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  • What's Your Diagnosis
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Diagnosis | Thymoma

Lab Animal volume 39, pages 264–265 (2010)Cite this article

Bilateral exophthalmos in a rabbit should lead a clinician to consider thymoma or thymic lymphoma. This clinical sign is consistent with cranial vena cava syndrome caused by a space-occupying mass that compresses the blood vessels of the cranial thorax and impedes vascular return to the heart. Rabbits have a well-developed retroorbital sinus, and in cranial vena cava syndrome, blood accumulates in the retroorbital sinus and pushes the eye out and over the orbital cavity. Exophthalmos can be distinguished from buphthalmia by the springy nature of the eyes: they can be digitally retropulsed easily. In buphthalmia, the eyes are firmer and resist digital retropulsion. Measurement of intraocular pressure can help to confirm the clinical findings: it is within normal range in exophthalmos and abnormally increased in buphthalmia. Normal intraocular pressure using a Tono-Pen-XL in rabbits is 15–23 mmHg1. Bilateral exophthalmos has been described in three rabbits with thymoma and in a rabbit with mediastinal lymphoma2,3,4,5. In most other cases of thymoma, exophthalmos was not observed6,7,8,9,10,11.

By light microscopy, we examined Giemsa-stained slides of the thoracic mass fine needle aspirates. We saw clusters of epithelial cells (consistent with thymic reticular cells) and small, mature lymphocytes. Although analysis of fine needle aspirates alone is not definitive, we made a presumptive diagnosis of thymoma based on the clinical signs (bilateral exophthalmos, tachypnea) and the radiography and ultrasound results5.

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Figure 4: Transverse computed tomography image through cranial thorax at level of scapulae.
Figure 5
Figure 6

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Diagnosis | Thymoma. Lab Anim 39, 264–265 (2010). https://doi.org/10.1038/laban0910-264

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