Erythrocytosis and pleural effusion associated with a hepatoblastoma in a Thoroughbred yearling.

The research article discusses a case of a 10-month-old Thoroughbred filly which had symptoms of recurrent fever and fluid accumulation in the chest cavity (pleural effusion) and was found to have a type of liver cancer (hepatoblastoma), which led to higher than normal red blood cell count (erythrocytosis).

Initial Physical Examination and Clinical Signs

• The filly presented symptoms such as a high body temperature (pyrexia) and congestion in the mucous membranes. These symptoms were not typical of horses of her age.
• Ultrasonography revealed the presence of fluid in the chest cavity (pleural effusion). This fluid was found to be a lymphocytic, modified transudate, i.e., a fluid shift with certain cellular changes. This might have cause discomfort to the horse and is one of the reasons the filly was brought in for examination.

Laboratory and Clinical Pathology Work-up

• Laboratory tests showed erythrocytosis or an abnormally high count of red blood cells, hyperfibrinogenaemia (elevated levels of fibrinogen, a protein essential to wound healing and blood clot formation), and hyperglobulinaemia (high levels of globulins, proteins made in your liver or immune system).
• The erythrocytosis persisted despite attempts to decrease the blood cell count through intravenous fluid therapy. As pulmonary function and bone marrow were unaffected, the erythrocytosis was deemed “inappropriate” or secondary, indicating another cause for these symptoms.

Ultrasonography and Histopathological Examination

• Further examination of the abdomen via ultrasound revealed a large, irregularly-shaped mass in the left lobe of the liver.
• A biopsy of the liver mass followed by examination under a microscope indicated that the mass was a type of liver cancer, specifically a hepatic carcinoma.

Euthanasia, Necropsy and Final Diagnosis

• Given the poor prognosis, the decision was made to humanely end the filly’s life. A post-mortem examination (necropsy) confirmed the presence of a liver tumor with no evidence of the cancer spreading to other parts of the body (systemic metastasis).
• Further examination of the tumor tissue established the cancer to be a rare type of hepatoblastoma (a type of liver cancer) called an embryonal macrotrabecular epithelial-type hepatoblastoma. To the researchers’ knowledge, this specific type of liver cancer had not been previously reported in a horse.