History
An 8-year-old 34.2-kg spayed female Labrador Retriever was evaluated for a 1-week history of coughing and retching episodes, labored breathing, lethargy, and hyporexia. Four months prior, the dog had undergone left forelimb amputation FOR AN osteosarcoma of the distal aspect of the left humerus, and the dog was still undergoing chemotherapy. Thoracic radiography 3 weeks prior to the present examination had revealed 3 pulmonary nodules, each approximately 5 mm in diameter, but no other radiographic abnormalities.
On physical examination, the dog was lethargic and panting, had occasional hacking episodes but vital signs within reference limits, and the left forelimb amputation site appeared healed. Hematologic evaluation revealed leukocytosis (20.6 X 109 cells/L; reference range, 4.9 X 109 to 15.4 X 109 cells/L), neutrophilia (18.540 X 109 cells/L; reference range, 3.0 X 109 to 10.0 X 109 cells/L), lymphopenia (0.206 X 109 cells/L; reference range, 1.2 X 109 to 5.0 X 109 cells/L), and monocytosis (1.648 X 109 cells/L; reference range, 0.08 X 109 to 1.0 X 109 cells/L). In addition, the dog had hypokalemia (3.6 mmol/L; reference range, 3.8 to 5.6 mmol/L), hyperamylasemia (1,770 U/L; reference range, 343 to 1,375 U/L), hyperglobulinemia (36 g/L; reference range, 20 to 34 g/dL), and high serum activities of alkaline phosphatase (92 U/L; reference range, 9 to 90 U/L). Thoracic radiography was performed (Figure 1).
Right (R) lateral (A), left (L) lateral (B), and ventrodorsal (C) thoracic radiographic images of an 8-year-old 34.2-kg spayed female Labrador Retriever with a 1-week history of coughing and retching episodes, labored breathing, lethargy, and hyporexia 4 months after amputation of the left forelimb because of osteosarcoma of the left humerus.
Citation: Journal of the American Veterinary Medical Association 259, S1; 10.2460/javma.21.05.0256
Formulate differential diagnoses, then continue reading.
Diagnostic Imaging Findings and Interpretation
Thoracic radiography revealed a large, bilobar, caudodorsal mediastinal mass that coursed from the heart base region to the diaphragm and caused widening of the angle between the main bronchi, compression of the left main bronchus, and mild ventral deviation of the tracheal bifurcation (Figure 2). The mass was primarily soft tissue– and fluid–opaque but did have a few subtle, irregular regions of mineral opacity in the hilar region. Progression of the pulmonary metastasis was noted because there were more pulmonary nodules evident, compared with findings from 3 weeks prior. An increase in soft tissue and fluid opacity in the region of the accessory lung lobe was identified on the left lateral view.
Same images as in Figure 1. A large, predominantly soft tissue–opaque mass (outlined with asterisks) with well-circumscribed, smooth contours is in the mid to caudal and dorsal aspects of the mediastinum. Superimposed with the cranial aspect of the mass, there are several subtle, amorphous, ill-defined regions of mineralization (black arrows), and there are several soft tissue–opaque nodules (squares) in the pulmonary parenchyma. A focal region of soft tissue– and fluid–opacity is ventral to the caudal vena cava, in the region of the accessory lung lobe (black dotted arrow). The mass causes mild ventral deviation of the tracheal bifurcation, widening of the distance between the main bronchi (outlined with arrowheads), and compression of the left main bronchus. Gas is in the esophagus (white dotted arrows) cranial to the mass. The left front limb has been amputated.
Citation: Journal of the American Veterinary Medical Association 259, S1; 10.2460/javma.21.05.0256
On the basis of radiographic identification of a bilobed mass in the caudal aspect of the mediastinum, differential diagnoses were listed for the possibility of 2 separate, adjacent masses versus a single, multilobulated mass. The heart base location of the mass causing ventral compression of the tracheal bifurcation and widening of the separation of the main pulmonary bronchi made tracheobronchial lymph node involvement a primary concern. Therefore, the primary differential diagnosis list for 2 separate masses included marked inflammatory lymphadenopathy associated with a granuloma (parasitic, fungal), an abscess, or a cystic structure, whereas the differential diagnosis list for a single mass included lymphoma or a paraesophageal or eccentric esophageal mural abscess, granuloma, or cyst. Metastatic neoplasia from the reported osteosarcoma was thought unlikely given the location and rapid progression, although the mineralization of the mass did raise this as a possibility. Primary neoplasia and other metastatic disease were also downgraded as possible etiologies given the relatively sudden onset. A hiatal hernia and gastroesophageal intussusception were not included as differential diagnoses due to the radiographically normal in situ positioning of the stomach in the abdomen.
Positive-contrast swallow esophagography was performed to evaluate the involvement and position of the esophagus. Postcontrast radiographic images showed dorsal and leftward displacement of the esophagus, without pronounced dilation, which was suggestive of a para-esophageal or eccentric mural mass (Figure 3).
Left lateral (A) and ventrodorsal (B) barium-swallow esophagographic images of the dog described in Figure 1, showing dorsal and leftward displacement of the esophageal lumen (black arrows). In both images, the intraluminal barium is smoothly margined, and the intraluminal diameter of the esophagus is within reference limits. Barium is evident in the gastric fundus (asterisk). DV = Dorsoventral.
Citation: Journal of the American Veterinary Medical Association 259, S1; 10.2460/javma.21.05.0256
Thoracic CT revealed a large mass with mixed attenuation (soft tissue in the periphery and mineralization in the central portion) located in the region of the middle tracheobronchial lymph node (Figure 4). Confluent with and caudal to this mass was a large, tubular fluid–attenuating structure that extended into the caudal aspect of the mediastinum, through the esophageal hiatus, and into the most cranial portion of the abdomen. The fluid structure was directly adjacent to the ventral aspect of the esophageal wall and caused leftward and dorsal displacement of the esophagus, consistent with findings on esophagography. In postcontrast images, heterogeneous contrast enhancement was noted associated with the cranial mass, whereas ring enhancement was seen with the fluid–attenuating structure. Multiple soft tissue– to mineral–attenuating pulmonary nodules were also confirmed on CT as well as a solitary mineral–attenuating nodule in the right lateral liver lobe. Ground glass attenuation in the accessory lung lobe was identified, consistent with atelectasis, which we suspected was secondary to the mass effect. This finding matched the radiographic finding of increased soft tissue and fluid opacity seen in this region.
Precontrast multiplanar reconstruction sagittal (A) and dorsal (at the level of mainstem bronchi; B) and postcontrast transverse (at the level of T8; C) plane thoracic CT images of the dog described in Figure 1, showing a mixed soft tissue (outlined with white arrowheads) and mineral (black asterisk) attenuating mediastinal mass located in the region of the middle tracheobronchial lymph node. Caudal to this mass is a fluid–attenuating tubular structure (outlined with white asterisks) that extends into the abdomen. There is a widening of the angle of the mainstem bronchi (white arrows) with compression on the left side. Mineralized pulmonary nodules (white squares) are present, and the esophagus (dotted arrow) is displaced dorsally and leftward.
Citation: Journal of the American Veterinary Medical Association 259, S1; 10.2460/javma.21.05.0256
Abdominal ultrasonography, done for purposes of staging, found multiple mineral foci in the cortices of both kidneys. No other ultrasonographic changes in the abdomen were noted. An ultrasound-guided transabdominal fine-needle aspirate sample of the caudal mediastinal mass was obtained. The sample was a brown-red, cloudy fluid. Cytology indicated nonseptic and predominantly neutrophilic and macrophagic inflammation. Evaluation of cell morphology was limited due to the low number and condition of cells, some of which were atypical. No evidence of a lymphoid population was identified; therefore, a lymph node origin could not be substantiated. Neoplastic etiology could not be excluded. Aerobic and anaerobic cultures of the sample yielded no growth. Results of a Blastomyces quantitative antigen test performed on a urine sample were negative.
Treatment and Outcome
The dog was hospitalized, and surgical treatment was planned; however, the dog’s clinical condition deteriorated prior to surgery. The owner elected euthanasia for the dog, followed by necropsy.
Gross necropsy findings revealed a complex, multilobulated structure in the caudodorsal aspect of the mediastinum that extended from the heart base region to the diaphragm. Pulmonary nodules, a solitary nodule in the liver, and multiple nodules in both kidneys were also noted. Histologic results indicated metastasis of osteosarcoma from the left humerus (limb amputated 4 months earlier) to the caudal mediastinum, lungs, middle tracheobronchial lymph node, liver, and kidneys. It was thought that the large mass in the mediastinum originated from the middle tracheobronchial lymph node due to the caudal heart base location. The tubular fluid-filled structure was characterized as a seroma. It was thought to have occurred due to separation of the connective tissues along the esophageal serosa, likely due to the presence of the mass.
Comments
In the dog of the present report, histologically confirmed osteosarcoma of the distal aspect of the humerus metastasized to the mediastinum, among other sites. To our knowledge, distant metastasis of appendicular osteosarcoma to tracheobronchial lymph nodes or the caudal region of the mediastinum had not been reported previously in dogs; therefore, metastatic disease was considered low on our list of differential diagnoses.
The most-reported metastatic site of appendicular osteosarcoma in dogs is the pulmonary parenchyma and, less frequently, bones and other soft tissue sites.1 An interesting finding that may have raised particular concern for metastatic osteosarcoma to the mediastinum was the presence of mineralization within the mass, suspected on radiography and confirmed on CT. In humans, ossified intrathoracic lymphadenopathy secondary to hematogenous spread of osteosarcoma has been reported but considered uncommon.2
Interestingly, a heterogeneous mass with mineralization, in a similar caudal mediastinum location, has been reported in a five-year-old male Boerboel dog and was diagnosed as extra-skeletal osteosarcoma.3 However, the mass was confirmed as neoplastic transformation from a primary Spirocerca lupi esophageal granuloma,3 whereas the dog of the present report had no evidence of parasites or lesions consistent with spirocercosis noted on necropsy or histopathology. The sudden onset of clinical signs in our patient also made such transformation unlikely as an underlying etiology. Furthermore, the location of the mass was described as esophageal in the patient with spirocercosis; however, the mass in our patient was thought to have originated from a tracheobronchial lymph node.
The use of barium esophagography and the use of CT tomography were important complementary imaging modalities that provided further information than survey radiography. Computed tomography was essential to confirm the presence of mineralization in the mass and provide more detail as to the exact location and involvement of the mass. In addition, it allowed characterization of the caudal fluid-filled structure as an additional lesion that was confluent with the mass.
For the dog of the present report, a multimodality imaging approach improved characterization of the lesion. Metastasis of appendicular osteosarcoma to ≥ 1 distant lymph node and the mediastinum, although rare, should be considered, especially when mineralization is present within the lesion.
References
- 1.↑
Ehrhart NP, Ryan SD, Fan TM. Tumors of the skeletal system. In: Withrow SJ, Vail DM, Page RL, eds. Withrow and MacEwen’s Small Animal Clinical Oncology. 5th ed. Saunders Elsevier; 2013:463–503.
- 2.↑
Rastogi R, Garg R, Thulkar S, Bakhshi S, Gupta A. Unusual thoracic CT manifestations of osteosarcoma: review of 16 cases. Pediatr Radiol. 2008;38:551–558. doi:10.1007/s00247–007–0735–3.
- 3.↑
Pazzi P, Tompkins S, Kirberger RM. Canine spirocercosis-associated extraskeletal osteosarcoma with central nervous system metastasis. J S Afr Vet Assoc. 2013;84(1):1–4. doi:10.4102/jsava.v84i1.71.
