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Hydrops may be difficult
to diagnose early because of the gradual progression of clinical signs
including excessive abdominal distention, dyspnea, and flank edema.
Life-threatening complications -abdominal herniation or abdominal
compartment syndrome - have been recognized.
A 15-year old
multiparous Arabian mare was referred to New Bolton Center on day 278 of
gestation with a complaint of premature mammary gland development and
abdominal distention. Previous parturitions (gestations of 330-336 days)
had been normal. Colic surgery for right dorsal colonic displacement was
performed at 28 days of gestation; recovery was uneventful. Upon
presentation the mare was larger than expected for gestational age, had
ventral edema and slight mammary development. Routine clinical chemistry
and hematology testing was unremarkable. Transabdominal and transrectal
ultrasound examinations revealed an active fetus that could be readily
imaged, but an allantoic fluid depth >20cm could be imaged transrectally
when the fetus moved cranially suggesting hydroallantois. The cervical
star region of the uteroplacental unit was thick (14.7 - 17.3 mm) and
hypoechoic. Based on the economic value of the mare as a potential
embryo donor, the poor prognosis for foal survival and potential for
abdominal herniation due to increased intra-abdominal pressure,
induction of parturition was elected. Intravenous catheters were placed
in each jugular vein and a bolus of 35 L Normasol R was administered.
Misoprostol (200 ug) was infused into the cervical canal. A trocar
thoracic catheter (32 Fr) was inserted through the cervical portion of
the chorioallantois. Allantoic fluid was slowly drained. The fetus was
positioned in anterior longitudinal presentation with head, neck and
forelimbs extended for assisted vaginal delivery. As parturition
progressed the mare experienced an episode of syncope, possibly
associated with xylazine administration and/or fluid shifts as abdominal
hypertension was alleviated. A premature 25.5 kg foal was delivered and
euthanized. The mare experienced no additional complications. The
placenta was passed after 30 minutes.
The fetal
membranes weighed 20.5 kg, and the umbilical cord was 85 cm with a large
focal cyst, marked focal osseous metaplasia, and focal stromal
fibroplasia. The entire chorioallantois had severe diffuse stromal edema
with early granulation tissue and numerous > 5 cm allantoic cysts.
Necropsy of the foal revealed the presence of encephalopathy with edema
and Alzheimer type II cell hyperplasia.
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