Here’s a case of a 5-year-old male Dogue de Bordeaux who was anorexic and lethargic. Bloodwork showed hematocrit 52.3%, platelets 84,000, WBC 6,350. BUN 44, creatinine 2.2, PO4 5.0, Ca 16.0, cholesterol 443, Na 159. USG – 1.015.
There is increased soft tissue opacity in the cranial mediastinum on both lateral projections. The cranial mediastinum is also widened on the d/v projection. The trachea is elevated on both laterals suggesting a cranial mediastinal mass. The esophagus is mildly dilated with air on both projections. The remainder of the intrathoracic structures appear normal.
- malignant histiocytosis
- ectopic thyroid/parathyroid tumor
- mediastinal cyst
High grade lymphoma
Mediastinal masses can be difficult to diagnose in large breed dogs that usually have a fair amount of fat in the cranial mediastinum. The persistent elevation of the trachea is confirmatory in this case. Ultrasound can be useful in distinguishing between a cranial mediastinal mass and fat, especially if there is contact with the chest wall or there is pleural effusion.
The esophageal dilation makes thymoma a top differential as it can cause myasthenia gravis and megaesophagus. This mass was caused by enlarged cranial mediastinal lymph nodes from high grade lymphoma.
This dog also had hypercalcemia of malignancy. Certain types of lymphoma can produce a molecule called parathyroid hormone related peptide (PTHrP), which increases calcium levels by mimicking PTH. Once aggressive fluid treatment was implemented and chemotherapy was administered (Elspar), the calcium level began to decrease. Approximately one day after the calcium level decreased, the azotemia began to resolve. The fluids were weaned over the next three days and were discontinued just prior to discharge.