The animal of this report was a 466-g, 6.5-year-old female pet common marmoset (Callithrix jacchus) with a diet consisting of a commercial cereal mix, fruits, calcium supplements, and, occasionally, meat and fish. This marmoset was presented at the Clínica Exòtics (Barcelona, Spain) with a 4-day history of weakness, anorexia, occasional vomiting, ptyalism and sialorrhea, and a previously unremarkable clinical history.
Upon clinical examination, some of the very striking findings were the unexpected, marked docility of this animal, that did not react to any of the clinical procedures (e.g., auscultation, positioning for radiographs, or taking of the rectal temperature), abdominal distension, enlarged kidneys and venous stasis, especially visible in both hindlimbs. Rectal temperature (37°C) was normal. Dorsoventral and lateral radiographs demonstrated the abdominal distension associated with a diffuse moderate radiodensity that did not allow identification of abdominal organs. There was cranial displacement of the diaphragm and at least two intercostal spaces; the lung fields and cranial abdominal structures overlapped markedly as a result of such displacement. The diaphragm was more rounded than normal. These radiographic findings suggested hepatomegaly and/or ascites. The animal died a few hours after presentation with convulsions, seizures and generalized tremors.
At necropsy, fat stores were almost completely depleted. The liver, spleen and, to a lesser extent, the kidneys and adrenal glands were markedly enlarged and pale. Most abdominal and hindlimb veins were prominently engorged, and there was generalized lymphadenopathy, especially of mesenteric lymph nodes. The brain had a reddish mass occupying most of the caudal half of the left cerebral hemisphere. The heart was apparently enlarged, with a moderately enlarged right atrium and thickened left ventricular wall. There were no gastric contents. A complete set of tissues was fixed in 10% buffered formalin and routinely processed for histopathology and stained with hematoxylin and eosin. Special stains on selected tissues included periodic acid-Schiff (PAS), Ziehl-Neelsen (ZN), Masson’s trichrome, Congo red, and chloroacetate esterase. An immunohistochemical panel including keratin, vimentin, lymphocyte common antigen (LCA), MAC 387 (histiocytes), HMB-45 (melanocytes), glial fibrillar acid protein (GFAP), and CD31 (endothelial cells) was done on the brain tumor.
Microscopic examination of the brain mass revealed an angiocentric proliferation of a relatively homogeneous cell population characterized by large nuclei and moderately abundant, slightly basophilic cytoplasm; intravascular invasion or growth within the tumor was a prominent finding, occasionally associated with thrombosis, necrosis and hemorrhage. The tumor was poorly delimited and, although it mostly grew in the white matter, there were focal perivascular proliferations in the grey matter as well. The results of the immunohistochemical panel were as follows: keratin negative, vimentin positive, and MAC 387-, LCA-, HMB45-, CD31- and GFAP-negative. The tumor did not have myeloperoxidase activity. Histopathology also revealed important lesions in multiple organs, especially the kidneys and liver. Some of the renal lesions (chronic diffuse mesangioproliferative glomerulonephritis with interstitial fibrosis) resembled those reported in mesangial nephropathy of callitrichids but were associated with abundant hyaline and cellular casts; multinucleate giant cells within tubules and phagocytosis of hyaline casts were prominent. A striking finding in the kidneys and liver (and less prominent in adrenal glands, adipose tissue and gastrointestinal tract) was the presence of marked infiltrates predominantly of mature myeloid cells (relatively homogeneous in morphology, with indented or polylobulated nuclei, and eosinophilic cytoplasm). The liver also had diffuse hydropic degeneration, and perivascular fibrosis (especially of sublobular veins). There was a myelolipoma in one of the adrenal glands. Other findings were neuronal lipofuscinosis of sympathetic ganglia, mild granulomatous pansteatitis with ceroid, decreased erythroid:myeloid ratio in the bone marrow (that was hypercellular), hyperplasia of splenic red pulp, excessive erythrophagocytosis, and generalized lymphoid hyperplasia.
The results of the immunohistochemistry panel and stain for myeloperoxidase activity on the brain tumor are consistent with a diagnosis of undifferentiated angiocentric cerebral sarcoma. The absence of neoplastic growths in other tissues despite extensive histologic studies suggests that this tumor is a primary cerebral neoplasia. Neoplasia of the central nervous system has not been previously reported in New World primates and occurs sporadically in Old World species.2,4,8
The disseminated myeloid infiltrates were considered to correspond to extramedullary hematopoiesis (EMH). EMH with predominating myeloid cells and leukemoid reaction occur chiefly as a result of severe, localized pyogenic infections (e.g., pyometra in the bitch); despite extensive histologic studies no evidence of such infections was found in this animal. Prominent EMH is a common microscopic finding in callitrichids in captivity6 (Dr. B. Rideout, personal communication). Adrenal and hepatic myelolipomas are not uncommon lesions in callitrichids and Goeldi’s monkeys.3,5,7 Most renal lesions were considered to fit well in the overall picture of mesangial nephropathy commonly found in callitrichids,1 except for the extensive hyaline and cellular cast formation. Pansteatitis with ceroid was an incipient lesion in this animal that may have been the result of an inadequate diet (deficient in vitamin E as for its contents in polyunsaturated fatty acids) and/or increased production of peroxides in severely damaged tissues such as the liver and kidneys.
The authors thank Hospital Sant Jaume de Calella for assistance with immunohistochemistry, and Blanca Pérez and Pere Losada for histotechnology.
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