Diagnosing Canine Bone Lesions: Fine-Needle Aspiration vs Biopsy

In a recent study, fine-needle aspiration cytology was as accurate as histologic biopsy for diagnosing destructive bone lesions in dogs. The report was published in the Journal of Veterinary Internal Medicine.

Osteodestructive lesions in dogs are usually neoplastic, but some benign conditions can mimic malignancies on radiographs. Because the usual treatment of choice for malignant bone cancer is amputation, obtaining a preoperative histologic diagnosis (rather than a presumptive diagnosis based on clinical signs and radiographic appearance) is ideal.

Bone biopsy requires general anesthesia and can be associated with pathologic fracture and other complications, say the authors. Fine-needle aspiration of bone lesions is minimally invasive and rapid, but one potential limitation is that it may not yield a diagnosis of the tumor type.

The investigators conducted a retrospective review of destructive bone lesions in 68 dogs seen at 2 academic veterinary hospitals in Italy from 2000 to 2016. Lesions included in the study had been tested with fine-needle aspiration, biopsy, or both.

The final diagnosis was confirmed in 58 dogs by histology of samples obtained during a surgical procedure or necropsy. Of these, 56 were malignant and 2 were benign. Final diagnoses in these dogs were as follows:

• Osteosarcoma
• Carcinoma metastasis (mammary carcinoma and tonsillar squamous cell carcinoma)
• Chondrosarcoma
• Poorly differentiated sarcoma
• Fibrosarcoma
• Granulomatous mycotic osteomyelitis
• Foreign body osteomyelitis

In 10 dogs, surgical or necropsy samples were unavailable but benign processes were confirmed by long-term survival with no chemotherapy or surgical treatment. Diagnoses made by either fine-needle aspiration cytology or histologic biopsy in these dogs were as follows:

• Reactive bone
• Osteomyelitis
• Normal bone
• Osteochondroma

Histologic bone biopsy was performed with 8- to 11-gauge Jamshidi needles in 28 of the 68 lesions. This method correctly identified 13 of 18 malignant lesions and 10 of 10 benign lesions (overall accuracy, 82%) and correctly identified the tumor type in 10 of 18 malignant lesions (56%).

Fine-needle aspiration cytology was obtained with 21- or 22-gauge needles in 53 of the 68 lesions, correctly identifying 40 of 48 malignant lesions and 4 of 5 benign lesions (overall accuracy, 83%). This method accurately identified the tumor type in 24 of 48 malignancies (50%).

Both procedures were performed in 13 cases, with results of the 2 methods agreeing in 9 cases (69%). At least 1 of the methods yielded an accurate result in all 13 cases.

The overall accuracy of the 2 techniques was similar, conclude the authors, adding that “quite surprisingly,” the accuracy of identifying tumor type was also similar. However, identification of specific tumor type with either technique was correct in only about half of the malignancies. Both methods identified all of the epithelial metastatic lesions and most of the chondrosarcomas but returned a general “sarcoma” diagnosis for over half of the osteosarcomas.

“Overall, the concordance of cytology and histology with the final diagnosis was not completely satisfactory,” write the authors. In most cases, incorrect diagnoses resulted from sampling errors, not from mistakes in interpretation. For example, bone biopsies of some neoplastic lesions collected only reactive bone and missed the malignancy. The authors note that sampling technique, number of samples, and choice of site all affect the accuracy of either technique. They also point out that using both methods increased the accuracy.

The authors conclude that the accuracy of cytology and biopsy were similar and that neither method incorrectly identified benign lesions as malignant. “This is the most important error to prevent,” they write, “as treatment for malignant bone tumors includes aggressive surgery.”

Dr. Laurie Anne Walden received her doctorate in veterinary medicine from North Carolina State University. After an internship in small animal medicine and surgery at Auburn University, she returned to North Carolina, where she has been in small animal primary care practice for over 20 years. Dr. Walden is also a board-certified editor in the life sciences and owner of Walden Medical Writing, LLC. She works as a full-time freelance medical writer and editor and continues to see patients a few days each month.