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
- The maternal cell layers between the fetal chorionic ectoderm and the maternal blood
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:
- Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016: 174, 200.
- 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.
- Hamir AN, Rupprecht. Trophoblast-like cells in the tissues of porcupines (Erethizoon dorsatum). Vet Pathol. 2008;45:409-411.
- La Perle KM, Green MG, Niewiesk S. Trophoblast deportation to the lungs of cotton rats (Sigmodon hispidus). Comp Med 2014;64(6):448-55.
- Noden DM, De Lahunta A. The Embryology of Domestic Animals: Developmental Mechanisms and Malformations. Baltimore, MD: Williams and Wilkins;1985:50‑69.
- Suckow MA, Stevens KA, Wilson RP. The Laboratory rabbit, guinea pig, hamster, and other rodents. London, UK: Academic Press;2012:1005.
- Tvedten HW, Langham RF. Trophoblastic emboli in a chinchilla. J Am Vet Med Assoc. 1974;165:828-829.