ABSTRACT
The lymphatic organs are classified as primary (thymus and bursa of Fabricius) or secondary tissue (spleen; Harderian gland; pineal gland; bone marrow; scattered aggregates of lymphoid tissue). The aetiology of thymic cysts is unknown, but they may be congenital abnormalities associated with persistent thymopharyngeal ducts, or acquired during thymic involution. They are similar in appearance and location to ultimobranchial cysts. Hypoplasia or atrophy of the spleen may occur secondary to bursal disease. Lymphoid necrosis can be due to chronic disease or other severe stress. Atrophy also occurs naturally with age. Diagnostic imaging (radiology, CT and ultrasound) can indicate splenomegaly but not determine the cause. Haematology, biochemistries and other diagnostic modalities for infectious disease (e.g. serology, PCR) should be pursued. Haematology may demonstrate a leukaemic profile, although the combination of leukaemia and lymphosarcoma is uncommon in birds. Myeloproliferative disorders (neoplastic proliferation of non-lymphoid haematopoietic cells in the bone marrow which subsequently invade the spleen and liver) are uncommon.
