What Is Your Diagnosis?

Morgan R. Biggo Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80525.

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Seng W. Yap Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80525.

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Ruth J. Rose Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, CO 80525.

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History

A 10-year-old 29-kg (63.8-lb) spayed female Rottweiler mixed-breed dog was referred for evaluation of a swelling in the right caudal thoracic and cranial abdominal areas. The owner reported that the swelling was noticed 17 days earlier and that the dog was doing well at home with normal levels of energy, appetite, and thirst but had intermittent diarrhea and possible polyuria. The referring veterinarian had performed thoracic and abdominal radiography, revealing a mass (approx 21 × 18 × 18 cm) in the thoracic wall that appeared to have arisen from the right 11th or 12th rib (not shown).

On referral examination, the dog was bright and alert and had vital signs within reference limits, with the exception of the respiratory rate (continuous panting). On the dog's right side, there was a large firm mass that was palpable through the abdominal wall and extended caudally from the 13th rib to the midregion of the abdomen. The dog also had a soft, fluctuant, freely movable subcutaneous mass (approx diameter, 1.5 cm) just right of dorsal midline on the thorax. No clinically relevant abnormalities were detected on a CBC; however, serum biochemical analyses revealed high activity of alkaline phosphatase (582 U/L; reference range, 15 to 150 U/L). A fine-needle aspirate sample was obtained from the large lateral abdominal mass, and cytologic examination yielded inconclusive results. Abdominal CT angiography (CTA) was recommended.

Six days later, the dog underwent general anesthesia for abdominal CTA,a biopsy of the large, lateral abdominal mass, and potential radiation treatment planning. For CTA, the dog was positioned in sternal recumbency, and CT images were obtained before and after administration of contrast medium (iohexol, 772 mg of I/kg [350.9 mg I/lb], IV; Figure 1). Precontrast images were obtained in a soft tissue window (window width, 400 HU; window level, 40 HU) with a 2-mm slice thickness and a bone window (window width, 3,000 HU; window level, 400 HU) with a 1-mm slice thickness, whereas the postcontrast images (ie, during arterial and venous phases and at 3 minutes after administration of the contrast medium) were obtained in a soft tissue window (window width, 400 HU; window level, 40 HU).

Figure 1
Figure 1

Precontrast (A) and postcontrast venous phase (B) transverse plane and postcontrast reconstructed sagittal plane (C) CT images of the abdomen of a 10-year-old 29-kg (63.8-lb) spayed female Rottweiler mixed-breed dog with a 3-week history of a firm mass that was palpable through the abdominal wall and that extended caudally from the 13th rib to the midregion of the abdomen on the dog's right side. The images are displayed in a soft tissue window (window width, 400 HU; window level, 40 HU) with a slice thickness of 2 mm. A and B—In each image, the dog's right is toward the left, and the line represents the level of the sagittal plane image. C—The dog's head is toward the left, and the line represents the level of the transverse plane images.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.709

Diagnostic Imaging Findings and Interpretation

A large (approx 17.0 × 13.9 × 16.3 cm [length × width × height]), expansile mass with a mixed fluid, soft tissue, and irregular mineral-attenuating matrix was identified arising from the right 12th rib (Figure 2). Contrast enhancement of the mass was difficult to determine, given the blooming artifact associated with its internal mineral components. The mass had invaded the adjacent abdominal wall musculature; medially displaced the duodenum, pancreas, right kidney, and right adrenal gland; and laterally displaced the right 13th rib. The mass spanned from the renal fossa of the caudate lobe of the liver to the level of the caudal aspect of L4. Additionally, the ventral aspect of the 12th rib had evidence of lysis, and the right caudal lung lobe had a round, soft tissue–attenuating, mildly contrast-enhancing nodule (diameter, 5.9 mm). The anatomic location and CT appearance of the abdominal mass were most consistent with osteosarcoma, chondrosarcoma, osteochondroma, or osteoma. Osteoma was considered less likely because of the heterogeneity of the mass.

Figure 2
Figure 2

Same images (A through C) as in Figure 1, with additional precontrast transverse plane CT images (D and E), in which the dog's right is to the left of the image. There is a large (approx 17.0 × 13.9 × 16.3 cm [length × width × height]), mixed soft tissue-to-mineral-attenuating mass (arrowheads) arising from the right 12th rib (arrows). The mass has invaded the adjacent abdominal wall musculature (1) and medially displaces the duodenum (2), pancreas, right kidney (3), and right adrenal gland. The 12th rib has evidence of lysis (4). A, B, D, and E—In each image, the line represents the level of the sagittal plane image. C—The lines represent the levels of the transverse plane images (green, A and B; blue, D; and yellow, E). D—The image is in a soft tissue window (window width, 400 HU; window level, 40 HU) with a slice thickness of 2 mm. E—The image is in a bone window (window width, 3,000 HU; window level, 400 HU) with a slice thickness of 1 mm.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.709

Treatment and Outcome

A 16-gauge, 15-cm biopsy needle was used to obtain an ultrasound-guided core-needle biopsy sample of the abdominal mass, and the preliminary diagnosis on the basis of histologic examination results was chondrosarcoma. The dog underwent surgery for en bloc resection of the right 10th through 13th ribs with transection at the costochondral junction, yielding 5-cm dorsal and ventral margins of the mass. A right caudal lung lobectomy was also performed. During surgery, the omentum was observed to have been adhered to the visceral surface of the mass (Figure 3). Diaphragmatic advancement was performed to assist reconstruction of the diaphragm, and the right latissimus dorsi muscle was used to reconstruct the thoracic and abdominal walls. The dog recovered well and was discharged 2 days after surgery. Histologic examination of the removed tissues revealed that the large mass arising from the right 12th rib was an osteochondroma, the nodule in the right caudal lung lobe was grade 1 pulmonary carcinoma, and both tumors had been completely excised. Approximately 5 months after surgery, the dog was reportedly doing well and had no evidence of recurrence.

Figure 3
Figure 3

Intraoperative photograph of the dog described in Figure 1 showing the en bloc rib resection and exteriorized large mass that arose from the right 12th rib. The surgeon is holding the resected rib section, and the omentum (arrow) is diffusely adhered to the medial visceral aspect of the mass. The dog is positioned in left lateral recumbency with its head toward the left of the image.

Citation: Journal of the American Veterinary Medical Association 258, 7; 10.2460/javma.258.7.709

Comments

Osteochondromas are benign tumors of bone that primarily grow through endochondral ossification and that are most commonly reported in the ribs, vertebrae, and long bones of dogs and cats.1 Additionally, reports describe a solitary osteochondroma in a 20-year-old ring-tailed lemur (Lemur catta)2 and multiple osteochondromas in the antlers and cranium of a free-ranging white-tailed deer (Odocoileus virginianus).3 Osteochondromas typically arise during periods of active bone growth in skeletally immature dogs1; however, in cats, these tumors tend to arise following skeletal maturity.4 Clinical signs are typically observed in young dogs with tumor impingement on normal structures (eg, spinal cord, peripheral nerves, tendons, or vessels), and resulting signs vary (eg, pathological fractures [owing to thinning of the adjacent cortex] and neurologic signs).1,5 The dog of the present report was atypical for both the age of onset and the lack of clinical signs attributed to the mass. Although the lack of clinical signs could have been attributed to the anatomic location of the mass in this dog, the late age of onset was not easily explained. Relatedly, malignant transformation of osteochondroma has been reported in mature dogs with multiple cartilaginous exostoses (the term applied when multiples of such tumors are present) or solitary spinal osteochondroma.1 For instance, in 2 dogs with solitary spinal osteochondroma, the osteochondroma transformed into osteosarcoma.1 Therefore, despite benign radiographic appearance, the onset of clinical signs should alert clinicians to possible malignant transformation.1

Definitive diagnosis of bone tumors can be challenging. For the dog of the present report, fine-needle aspiration and core-needle biopsy of the tumor were performed, and examination of the obtained samples did not result in an accurate diagnosis of the mass with either technique. Aggressive excision was performed in this dog, with the goals of obtaining tumor-free margins and best facilitating definitive diagnoses of the rib and pulmonary masses.

Given the location of the rib mass, preoperative surgical planning with diagnostic imaging was critical to best ensure successful excision. Multiple imaging modalities, including radiography, CT, MRI, and scintigraphy, have been used to evaluate bone and thoracic wall tumors.5,6 Findings on radiography combined with results of histologic examination of biopsy samples are typically used to diagnose primary bone tumors.5 Radiography allows for evaluation of the degree of bone lysis or production associated with primary costal neoplasia but may prove insufficient for surgical treatment planning.6 With thoracic wall tumors, CT is the modality of choice and critical for surgical planning because it allows for accurate evaluation of the structures involved.6 Radiography and CT were both used for the dog of the present report, and an added benefit of CT was the presurgical discovery of a pulmonary nodule. This discovery on CT prompted the removal of the affected lung lobe during the same anesthetic procedure as the removal of the rib mass. This dog's long-term prognosis was good because complete excisions of the dog's osteochondroma and grade 1 pulmonary carcinoma were confirmed histologically and because complete excision of osteochondroma is associated with excellent prognosis for long-term tumor control.4

Footnotes

a.

Gemini 16-slice positron emission tomography CT system, Koninklijke Philips NV, Amsterdam, Netherlands.

References

  • 1.

    Green EM, Adams WM, Steinberg H. Malignant transformation of solitary spinal osteochondroma in two mature dogs. Vet Radiol Ultrasound 1999;40:634637.

    • Search Google Scholar
    • Export Citation
  • 2.

    Hope KL, Boedeker NC, Gordon SS, et al. Solitary osteochondroma in a ring-tailed lemur (Lemur catta). Comp Med 2015;65:348351.

  • 3.

    Kierdorf U, Miller KV, Flohr S, et al. Multiple osteochondromas of the antlers and cranium in a free-ranging white-tailed deer (Odocoileus virginianus). PLoS One 2017;12:e0173775.

    • Search Google Scholar
    • Export Citation
  • 4.

    Dernell W, Ehrhart N, Straw R, et al. Tumors of the skeletal system. In: Withrow S, Vail D, eds. Small animal clinical oncology. 4th ed. St Louis: Saunders Elsevier, 2007;540582.

    • Search Google Scholar
    • Export Citation
  • 5.

    Vanel M, Blond L, Vanel D. Imaging of primary bone tumors in veterinary medicine: which differences? Eur J Radiol 2013;82:21292139.

  • 6.

    Martano M, Boston S, Morello E, et al. Respiratory tract and thorax. In: Kudnig ST, Seguin B, eds. Veterinary surgical oncology. Chichester, England: Wiley Blackwell, 2012;316.

    • Search Google Scholar
    • Export Citation
  • Figure 1

    Precontrast (A) and postcontrast venous phase (B) transverse plane and postcontrast reconstructed sagittal plane (C) CT images of the abdomen of a 10-year-old 29-kg (63.8-lb) spayed female Rottweiler mixed-breed dog with a 3-week history of a firm mass that was palpable through the abdominal wall and that extended caudally from the 13th rib to the midregion of the abdomen on the dog's right side. The images are displayed in a soft tissue window (window width, 400 HU; window level, 40 HU) with a slice thickness of 2 mm. A and B—In each image, the dog's right is toward the left, and the line represents the level of the sagittal plane image. C—The dog's head is toward the left, and the line represents the level of the transverse plane images.

  • Figure 2

    Same images (A through C) as in Figure 1, with additional precontrast transverse plane CT images (D and E), in which the dog's right is to the left of the image. There is a large (approx 17.0 × 13.9 × 16.3 cm [length × width × height]), mixed soft tissue-to-mineral-attenuating mass (arrowheads) arising from the right 12th rib (arrows). The mass has invaded the adjacent abdominal wall musculature (1) and medially displaces the duodenum (2), pancreas, right kidney (3), and right adrenal gland. The 12th rib has evidence of lysis (4). A, B, D, and E—In each image, the line represents the level of the sagittal plane image. C—The lines represent the levels of the transverse plane images (green, A and B; blue, D; and yellow, E). D—The image is in a soft tissue window (window width, 400 HU; window level, 40 HU) with a slice thickness of 2 mm. E—The image is in a bone window (window width, 3,000 HU; window level, 400 HU) with a slice thickness of 1 mm.

  • Figure 3

    Intraoperative photograph of the dog described in Figure 1 showing the en bloc rib resection and exteriorized large mass that arose from the right 12th rib. The surgeon is holding the resected rib section, and the omentum (arrow) is diffusely adhered to the medial visceral aspect of the mass. The dog is positioned in left lateral recumbency with its head toward the left of the image.

  • 1.

    Green EM, Adams WM, Steinberg H. Malignant transformation of solitary spinal osteochondroma in two mature dogs. Vet Radiol Ultrasound 1999;40:634637.

    • Search Google Scholar
    • Export Citation
  • 2.

    Hope KL, Boedeker NC, Gordon SS, et al. Solitary osteochondroma in a ring-tailed lemur (Lemur catta). Comp Med 2015;65:348351.

  • 3.

    Kierdorf U, Miller KV, Flohr S, et al. Multiple osteochondromas of the antlers and cranium in a free-ranging white-tailed deer (Odocoileus virginianus). PLoS One 2017;12:e0173775.

    • Search Google Scholar
    • Export Citation
  • 4.

    Dernell W, Ehrhart N, Straw R, et al. Tumors of the skeletal system. In: Withrow S, Vail D, eds. Small animal clinical oncology. 4th ed. St Louis: Saunders Elsevier, 2007;540582.

    • Search Google Scholar
    • Export Citation
  • 5.

    Vanel M, Blond L, Vanel D. Imaging of primary bone tumors in veterinary medicine: which differences? Eur J Radiol 2013;82:21292139.

  • 6.

    Martano M, Boston S, Morello E, et al. Respiratory tract and thorax. In: Kudnig ST, Seguin B, eds. Veterinary surgical oncology. Chichester, England: Wiley Blackwell, 2012;316.

    • Search Google Scholar
    • Export Citation

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