CASE OF INTEREST

Cytology as an aid to the diagnosis of subinvolution of placental sites in a bitch.

By: Malcolm Silkstone, Veterinary Pathologist.

A 2 year old Rottweiler bitch presented with a history of persistent post-partum vaginal haemorrhage of 9 weeks duration. There were no other clinical signs and the bitch was not febrile.

Smears of the vaginal discharge revealed innumerable eythrocytes with a few non-degenerate neutrophils and foamy macrophages admixed. There were also several variably sized clusters of cohesive, polyhedral, epithelial-like cells (figure 1) that had abundant vacuolated cytoplasm. Bacteria and other infectious agents were not evident.

The epithelial-like cells were reminiscent of placental trophoblastic or decidua-like cells, and suggested a problem with uterine involution and a probable diagnosis of subinvolution of placental sites. In that the neutrophils were non-degenerate and present in only haemic numbers, and bacteria were not evident, it was felt that significant post-partum infection was unlikely.

Subinvolution of placental sites (SIPS) was first described as a clinical and pathological condition in 1966. Subinvolution of placental sites is an important differential diagnosis in the postpartum bitch that has a persistent bloody uterine and vaginal discharge. In the normal postpartum bitch, uterine hemorrhage usually ceases within 1 to 2 weeks. Bleeding from the uterus in SIPS can continue well into the postpartum period and can last up to 12 weeks following whelping. The condition is usually treated with an ovariohysterectomy but can resilve spontaneously.

Following ovariohysterectomy, histological examination of uterine tissues reveals irregular, ulcerated lumenal surfaces covered with necrotic cellular debris and erythrocytes. Beneath, degenerating placental trophoblast-like cells are identified which have eosinophilic cytoplasm. These epithelial cells have distinct cytoplasmic borders and variable amounts of finely to moderately vacuolated eosinophilic cytoplasm. They are mono- and multinucleate. Deep to the degenerating and viable placental epithelium are scattered normal uterine glands.

Cytology, although not definitive in this case, was highly suggestive of SIPS due to the presence of foamy cohesive epithelioid cells. Cytology can help to rule out significant post-parturient endometritis which would be a differential diagnosis of a haemorrhagic discharge in the bitch.

References:

1. Al-Bassam MA, Thomson RG, O’Donnell L: Involution abnormalities in the postpartum uterus of the bitch. Vet Pathol 18:208-218, 1981.
2. Fernandez PE, Portiansky EL, Barbeito CG, Gimeno EJ. Characterisation of cytotrophoblastic-like cells present in subinvolutioned placental sites of the bitch. Histol Histopathol. 1998 Oct;13(4):995-1000.
3. Kennedy PC, Miller RB: The female genital system. In: Pathology of Domestic Animals, eds. Jubb KVF, Kennedy PC, Palmer N, 4th ed., vol. 3, pp. 444-445. Academic Press, San Diego, California, 1993.
4. Acland HM: Reproductive system: Female. In: Thomson’s Special Veterinary Pathology, eds. McGavin MD, Carlton WW, Zachary JF, 3rd ed., p. 607. Mosby, St. Louis, Missouri, 2001.