JPC SYSTEMIC PATHOLOGY

HEMOLYMPHATIC SYSTEM

February 2024

H-N04 (NP)

 

Signalment (JPC #3167242): Female chicken.

 

HISTORY: None.

 

HISTOPATHOLOGIC DESCRIPTION: Liver: Expanding the hepatic parenchyma and compressing adjacent tissue there is a focally extensive, unencapsulated, multilobular, moderately cellular, well demarcated 10 mm nodular 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 2.37mm^2). 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.

 

GENERAL DISCUSSION:

• 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 reported in the 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

 

PATHOGENESIS: 

• 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 hamartomas

 

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

 

ADDITIONAL DIAGNOSTIC TESTS:

• Fine needle aspirate: large lipid vacuoles, mature adipocytes, hematopoietic cells, hemosiderin-laden macrophages
• Ultrasound: Small, focal hyperechoic mass in the spleen (rarely large)

 

 

DIFFERENTIAL DIAGNOSIS:

• 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

 

COMPARATIVE PATHOLOGY: 

• Reported in dogs, cats, cattle, several bird species (liver, spleen, and subcutis), 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
• Marmosets, tamarins, chimpanzees, and Goeldi’s monkeys develop myelolipomas of the liver
• Can be experimentally induced in rats

 

REFERENCES: 

1. Abdul-Aziz T, Fletcher O, Barnes HJ. Avian Histopathology. Madison, WI: AAAP. 2016: 623.

2. Cullen JM, Stalker MJ. Liver and biliary system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 2. 6th ed. St. Louis, MO: Elsevier Limited; 2016:350-351. 

3. Little EK, Wills TB, Haldorson GJ. The Adrenal Gland. In: Valenciano AC, Cowell RL, eds. Cowell and Tyler’s Diagnostic Cytology and Hematology of the Dog and Cat. 5^th ed. St. Louis, MO: Elsevier. 2020; 509.

4. Miller AD. Neoplasia and Proliferative Disorders of Nonhuman Primates. In: Abee CR, Mansfield K, Tardif S, Morris T, eds. Nonhuman Primates in Biomedical Research. 2^nd ed. Waltham, MA: Elsevier. 2012: 335.

5. Raskin RE. Hemolymphatic System. In: Raskin RE, Meyer DJ, Boes KM. Canine and Feline Cytopathology. St. Louis, MO: Elsevier. 2023; 171-173.

6. Terio KA., McAloose D, Mitchell EL. Felidae. In: Pathology of Wildlife and Zoo Animals. London, UK. Academic Press, 2018: 269. 

7. Rosol TJ, Groene A. Endocrine glands. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. St. Louis, MO: Elsevier Limited; 2016:343-344. 

8. Schmidt RE, Reavill DR, Phalen DN. Pathology of Pet and Aviary Birds. 2^nd ed. Ames, IO: John Wiley & Sons, Inc. 2003: 120, 191-192.

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