JPC SYSTEMIC PATHOLOGY

RESPIRATORY SYSTEM

September 2017

P-M07 (NP)

 

Signalment (JPC #2142217):  Adult female chinchilla

HISTORY:  This chinchilla died due to bacterial septicemia

HISTOPATHOLOGIC DESCRIPTION:  Lung:  Multifocally, alveolar septal capillaries are expanded and occluded by polygonal cells that are up to 150 um diameter with abundant amphophilic granular cytoplasm, nuclei that  are 25-45 um in diameter with reticular chromatin, and 1-2 irregularly shaped to oval magenta nucleoli (placental trophoblasts).  Few trophoblasts are binucleate. 

MORPHOLOGIC DIAGNOSIS: 

Lung, septal capillaries:  Trophoblastic emboli, multifocal, mild.

ETIOLOGIC DIAGNOSIS:  Trophoblastic embolism

GENERAL DISCUSSION: 

• Trophoblasts: cells covering the embryonic blastocyst; early in development they function to facilitate absorption of nutrients, and later participate in the formation of fetal membranes that contribute to the formation of the placenta
• The trophoblast has an erosive action on the endometrium; during early pregnancy, trophoblasts cross the basement membrane of the uterine epithelium and vasculature to initiate implantation of the blastocyst
• The degree of endometrial erosion by trophoblasts is dependent on species
• Placentation can be classified by:
  • The maternal cell layers between the fetal chorionic ectoderm and the maternal blood
    • Hemochorial placentation: maternal blood comes in direct contact with fetal chorion, increasing the chances that trophoblasts will dislodge into the maternal bloodstream and be carried as emboli to other organs
    • Endotheliochorial placentation: maternal endothelium in contact with fetal chorion
    • Epitheliochorial placentation: maternal epithelium in contact with fetal chorion
  • The distribution of the attachment sites
  • The type of maternal-fetal interdigitation

 

Species	Distribution of contact	Classification by maternal cell layers	Maternal-fetal interdigitation
Mare, Sow	Diffuse	Epitheliochorial	Villi (horse: “cups”, pig: folded villi)
Ruminant	Cotyledonary	(Syn)epitheliochorial (combination)	Villi
Bitch, Queen	Zonary	Endotheliochorial	Labyrinth
Rhesus macaque	Double discoid	Hemochorial	Villi
Ape, human	Discoid	Hemochorial	Villi
Rabbits, rodents	Discoid	Hemochorial	Labyrinth

 

PATHOGENESIS: 

• Hemochorial placentation (fetal trophoblastic cells in direct contact with the maternal circulation) à trophoblasts erode the endometrium and migrate to lumina of maternal blood vessels à can dislodge (physiologic desquamation) and are carried to small capillary beds (e.g. lungs, spleen, liver, and adrenal glands) as emboli
• In endometrium at sites of trophoblast erosion, there is loss of endothelium, elastic membrane, and smooth muscle in affected arteries with no reaction from the maternal immune system
• Substantial numbers of trophoblasts may be located in various maternal tissues during normal pregnancy
• Domestic animals without hemochorial placentation are not prone to trophoblastic emboli

TYPICAL CLINICAL FINDINGS:

• Usually clinically insignificant, incidental findings in animals; in humans it has been linked to life-threatening conditions including infarcts and right‑sided heart failure

TYPICAL GROSS FINDINGS:

• None

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Trophoblast cells can be found in the lungs and in the uterus (gravid or postparturient), lungs, spleen, liver, or adrenal glands; normally there is no maternal immune reaction to these cells

DIFFERENTIAL DIAGNOSIS:

• Neoplastic embolus, choriocarcinoma: trophoblasts may undergo neoplastic transformation into choriocarcinoma and metastasize or release tumor emboli

COMPARATIVE PATHOLOGY:

• The Syrian hamster has been used as a model for the study of vascular invasion by trophoblasts
• Intravascular dissemination of placental trophoblasts may be present in pregnant gerbils

REFERENCES:

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016: 174, 200.
2. Burek JD, Goldberg B, Hutchins G, Strandberg JD. The pregnant Syrian hamster as a model to study intravascular trophoblasts and associated maternal blood vessel changes. Vet Pathol. 1979;5:556‑566.
3. Hamir AN, Rupprecht. Trophoblast-like cells in the tissues of porcupines (Erethizoon dorsatum). Vet Pathol. 2008;45:409-411.
4. La Perle KM, Green MG, Niewiesk S. Trophoblast deportation to the lungs of cotton rats (Sigmodon hispidus).  Comp Med 2014;64(6):448-55.
5. Noden DM, De Lahunta A. The Embryology of Domestic Animals: Developmental Mechanisms and Malformations. Baltimore, MD: Williams and Wilkins;1985:50‑69.
6. Suckow MA, Stevens KA, Wilson RP. The Laboratory rabbit, guinea pig, hamster, and other rodents.  London, UK: Academic Press;2012:1005.
7. Tvedten HW, Langham RF. Trophoblastic emboli in a chinchilla. J Am Vet Med Assoc. 1974;165:828-829.

Click the slide to view.

---