Case study: Diagnosis and surgical treatment of thymoma

canine thymoma

Max is a 10-year-old, male neutered border collie who presented to BVSC for hypercalcaemia of unknown origin. He had recently become lethargic with polydipsia and polyuria and his referring veterinarian had discovered an elevated total calcium level on blood tests. Work-up at BVSC included ionized calcium level test, a detailed physical examination including a rectal exam, thoracic radiographs and abdominal ultrasound. The critical finding was a large cranial mediastinal mass. Ultrasound-guided fine-needle aspirates were performed and the samples were sent to QML for cytology and flow cytometry assessment, which returned a diagnosis of thymoma.

canine thymoma

Up to two thirds of canine thymic masses are thymoma and these tumours commonly present with paraneoplastic syndromes such as myasthenia gravis, hypercalcaemia or cranial vena cava syndrome. They can be difficult to diagnose from cytology alone and flow cytometry is useful to differentiate between thymoma and lymphoma. 

The recommended treatment is surgical removal if possible, with reported median survival times of 617 to 635 days. However, these masses can be locally aggressive, and if the mass is not surgically resectable then radiation therapy can be performed.

canine thymoma
Sagittal, Transverse, and Dorsal Computed Tomography (CT images showing cross section of the thymoma)

Following his diagnosis, Max was booked for contrast enhanced computed tomography (CT) of his chest to determine if the mass was invading local structures. At BVSC we are able to perform CT in-house and then when appropriate, move the patient directly from CT to the operating theatre. In Max’s case, we discovered the mass was very large (with a diameter of 20cm) but there was no obvious invasion of vital structures and the decision was made to proceed with surgical removal. A ventral midline thoracotomy was performed using an oscillating saw for the sternotomy. The mass was filling the entire cranial and ventral thoracic cavity. The mass was adhered to but not invading the major vessels and pericardium and was able to be very carefully dissected free. At BVSC we use Ligasure with ForceTriad® electrosurgical system to provide cutting, coagulation and vessel sealing functionality. This gold standard system ensures safe and efficient haemostasis during soft tissue surgery. The left phrenic nerve was engulfed within the tumour and had to be sacrificed and the large mass was removed en-bloc without complication. A thoracostomy tube was placed for post-operative air and fluid evacuation, and Max recovered in our intensive care unit (ICU) where he received 24 hour a day care. He was administered fentanyl, ketamine and lignocaine as a continuous rate infusion for analgesia. There were no adverse effects from the surgery including the removal of the left phrenic nerve. His ventilation was normal with excellent oxygen saturation parameters which were closely monitored.

Max recovered very well and his hypercalcaemia resolved within 48 hours of surgery. He was discharged to his owners’ care after spending three days in the ICU. At his two week revisit, Max had resolution of his polyuria, polydipsia and lethargy; he was bright, alert, responsive and comfortable. He will be visiting every three months for the next year for a physical examination and chest radiographs to assess for recurrence. There is a 17 per cent risk of recurrence; if the thymoma does return then we will recommend Max visit with our radiation oncologist, Dr Elias Gumpel, for radiation therapy with three-dimensionally planned multiple beam photon radiation therapy.

Dr Katherine Steele, BVSc MVS MVSc MANZCVS DipECVS, Small Animal Surgery Specialist

canine thymoma
Dr Katherine Steele, BVSc MVS MVSc MANZCVS DipECVS, Small Animal Surgery Specialist

Dr Katherine Steele, a board certified small animal surgeon, graduated from the University of Queensland in 2008. She completed a rotating and surgical internship in Brisbane prior to relocating to Victoria for a residency at Melbourne University in a small animal surgery. She completed a Masters of Veterinary Studies in 2016 and a Masters of Veterinary Science in 2017. Her interest in oncology led her to Brisbane Veterinary Specialist Centre.

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