JPC SYSTEMIC PATHOLOGY

CARDIOVASCULAR SYSTEM

February 2025

C-M08 (NP)

 

Signalment (JPC #2417289): One week-old Holstein calf

 

HISTORY: This calf was clinically normal and sacrificed for the collection of cardiac tissue for experimental purposes. 

 

HISTOPATHOLOGIC DESCRIPTION: Heart: Multifocally, including within one papillary muscle, subjacent to and elevating the endocardium, and extending into the myocardium, are two expansile, unencapsulated, well-demarcated masses up to 0.75 cm x 1.5 cm that separate, surround, isolate, and replace individual cardiomyocytes and Purkinje fibers. The masses are composed of epithelial cells that form variably sized (up to 2.5 mm diameter) acini and tubules lined by one to multiple cell layers on a dense collagenous stroma. These epithelial cells are squamous to cuboidal, have distinct cell borders, a scant amount of eosinophilic cytoplasm, and a round to oval nucleus with indistinct nucleoli and no mitoses or atypia. Between the tubules within the collagenous stroma are multifocal small nests of similar epithelial cells. The interstitial tissue subjacent to the endocardium is mildly expanded by clear space (edema).

 

MORPHOLOGIC DIAGNOSIS: Heart, myocardium, subendocardial: Epithelial inclusions, multifocal, Holstein, bovine.

 

CONDITION: Myocardial epithelial inclusions

 

GENERAL DISCUSSION:

• Bovine myocardial epithelial inclusions are congenital masses that do not proliferate, metastasize, or undergo malignant transformation
• Incidental finding that usually occurs in the left ventricular free wall, less commonly in the interventricular septum
• Closely resemble benign adenomatoid tumors of humans which are of mesothelial origin
• Can be considered a choristoma; may be endodermal in origin from the foregut misplaced during organogenesis

 

PATHOGENESIS:

 

TYPICAL CLINICAL FINDINGS: 

 

TYPICAL GROSS FINDINGS:

• Single to multiple, well-circumscribed, firm, plaque-like mass(es) in the left ventricular wall and, less commonly, the interventricular septum
• Affected area is discolored or spongy

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Lesions composed of squamous to cuboidal epithelial cells that form tubular, ductular, and acinar structures; lumina may be empty or contain amorphous protein globules
• Epithelial cells occasionally form small, scattered nests
• Abundant collagen separates and surrounds the tubular and acinar structures

 

ULTRASTRUCTURAL FINDINGS:

• Brush border of elongated, thin microvilli
• Well-formed desmosomes associated with tonofibrils

 

ADDITIONAL DIAGNOSTIC TESTS:

• Immunohistochemistry: 
  • Cytokeratin positive
  • A study showed these “epithelial” cells have an immunohistochemical profile consistent with mesothelial differentiation (Tursi, Vet Pathol. 2009)

 

DIFFERENTIAL DIAGNOSIS:

• Entrapped mesothelium (during embryogenesis)
• Mesothelioma

COMPARATIVE PATHOLOGY:

• Humans: One case report of a similar lesion in the ventricle of a patient undergoing bypass surgery; diagnosed as adenomatoid tumor. Adenomatoid tumors in man primarily occur in the urogenital tracts and are of mesothelial origin
• Rats: Usually affects older rats; proliferative; usually in the atrial free wall, but may extend into the interatrial and left atrial free walls; appear to be true neoplasms rather than ectopic rests of tissue
• Swine: Single report in fetal pigs with lesions in the ventricular wall and sinoatrial node; solid and vesicular patterns lined by columnar epithelium
• Guinea pigs: Intracytoplasmic inclusions in cardiomyocytes, usually older animals; most commonly right ventricular free wall (Southard, Vet Pathol. 2022)

REFERENCES:

1. Baker DC, Schmidt SP, Langheinrich KA, Cannon L, Smart RA. Bovine myocardial epithelial inclusions. Vet Pathol. 1992;30:82-88.
2. Novilla MN, Sandusky GE, Hoover DM, Ray SE, Wightman KA. A retrospective survey of endocardial proliferative lesions in rats. Vet Pathol; 1991;28:156-165.
3. Robinson WF, Robinson NA. The cardiovascular system. In: Maxie MG, ed Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. Philadelphia, PA: Elsevier; 2016:22.
4. Southard T, Kelly K, Armien AG. Myocardial protein aggregates in pet guinea pigs. Vet Pathol. 2022 Jan;59(1):157-163.
5. Tursi M, Martinetti M, Gili S, et al. Myocardial adenomatoid tumor in eight cattle: evidence for mesothelial origin of bovine myocardial epithelial inclusions. Vet Pathol. 2009; 46:897-903.

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