The feline vestibule and vagina.

Keywords: anatomy, cat, feline, vagina

It is sometimes stated that a swab can be used to stimulate the feline cervix  to cause LH release and ovulation. However, the cat has a vagina that is too narrow to accommodate the tip of a common rayon swab. Only the portion of the tract that is caudal to the external urethral orifice (Ex U.O. below) i.e. the vestibule, can accommodate a swab tip. Interestingly, the distance from the vulva lips to the cervix appears to be too long for a feline penis. Cranial to the Ex U.O. it also becomes too narrow to accommodate the penis. This anatomy suggests that the short, barbed feline penis only locks into the vestibule and that  a tom cat ejaculates some distance caudal to the cervix.

Legend: VL = Vulva lips, Cx = cervix.

Image size: 3072 x 2200 px

Feline pyometra

Keywords: feline, pyometra, uterus

Case #1. This shelter cat was bright, alert, and responsive upon presentation. Apart from an enlarged abdomen, she appeared normal. No history was available. Financial constraints prevented radiology, ultrasonography, UA, serum chemistry and hematology i.e. common diagnostic tools used to diagnose this syndrome. 

A purulent vaginal discharge was observed and an abdominocentesis produced pus. Laparotomy revealed a markedly enlarged, pus filled uterus.

Image size: 1306 x 1338px Copyright: Dr S. N. Simpson. stephanienicolesimpson@gmail.com

Although this cat appeared to be healthy, it is likely that its condition would have degenerated rapidly over the next few days. Cats with advanced pyometra are often severely dehydrated and debilitated. Vomiting may occur. This cat was dropped off anonymously at the shelter, possible because her enlarged abdomen suggested that she was pregnant. That error that may have saved this animal's life. 

Case # 2: A mature cat of unknown age was presented with a history of anorexia of 2 days duration. This was an indoor-outdoor cat, with no history of estrous activity.  She was febrile (39.8 deg C) and mildly dehydrated. Palpation suggested that a distended uterus was causing abdominal enlargement. Financial constraints prevented additional diagnostic tests.  As shown below, ovariohysterectomy revealed pyometra.

Image size: 426 x 588px. Copyright: Dr Jonathan Spears. jspears@upei.ca

Case # 3: A nine year old Bengal cat that had been nursing kittens for seven weeks was presented with a purulent vaginal discharge. The cat had a normal appetite and was bright, alert and responsive. Yet remarkably, her CBC showed an extremely high neutrophil count (134 x 109/L) with toxic changes, 52 % bands and occasional myelocytes. Her hematocrit and hemoglobin were normal. There was no history of PU/PD.

Because this cat was still suckling kittens and there was no record of postpartum breeding, luteal support for a suspected case of pyometra would have been remarkable. Interestingly, her serum progesterone concentration was 13.3ng/ml indicating that she did indeed have corpora lutea in her ovaries. Although ovulation in the absence of copulation is common in cats, it is statistically more likely that she had been bred than ovulated spontaneously. Cats can show (fertile) estrus within 10 days postpartum. Therefore it is is likely that she had left her kittens, returning to them after being bred by the resident tom cat in this house. Alternatively ovulation in could also have been stimulated by the mere presence of this male (see below).

The uterine contents of the Bengal cat consisted of cell debris and many degenerate neutrophils with a moderate number of intracellular and extracellular rod-shaped bacteria (E.coli?). Neither Gram staining nor culture were performed.

Image size: 648 x 868px  Copyright: Dr Jane Eye. janeeye@fundyvets.com

Cases 3 and 4.

Both tracts (animals and tracts A & B) were from feral cats presented for routine ovariohysterectomy. Neither cat was symptomatic. Because of cost constraints, blood chemistry and hematology were not requested for either cat. Animal A was estimated to be less than one year of age; certainly a young cat, based on the appearance of her teeth. No record was made as to the presence or absence of luteal tissue in this animal. Certainly, pyometra was supported by progesterone in cat B. Her left ovary was transected to reveal three corpora lutea.

Photographic white balance was matched for both images, therefore the tract from cat A is indeed purple and congested in comparison to that of cat B, the older animal. Also interesting is the difference in color of the pus that had accumulated in each animal. The reason for these differences is unknown.

Image size: 1555 x 892px

Interestingly, vaginal cytology from cat A and uterine cytology from cat B showed no bacteria. Presumably most of the bacteria had been phagocytosed by the influx of neutrophils, most of which had undergone karyorrhexis and karyolysis. Only a few partially intact neutrophils were evident in the uterine cytology of cat B (black arrows).  Indeed, data show that vaginal cytology in cats with pyometra will often be devoid of bacteria.

Image size: 1632 x 1238px

Copyright for the images from Cat A belongs to: Dr Deirdre Carver deecraffa@gmail.com

Case # 5

The following image shows the radiographic appearance of pyometra in a cat of unknown breed and age; its enlarged uterus is indicated by arrows.

Image size: 3373 x 2192px

The author acknowledges the assistance of Dr L. Zwicker ACVR in retrieving this image for the LORI collection.

Case # 6

A striking DV radiograph of pyometra in a fifteen year old cat presented for  sudden inappetence. Interestingly, there was no overt vaginal discharge and the cat was bright, alert and responsive, with a normal CBC and and only a mildly elevated BUN.

The smooth-bordered, bilateral, radio opaque masses are pus-filled uterine horns.

Image size: 705 x 720px. Copyright Dr Megan Yanos. myanos@upei.ca.

There was no history of breeding and because the ovaries were not examined during surgery, it was not known if this case of pyometra was supported by a progesterone dominated environment. The uterine horns were distended with 2.26 liters of pus, a figure derived through pre- and postoperative weighing of the cat. Uterine cytology was characterized by a mixture of neutrophils and lymphocytes. No bacteria were isolated. Recovery was uneventful.

________________________


Notes: Pyometra in cats shares many similarities with pyometra in dogs but remarkably and in contradistinction to the situation in dogs, luteal support is often absent in cats. In a recent review, corpora lutea were only present in 40 to 70% of cats with pyometra. Other cats in that review were either anestrus or in a follicular phase.

It is noteworthy that PU/PD appears to occur less frequently in cats than dogs; in less than 10% of cats in one review. However, trends in blood chemistry and cytology are similar to those seen in bitches However, the cases in this LORI entry demonstrate that cytology and clinical chemistry can be quite variable.

Although pyometra can occur in the absence of corpora lutea in cats, data in other species suggests that pyometra in cats is probably exacerbated in a progesterone-dominated environment. In that regard, it should be noted that spontaneous ovulation is common in cats, especially in some individuals, so luteolysis (using prostaglandin) should always be part of medical treatment, even if there is no history of breeding. As mentioned, the well known pheromone effect of  males on induction of ovulation in other species has its counterpart in cats as well i.e. the presence of males can  increase the incidence of spontaneous ovulations in non-mated queens.

Spontaneous ovulations also occur in wild felids therefore the stimulatory effect of males should be considered when housing is planned for those animals. Not surprisingly, pyometra has been reported in captive lions, tigers, ligers (lion x tiger) and leopards. Symptoms, diagnosis and treatment in wild felids are essentially the same as for domestic cats and presumably just as variable!

The value of vaginal cytology for the diagnosis of feline pyometra must be emphasized, especially because all cats are fastidious, eliminating evidence of vaginal discharges.

The progesterone receptor site antagonist aglepristone, has been used safely for medical treatment of pyometra in domestic cats but the author is not aware of it use in wild felids .

In general, E.coli is the principle pathogen involved in feline pyometra but as is the case in canine pyometra, many other bacteria have been isolated.

Selected references:

1.Agudelo CF. Cystic endometrial hyperplasia-pyometra complex in cats. A review. Vet Q. 2005;27:173–182.)

2. Gudermuth, D.F. et al 1997 Incidence of spontaneous ovulation in young, group-housed cats based on serum and faecal concentrations of progesterone.J. Reprod Fert. Supplement. 51:177-184.

3. Nak, D. et al. 2009. Follow-up examinations after medical treatment of pyometra in cats with the progesterone-antagonist aglepristone Journal of Feline Medicine and Surgery (2009) 11, 499-502.

4. Schramm, R.D. 1994. Spontaneous and induced ovulation in the lion (Panthera leo). Zoo Biology. 13:301-307

5. McCain, S. 2009. Pyometra in captive large felids: a review of eleven cases.J Zoo Wildl Med.40:147-51

6. Munro, R and Munro, H.M. 1974. A case report of pyometra in the leopard (Panthera pardus).Br Vet J. 130:175-179.

Possible superfetation

Keywords: superfetation, feline, diapause, pregnancy.

This old but unique image provokes the question: Can superfetation occur in cats?

Figure 1. This uterus was extracted during routine ovariohysterectomy. The small embryos  seen in this pregnancy were examined histologically. This suggested that they were normal. The author suggests that this may be a case of superfetation. Image size: 1399 x 843 px

Queens can exhibit sexual behavior and breed during gestation. However, the fertility of  such breedings is not known. It is highly unlikely that additional conceptions could occur in one uterine horn after an earlier pregnancy had been established in the same horn. The intimate zonary structure of feline placentation forms a barrier to both oocytes and spermatozoa, preventing such conceptions. However, the two younger embryo/fetuses in this case were located in the horn contralateral to the older fetuses. Therefore superfetation may have occurred in this case. An immediate and obvious objection to this suggestion would be cervical integrity, preventing sperm from entering the uterus. This is a valid argument but may be based on simplistic dogma of progesterone and cervical closure. For example, in species that show embryonal diapause, the cervix remains open while embryos lie within the uterus in a state of suspended development. Indeed, in black bears, multiple conceptions from different sires can occur during pregnancy. This is not due to superfecundation (a well understood phenomenon in polytocous species) but breeding by different sires in separate periods of receptivity. In bears then, following variable periods of diapause (according to when matings took place) the cubs are born synchronously. Admittedly, progesterone does not dominate the endocrine environment in that case until activation of embryonal growth occurs.

The author does not suggest that the case entered here is one of embryonal diapause; in such a case, the development of the embryos is synchronous once re-activation of embryonic growth occurs. The conceptuses here are clearly not in synchronous development.

Superfetation has been suspected in cats because of the long breaks that occasionally occur during parturition. These may be several days in duration. However, the age discrepancy between the large and small fetuses in this case was estimated to be about 30 to 35 days i.e. extreme asynchrony, unlikely to result in normal birth of the younger fetuses.

This case remains an enigma but most closely resembles one of superfetation.

Selected references:

Chan, S.Y.W. 1982 Ovarian-endocrine-behavioural function in the domestic cat treated with exogenous gonadotrophins during mid-gestation. J. Reprod Fert. 65:395-399

Ptak, G.E. Embryonic Diapause is conserved across mammals. www.plosone.org Volume 7. Iss. 3  e33027

Roellig, K. et al. 2011 The concept of superfetation: a critical review on a ‘myth’ in mammalian reproduction. Biol. Rev. 86:77–95

Schmidt, P.M. et al 1983. Ovarian activity, circulating hormones and sexual behavior in the cat. II. Relationships during pregnancy, parturition, lactation and the postpartum estrus. Biol. Reprod. 28: 657-671

 Feline tract with corpora lutea

Key words: ovary, CL, corpora, lutea, uterus, feline, cat

Image size: 1200 x 671 px

The uterus and ovaries of a mature, cycling queen (female cat). Because of the absence of an ovarian bursa, one is able to see corpora lutea once the tract has been removed; this is not possible in bitches. On the right-hand side of this image, an ovary has been transected to show four corpora lutea. Queens usually ovulate only 4 or 5 oocytes, a number that closely parallels the average litter size in this species.

The absence of an ovarian bursa also allows small pieces of the ovary to fracture off the main structure during ovariectomy and to implant in the abdomen. This is a cause of the ovarian remnant syndrome in cats.