Subinvolution of Placental Sites (SIPS)

Subinvolution of placental sites (SIPS) is a delay in the process of placental degeneration and endometrial reconstruction that normally takes place after whelping.

Etiology

The cause of this subinvolution of placental sites (SIPS) condition is unknown.

It is unlikely to be caused by bacterial infection or a failure to administer oxytocin in the immediate postpartum period.

Pathophysiology

Affected placental sites grossly appear as large ellipsoidal swelling with a thick, rough, gray to brown endometrial surface with areas of hemorrhage.

Not all placental sites in a uterus are affected.

Histologically, fetal trophoblastic cells invade the myometrium. They produce thinning and herniation of the subinvoluted endometrium through the muscle layer.

Trophoblastic cells usually die promptly and spontaneously in the postpartum endometrium, and the reason for their persistence in SIPS is unknown.

Clinical Signs

• Young (<3 years) bitches are most commonly affected.
• Serosanguineous discharge persists beyond 6 weeks postpartum.
• Bitch is otherwise normal.

Diagnosis

• Physical examination reveals sanguineous vaginal discharge as the only abnormality.
• Exfoliative vaginal cytology is indicative of anestrus. Parabasal cells predominate; cellular debris and RBCs may be seen. Syncytial trophoblast like cells may be found.
• Culture of the vaginal vault reveals normal flora.
• Laboratory parameters (haemogram, serum biochemistry profile, urinalysis, coagulation profile) are normal.
• Ultrasonography may revela echogenic voci in the endometrium, but often no abnormalities are detected.
• Vaginoscopy is performed to rule out vaginal causes of hemorrhage.
• Any bitch with an abnormal vaginal discharge should be tested for Brucella canis.

Differential Diagnosis

• Vaginal origin hemorrhage, or proestrus
• Endometritis
• Coagulatopahty
• Neoplasia of the uterus, vagina or urethra

Treatment

• Specific treatment is not indicated if the bitch is intended for future breeding, because the lesions resolve spontaneously.
• Ovariohysterectomy is curative.

Patient Monitoring

• Vaginal hemorrhagic discharge can persist until the next proestrus.
• Tendency for recurrence following future pregnancy is unknown but appears to be uncommon.
• SIPS does not appear to diminish future fertility.