History

A 6-year-old multiparous Welsh Pony mare weighing approximately 350 kg (770 lb) was evaluated to determine the cause for dystocia of 4 hours' duration. The mare had been bred by the same sire and given birth to a clinically normal foal the preceding year. The mare was currently at 338 days of gestation.

The mare was bright and alert, with a rectal temperature of 37.8°C (99.9°F), heart rate of 36 beats/min, and respiratory rate of 18 breaths/min. The mare was sedated by administration of xylazine hydrochloride (0.8 mg/kg [0.36 mg/lb], IV). An obstetric examination was conducted, which revealed a fetus in cranial longitudinal presentation and dorsosacral position, with both forelimbs extended into the birth canal. The cranium of the fetus was at the level of the pelvic inlet. The cranium of the fetus was greatly enlarged, and open fontanelles were palpable. No response was detected from the fetus when the distal portion of a forelimb was pinched or a finger was inserted into the fetus' mouth.

Question

What is the likely cause of the dystocia in this mare? Please turn the page.

Answer

Dystocia attributable to fetal hydrocephalus.

Results

Anesthesia was induced by administration of ketamine hydrochloride (2.2 mg/kg [1 mg/lb], IV) and diazepam (0.05 mg/kg [0.023 mg/lb], IV) and maintained with isoflurane in oxygen. The hind limbs and caudal portion of the mare were elevated to assist positioning of the fetus. Attempts were made to reduce the size of the fetal head by use of manual pressure to collapse the cranium; however, these attempts were unsuccessful. On the basis of the experiences and preferences of the attending clinicians, a decision was made to perform a cesarean section to minimize trauma to the reproductive tract via continued obstetric manipulations.

The anesthetized mare was moved to a surgery suite and prepared for abdominal surgery. Preoperative medications included gentamicin sulfate (6.6 mg/kg [3.0 mg/lb], IV), flunixin meglumine (1.0 mg/kg [0.45 mg/lb], IV), and procaine penicillin G (22,000 U/kg (10,000 U/lb, IM). Tetanus toxoid was also administered. A 50-cm ventral midline incision was made cranial to the udder. The uterus was identified, exteriorized, and isolated with laparotomy sponges. A hind limb of the fetus was identified, and stay sutures were placed through the uterus corresponding to the level of the tarsus and hoof. A 40-cm incision was made through the uterus and chorioallantois; the incision extended between the stay sutures from the level of the tarsus to the tip of the hoof. The hind limbs were manually exteriorized, and the foal was extracted from the uterus. The foal was nonviable at the time of delivery, and hydro cephalus was evident (Figure 1). Several small pieces of unattached chorioallantois were detected within the uterine lumen and removed prior to closure of the uterine incision. Most of the chorioallantois was intact and was not removed because it was firmly attached to the endometrium.

Photograph of the head of a hydrocephalic Welsh Pony foal that resulted in dystocia and necessitated delivery via cesarean section. Notice the greatly enlarged cranium and the extensive open fontanelles. Bar = 5 cm.

Citation: Journal of the American Veterinary Medical Association 232, 2; 10.2460/javma.232.2.211

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Photograph of the head of a hydrocephalic Welsh Pony foal that resulted in dystocia and necessitated delivery via cesarean section. Notice the greatly enlarged cranium and the extensive open fontanelles. Bar = 5 cm.

Citation: Journal of the American Veterinary Medical Association 232, 2; 10.2460/javma.232.2.211

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Photograph of the head of a hydrocephalic Welsh Pony foal that resulted in dystocia and necessitated delivery via cesarean section. Notice the greatly enlarged cranium and the extensive open fontanelles. Bar = 5 cm.

Citation: Journal of the American Veterinary Medical Association 232, 2; 10.2460/javma.232.2.211

• Download Figure
• Download figure as PowerPoint slide

The chorioallantois was dissected away from the incision, and a continuous interlocking hemostatic suture of No. 1 polyglactin 910^a was placed on both sides of the uterine incision to minimize hemorrhage. The uterine incision was closed with No. 1 polyglactin 910^a in a Cushing inverting suture pattern, which was then oversewn by use of No. 1 polydioxanone^b in a Lembert inverting pattern. Oxytocin was administered (10 units, IV) to assist uterine involution, and the abdomen was lavaged with 5 L of physiologic saline (0.9% NaCl) solution. The abdominal incision was closed in a routine manner, and the mare recovered from anesthesia without incident.

Postoperative treatment consisted of gentamicin sulfate (6.6 mg/kg, IV, q 24 h) for 3 days, flunixin meglumine (0.5 mg/kg, IV, q 8 h) for 3 days, and procaine penicillin G (22,000 U/kg, IM, q 12 h) for 5 days. The mare passed most of the fetal membranes within 6 hours after surgery. However, examination of the fetal membranes did not reveal the portion from the nongravid horn. No portion of the fetal membranes was visibly protruding from the vulva, nor was any seen protruding through the external os of the cervix during vaginoscopic examination. Retention of the portion of fetal membranes in the nongravid horn was confirmed by transrectal ultrasonography and intrauterine palpation. Specific treatment to facilitate removal of the retained portion of the fetal membranes consisted of oxytocin (5 units, IV) every 3 hours and daily uterine lavage, with the clinicians being careful not to cause excessive distention of the uterus. On the second day after surgery, manual examination of the uterus via the cervix and gentle traction on the fetal membranes resulted in removal of the remaining portion of the retained fetal membranes. The mare was discharged to the owners 6 days after surgery.

Discussion

Hydrocephalus is a congenital or acquired condition characterized by the accumulation of excessive amounts of CSF within the cranium. In most instances, this results from an obstructive condition that prevents the normal flow and resorption of CSF.¹ Congenital hydro cephalus is often accompanied by enlargement and deformation of the bones of the cranium.

Hydrocephalus may be classified on the basis of the site of fluid accumulation. Internal hydrocephalus refers to the accumulation of excessive CSF within the ventricular system of the brain, whereas external hydrocephalus refers to CSF accumulation in the arachnoid space. Communicating hydrocephalus results when there is excessive CSF in both anatomic locations. Communicating and external hydrocephalus are considered rare in domestic animals.¹

Congenital hydrocephalus has been described in many domestic animal species, most commonly in calves, lambs, and puppies but also in pigs, foals, and kittens.¹ Although congenital hydrocephalus is often anatom ically obvious, the cause of the condition typically remains unknown. Congenital hydrocephalus may develop concurrently with other abnormalities of the nervous system. Reported causes of hydrocephalus include viral infections, vitamin A deficiency, and autosomal recessive inheritance.¹ In 1 report,² none of 7 stillborn foals with congenital hydrocephalus sired by the same stallion had evidence of an autosomal recessive defect. Investigators in that study determined that the most likely cause was a dominant mutation in the germ line of the sire or dam or a defect in the embryo or fetus.

In a review of 608 foals and fetuses found during necropsy to have congenital defects,³ hydrocephalus was diagnosed in 18 (3%). Of these, 10 had a greatly enlarged cranium, whereas 8 had nearly normal cranial conformation. Hydrocephalus was diagnosed in the latter group only after the cranium was opened and examined.

Congenital hydrocephalus may cause dystocia in mares, accounting for 5% of all dystocias in 1 study.⁴ In that study, investigators did not report a breed predisposition; however, others have described the condition to be more common in ponies.⁵

It is relatively easy to diagnose hydrocephalus in fetuses positioned in cranial longitudinal presentation in which manual vaginal examination will reveal a greatly enlarged cranium, often with extensive fontanelles. The forelimbs may or may not be positioned in the birth canal. Although hydrocephalus is rarely found in fetuses in caudal longitudinal presentation, it should be suspected when fetal expulsion ceases after passage of the hind limbs and thorax.

When vaginal delivery of a fetus is attempted, it may be necessary to reduce the size of the enlarged cranium to allow passage through the birth canal, although in some mares, this may not be necessary. Reduction may be achieved by manually collapsing the enlarged cranium. This may be facilitated by use of a finger knife to incise a soft region of the skull.⁶ When manual reduction and vaginal delivery are not possible, dystocia attributable to fetal hydrocephalus may be resolved by fetotomy or cesarean section. The economic considerations, experience of the veterinarian, and facilities and equipment available will influence the option selected.⁶

During partial fetotomy, the dorsal half of the fetal head may be removed via a single fetotomy cut. This can be accomplished by use of a wire saw loop positioned behind the ears of the fetus, with the head of the fetotome positioned in the mouth of the fetus or near the fetus' eyes.⁶ After the fetotomy cut, the dorsal half of the fetal head can be removed, followed by the remainder of the fetus. The trunk is generally smaller than is typical and rarely interferes with delivery. Partial fetotomy performed by a veterinarian familiar with the technique can result in less trauma to the uterus, less expense to the owner, and a shorter recovery time, compared with results for a cesarean section.⁶ However, when a veterinarian lacks the equipment or expertise to perform a partial fetotomy correctly, a cesarean section should be considered.

Mares may conceive in the same year that they undergo a cesarean section. However, live foaling rates from such conceptions are lower than expected and range from 11% to 60%.^7,8 It has been suggested that this reduction in fertility is more likely the result of trauma to the genital tract caused by attempts at vaginal delivery than to the effects of the cesarean section.^7,8 To maximize postoperative fertility, prolonged attempts for vaginal delivery of a hydrocephalic foal should be avoided when cesarean section is an available treatment option.

Outcome

Inquiries into the pedigrees of the mare and stallion yielded no relevant information. All other foals sired by the stallion have reportedly been clinically normal. The owners elected not to rebreed the mare.