Incomplete Müllerian duct fusion and canalizing.

Keywords: luteolysis, segmental aplasia, bovine, cervix, mucometra, infertility

A fascinating tract, no doubt from a heifer culled for infertility.

Image size: 988x577px

This tract shows two principal abnormalities. The first is partial aplasia of both uterine horns. However, this aplasia was not in the form commonly encountered, where a segment of one uterine horn is missing. Instead, the Müllerian (paramesonephric) tubes had never canalized to form uterine horns except for a segment in the right Müllerian tube. In that region, a substantial lumen had formed and the uterus contained clear mucoid fluid. The ovaries appeared to be normal and functional, a recent ovulation having occurred from the right ovary. 

The ability of the uterus to produce sufficient amounts of prostaglandin F2 alpha (PGF) to cause luteolysis was of particular interest. In that regard, readers will recall that luteolysis in ruminants depends on production of PGF by the endometrium in the uterine horn ipsilateral to the corpus luteum (CL). In the left ovary of this specimen, there was a small corpus albicans, suggesting that the left uterine horn had indeed produced enough PGF to bring about luteolysis. Yet, there was no apparent lumen in that horn, so the question arises: Were there endometrial mucosal fragments in that horn, not visible to the author? 

It is possible that luteolysis could have occurred by slow (degenerative?) luteolysis in the left ovary. This is known to occur in cattle with complete absence of one uterine horn. In other words, cows or heifers with ovulations ipsilateral to completely aplastic uterine horns do not experience interminable luteal phases.

The second feature of this tract that was particularly interesting was the complete separation of the two uterine horns, including it would appear, their cervixes as well. This is akin to the situation in lagamorphs (rabbits and hares) where the two Müllerian tubes only fuse distal to the cervixes. That is referred to as uterus didelphys (< Gr Delphus meaning womb.). In cattle, it is not rare to encounter two separate or partially fused cervical canals within a large cervical body or even bands of incomplete fusion of the Müllerian system in the vagina but a situation where there are two completely separate Müllerian tubes is indeed rare. Unfortunately the vagina of this specimen was unavailable; it would have been fascinating to see if the cranial vagina (also part of the Müllerian system) was completely separate as well.

Spiral penile deviation

Keywords: penis, bovine, corkscrew, anatomy, infertility

This image shows severe spiral ("corkscrew") deviation of the penis of a three year Polled Limousin bull. As is typical, the bull had produced calves from his first breeding season but during his third year of life and second breeding season, the owner had observed spiral deviation during the bull's attempts to breed.

 

Image size: 790 x 1000 px

The image was taken during stimulation with an electroejaculator. Pre-ejaculate accessory fluid can be seen dripping from the penis.

Notes:
Under certain conditions spiral deviation can be considered normal; about half of the bulls in one study (where a transparent artificial vagina was used) showed slight to pronounced spiral deviation during ejaculation. However, the problem arises when pronounced spiral deviation occurs before penetration, preventing penetration itself. The incidence of that situation varies considerably, but in a large study in New Zealand, just over 10% of the tested bulls showed this problem. It is interesting and potentially important to note that there have been at least two independent observation (one Australian and the other North American) where spiral deviation was more common in polled than horned bulls. This suggests that the condition has a heritable nature; something to bear in mind when considering corrective surgery.

One may ask why it is that even normal bovine penises have a tendency to spiral when fully erect. After reading Ashdown and Smith's paper, the author dissected the terminal portion of a bulls penis to assess its peculiar anatomy first-hand. The image below is the product of that dissection, some 31 years ago! It has been sharpened and annotated for clarification.  The anatomy of the bovine penis is not symmetrical. The apical ligament widens out distally from its origin, about 20 cm proximal from the glans. Strangely, it is attached firmly to the left side of the corpus cavernosum but on the right, its attachment could be described as "flimsy".  Ashdown had a more elegant description and also described an asymmetric arrangement of collagen fibers in the tunica albuginea of the corpus cavernosum itself.

Image size: 1478 x 971 px

In the image of the author's dissection, the dotted green line (A) indicates the firm and thick attachment of the apical ligament to the tunica albuginea on its left side. The dashed black line (B) marks the approximate dorsal center line of the penis. The apical ligament itself (C) is shaded green. The thin and rather flimsy attachment of the apical ligament to the tunica albuginea on its right side is marked by the red dotted line (D).

During erection, the blood pressure in the corpus cavernosum penis increases to about 200 kPa  or (~30psi, close to the pressure in a car tire) or higher, expanding it distally. As the corpus cavernosum expands maximally, it pushes against the thin and loosely attached right side of the dorsal ligament. This allows the corpus cavernosum to "break away" and move sideways and distally from the sturdy, linear attachment of the ligament on the left side. That part of the ligament therefore provides an axis for a spiral deviation to form. This is further explained in  the diagram below.

Image size: 1312 x 1483 px

As mentioned, some degree of spiraling is normal but when the right-sided attachment between the corpus cavernosus and the dorsal ligament is stretched beyond its normal limits, the penis begins to spiral prematurely, preventing penetration.

Several surgical approaches have been described to treat excessive, premature spiraling. One of these (braiding of the dorsal ligament) aims to strengthen the attachment between the apical ligament and the dorsal section of the tunica albuginea through fibrous tissue formation. Autogenous transplants of fascia lata to this area have the same outcome but introduce additional tissue strength as well. Carbon fiber implants merely strengthen the dorsal and right side of the area of attachment between the apical ligament and the tunica albuginea.  Although success (return to breeding) has been reported with all methods, they have not been compared in controlled studies. Also, the rate of relapse has not been well documented.  Because the potentially heritable nature of spiral deviation (recessive, dominance or penetrance)  it is probably prudent to avoid surgery in these cases.

References:

Anderson, D.E. 2008. Surgery of the Prepuce and Penis. Vet. Clin. North America: Food Animal Practice. 24: 245-251

Ashdown, R.R. and Smith, J.A. 1969.The anatomy of the corpus cavernosum penis of the bull
and its relationship to spiral deviation of the penis. J. Anat. 104:153-159

Becket, S.D et al 1974. Corpus cavernosum penis pressure and penile muscle activity in the bull during coitus. Am. J. Vet. Research 35: 761-764

de Blockey, M.A.B. and Taylor, E.G. 1984. Observations on spiral deviation of the penis in beef bulls. Australian. Vet. J. 61:141-145

Lewis, J.E. et al. 1968. Blood pressure within the corpus cavernosum penis of the bull. J.Reprod. Fert. 17:155-156

McDiarmid, J.J. 1981 "Corkscrew penis" and other breeding abnormalities in beef bulls
 N. Zealand. Vet. J. 29:35-36

Mobini, S. 1982. An experimental evaluation of the response of the bull penis to carbon fiber implants Cornell Vet. 72:350-360

Pearson, H. 1974. Corkscrew penis: relapse in a bull after surgical correction, Corkscrew penis: relapse in a bull after surgical correction. Vet. Record. 94:225

Seidel, G.E. and Foote, R.H. 1969 Motion picture analysis of ejaculation in the bull. J. Reprod. Fert. 20: 313-317

Whitsell, D. 1969. Deviations of the bovine penis Iowa State University Veterinarian. 31. Article 5. 25-28.

A penile hair ring

Keywords: penis, infertility, hair, ring

A hair ring around the base of the glans penis in a young bull. The bull was presented for phimosis (an inability to extend the penis) and the presence of a purulent preputial discharge. The hair ring had caused abrasion, posthitis (inflammation of the preputial cavity) and adhesion formation.

Image size: 1200 x 838 px

It is thought that hair rings form during attempts at breeding, as a result of the penis moving across the rump of females that are shedding their winter coats. This seems likely because it is during the breeding season that cattle shed their coats.  The loose hair from the female is carried into the sheath, rolling up on the penis as shown here. Therefore, the hair seen on the penis is not that of the bull, but the female he has attempted to breed. Also, anecdotal data (there is a paucity of published data on the condition) suggests that it is most common in young bulls. This is understandable because young bulls have higher mounts per service ratios than older bulls i.e. in a young bull, it is likely that his penis will travel across the rump of the female (seeking the vulva) more frequently than in older bulls, before copulation occurs.

Hair rings are also commonly seen in young bulls penned together e.g. during feeding trials (Dr Rocky Crisman, docroc@peak.org, personal communication). In such cases, bulls may mount one another to establish dominance within the group.

Hair rings can cause urethral constriction as well as posthitis and adhesions.  In small herds therefore it may be feasible to run females into chutes and occasionally brush their rumps during the breeding season.

References:

Gray et al. 2011. Hair coat shedding in Angus cows.  2011 Beef Improv. Fed. Conference. Bozeman, Montana.

Freemartinism

Keywords: Freemartin, bovine, infertility

The image below shows the reproductive tract from a freemartin heifer. Although there is great variation in the manifestation of Freemartinism, this tract shows some characteristics that are common to many of these animals.

Image size: 1000 x 557px

Note how the development of the Müllerian tubes (precursors of the cranial vagina, cervix, uterus and uterine tubes) was suppressed by anti-müllerian hormone (AMH). AMH was presumably produced by the small gonads seen here where ovaries are usually found. Although it was not verified histologically in this case, these gonads would have contained cells from the male co-twin, including Sertoli-like cells that produce AMH. Of course, it is normal for a male fetus to produce AMH because the Müllerian system must be suppressed if the male is to develop normally. However, in female fetuses where the gene for AMH production is inactive, AMH production by the gonads is disastrous.

As alluded to above, gene coding for AMH production is active in the male co-twin. Therefore gonadal cells derived from the male produce AMH in the co-twin's (Freemartin) gonad. In addition, AMH from the male twin circulates in the female co-twin, amplifying the suppressive effect on the female tract. That has occurred here; the uterus is a mere thread, the cervix is absent and the cranial vagina is also absent. The caudal vagina develops from the ectoderm in a fetus, a system that is not affected by AMH, so it is virtually normal in Freemartins. In this image, a probe has been inserted into the vagina, demonstrating the presence of a normal vestibule i.e. cranially, up to the level of what would have been the hymen. More cranial to that, normal tract is almost absent.

As discussed below, there is a considerable range in the manifestation of Freemartinism;  the tract may be barely affected or may be extremely masculinized. The specimen shown here would probably be considered modal within that range.

Notes: 

In 2005, A.M. Padula  published an excellent review of  Freemartinism (Padula. A.M. 2005. The freemartin syndrome: an update. Anim. Reprod. Sci. 87: 93–109). For additional detail, one should consult that article and others cited within.

At approximately 28 to 30 days of gestation, the allantochorion membranes of most ruminant co-twins fuse. This causes vascular anastomoses to form between the two conceptuses, resulting in freemartinism, a condition that is especially common in cattle. Freemartins occur in other ruminants, cervids and even pigs. However, the condition is comparatively rare in those species (except perhaps for sheep). This author is not aware of any well-documented case in a horse.

Cellular or humoral influences (or a combination of both) circulate between the two fetuses and affect gonadal development. The earlier the fusion, the more masculinized the female tract will be.  In a few cases, the tract is so highly masculinized that it is only slightly ambiguous. The opposite is also true i.e. females can be so mildly masculinized that they are not even recognizable as freemartins, apart from being subfertile.

Interestingly, exchange of cellular material early in gestation also makes freemartins highly tolerant of organ allografts.

Although it is often stated that male co-twins to freemartins are also affected and show deficient spermatogenesis, this is not always so. In fact, males are often completely fertile into adulthood.

On occasion, a male co-twin may die in utero after vascular anastomosis has occurred and although it is unusual (recall that their blood supplies are fused) the female co-twin may survive. In such cases a freemartin may be born as a singlet.

Typically, the Müllerian system in freemartins is severely suppressed; in most cases almost impossible to delineate clearly by transrectal palpation (see the image in this entry). This is because the gonads are a mixture of testicular and ovarian tissue, (freemartins are true hermaphrodites). Sertoli cells in the testicular tissue appear to produce müllerian inhibiting factors as they do in normal males. The gonads are also very small and very difficult or impossible to define on transrectal palpation. The vagina of a freemartin is very short (usually less that 12 cm) and it has a blind ending, the cervix being part of the müllerian system.

Statistically speaking, a female calf born co-twin to a male has approximately a 95% chance of being a freemartin. However one may need further assurance that this is the case.  In newborn calves, where a transrectal examination is impossible, this author uses the cover sheath of Cassou artificial insemination pipette as a vaginal ‘depth gauge’. The sheath is inserted into the vagina of the suspect freemartin and bent at the level of the vulva lips. A second sheath is inserted into the vagina of a normal calf and bent at the same level. One then compares the length of  sheaths to the point at which they were bent.  The length of the section of interest is far shorter in the suspect freemartin calf than the normal calf. The only chance of an error with this method is in normal heifer calves that have imperforate hymens. In a farm setting, one may have to wait for a suspect freemartin heifer to reach an age at which she can undergo transrectal palpation safely.

If a diagnosis of freemartinism is still uncertain after considering the history, palpable findings, and external and internal appearance of the heifer, numerous other tests can be performed, mostly of a genetic nature. Sex chromosome chimerism (xx and xy) is present within nucleated blood cells and contrary to older data, in lower numbers in other cells throughout the body as well.

The origin of the term freemartin (also free-martin) is a subject of great uncertainty. As discussed by J.B. Marcum in the Commonwealth Bureau of Animal breeding and Genetics abstracts in 1974 (42: 227) the term may have originated in 1593 when "Martin" was a word used a England and Scotland for a cow or ox. The etymology of the prefix "Free-" is more obscure, possibly arising as a contraction of  'farrow" meaning a barren or non-lactating cow or perhaps the German term "farre" meaning bull, denoting a cow that was like a bull.

Severe adhesions

Keywords: adhesions, inflammation, uterus, infertility, bovine

This bovine reproductive tract was from a slaughter plant specimen.

Image size: 3307 x 4218px

Severe adhesions arising from an inflammatory process were present around the ovaries and adnexa, obscuring the anatomy of those structures. Adhesions were also present over the entire surface of the ovary. Readers are encouraged to see the extent of these adhesions by clicking on this large image. However, to fully appreciate the adhesions, it should be downloaded by right-clicking on the image, saving it, then viewing it in an appropriate program.

The cow from whence this uterus came was either infertile or sterile as a result of these lesions; probably the reason for which she was culled.

Adhesions such as these can arise from endometritis due to a multitude of bacteria including Mycobacterium bovis (less so M. bovigenitalum), Fusobacterium necrophorum, Bacteroides spp.
Escherichia coli  and commonly, Trueperella pyogenes (previously known as Corynebacterium pyogenes and after that, Arcanobacterium pyogenes but recently renamed to  Trueperella pyogenes ).

The cow has a utero-tubal junction that does nor perform adequately as a one-way valve between the uterus and uterine tubes (fallopian tubes). Therefore ascending infections of the ovaries and adnexa are common in cases of metritis. Comparatively speaking, mares are far less inclined to this pathology because of a well developed utero-tubal junction that appears to function as a one-way valve. In humans, the utero-tubal junction is far larger than in any domestic animal and is a virtual highway to the ovaries. Therefore peri-ovarian adhesions are a major cause of infertility in humans. So called "pelvic inflammatory disease" is well known in women.

It is also possible for adhesions such as these to form as a result of peritonitis following a laparotomy; commonly a cesarian section. In this case it was impossible to detect a uterine incision scar because of the adhesions. The etiology of adhesions in this case is unknown.

Freemartin placentation

Keywords: freemartins, bovine, slip, membrane, diagnosis, pregnancy, chorion, infertility, twins

This image of a 38 day twin bovine pregnancy shows the outer chorio-allantoic membrane  and the two inner amnionic vesicles. Although the allantoic cavities remain separate (as shown here; one stained with iodine and the other not stained) the chorionic membranes fuse early, usually before this stage of gestation, allowing cell and hormonal exchange between the developing embryos. If one of the embryos is a female, it causes freemartinism in that embryo.

Image size: 1067 x 664 px

At approximately 28 to 30 days of gestation, the allantochorion membranes of most (not all) ruminant co-twins fuse, which causes vascular anastomoses to form between the two conceptuses. This results in freemartinism.  Freemartinism is discussed in some detail elsewhere in LORI.

Heifer with an XY karyotype

Keywords: XY, heifer, bovine, infertility, karyotype, Sry

A heifer was examined because she had not shown signs of estrus although she was significantly larger than normal, cycling, age-matched herd mates.

Image size: 1203 x 656 px

On transrectal examination, the genital tract was difficult to define but a cervix and small ovaries were detected. The presence of a vagina and cervix excluded the possibility of freemartinism. Cultures of skin fibroblasts and lymphocytes revealed a homogeneous population of X-Y bearing cells i.e. this animal was genetically a male. It was not possible to determine the Sry status of this animal because suitable primers for the Sry sequence were not available to us at that time (2001).

The animal was donated for further study. The tract was smaller than that of a heifer but a uterus with two horns and a body, a cervix and a vagina was present. The ovaries measured approximately 2.5 x 1 x 1 cm but were firm, wrinkled and devoid of any obvious follicles.

Image size: 1203 x 808 px

A close up view of the right ovary:

Image size 1604 x 908px

On histological examination o the ovaries, there was no evidence of any primordial follicles (oocytes) but a mass of swirling fibrous interstitial tissue contained "islands" of cells.

Image size: 4080 x 3072 px

Examination on high-power did not lead to additional clarification as to the nature of these structures.

Image size: 3000 x 1987 px

Because of the presence of an intact Müllerian system (the uterus, cervix and cranial vagina) in this animal, it is unlikely that there were Sertoli cell components in the gonads. Sertoli cells are a source of anti Müllerian hormone and inhibin, two closely related hormones that actively suppress the formation of the Müllerian system in the fetus. Therefore it is tempting to suggest that the islands of cells were abortive attempts to form a follicles, in the absence of oocytes.

A follicle and a luteinized cystic follicle

Keywords: CL,corpus, luteum, cystic, bovine, cycle, infertility, cow, ultrasound

Image size: 640 x 480px

A follicle and a luteinized cystic follicle seen by transrectal ultrasonography in a cow.

Together with its appearance, a history of postpartum anestrous allowed a diagnosis of a luteinized cystic follicle (sometimes referred to a luteal cyst) in this cow.  Cystic follicles and the luteinized structures they develop into, are abnormal structures, associated with an absence of estrous cycles in the early to late postpartum period; almost always in dairy cows. In dairy cows, abnormal estrogen secretion and abnormal LH surges are thought to be important in the syndrome. Cystic follicles are also seen in beef heifers, but usually only after the use of steroid growth promoters.

Clarification: Cystic corpora lutea are normal structures, associated with normal estrous cycles.  Most corpora lutea luteinize completely, obliterating the antrum of the ovulated follicle but many are left with small to large cysts in the center.  This author does not use the term “luteal cyst” (an abnormal structure) because it can easily be confused with the term “cystic corpus luteum” (a normal structure). Instead, the term luteinized cyst (a cystic follicle that has become luteinized) should be used.

Leucosis in the uterus of a cow

Keywords: bovine, COD, cystic, BLV, leucosis, uterus, bovine

Image size: 1200 x 807px

Bovine leucosis is caused by the bovine leukemia virus (BLV). Many cows are carriers and asymptomatic. In this case, as shown by the arrows, there are multiple foci of leucosis in the uterus of the cow. This cow also had a cystic CL,in the right ovary; a normal structure in many cycling cows (not to be confused with a luteinized cyst).

Adventitious placentation in a cow. 

Keywords: placenta, adventitious, placentitis, bovine, cow, infertility

Small to large irregular placentome-like structures may develop on the placenta adjacent to normal placentomes. These have been referred to as "adventitious" placentomes and the condition itself as "adventitious placentation". The word adventitious is derived from the Latin meaning "coming from outside" but in zoology, it refers to something that is in an unusual position or place. The adventitious placentomes may be localized or spread throughout the allantochorion/endometrium.

It is often stated that adventitious placentation is associated with hydrops conditions but it may occur in seemingly normal pregnancies. However, when adventitious placentation is obvious, one should probably consider the placenta and uterus as a unit and cull the cow because of the potential for infertility.

Leucosis in a bovine uterus

Keywords: leucosis, bovine, neoplasia, uterus, infertility

Image size: 1600 x 961px

Enzootic bovine leukosis is a result of infection by bovine leukemia virus (BLV). Interestingly, less than 1% of all the cattle infected with this virus actually develop lymphoid sarcomas.  It is characterized by the development of tumors of lymphatic tissues but tumors can be found throughout the body; in this case, the uterus. Although substantial numbers of nodules and diffuse thickening due to leucosis can be found in the uterus, severely affected genital tracts are occasionally found to be pregnant.

Management procedures that transmit blood have the potential to transmit BLV i.e. injections, surgery, tattooing, dehorning etc. It is not clear if biting flies are able to transmit this disease. Although rectal examinations were once incriminated in the spread of BLV, research suggests that under normal conditions this does not occur.

Metestrus 1: Metestral hemorrhage in bedding.

Keywords:  metestrus, bovine, management, cow, estrous, cycle, detection, hemorrhage

Image size:454 x 326px

This is seen in about 50 to 60% of cows and 75 to 85% of heifers.  It is usually seen in the first 48 hours after ovulation but because the vagina may slope downward at its cranial end (especially in older animals) vaginal mucus and metestral hemorrhage may be retained in the vagina for several days, being discharged several days after estrus. If metestrus is suspected, one should look at the rump of the animal and her dung and bedding where there is often evidence of hemorrhage.

Careful observation is warranted because hemorrhage may be difficult to spot:

Image size: 750 x 526 px

Metestrus 2: Metestral hemorrhage on the tail

Keywords:  metestrus, bovine, management, cow, estrous, cycle, detection, hemorrhage

Image size: 1584 x 2816px

This is seen in about 50 to 60% of cows and 75 to 85% of heifers.  It is usually seen in the first 48 hours after ovulation but because the vagina may slope downward at its cranial end (especially in older animals) vaginal mucus and metestral hemorrhage may be retained in the vagina for several days, being discharged several days after estrus. If metestrus is suspected, one should look at the rump of the animal and her dung and bedding where there is often evidence of hemorrhage.

Metestrus 3: Metestral hemorrhage on the tail 

Typical metestral hemorrhage; seen on the tail of a cow.

Image size: 1584 x 2816px

This is seen in about 50 to 60% of cows and 75 to 85% of heifers.  It is usually seen in the first 48 hours after ovulation but because the vagina may slope downward at its cranial end (especially in older animals) vaginal mucus and metestral hemorrhage may be retained in the vagina for several days, being discharged several days after estrus. If metestrus is suspected, one should look at the rump of the animal and her dung and bedding where there is often evidence of hemorrhage.

Metestrus 4. Hemorrhage seen in bedding 

Typical metestral hemorrhage; seen on the bedding of a cow.

This is seen in about 50 to 60% of cows and 75 to 85% of heifers.  It is usually seen in the first 48 hours after ovulation but because the vagina may slope downward at its cranial end (especially in older animals) vaginal mucus and metestral hemorrhage may be retained in the vagina for several days, being discharged several days after estrus. If metestrus is suspected, one should look at the rump of the animal and her dung and bedding where there is often evidence of hemorrhage.

Metestrus 5. Hemorrhage seen in bedding

Keywords:  metestrus, bovine, management, cow, estrous, cycle, detection, hemorrhage

Image size:1164 x 774px

This is seen in about 50 to 60% of cows and 75 to 85% of heifers.  It is usually seen in the first 48 hours after ovulation but because the vagina may slope downward at its cranial end (especially in older animals) vaginal mucus and metestral hemorrhage may be retained in the vagina for several days, being discharged several days after estrus. If metestrus is suspected, one should look at the rump of the animal and her dung and bedding where there is often evidence of hemorrhage.

Metestrus 7. Hemorrhage on the rump of a cow.

Keywords:  metestrus, bovine, management, cow, estrous, cycle, detection, hemorrhage

Image size:1584 x 2816px

Typical metestral hemorrhage; seen on the rump of a cow that was recently in heat. This is seen in about 50 to 60% of cows and 75 to 85% of heifers.  Metestral hemorrhage is usually seen in the first 48 hours after ovulation but because the vagina may slope downward at its cranial end (especially in older animals) vaginal mucus and metestral hemorrhage may be retained in the vagina for several days, being discharged several days after estrus. If metestrus is suspected, one should look at the rump of the animal and her dung and bedding where there is often evidence of hemorrhage.

Cattle are the only domestic animals that show hemorrhage as a result of estrogen withdrawal.

Cystic follicle in a cow

Keywords:  anestrus, COD, cyst, cystic, follicle, bovine, management, cow, estrous, cycle

Reproductive tract from a cow with cystic ovarian disease (COD); a syndrome associated with high milk production and negative energy balance in high producing dairy cows. COD is usually associated with persistence of large, un-ovulated follicles in the absence of standing estrus, probably because of luteinization (with progesterone production) of the cystic structures due to low pulsatile releases of LH. Nevertheless, this illustration shows that ovulation occasionally occurs in the presence of a cystic follicle. Note the corpus luteum in the left ovary, in the same ovary as the cyst.

In these cases, the cyst may then regress and may even be replaced by other cysts until ovulation becomes predictable and cyclicty returns to normal.

This illustration also suggests that luteinization of cystic follicles may be so limited that they not produce enough progesterone to suppress LH and block ovulation.

The terminology of COD can be confusing, with cystic follicle occasionally being referred to as luteal cysts. In the author's opinion this term should not be used because it can be confused with a structure called a cystic corpus luteum; a non-pathological entity. Instead, when a cyst becomes luteinized it should be called a luteinized cyst rather than a luteal cyst.