JPC Systemic Pathology
Reproductive System
January 2022
R-M04

SIGNALMENT (JPC # 2755480):  A 4-year-old bearded collie

HISTORY:  This dog presented with clitoral enlargement, and progesterone levels cycled normally with estrus, indicating ovulation.

HISTOPATHOLOGIC Description:  Gonad: The gonadal tissue is composed of a peripheral zone of ovarian tissue which surrounds a central zone of testicular tissue. The ovarian tissue is composed of ovarian stroma which surrounds ovarian follicles in various stages of development and several variably sized (up to 3mm diameter) corpora lutea. There are numerous primordial follicles deep to the tunica albuginea, each with a primary oocyte and surrounded by a single layer of flattened follicular cells. Primary follicles contain a larger oocyte which is surrounded by a zona pellucida, further surrounded by a single layer of cuboidal to columnar follicular granulosa cells. Secondary follicles contain a primary oocyte which is rimmed by a zona pellucida and is surrounded by a radially arranged cluster of granulosa cells (corona radiata) with a small fluid filled antrum, and the zona granulosa is bounded by the theca interna and theca externa. Tertiary follicles (Graafian follicles) contain large, fluid-filled spaces between granulosa cells which fuse to form a large antrum filled with basophilic to amphophilic homogenous material; no oocytes are seen in the few tertiary follicles (out of plane of section). There are scattered atretic follicles with a swollen, undulant zona pellucida. The corpora lutea consist of granulosa lutein cells surrounded by theca lutein cells. There are numerous Sertoli cords embedded within the intervening ovarian stroma. The testicular tissue is composed of hypoplastic seminiferous tubules that lack germ cells and spermatozoa and are lined by Sertoli cells that extend from the undulant basement membrane into the lumen. Interstitial cells are interspersed between hypoplastic tubules and have small, round nuclei and eosinophilic, foamy cytoplasm.  

Oviduct:  Essentially normal tissue.

Morphologic diagnosis:  Gonad: Ovotestes, bearded collie, canine.

Condition:  XX, SRY-, ovotestes disorder of sexual development (DSD), with female phenotype

GENERAL DISCUSSION:

• The terms “hermaphrodite”, “intersex”, and “pseudohermaphrodite” are discarded in favor of “disorder of sexual development” with a more complete description including sex chromosome (i.e. XX, XY), SRY presence, gonad type, tubular gentalia, and external genital phenotype
• Caused by genetic or chromosomal abnormalities or inappropriate hormone exposure at the time of reproductive tract differentiation
• This particular DSD is reported in all species, and in goats is associated with a polled phenotype (polled/intersex syndrome)

PATHOGENESIS:

• Sexual development occurs in three steps:
  • 1) the establishment of chromosomal/genotypic sex
  • 2) the determination of gonadal sex,
  • 3) the development of phenotypic sex; a functional testis is critical to male phenotypic development
• Chromosomal sex is determined at fertilization: XX or XY
  • Rarely, aneuploidy can occur resulting in XXX, XXY (Kleinfelter-like syndrome), or X_ (Turner-like syndrome)
• Gonadal sex is determined by a variety of genes
  • Female:
    • XX chromosomal sex lacks the SRY and testis-determining factors
    • WNT4 is important and upregulates folistatin (FST) and DAX1; it also inhibits SOX9 (a male specific gene)
    • FOXL2 and BMP2 also are important in upregulation of FST
    • Wolffian (mesonephric, male) ducts regress in the absence of SRY gene product
    • Outer cortical layer of bipotent gonad becomes ovarian tissue first - ovotestes are usually ovarian tissue on the periphery with varying amounts of testicular tissue in the medulla
  • Male:
    • SRY gene is the sex determining region of the Y chromosome
    • In the presence of SRY, SOX9 expression is increased, promoting the testicular pathway and blocking the ovarian pathway
    • SRY is also important in early Sertoli cell differentiation
• Phenotypic sexual development: Abnormal sexual development often leads to abnormal appearing external genitalia
  • Driven by gonadal factors
  • Female tubular and external genital development form from paramesonephric (Mullerian) ducts – will develop in the absence of hormones
  • The presence of testosterone and anti-Mullerian hormone (AMH) cause regression of paramesonephric (Mullerian, female) ducts and development of mesonephric (Wolffian) ducts into male genitalia and accessory sex glands
  • AMH is produced by Sertoli cells and testosterone is produced by interstitial (Leydig) cells
• Ovotestis usually results in varying degrees of masculinization of the tubular and external genitalia – e.g. clitoral hypertrophy, hypospadias

TYPICAL GROSS FINDINGS: 

• Ovotestis
  • Bilateral - ovotestis on each side
  • Unilateral - ovotestis on one side and ovary or testis on opposite side
  • Lateral - testis on one side and ovary on the other
  • Masculinization of tubular and external genitalia (varying degrees)

Typical LIGHT Microscopic Findings:

• Ovotestis - testicular portion always located in medulla with the ovarian tissue external to it, located in the cortex
  • Testicular portion - Hypoplastic seminiferous tubules lined by Sertoli cells; interstitial cells between hypoplastic tubules; rare (or no) germ cells
  • Ovarian portion with oogonia, oocytes, primary and secondary follicles
  • Relative quantities of testicular versus ovarian tissue varies dramatically between affected individuals

Differential Diagnosis: 

Anomalies of sexual development in various species:

• Cryptorchidism - most common disorder of sexual development in the dog
• Ovarian agenesis - ruminants, swine, dogs
• Ovarian dysgenesis - horses; small, inactive ovaries that lack germ cells
• Ovarian hypoplasia and genital infantilism - occurs in many species, but described primarily in cattle
  • Swedish Highland cattle - occurs as a genetic defect
• Testicular hypoplasia

Drug-Induced intersexuality: 

• Androgens and many progestins induce masculinization of the genitalia in female offspring of rats, mice, guinea pigs, rabbits, cattle, sheep, dogs, monkeys, and women
  • Estrogens, progestins, and antiandrogens - feminization of the reproductive tract and external genitalia of the male rat fetus
  • Testosterone given to pregnant bitches induces female pseudohermaphrodites (i.e. XX, SRY-, variably male phenotype) in her offspring; male offspring are normal

Comparative Pathology: 

Specific, well described anomalies of sexual development:

• Freemartinism - abnormality of chromosomal sex, chimerism (XX/XY)
• Reported primarily in cattle; rarely in sheep, goats, and swine (don’t usually have shared placental circulations)
  • Freemartin is the female born as co-twin to male calf; female twin exhibits masculinization and is sterile, male twin minimally affected
  • Anastomoses develop between the placental circulations > true chimerism of hematopoeitic cells, and androgenic hormones from male fetus reach female fetus > suppress female genital system and allow male vestiges to develop in the female
  • Gross findings include: Female phenotype; stunted gonads; paired hypoplastic seminal vesicular glands; hypoplastic seminiferous tubules (ovotestes); hypoplastic internal uterine tubes, a short nonpatent vagina, vestibule, a small vulva with prominent tuft of hair; and enlarged clitoris
  • Vesicular glands always present
• Androgen insensitivity (XY, SRY+, cryptorchid testes, female external genitalia; AKA testicular feminization, XY sex reversal, male pseudohermaphrodite)
  • Mice, rats, cattle, and horses
  • Inherited form of XY DSD (female external genitalia and cryptorchid testis) transmitted by females to half of their offspring
  • Mutation in the Tfm (testicular feminization) gene > deficiency of intracellular androgen receptors, rendering all cells insensitive to androgens; or lack of AMH
  • Equine male pseudohermaphrodites have normal female external genitalia but show male behavior patterns - unique to horses
• Persistent Mullerian Duct Syndrome (PMDS) - rare disorder of AMH production or function
  • Miniature Schnauzers and goats
• Sex reversal - Gonad is not the type corresponding to the XX or XY genotype of that individual
• American Cocker Spaniel, Chinese pug, German shorthaired pointer, Kerry blue terrier, Norwegian elkhound, cat, pigs, goats, horses
• XX ovotesticular or testicular DSD:
  • Goats: Loss of FOXL2 gene product and translocation of testis-determining gene
• Tortoiseshell/calico male cat
  • XXY sex chromosome constitution (Klinefelter-like syndrome)
  • Gene for black and gene for orange are carried one per X chromosome (normal male should not have both hair colors)
  • Testicular hypoplasia and sterility

REFERENCES:

1. Foster RA. Female reproductive system and mammae. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:1156-1157.
2. Foster RA. Male Genital system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. 3 6^th ed. St. Louis, MO: Elsevier; 2016:468-471.
3. Schlafer DH, Foster RA. Pathology of the genital system of the nongravid female. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. St. Louis, MO: Elsevier; 2016:361-366.

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