activity via bone uptake of the 99mTc methylene diphosphate radionuclide at sites other than the primary tumor site were compared with scintigrams obtained from dogs without osteosarcoma. Secondary scintigraphic sites were evaluated by survey radiography and, if possible, by histologic examination (biopsy or necropsy specimens). On the basis of our findings, scintigraphy seems to be more efficient than physical examination and radiographic bone survey for the diagnosis of multicentric, metachronous, or metastatic canine osteosarcoma.     

Use of an ipsilateral vascularized ulnar transposition autograft for limb-sparing surgery of the distal radius in dogs: an anatomic and clinical study

OBJECTIVE: To develop a surgical technique for using the distal aspect of the ulna as a transposition autograft in a distal radial defect and to assess patency of vascular supply and viability of the distal ulna in a heterotopic position. STUDY DESIGN: Cadaveric study and clinical cases. ANIMALS: Twenty-two normal canine thoracic limbs; 3 dogs with distal radial osteosarcoma. METHODS: The arteries and veins of 12 limbs were injected with latex. Barium sulfate suspension was injected into the brachial artery of 10 other limbs after removal of the distal radius only (n = 2), ulna transposition (UT) (n = 6), or no procedure (n = 2). The distal ulna grafts were then harvested and decalcified in formic acid. The grafts were cut into 3-5 mm transverse sections and radiographed with a nonscreen film system to determine filling of intramedullary vessels with barium suspension. UT was performed in 3 dogs with distal radial osteosarcoma. Bone scintigraphy was performed 2-7 days after surgery to assess viability of the transposed ulna graft. RESULTS: Angiography confirmed patency of the caudal interosseous artery in all but 2 limbs in which the UT technique was performed; however, barium-filled vessels were identified in the medullary cavity of all ulnar grafts. Scintigraphy confirmed graft viability in the 3 dogs, all of which had good to excellent limb function. CONCLUSIONS: The distal aspect of the canine ulna can be used as a vascularized transposition autograft to replace distal radial defects, and viability can be maintained. CLINICAL RELEVANCE: The UT technique appears to be an acceptable limb-sparing technique for dogs with tumors of the distal aspect of the radius.     

Radiography, 99mTc-HDP, and 111In labeled vitamin B12 SPECT of canine osteosarcoma: a comparative study

The objective of this article was to compare radiography, planar bone scintigraphy, and single-photon emission computed tomography (SPECT) to determine the size of osteosarcomas in long bones of dogs. Ten dogs with osteosarcoma in six radii, two humeri, one tibia, and one ulna were evaluated. Macroslides, mediolateral radiographs, planar scintigrams, and sagittal images from SPECT scans were used to obtain measurements. On the scintigraphic images, the edges of the tumor were established using the activity profile imaging tool. The radiographic magnification was factored. The mean percentage of tumor size overestimation was 9.29% on mediolateral radiographs, 5.35% on planar scintigrams, and 33.25% on SPECT images. The correlation coefficient adjusted for sample size was significantly higher (P<0.01) for technetium 99m ((99m)Tc) hydroxyethylene diphosphonate (HDP) (75.5%) and radiography (61.3%) compared with indium 111-vitamin B(12) (28.3%). The correlation coefficient for (99m)Tc-HDP was higher than that obtained for radiographs; however, statistical difference between the two variables was not demonstrated (P>0.05). (99m)Tc bone scan is a good estimator of intramedullary size of osteosarcoma in long bones when the activity profile tool to determine the margin of the tumor is used.     

Nuclear scanning with 99mTc-HDP for the initial evaluation of osseous metastasis in canine osteosarcoma

The purpose of this retrospective analysis was to evaluate the use of nuclear scintigraphy in determining the rate of secondary sites of osseous malignancy at initial presentation in dogs with osteosarcoma. Radiographs of suspicious secondary lesions were reviewed and placed into four separate categories: benign lesions; no lesion seen on radiographs; subtle radiographic changes suggestive of, but not conclusive for, metastasis; and metastatic lesions highly suspected on radiographs. Three hundred and ninety‐nine dogs were evaluated by technetium nuclear scanning for suspected osteosarcoma. Three hundred and twenty‐six of 399 dogs (82%) had only one apparent site on the nuclear scan, whereas 72 dogs (18%) had more than one suspicious site on the nuclear scans. Highly suspected secondary metastatic lesions were detected by nuclear scans in 7.8% of cases. Although interpretation of nuclear scans is subjective, this study showed a 7.8% chance of detecting unsuspected osseous metastasis with nuclear scans in canine osteosarcoma patients on initial presentation.     

Fatigue microdamage in the radial predilection site for osteosarcoma in dogs

OBJECTIVE: To evaluate whether body size and anatomic site influence the quantity of bone microdamage in dogs without osteosarcoma (OS). SAMPLE POPULATION: Pairs of radii were collected from 10 small dogs (< 15 kg) and 10 large dogs (> 25 kg). PROCEDURE: Specimens were stained in basic fuchsin for bone microdamage. Transverse sections were cut from each proximal and distal radial metaphysis at 15 and 85% of bone length. The following variables were determined for each region: mean microcrack length (CrLe, microM), microcrack density (CrDn, microcracks/mm2), microcrack surface density (CrSDn, microm/mm2), and estimated activation frequency (Acf, microcracks/mm2/y). RESULTS: Metaphyseal region did not significantly influence CrDn, CrLe, and CrSDn. The CrDn and CrSDn were influenced by body size, with microdamage being increased in large dogs, compared with small dogs. However, mean CrLe was not significantly influenced by body size. Acf significantly decreased with age and was significantly decreased in large dogs and in the distal radial metaphysis, compared with small dogs and the proximal radial metaphysis, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: Our data did not reveal an increase in microdamage or remodeling at the OS predilection site (ie, the distal metaphysis of the radius), suggesting that induction of microdamage and an associated increase in bone remodeling are unlikely to be an important risk factor for induction of OS.     

SCINTIGRAPHIC DETECTION OF SUBCUTANEOUS METASTASIS IN A DOG WITH APPENDICULAR OSTEOSARCOMA

This report describes the detection of subclinical soft tissue metastasis of an appendicular osteosarcoma in a dog using bone scintigraphy. A 7-year-old spayed female Rottweiler was presented with a biopsy confirmed diagnosis of osteosarcoma. Initial radiographs revealed an aggressive bone lesion of the left distal radius. At presentation, there was no clinical or radiographic evidence of metastasis; however, a nuclear bone scan showed the primary bone lesion of the distal left radius and numerous soft tissue lesions consistent with diffuse soft tissue metastases. A left foreleg amputation was performed and cisplatin chemotherapy was given post-operatively. A second bone scan performed one month following initial presentation showed progression in size and number of soft tissue masses. Many of the lesions had become apparent on physical exam and survey radiographs. Excisional biopsy was performed on one of the soft tissue masses and a diagnosis of metastatic osteosarcoma was made. The dog was euthanized 2 months after initial presentation at the owners request due to deterioration of the animals physical condition.     

Accuracy of computed tomography in determining lesion size in canine appendicular osteosarcoma

Multidetector contrast enhanced computed tomography with acquisition of 0.625-mm thick transverse images was used to measure the extent of appendicular osteosarcoma in 10 dogs. The measured length of tumor based on CT was compared to the true length of tumor using histopathology. There was a statistically significant association with good correlation between the true length of osteosarcoma compared to the length of intramedullary/endosteal abnormalities on CT with a mean overestimation of 1.8% (SD = 15%). There was not a statistically significant association between the true tumor length and the length of periosteal proliferation on CT with a mean overestimation of 9.7% (SD = 30.3%). There was a statistically significant association, but with poor correlation, between the true tumor length compared to the length of abnormal contrast enhancement with a mean overestimation of 9.6% (SD = 34.8%). The extent of intramedullary/endosteal CT abnormalities assessed from submillimeter transverse images may be of value in assessing patient candidacy and surgical margins for limb-sparing surgery.     

STRESS FRACTURES OF THE HUMERUS, RADIUS, AND TIBIA IN HORSES

The medical records, radiographic and nuclear scintigraphic findings of 26 racing horses with 27 stress fracture episodes of the humerus, radius, or tibia were reviewed. The purposes of this study were to describe the radiographic and/or scintigraphic features of stress fractures of the humerus, radius, or tibia, and to evaluate the signalment and history of horses in which stress fracture occurred. Stress fractures of the three long bones examined were primarily seen in 2-and 3-year-old male Thoroughbred horses; commonly, the onset of lameness was immediately following training gallops or racing. There were 13 humeral stress fracture episodes in 12 horses. Ten were in the proximal caudolateral cortex, and three were in the distal craniomedial cortex. Radial stress fractures were seen in three horses, all in the midshaft radius. Tibial stress fractures were diagnosed in 11 horses. They were located in the proximal lateral tibia in six horses, the distal caudolateral tibia in three horses, and the midshaft tibia in three horses. Fifteen stress fractures were diagnosed with radiographs alone, one was diagnosed with scintigraphy alone, nine were diagnosed with radiographs and scintigraphy, and, in two horses, radiographs were negative, but the scintigraphic findings were consistent with stress fracture.     

Intraoperative radiation for limb sparing of the distal aspect of the radius without transcarpal plating in five dogs

Objectives— To evaluate intraoperative irradiation (IORT) as a method of limb spare with preservation of the radiocarpal joint.
Study Design— Prospective case series.
Animals— Dogs (n=5) with stage II sarcoma of the distal aspect of the radius.
Methods— A bone segment containing the tumor was isolated surgically, treated by IORT, reimplanted, and secured by internal fixation. In 1 dog, the postradiation tumor bed was curetted and filled with bone cement. Dogs were administered alternating adriamycin and carboplatin starting 2 weeks after IORT and monitored at regular intervals.
Results— Four dogs had osteosarcoma and 1 had undifferentiated sarcoma. Implant failure (n=3), deep tissue infection (3), and pathologic fracture (3) resulted in amputation (3) or pancarpal plating (2). The dog with undifferentiated sarcoma was euthanatized because of suspected tumor recurrence 4 months postoperatively. Osteotomy healing was documented by radiography (1), histopathology (2), or by direct observation (2).
Conclusions— A technique for limb-sparing surgery of the distal portion of the radius in dogs using IORT had advantages include healing of the autograft and a source for a perfectly fitting autograft but did not appear to offer any advantage with respect to infection rate. Long-term preservation of the radiocarpal joint was not successful.
Clinical Relevance— It was not possible to preserve the function of the radiocarpal joint and so this technique cannot be recommended currently. Further study is needed to evaluate whether or not IORT can be considered in combination with pancarpal plating and possibly curettage and cementation of the tumor to prevent subchondral bone collapse.     

Use of a Medial Bone Plate for Repair of Radius and Ulna Fractures in Dogs and Cats: A Report of 22 Cases

Objective —This study evaluates the technique of medial bone plating in the repair of radius fractures in dogs and cats.
Study Design —A retrospective study was made of patients diagnosed with fractures of the radius that were stabilized by application of a bone plate to the medial side of the bone.
Animal Population —Sixteen client-owned dogs and 4 client-owned cats. The animals' ages varied from 5 months to 8 years, and their weight varied from 1.3 to 49 kgs.
Methods —Animals were evaluated using radiography or client assessment, or both.
Results —Medial plate application was technically easier to do than cranial plate application, the technique avoided the extensor tendons, and permitted greater versatility in the selection of smaller plates for the fixation of distal radius fractures. All fractures repaired by this method healed with no postoperative complications.
Conclusions —Medial plate application may be used for osteosynthesis of distal or middiaphy-seal radius fractures. Further studies are needed to evaluate the use of this technique in morphologically complex fractures. In patients with fractures of the proximal radius, cranial plate application is considered more appropriate.
Clinical Relevance —Medial plating of radial fractures has significant advantages compared with conventional plate application; it provides the surgeon with an alternative method of fixation for selected radius fractures in dogs and cats.     

URETERAL FIBROEPITHELIAL POLYPS IN FOUR DOGS

Four dogs with ureteral fibroepithelial polyps, ranging from 9-12 years of age, are presented in this report. The patients presented with urinary incontinence, urinary tract infection, and/or polydypsia and pollakiuria. All dogs were intact at the time of diagnosis or for the majority of their lives and three were male. Various diagnostic procedures were performed including ultrasonography, contrast radiography, and nuclear scintigraphy. Not all procedures were performed in all patients. Findings included ureteral dilation proximal to the level of an intraluminal mass and ipsilateral hydronephrosis. Unilateral ureteronephrectomy was performed in three dogs with masses in the proximal ureter; ureteral resection and anastamosis was performed in the remaining patient with a mass located in the distal ureter. The same pathologist (RAP) reviewed all four lesions. The lesions appeared polypoid and were attached to the ureteral wall by a thin stalk. Histopathologically, they contained a superficial layer of well-differentiated transitional epithelial cells overlying a prominent fibrovascular stroma with a mild (three dogs) or marked (one dog) degree of lymphoplasmacytic inflammation. This disease may represent a benign neoplasm or a chronic inflammatory reaction and has a good prognosis with surgical removal. Its histopathological characteristics, higher incidence in males, and location more commonly within the upper third of the ureter is remarkably similar to the disease in humans.     

Resection of Pulmonary Metastases in Canine Osteosarcoma: 36 Cases (1983–1992)

Thirty-six dogs underwent pulmonary metastatectomy for osteosarcoma. All patients had been treated for histologically confirmed osteosarcoma of the appendicular skeleton. Treatment for the primary tumor consisted of amputation or a limb sparing procedure in conjunction with adjuvant chemotherapy, local radiation therapy, or both.
Significant factors in determining prognosis included the disease-free interval (DFI) between treatment of the primary tumor and development of pulmonary metastases and the number of metastatic nodules present at surgery. Dogs that developed pulmonary metastases 300 days or more after diagnosis of the primary tumor had a median DFI of 128 days after metastatectomy. Dogs that developed pulmonary metastases fewer than 300 days after diagnosis had a median DFI of 58 days. Dogs with one or two metastatic nodules removed had a median DFI of 95 days, whereas dogs with three or more nodules removed had a median DFI of 53 days. The results of this study indicate that prognostic variables exist for dogs with metastatic pulmonary osteosarcoma and can help predict survival after metastatectomy. These variables are similar to the prognostic variables that have been determined for human patients undergoing pulmonary metastatectomy because of osteosarcoma. Though a controversial procedure, pulmonary metastatectomy seems to be a valid treatment option for selected dogs with metastatic pulmonary osteosarcoma.     

BONE SCINTIGRAPHY FOR METASTASIS DETECTION IN CANINE OSTEOSARCOMA

The purpose of this study was to assess the usefulness of serial bone scintigraphy in the detection of skeletal and extraskeletal metastases in dogs with appendicular osteosarcoma. Twenty-six dogs with primary, appendicular osteosarcoma were entered into a limb-sparing protocol. Bone scintigraphy was performed upon presentation, after neoadjuvant therapy but prior to surgery and at selective intervals after limb-sparing surgery to evaluate for the presence of metastasis. Thoracic radiographs, and radiographs of other sites, were also made at the time of each bone scan. All dogs had a complete necropsy. No dog had bone or lung metastases detected prior to treatment. The bone scans, medical records, and radiographs of each dog were reviewed retrospectively. All but one dog developed metastatic disease. Bone metastatic sites were confirmed at necropsy in 12 of the 26 dogs. Seven of these 12 dogs had bone metastatic sites which were not producing clinical signs, i.e. an occult metastasis. In five of the seven dogs, the occult site was the first metastatic site detected. Extraskeletal metastases were identified scintigraphically in six of the 26 dogs, but these were clinically apparent prior to bone scintigraphy in each dog. Suspected malignant scintigraphic lesions were proven benign in six dogs. In five dogs with malignant bone lesions at necropsy the last bone scan prior to euthanasia was normal. The time interval between scintigraphy and necropsy was variable in these five dogs. All dogs without bone metastases at necropsy had normal bone scans. This study validates the usefulness of bone scintigraphy for detection of occult bone metastasis and improved ability for tumor staging in dogs with appendicular osteosarcoma.