Disorders of Sexual Development of Cats

Dr Rob Foster

University of Guelph

Persons unfamiliar with the nomenclature of Disorders of Sexual Development (DSD) are advised to review the general section on DSD.

The nomenclature was agreed upon in 2005 at the International Consensus Conference on Intersex and called the Chicago Consensus of 50 International Experts in the field of intersex in humans. It was updated in 2016. This nomenclature was accepted and used in Veterinary Medicine soon after.

Houk CP, Hughes IA, Ahmed SF, Lee PA; Writing Committee for the International Intersex Consensus Conference Participants. Summary of consensus statement on intersex disorders and their management. International Intersex Consensus Conference. Pediatrics 2006; 118: 753-757.

Lee PA, Houk CP, Ahmed SF, Hughes IA; International Consensus Conference on Intersex organized by the Lawson Wilkins Pediatric Endocrine Society and the European Society for Paediatric Endocrinology. Consensus statement on management of intersex disorders. International Consensus Conference on Intersex. Pediatrics 2006; 118: e488-500.

Lee PA, Nordenström A, Houk CP, Ahmed SF, Auchus R, Baratz A, Baratz Dalke K, Liao LM, Lin-Su K, Looijenga LH 3rd, Mazur T, Meyer-Bahlburg HF, Mouriquand P, Quigley CA, Sandberg DE, Vilain E, Witchel S; Global DSD Update Consortium. Global Disorders of Sex Development Update since 2006: Perceptions, Approach and Care. Horm Res Paediatr. 2016; 85: 158-180. Erratum in: Horm Res Paediatr. 2016; 85: 180. Koopman, Peter [added]. Erratum in: Horm Res Paediatr. 2016;86(1):70.

Little S. Feline reproduction: problems and clinical challenges. J Feline Med Surg. 2011; 13: 508-515.


There are reviews on disorders of sexual development in cats.


Centerwall WR, K Benirschke K. Male Tortoiseshell and Calico (T-C) Cats. Animal Models of Sex Chromosome Mosaics, Aneuploids, Polyploids, and Chimerics. J Hered 1973; 6: 272-278.

Christensen BW. Disorders of sexual development in dogs and cats. Vet Clin North Am Small Anim Pract. 2012; 42: 515-526.

Foster RA. Disorders of sexual development in the cat: Current state of knowledge and diagnostic approach. J Feline Med Surg. 2022; 24: 257-265.

Meyers-Wallen VN. Gonadal and sex differentiation abnormalities of dogs and cats. Sex Dev. 2012;6: 46-60.

Szczerbal I, Switonski M. Genetic disorders of sex development in cats: An update. Anim Reprod Sci. 2020; 216: 106353


Sex Chromosome DSD

Cats have 38 pairs of chromosomes.

The male tricolored or calico cat is a well known Disorder of Sexual Development. To achieve 3 colors in a cat requires two X chromosomes. Most male tortoiseshell / calico cats are XXY or another combination of multiple X and a Y.

The seminal paper is by Centerwall and Benirschke (1973).

Cats with chromosomal abnormalities and scrotal testes often have testicular hyoplasia. Axner et al (1996) report 3 cats with hypoplasia. 2 had chromosomal anomalies (XXY, XY/XXY) and one did not. Long et al 1981 report on 6 cats that were tortoiseshell cats. Some had testicular hypoplasia to varying degrees (3 cats). They had various chromosomal abnormalities including XXY, XX/XY/XXY/XO, XY/XXY. Centerwall and Benirschke (1973) report on 25 tortoiseshell or calico cats with aneuploidy, polyploidy, mosaicism and chimerism. They have varying degrees of hypoplasia.

Szczerbal and Switonski (2020) provided an update on genetic causes of DSD in cats.




Axner E, Strom B, Linde-Forsberg, Gustavsson L, Lindblad K, Wallgren M (1996). Reproductive disorders in 10 domestic male cats. J Small Anim Pract 37: 394-401.

Centerwall WR, K Benirschke K. Male Tortoiseshell and Calico (T-C) Cats. Animal Models of Sex Chromosome Mosaics, Aneuploids, Polyploids, and Chimerics. J Hered 1973; 6: 272-278.

Long SE, Gruffydd-Jones T, David M. (1981). Male tortoiseshell cats: an examination of testicular histology and chromosome complement. Res Vet Sci 30: 274-280

Szczerbal I, Krzeminska P, Dzimira S, Tamminen TM, Saari S, Nizanski W, Gogulski M, Nowacka-Woszuk J, Switonski M. Disorders of sex development in cats with different complements of sex chromosomes. Reprod Domest Anim. 2018; 53: 1317-1322.

Szczerbal I, Switonski M. Genetic disorders of sex development in cats: An update. Anim Reprod Sci. 2020; 216: 106353


Aneuploidy is an abnormal number of chromosomes


In humans, monosomy of the sex chromosome (X_; X monosomy) is called Turners syndrome.

X Monosomy (X_) is reported in a phenotypic female Siamese cat with ambiguous genitalia. The cat had ovaries with strutures they considered degenerate primordial follicles and a corpus luteum and a uterus but the externa genitalia was vulva and vagina, rudimentary penis/ enlarged clitorus and swellings resembling a scrotum.

Szczerbal I, Nizanski W, Dzimira S, Nowacka-Woszuk J, Ochota M, Switonski M. X monosomy in a virilized female cat. Reprod Domest Anim. 2015; 50: 344-348.

Johnston SD, Buoen LC, Madl JE, Weber AF, Smith FO. X-Chromosome monosomy (37,XO) in a Burmese cat with gonadal dysgenesis. J Am Vet Med Assoc. 1983; 182: 986-989.


In humans this is called trisomy, and trisomy of the sex chromosome is XXY and called Kleinfelters syndrome.

XXY trisomy is reported in cats and is the typical calcio or tricoloured male cat.

Konig et al (1983) reported on a case of XXY DSD. This was a tricoloured cat with testicular hypoplasia and it also had segmental aplasia of the mesonephric duct, with a lack of epididymis and deferent duct - complete absence of the mesonephric derivatives.

A typical example is reported by Pedersen et al (2014). They correlated chromosomal analysis (39 XXY) with testicular histology. They called the lesion degeneration instead of hypoplasia.

Szczerbal et al (2018) reported on 3 cats with chromosomal abnormalities. One was a trisomy XXY tortoise shell male cat,

Centerwall WR, Benirschke K (1975). An animal model for the XXY Klinefelter's syndrome in man: tortoiseshell and calico male cats. Amer J Vet Res 36: 1275-1280.

König H, Schärer V, Küpfer U, Tschudi P. Hodenhypoplasie (Fehlen von Spermiogonien) und linksseitige Nebenhodenaplasie bei einem dreifarbigen Kater vom 39/xxy-Karyotyp [Testicular hypoplasia (lack of spermatogonia) and left-sided epididymal aplasia in a tricolored male cat with 39/xxy karyotype]. Dtsch Tierarztl Wochenschr. 1983; 90: 341-341. German.

Pedersen AS, Berg LC, Almstrup K, Thomsen PD. (2014) A Tortoiseshell Male Cat: Chromosome Analysis and Histologic Examination of the Testis. Cytogenet Genome Res. 2014; 142: 107-111.


Polyploidy is having 2 paired sets of chromosomes. In a normal organism this means duplication of one set of chromosomes.

Centerwall and Benirschke (1975) reported cases of polyploid cats such as XXXY sex chromosomes.



Centerwall WR, K Benirschke K. Male Tortoiseshell and Calico (T-C) Cats. Animal Models of Sex Chromosome Mosaics, Aneuploids, Polyploids, and Chimerics. J Hered 1973; 6: 272-278.



A mosaic has 2 or more genetically different sets of cells. Some may be normal and others are aneuploid or polyploid. They are from the same individual and represents

In cats, mosaicism is reported. Centerwall and Benirschke (1973) reported on cats with

Balogh et al (2015) report on a cat with X/XY mosaicism. The male phenotype cat had cryptorchidism and persistent paramesonephric (Mullerian) ducts.


Centerwall WR, K Benirschke K. Male Tortoiseshell and Calico (T-C) Cats. Animal Models of Sex Chromosome Mosaics, Aneuploids, Polyploids, and Chimerics. J Hered 1973; 6: 272-278.

Balogh O, Berger A, Pieńkowska-Schelling A, Willmitzer F, Grest P, Janett F, Schelling C, Reichler IM. 37,X/38,XY Mosaicism in a Cryptorchid Bengal Cat with Müllerian Duct Remnants. Sex Dev 2015; 9: 327-332.


Chimerism is when there are chromosomes from different individuals in one person. This required the acquisition of chromosomes from 2 zygotes.

Szczerbal et al (2018) reported on 3 cats with chromosomal abnormalities. One was an XX/XY chimera.

This is reported in cats by Bugno-Bugno-Poniewierska et al (2020) who reported on a case of a maine coon cat tom cat with a tortoiseshell coat colour that was fertile. The cat was shown to be a 38XY/38XY chimera based on microsatelite polymorphism.

Bugno-Poniewierska M, Kij B, Witarski W, Wojtaszek M, Radko A, Podbielska A, Szczerbal I, Murphy WJ. Fertile male tortoiseshell cat with true chimerism 38,XY/38,XY. Reprod Domest Anim. 2020; 55: 1139-1144.



XX ovarian DSD and female phenotype


These are very common in cats. and are detailed in Disorders of Sexual Development in cats

There are 3 parts to the rete ovarii - the intraovrian rete, the extraovarian rete, and a connecting rete. The rete are supposed to have a secretory activity. The intraovarian rete is supposed to be noncilited, whereas the connecting rete is lined by ciliated epithelial cells.

Cystic rete ovarii are when the rete ovarii become distened with fluid. It would be expected that the rete would enlarge with age, as the remnants are supposed to be secretory, and as an extension to this, all old cats should have cystic rete. This is not the case! They occur in young as well as old cats (McEntee 1990)

Rete cysts are thin walled structures that occur within the ovary and displace ovarian tissue peripherally. They can be up to 2.5 cm diameter. They are lined by a flattened single layer of epithelium. A thin layer of connective tissue is at the periphery, and this included compressed ovarian stroma.

Gelbert et al (1984) described cystic rete ovarii in 20 cats. The cysts were within the ovary or at the tubal extremity of the ovary. The cyst lining was variable - they were single or multilayered, cuboidal to columnar, ciliated and nonciliated, or combinations of these.

Figure : Unilateral cystic rete ovarii.

Figure : Cystic rete ovarii. Wall of cyst.

Figure : Cystic rete ovarii. Wall of cyst has this layer of epithelium then compressed collagen and ovarian stroma.

Gelberg HB, McEntee K, Heath EH (1984) Feline cystic rete ovarii. Vet Pathol 21: 304-307

McEntee K (1990) Reproductive Pathology of Domestic Mammals. Academic press p61

Segmental aplasia of paramesonephric duct (aka Uterine unicornis)

The failure of development of a part of the uterus is segmental aplasia, as a segment of the paramesonephric duct fails to develop. The cause of this is not known.

One would expect that with a failure to develop, there would not be any tissue present. This is seldom the case. Usually though there is mesometrium and a thin thread of tissue where the uterus should be. The tubular genitalia proximal to the aplastic region is usually dilated and has hydrometra (see above).

Marcella et al (1985) report one case or segmental aplasia. Memon and Schelling (1992) report a cat with segmental aplasia of the right uterine horn and nonpatency of the left horn. The upstream portion of the uterine horn was informally distended. McEntee (1990) reports seeing one case.

McEntee (1990) reports seeing one case of cervical aplasia where the uterine body ended blindly, as did the vagina.

McIntyre et al (2010) reports on a large number, observed from 46,229 cat neuters. 33 cats had an absence of one horn (they called this uterus unicornus), 16 left and 17 right. 15 cats had segmental aplasia of a segment of one horn. 1 had hypoplasia of a horn. Many had ovaries in place despite the segmental aplasias.

Batista-Arteaga et al (2012) reports on a cat with atresia of the cervix and secondary mucometra.

Brookshire et al (2017) reported on two cases where one cat was pregnant and the other had renal agenesis on the same side.

Souther et al (2019) reported on a cat with an absence of the cervix and cranial vagina. There was a bulbous dilation of the cranial uterine body.

Puchalski and Ogilvie (2022) reported on 2 cats with segmental aplasia.

Histologically, there will be nothing to see in those cases where there is no tissue. Most have a thin strip of smooth muscle likely the external smooth muscle layer that is present in the mesometrium. No distinct myometrium and endometrium is present.


DSD fel segmental aplasia 01

Figure : Segmental aplasia of uterine horn and body. There is only a thin cord of issue instead of one uterine horn and body. The remaining horn is distended with hydrometra.

DSD fel segmental aplasia 02

Figure : Segmental aplasia of uterine horn. The remaining tissue is a cord of mesometrium with smooth muscle.

Batista-Arteaga M, Santana M, Espinosa-de-los-Monteros A, De´niz S, Alamo D, Herra´ ez P. Exuberant Mucometra Associated with Atresia of the Cervix in a Queen. Reprod Dom Anim 2012, 47: e71–e74

Brookshire WC, Shivley J, Woodruff K, Cooley J. Uterus unicornis and pregnancy in two feline littermates. JFMS Open Rep. 2017; 3: 1-5

Marcella KL, Ramirez M, Hammerslag KL. Segmental aplasia of the uterine horn in a cat. J Am Vet Med Assoc. 1985; 186: 179-181.

McEntee K. Reproductive Pathology of Domestic Mammals. Academic Press 1990 p 120-121, 196.

McIntyre RL, Levy JK, Roberts JF, Reep RL. Developmental uterine anomalies in cats and dogs undergoing elective ovariohysterectomy. J Amer Vet Medl Assoc 2010, 237 (5): 542-546.

Memon MA, Schelling SH. Non-patent left uterine horn and segmental aplasia of the right uterine horn in an infertile cat. Vet Rec 1992; 131: 266-267.

Puchalski DM, Ogilvie AT. Laparoscopic ovariectomy in 2 queens with uterine unicornis. Canadian Vet J. 2022; 63: 1022-1026

Souther S, Baik NJ, Clapp K, Nappier M, Sponenberg DP, Cecere J. A Case of Segmental Aplasia of the Uterus, Cervix, and Cranial Vagina in a Cat. Front Vet Sci. 2019; 6: 145.



Immotile cilia (cilia dyskinesia)

There are isolated reports of immotile cilia syndrome (cilia dyskinesia) of cats with involvement of the uterine tube (Roperto et al 1996). One would not expect any lesions to in the uterine tube of affected cats.

Roperto F, Brunetti A, Saviano L, Galati P. Morphologic alterations in the cilia of a cat. Vet Pathol. 1996; 33: 460-462.


Embryonic remnants and duplications (mesonephric and paramesonephric ducts)

The most common location for these are in the mesometrium dorsal to the uterus. The usual manifestation is a cord that runs parallel with the uterus for its entire length.

DSD fel XX ovarian 05

Figure : Remnant of embryonic duct. The tubular structure is in the mesometrium and runs parallel with the uterus (lower cord with suture).

DSD fel XX ovarian 02

DSD fel XX ovarian 01

Figure : Remnant of embryonic duct. The duct is located in the mesometrium above the uterus.

Cats with sexual ambiguity have this identical arrangement. The location running parallel to the uterus, and the histological structure suggests these are remnants of the mesonephric duct. This is especially the case when they have a single cuboidal epithelium, with the cells having small nuclei.

I have also seen cystic structures in this location that have an epithelium that is the exact same appearance to the endometrium, complete with glands. This arrangement should make the structure a paramesonephric remnant and a 'duplication' of the uterus.

DSD fel XX ovarian 03

Figure : Duplication of uterus. The cystic structure was in the mesometrium above the uterus. The normal lumen is ventral.

DSD fel XX ovarian 04

Figure : Duplication of uterus. The wall of the duplication has endometrial tissue with invaginations resembling uterine glands.

Location, therefore does not seem to help as much with differentiation of these remnants.

McEntee reports seeing a uterine duplication in a cat.


McEntee K. Reproductive Pathology of Domestic Mammals. Academic Press. 1990, p122

Uterine tube

Paramesonephric duct remnants

The paramesonephric duct is the progenitor of the uterine tube, so remnants resemble the uterine tube. The most common of these is the Hydatid of Morgagni, but these are basically unknown in cats. An accessory or blind ended uterine tube is also possible.

These structures are located on the serosal surface of the mesosalpynx. They are supposed to have a pseudostratified epithelium that may be partly ciliated. The mucosa forms papillae of is folded. There is a thin lining of smooth muscle or collagen.

Mesonephric duct remnants

Remants of mesonephric ductules (especially the caudal mesonephric ductules - epiphoron) and ducts are very common (Shehata 1974). These are located in the mesosalpynx, connect with the rete ovarii and have a simple columnar to cuboidal epithelium. Ciliated cells may be present. Gelberg and McEntee (1986) report 5 cases. Microscopic vestiges are actually more common than reported - most are overlooked as incidental.

DSD fel vagina 02

+DSD fel vagina 01

Figure : Remnant of embryonic ducts. Based on location, these should be of mesonephric duct origin.


Mesonephric remnants (Gartner's ducts)

Shehata (1974) reports examining numerous kittens and adult cats and finding mesonephric duct remnants in the vaginal wall. These are microscopic, single ducts lined by columnar epithelium. They are also called Gärtners duct.

Shehata R. (1974) Mesonephric remnants in the female genital system of the domestic cat. Felis domestica. Acta Anat (Basel). 87(2): 301-310.


XX ovarian DSD Male phenotype

Knighton (2004) reported on a cat that had a penis, prepuce and scrotum, but no intrascrotal testes. Abdominal surgery was performed for gonadectomy, but ovaries, uterine tubes and uterus was found. There was also epididymis and ductus deferens. The cat was 38 XX. The cat was subsequently found to have congenital adrenal hyperplasia and 11Beta hydroxylase deficiency. This means adrenal precursors to the androgen pathway, and high androgens cause masculinisation of the external genitalia. An epididymis develops too

Knighton EL (2004) Congenital adrenal hyperplasia secondary to 11beta-hydroxylase deficiency in a domestic cat. J Amer Vet Med Assoc 225: 238-241.

XX testicular DSD

Szczerbal et al (2015) reported on a cat with an XX sex chromosomes, an SRY gene, efferent ductules but no gonads and a penis.

De Lorenzi et al (2017) report on a cat with XX testicular DSD


De Lorenzi L, Banco B, Previderè C, Bonacina S, Romagnoli S, Grieco V, Parma P. Testicular XX (SRY-Negative) Disorder of Sex Development in Cat. Sex Dev. 2017;11(4):210-216. doi: 10.1159/000479175. Epub 2017 Aug 26. PMID: 28848109.

Knighton EL (2004) Congenital adrenal hyperplasia secondary to 11beta-hydroxylase deficiency in a domestic cat. J Amer Vet Med Assoc 225: 238-241.

Szczerbal I, Stachowiak M, Dzimira S, Sliwa K, Switonski M. The first case of 38,XX (SRY-positive) disorder of sex development in a cat. Mol Cytogenet. 2015; 8: 22.

XX ovotesticular DSD

XX gonadal dysgenesis or aplasia

Ovarian aplasia and hypoplasia

Periodically, ovaries are found to be very small, so small that practitioners questions whether the ovary is present. In several such cases, ovarian stroma is present, but there are no primordial or other follicles. This might be explained by a lack of migration of the germ cells to the ovary, or a loss the germ cells after arrival.

DSD fel ovary hypoplasia 01

DSD fel ovary hypoplasia 01

Figure : Ovarian hypoplasia. Ovarian stroma is present, but no primordial follicles (with their germ cells)



XY Testicular DSD

A. Both scrotal contents present, and normal tubular genitalia and external genitalia

Appendix testis

The appendix testis is a remnant of the paramesonephric duct, and is located on the cranial or cranioventral surface (depending on the species orientation of the testes) of the testis near the head of the epididymis.

Cystic rete testis

Cystic rete testes are probably the result of obstruction of outflow and resultant pressure atrophy of the testis and dilation of the rete (both intratesticular, extratesticular or both). This was suspected to be the situation in the report by Gelberg and McEntee (1983) wherein a cat had a cyst in the head of the right epididymis that communicated with a large cystic structure in the testis. The efferent ductules were dilated and filled with spermatozoa, but the epididymis was empty, suggesting lack of communication between efferent ductules and epididymis.

Cystic rete testis, in its extreme form may appear to be a single large cyst.

Gelberg HB, McEntee K. Cystic rete testis in a cat and fox. Vet Pathol. 1983; 20: 634-636.

Cystic uterus masculinus

A cystic uterus masculinus is a paramesonephric remnant found on the external surface of the prostate and it is midline.

Paradidymis externa

A paradidymis is a remant of the mesonephric duct. It is found near the head of the epididymis, external to the epididymis.

Paradidymis interna

A paradidymis is a remant of the mesonephric duct. It is found in the head of the epididymis, and thus internal and within the epididymis.

Testicular hypoplasia

Testicular hypoplasia is where the testis does not develop to its normal size. It is always accompanied by a failure of the epididymis to acquire its normal size also. Most cases of hypoplasia are because of cryptorchidism, but in this section, primary hypoplasia is limited to those situations where the testis has descended normally. Hypoplasia is almost always seen as a failure of the prepubertal testis to enlarge, but there may be cases where even the prepubertal testis is smaller than normal. Hypoplasia is best diagnosed clinically by identifying that the testis has no increased in size from puberty, but this change is seldom monitored in cats and so the presence of a small testis could mean either hypoplasia or atrophy. Atrophy is an acquired condition, but hypoplasia is potentially a genetic and heritable condition, at least in other species.

Hypoplasia is variable in its degree. In production animals, testicular volume or scrotal circumference is measured and a certain size is deemed to be the minimum acceptible. Smaller testes than the minimum size have some degree of hypoplasia – in some, there are only mild changes, but in others, they are extreme. The literature suggests that many cats with testicular hypoplasia have chromosomal anomalies.

There are degrees of hypoplasia. While all retained testes are hypoplastic, in some the degree of hypoplasia is extreme. A microscopic focus of testicular tissue is present in some (see Fig).

Axner et al (1996) report 3 cats with hypoplasia. 2 had chromosomal anomalies (XXY, XY/XXY) and one did not.

Szczerbal et al (2018) reported on 3 cats with chromosomal abnormalities. One was an XY cat with small testes, bifid scrotum, rudimentary penis and no uterus.



Figure 9 : Marked testicular hypoplasia with only a few seminiferous tubules present. The epididymis was 'normal' for a retained testis (YB167169).






Figure 10 : Extreme testicular hypoplasia (YB69029).



Figure 11 : Hypoplastic epididymis attached to the tissue of fig 10.


I acknowledge that some would call this testicular aplasia. I have arbitrarily chosen to reserve testicular aplasia for those situations where absolutely no testis or remnant or epididymis is found.

Congenital phimosis

There are several reports of cats with congenital phimosis. (Bright and Mellanby 2004, ) obstruction or partial obstruction of the preputial orifice or tip of the penis. Surgical correction is reported. It is difficult to determine if the congenital phimosis was because of the normal fusion of penis and prepuce in a prepubertal animal.


Bright SR, Mellanby RJ. Congenital phimosis in a cat. J Feline Med Surg. 2004; 6: 367-370.

Scrotum with one or no contents, normal tubular genitalia and external genitalia


Milwright and Smith (1999) report finding a cat with 3 testes.

Roca-Ferrer et al (2015) reported on a cat with 4 intraabdominal testes. They were bilateral and close to each other on each side. Each testis had its own epididymis and epilateral deferent ducts fused to form one duct.

Lohr et al (2022) reported on a cryptorchid cat with 4 testes - each with epididymides.


Lohr BR, Lieske DE, Parry NM. Polyorchidism in a cat. J Vet Diagn Invest. 2022; 34: 1020-1022.

Milwright RD, Smith KC. Polyorchidism in a cat. Vet Rec. 1999 Dec 4;145(23):679-80.

Roca-Ferrer J, Rodríguez E, Ramírez GA, Moragas C, Sala M. A rare case of polyorchidism in a cat with four intra-abdominal testes. Reprod Domest Anim 2015; 50: 172-176.


Testicular aplasia, anorchia, monorchia

Testicular aplasia is when no testis develops. Separating testicular aplasia from extreme hypoplasia or degeneration is arbitary.  This diagnosis, to some extent is, is one of exclusion. The total absence of testicular tissue requires a diligent search for any tissue, and to be thorough, necessitates examining the surgically removed tissue, trimming all tissues and having all parts sectioned.

I have examined many cases of suspected anorchia. These are almost entirely cryptorchid tests and in most epididymis, deferent duct, and some remnant of the testis is present. Only rarely is there no evidence of any testicular structure.

McEntee (1990) reports seeing only one case.

Anorchia - No testis,


Previous surgical removal

When there has been previous surgical removal, the end of the ductus deferens can be found, and usually the ductus is well developed and at a size commensurate with the size of the ductus at the age of castration or removal. No epididymal tissues or embryonic remnants should be present.

DSD fel male

Figure 6 : Ductus deferens from suspected retained testis


Retained, undescended or ‘hidden’ testis is the most common disease of the feline male reproductive tract. Millis et al (1992) found that of 1,345 cats undergoing orchectomy, 23 or 1.7% were cryptorchid and 2 were monorchid. There was no predisposition for abdominal versus inguinal, and right versus left in unilateral cryptorchids. Yates et al (2003) castrated 3806 cats and 50 were cryptorchids. Left and right inguinal cryptorchidism was the most common form. Cryptorchidism is a feature of calico male cats (with XXY or mosaics of XX/XY).It is seen in other types of chromosomal anomalies see above.

Normally, the testes should be within the scrotum at or soon after birth. Most cases are handled clinically, so they do not enter the domain of the surgical pathologist. Before puberty, the retained testis is usually identical to the descended testis in every way except for location. With the onset of puberty, there is no spermatogenesis, so the histological appearance is identical to that of a prepubertal testis – and to a hypoplastic testis.


Figure 12: Histology of a cryptorchid testis.

Histologically, the testis is composed of seminiferious tubules that are lined by sustentacular (Sertoli) cells. Large mononuclear (germ) cells are often present in the lumen, or between sustentacular (Sertoli) cells – these are the spermatogonia. The interstitial endocrine cells are usually very obvious, and appear to be in greater numbers. Studies in other species suggest that their number is not increased over normal, but that the area taken up by the seminiferous tubules is greatly reduced.

Hakala (1984) reported on a cryptorchid cat.


Hakala JE. Reproductive tract anomalies in 2 male cats. Mod Vet Pract. 1984; 65: 629.

Memon M, Tibary A. Canine and feline cryptorchidism. In: Recent advances in small animal reproduction. PW Concannon, G England and J Verstegen (Eds) International Veterinary Information Service (www.ivis.org) 2001

Millis DL, Hauptman JG, Johnson CA.(1992) Cryptorchidism and monorchism in cats: 25 cases (1980-1989). J Am Vet Med Assoc 200(8):1128-1130.

Yates D, Hayes G, Heffernan M, Beynon R. Incidence of cryptorchidism in dogs and cats. Vet Rec. 2003; 152: 502-504.

Persistent paramesonephric (Mullerian) ducts (Uterus masculinus) - deficiency in Antimullerian hormone or receptor

This is a common anomaly in male cats. The paramesonephric ducts, those ducts that, in the female, would give rise to the uterine tube and uterus, are retained. In dogs this is called the persistent mullerian duct syndrome (PMDS). Affected cats are gonad and phenotypic males, but have a persistent paramesonephric duct. This can be found parrallel to the ductus deferens and also beside the epididymis.

Persistent paramesonephric duct (uterus masculinis) in a male cat. The inner two ducts have a uterine appearance, whereas the outer ducts are ducti deferentes.


Persistent paramesonephric duct in a male cat. The tube on the left resembles a uterine horn and the tube on the left is the ductus deferens. (YB135279).

Schulman and Levine (1989) reported a 10 month old castrated male cat with pyometra of a cystic uterus masculinus. It was a cryptorchid as the gonads were inguinally retained.

Vallefuoco et al (2013) reported on a 3 month old kitten with an anovaginal fistula, cloaca with vaginal but testes and an XY genotype.


Schulman J, Levine SH (1989) Pyometera involving uterus masculinus in a cat. J Amer Vet Med Assoc 194: 690-691.

Vallefuoco R, Alleaume C, Jardel N, Maenhoudt C, Cordonnier N. (2013) Type II atresia ani associated with rectovaginal fistula in a male pseudohermaphrodite kitten. Canadian Vet J 2013; 54: 475-478.

No scrotal contents, ambiguous genitalia including hypospadias

King and Johnson (1983) reported on one cat with hypospadias. It was XY with testes.

Hakada (1984) reported on 2 cats with external genital lesions. One had hypospadias.

Nowacka-Woszuk et al (2014) reported on 4 cats that were 38XY and normal SRY and ZFY and they had abnormalities of the external genitalia - 3 had hypospadias and one had a normal penis and a blind vulva. The molecular background for this is unknown.


Dzimira S, Nizanski W, Madej JA. Morphological analysis of testicles in cats with disorders of sex development. Pol J Vet Sci. 2017; 20: 123-131.

Hakala JE. Reproductive tract anomalies in 2 male cats. Mod Vet Pract. 1984 Aug;65(8):629. PMID: 6149456.

King GJ, Johnson EH. Hypospadias in a Himalayan cat. J Small Anim Pract. 2000; 41: 508-510.

Nowacka-Woszuk J, Szczerbal I, Salamon S, Kociucka B, Jackowiak H, Prozorowska E, Slaska B, Rozanska D, Orzelski M, Ochota M, Dzimira S, Lipiec M, Nizanski W, Switonski M. Testicular disorder of sex development in four cats with a male karyotype (38,XY; SRY-positive). Anim Reprod Sci. 2014; 151: 42-48.



No scrotal contents, phenotypic female


Disorders of androgen synthesis or action

There are many reports of male feminisaton in cats.

Meyers-Wallen et al (1989) examined one such individual in detail and determined that there was a testosterone receptor problem and that this was an X linked heritable disease.

Hakala (1984) reported male pseudohermaphroditism in a 3 year old cat. The owner reported that the cat had been castrated, but it had a vulva and a penis that could not be extruded and was 3 mm long. No gonads were found and the karyotype was unknown.

Meyers-Wallen et al (1989) reported on a phenotypically female cat with gonads in the location of the ovaries, but no tubular genitalia. The gonad was testis and the karyotype was 38 XY. Based on fibroblast cultures, there was no testosterone binding to receptors.

Bredal WP, Thoresen SI, Kvellestad A, Lindblad K. (1997) Male pseudohermaphroditism in a cat. J Small Anim Pract. 38(1):21-4.

Hakala JE. (1984) Reproductive tract anomalies in 2 male cats. Modern Vet 65: 629.

Meyers-Wallen, VN, Wilson JD, Griffin JE, Fisher S, Moorhead PH, Goldschmidt MH, Haskins ME, Patterson DF. Testicular feminization in a cat. Vet Med Assoc 1989; 195: 1456-1458.



XY ovarian DSD

XY ovotesticular DSD

Schlafer et al (2011) reported on a cat that was phenotypically male with penis and scrotum, but had ovotestes in the location of the ovaries. It had both male and female tubular genitalia. It was typed as an 38XY, SRY positive.


Schlafer DH, Valentine B, Fahnestock G, Froenicke L, Grahn RA, Lyons LA, Meyers-Wallen VN. (2011) A case of SRY-positive 38, XY true hermaphroditism (XY sex reversal) in a cat. Vet Pathol 2011, 48: 817-822

  XY gonadal dysgenesis