JPC SYSTEMIC PATHOLOGY
Signalment (AFIP #3167242): Female chicken
HISTOPATHOLOGIC DESCRIPTION: Liver: Focally extensively expanding the hepatic parenchyma up to 10 mm and compressing adjacent hepatocytes is an unencapsulated, multilobular, moderately cellular, well demarcated neoplasm composed of mature adipocytes and variable numbers of hematopoietic cells, in various stages of maturation, arranged in sheets on a scant fibrovascular stroma. Both progenitor and precursor cells are represented. There are also abundant mature red blood cells admixed with small amounts of eosinophilic proteinaceous fluid and scattered, golden to dark brown pigment-laden macrophages. Cellular atypia is minimal and mitotic figures are rare (<1 per 10 HPF). Focally within the neoplasm there is formation of immature woven bone (osseous metaplasia). Hepatocytes adjacent to the neoplasm are often degenerate (swollen, vacuolated cytoplasm), shrunken and atrophied, or lost with dissociation of hepatic cords. Multifocally low numbers of lymphocytes, histiocytes and heterophils expand the periportal regions and extend into adjacent parenchyma.
MORPHOLOGIC DIAGNOSIS: Liver: Myelolipoma, chicken, avian.
- A benign lesion found primarily in the adrenal glands of cattle and non-human primates, in the spleen of dogs, and in the liver of domestic cats and wild felids
- Have also been found in the spleen, omentum, epidural spinal canal, kidney, skin, subcutaneous tissues, and eye
- Metastasis to other organs has not been reported; the presence of multiple myelolipomas in a single animal are considered sites of de novo growth
- Usually noted in older animals
- The origin of myelolipomas is uncertain; they appear to develop by metaplastic transformation of cells in the adrenal cortex
- Some myelolipomas grow to a large size and behave like a neoplasm; others are small and multiple and are considered metaplastic or hamartomatous
TYPICAL CLINICAL FINDINGS:
- Usually an incidental finding
- Animals with tumors involving the liver may have non-specific hepatopathy, cholestasis, lethargy, anorexia, vomiting, or ascites
TYPICAL GROSS FINDINGS:
- Irregularly nodular growths that may project above the surface of the organ
- Friable, soft; yellow-orange (due to high fat content) to tan-white; may have dark red areas from hemorrhage
- Single or multiple nodules 0.5-10 cm in diameter
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Accumulations of well-differentiated adipose connective tissue cells and hematopoietic tissue, including both mature and immature cells of the myeloid, erythroid, and megakaryocytic series
- The amount of hematopoietic tissue present can vary greatly; tumors in birds tend to have predominance of heterophils
- Usually poorly to thinly encapsulated and well-demarcated
- Focal areas of bone formation may occur within the tumor
- Extramedullary hematopoiesis(EMH): Lacks adipose; had distributed, non-nodular appearance (EMH in dog spleens can occur in a nodular form)
- Lipoma: Lacks hematopoietic elements
- Splenic mesenchymoma: Reported in dogs to have three or more distinct stromal types that often included adipose and another mesenchymal type intermixed (such as osseous, chondromatous or myxomatous type matrix); lacks hematopoietic elements
- Reported in dogs, cats, cattle, several bird species, non-human primates, ferrets, rats and exotic large cats
- Cheetahs have been reported to have the highest prevalence of myelolipomas; tumors are usually in the spleen
- Callitrichid monkeys (marmosets, tamarins, Goeldi’s monkeys) appear to have similarly high prevalence of (hepatic) myelolipomas
- Can be experimentally induced in rats
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- Kleinschmidt LM, Langan JN, Warneke MR, et al. Retrospective review of the prevalence of myelolipoma in Goeldi’s monkeys (Callimico goeldii). J Zoo Wildl Med. 2015;46(2):273-278.
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- Valli VE, Bienzle D, Meuten DJ. Tumors of the hemolymphatic systems. In: Meuten DJ, ed. Tumors in Domestic Animals. 5th ed. Wiley Blackwell, Ames, IA, 2017:317-318.