History
A 14-year-old sexually intact male Labrador Retriever was evaluated because of coughing and lethargy of 3 to 4 months' duration. Approximately 1 week prior to initial evaluation, the dog became anorexic and the owners noticed acute development of swelling of the ventral aspect of the neck. Physical examination findings included signs of lethargy, mild dehydration, and generalized ventral cervical swelling. Coughing was noted, but no abnormalities were detected on thoracic auscultation. Mild anemia (PCV, 30%; reference range, 34% to 60%) was detected on CBC. Prothrombin time and partial thromboplastin time were within the reference ranges. Radiographs of the thorax were obtained (Figure 1).
Left lateral (A) and ventrodorsal (B) radiographic views of the thorax of a 14-year-old male Labrador Retriever evaluated because of coughing and lethargy of 3 to 4 months' duration.
Citation: Journal of the American Veterinary Medical Association 243, 7; 10.2460/javma.243.7.965
Determine whether additional imaging studies are required, or make your diagnosis from Figure 1—then turn the page →
Diagnostic Imaging Findings and Interpretation
Radiographic images of the thorax reveal widening of the cranial aspect of the mediastinum and marked rightward deviation of the trachea cranial to the thoracic inlet on the ventrodorsal view and an ill-defined soft tissue opacity mass effect causing ventral deviation of the intrathoracic portion of the trachea on the lateral projection. A 1-cm-diameter, round, sharply marginated soft tissue opacity can be seen ventral to the trachea at the second intercostal space on the left lateral view (Figure 2). Additionally, a 3.5-cm-diameter mass is seen silhouetting with the cardiac base and trachea immediately cranial to the carina.
Same left lateral radiographic view as in Figure 1 highlighting ventral deviation of the intrathoracic portion of the trachea (black arrows) and a 1-cm-diameter soft tissue opacity in the cranial lung field ventral to the trachea at the level of the second rib (single white arrow). An additional 3.5-cm-diameter soft tissue opacity (white arrowheads) is overlying the distal portion of the trachea at the level of the fourth intercostal space.
Citation: Journal of the American Veterinary Medical Association 243, 7; 10.2460/javma.243.7.965
Differential diagnoses for ventral deviation of the trachea included a dorsally located mediastinal mass such as a cyst, granuloma, hematoma, abscess, or neoplasia. Organs of origin for a mass dorsal to the trachea included cranial mediastinal lymph node, pulmonary parenchyma, trachea, esophagus, ectopic thyroid tissue, ectopic parathyroid tissue, or branchial remnants. Given the poor definition of the structure, focal or sequestered cranial mediastinal fluid (hemorrhage or pyogranulomatous or neoplastic effusion) was strongly considered. Hemorrhage of a tumor originating from tissues of the neck was considered. The presence of the 2 nodules made metastatic disease likely.
Computed tomography of the neck and thorax was performed to identify the etiology of the cervical swelling, evaluate the pulmonary parenchyma and lymph nodes for metastatic neoplasia, and further define the cranial mediastinal mass. The patient was anesthetized, and contiguous images were obtained with a single-slice CT scannera with a peak voltage of 120 kV, amperage of 101 mA, and slice thickness of 2.5 mm. Images were acquired before and after IV administration of a nonionic iodinated contrast agentb at a dose of 2.2 mL/kg (1 mL/lb).
Precontrast images demonstrate an ovoid, isoattenuating soft tissue density (42 Hounsfield units [HU]) measuring 3 cm in transverse section beginning immediately caudal and to the left of the larynx, displacing the left common carotid artery abaxially (Figure 3). Following contrast administration, a thick rim of enhancement could be seen surrounding the structure. The caudal aspect of the mass abuts a large, tubular, mildly heterogeneous structure with a thin, faintly contrast-enhanced wall and a radiodensity varying from 20 to 30 HU, consistent with fluid. The structure extends caudally into the craniodorsal aspect of the mediastinum up to the level of the cardiac base, causing rightward and ventral deviation of the trachea, esophagus, cranial vena cava, and heart base. A distinct mass corresponding to the 3.5-cm-diameter mass seen on the left lateral radiograph was not seen, and radiodensity measurements in the dorsal aspect of the mediastinum at the heart base were consistent with fluid. A left thyroid lobe was not seen. The right thyroid lobe was seen as a 5 × 10 × 23-mm, homogenous, oblong structure just caudal to the larynx and ventral to C2. It was hyperdense, compared with the surrounding soft tissues, with a precontrast radiodensity of 86 HU and a postcontrast radiodensity of 152 HU. A 1-cm-diameter nodule adjacent to the mediastinal pleura of the right cranial lung lobe was seen. On the basis of radiographic and CT findings, a mass involving the left lobe of the thyroid gland with metastasis to the right cranial lung lobe was suspected. The most likely differential diagnosis for the craniodorsal mediastinal mass effect was hemorrhage originating from a thyroid tumor, but abscess and branchial cyst could not be ruled out.
Computed tomographic images of the same dog in Figure 1. A—Transverse CT image following IV contrast administration of the cranial cervical region highlighting the normal right thyroid lobe (single white arrow), a mass associated with the left thyroid lobe (black arrows), and a hematoma (white arrowheads; radiodensity, 26 Hounsfield units [HU]; window width, 350 HU; window length, 40 HU). B—Sagittal reconstruction of postcontrast CT images, slightly left of midline. The cervical and mediastinal hematoma is evident (arrowheads). Notice the thyroid mass (3 small arrows) and ventral deviation of the thoracic portion of the esophagus (single arrow [window width, 350 HU; window length, 40 HU]). C—Transverse CT image following IV contrast administration at the level of the second intercostal space. Notice the 1-cm-diameter nodule adjacent to the mediastinal pleura of the right cranial lung lobe (arrow [window width, 1,500 HU; window length, −600 HU]).
Citation: Journal of the American Veterinary Medical Association 243, 7; 10.2460/javma.243.7.965
Treatment and Outcome
A fine-needle aspirate of the fluid-filled cervical mass was consistent with hemorrhage. Despite suspected metastatic disease, the owner elected cervical exploratory surgery. A ventral midline approach was made extending from the larynx to the manubrium. A large swelling was noted dorsal to the paired sternohyoideus muscles. As the muscles were bluntly separated, a fluid pocket filled primarily with coagulated blood and fibrin was entered. Once the coagulum was removed, a 6 × 5-cm-diameter mass originating from the left thyroid lobe could be seen. Vessels supplying the mass were ligated, and the mass was excised. From the caudal aspect of the cervical incision, a Poole suction tip was carefully advanced into the cranial aspect of the mediastinum. By means of copious lavage and suction, a large amount of coagulated blood was removed. Necrotic tissue from the periphery of the hematoma was debrided. Following closure, the patient recovered without complication. Ventral deviation of the trachea and the mass effect over the cardiac base had resolved on lateral thoracic radiographs taken following surgery. Findings on histologic evaluation of the mass were consistent with thyroid carcinoma. Tissue specimens taken from the periphery of the hematoma consisted of granulation tissue on histologic evaluation.
At the time of telephone follow-up at 18 months after surgery, the owner reported the dog was doing well clinically with no recurrence of clinical signs. The patient had been receiving piroxicam (0.1 mg/kg [0.045 mg/lb], PO, q 24 h) since the time of surgery.
Comments
Thyroid carcinomas or adenocarcinomas make up 90% of all thyroid tumors in dogs.1 Metastatic rates for these tumors are high, up to 33% at the time of diagnosis and 65% to 90% in untreated dogs at necropsy.2 Lung and regional lymph nodes are most commonly affected.2 Prognostic factors influencing outcome include local invasion, tumor size, and presence of metastatic disease.2
Substantial cervical hemorrhage secondary to thyroid carcinoma has been described.3 Some authors have advised caution when performing fine-needle aspiration and typically advise against needle or incisional biopsies of suspected thyroid tumors.2 In the dog of the present report, massive hemorrhage into the neck and cranial aspect of the mediastinum was likely spontaneous and associated with the left-sided thyroid carcinoma. The resulting mediastinal hematoma caused ventral and rightward deviation of the trachea that resolved following surgical evacuation of the hematoma. Computed tomography was helpful in this case in narrowing the list of differential diagnoses for the mass effect causing ventral deviation of the trachea seen on radiographs and for better defining the structures with transverse imaging. Determination of the radiodensity of different soft tissue structures (measured in HU) was particularly helpful in differentiating hemorrhage from surrounding soft tissues, including the thyroid mass, in this case.
Picker PQ 5000, Philips Healthcare, Andover, Mass.
Iversol (Optiray 320), Mallinckrodt Inc, Hazelwood, Mo.
1. Wucherer KL & Wilke V. Thyroid cancer in dogs: an update based on 638 cases (1995–2005). J Am Anim Hosp Assoc 2010; 46: 249–254.
2. Liptak JM. Canine thyroid carcinoma. Clin Tech Small Anim Pract 2007; 22: 75–81.
3. Slensky KA, Volk SW, Schwarz T, et al. Acute severe hemorrhage secondary to arterial invasion in a dog with thyroid carcinoma. J Am Vet Med Assoc 2003; 223: 649–653.
