Generalized lymphoma with a displacing mass in the orbital cavity of a Pacific parrotlet (Forpus coelestis)

In this case report, a 4.5-year-old Pacific parrotlet (Forpus coelestis) with a generalized hematopoietic neoplasia is described. The patient was presented with severe unilateral exophthalmos of the right eye and a poor general health condition. Neither in the general nor the ophthalmologic, nor the subsequent microbiological and mycological examination signs of infection were detected, and molecular tests for Chlamydia psittaci were negative. As the bird’s condition decreased despite intensive care treatment, euthanasia was performed. Postmortem examination revealed a large, space-occupying, bloody mass in the right orbita, displacing the globe. The calvaria seemed to be involved as well as the Paries dorsalis and Paries caudalis of the orbita. Histopathology identified tumor cells in the liver, the spleen, the kidneys, the right eye, and the surrounding orbita, indicating a generalized lymphoma as underlying cause. Immunohistochemical analysis confirmed the swelling to be of B-cell origin. This case report demonstrates that neoplasms should be included in the list of differentials for exophthalmos in psittacines. Moreover, diagnostic options to work off an exophthalmos are described with a special focus on hematopoietic neoplasms in psittacines.