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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Histopathologic evaluation of the endometrium to predict a mare's ability to carry a foal to term and to identify pathologies to direct medical management of reproductive disease.

Pathophysiology!!navigator!!

Normal Architecture and Seasonal Variation

  • The endometrium is the mucosal layer of the luminal surface of the uterus and consists of epithelium, stroma, glands, and vascular and lymphatic vessels. The stratum compactum and the stratum spongiosum are the superficial and deep layers, respectively
  • Normal changes are driven by ovarian estrogen and P4, with cycle and season—winter anestrus: atrophy; vernal (spring) transition: increasing estrogen stimulates activity; breeding season: estrus and diestrus variations:
    • Estrus—tall columnar luminal epithelium, stromal edema, PMNs marginate on vasculature, but do not enter stroma, straight glands
    • Diestrus—mostly columnar/cuboidal luminal epithelium, less edema, tortuous glands

Assessment for Inflammatory or Degenerative Pathologic Changes

  • Endometritis—inflammation and type of cell infiltration; bacterial or fungal/yeast organisms
  • Periglandular fibrosis, endometriosis
  • Cystic glandular distention with/without periglandular fibrosis
  • Lymphangiectasia
  • Vascular damage, angiosis
  • Endometrial maldifferentiation, inappropriate for season and/or cycle
  • Inflammation from coitus, pregnancy, infectious organisms, pneumovagina, urovagina, DUC, and other unknown causes
  • Other degenerative changes usually are progressive, associated with aging, exacerbated by parity and chronic inflammation
  • Cumulative pathologies decrease probability of term pregnancy

Systems Affected!!navigator!!

Reproductive

Genetics!!navigator!!

N/A

Signalment!!navigator!!

Aged mares and increased parity.

Signs!!navigator!!

Historical Findings

  • Infertility or subfertility
  • Barren from previous/current season, though bred ≤48 h preovulation with proven semen
  • Anestrus mare during breeding season
  • Reproductive tract abnormalities
  • EED, abortion
  • Cytology and culture inconclusive for endometritis diagnosis
  • Reproductive prepurchase examination of broodmare prospect

Physical Examination Findings

Perineal examination—poor vulvar conformation, associated pneumo- or urovagina.

Causes!!navigator!!

Inflammation

  • Most common abnormality, described by distribution—focal, diffuse; frequency—mild, moderate, severe; cell type—acute, chronic, chronic/active
    • Acute—PMNs predominate
    • Chronic—lymphocytes, plasma cells, macrophages
    • Chronic/active—PMNs, with lymphocytes, plasma cells
  • Inflammatory cells in stratum compactum and in chronic cases also in stratum spongiosum
  • Macrophages linked to irritating or poorly absorbed foreign matter
  • Siderophages (macrophage with hemoglobin pigment) indicate past foaling, abortion, hemorrhage, within last 2–3 years
  • Eosinophils due to pneumo- or urovagina, less often fungal endometritis

Fibrosis/Endometriosis

  • Considered irreversible degenerative change
  • Widespread distribution correlates with low foaling rate
  • Stromal cells deposit collagen in response to inflammation, aging, or other stimuli
  • Most collagen deposition is periglandular, resulting in fibrotic glandular nests, cystic glandular distention, epithelial atrophy, and decreased uterine milk secretion
  • Uterine milk provides early nutrition; when insufficient—EED or fetal loss by 45–90 days of gestation
  • Poorer prognosis with increased layers of collagen and frequency of nests

Cystic Glandular Distention without Periglandular Fibrosis

  • Normal seasonal variation during anestrus and transition
  • In breeding season, identified in old, pluriparous mares with repeat breeding
  • Glands have impaired flow of secretions, inspissation of content
  • Cystic glandular distention may precede periglandular fibrosis
  • Glands are uniformly dilated after abortion or pregnancy

Lymphangiectasia

  • Characterized by dilated dysfunctional lymphatic vessels
  • Common in mares with pendulous uterus and DUC
  • TRP may reveal thickened soft uterus with poor diestrous tone
  • Widespread severe lymphangiectasia reduces foaling rates
  • Lymphatic lacunae enlarge into gross lymphatic cysts, visible with US or endoscopy

Angiosis

  • Sclerotic changes of uterine vessels primarily related to parity, secondarily with aging
  • Younger maiden mares have intact vessels. Pluriparous mares have disruption of the intima with medial and adventitial elastosis and fibrosis
  • Severe angiosis decreases perfusion, results in edema
  • Negatively affects pregnancy outcome

Nonseasonal Glandular Atrophy, Hypoplasia, or Maldifferentiation

  • Decreased gland density during breeding season is abnormal and associated with ovarian dysgenesis or granulosa–theca cell tumor
  • Focal glandular atrophy in old pluriparous mares
  • Ovarian dysgenesis

Prognostic Categories

Category I

  • ≥80% of mares conceive and carry to term; endometrium is essentially normal
  • Changes, if present, are only slight, focal, scattered

Category IIA

  • Foaling rate of 50–80% with proper management
  • Changes—slight to moderate and scattered
    • Diffuse cellular infiltration of superficial layers or foci
    • Periglandular fibrosis of branches, 1–3 layers, or ≤2 fibrotic nests/LPF in 5 fields
    • Endometrial atrophy in late breeding season
  • Bred, but barren for ≥2 years, with a biopsy of category IIA change is downgraded to IIB
  • Category may improve with treatment

Category IIB

  • Foaling rate of 10–50% with proper management
  • Changes are more diffuse and severe than IIA and may include:
    • Moderately severe cellular infiltration of superficial layers
    • Periglandular fibrosis of branches, ≥4 layers, or 2–4 fibrotic nests/LPF in 5 fields
    • Widespread lymphangiectasia only (without other pathology)
  • A category IIB biopsy is downgraded to III when widespread lymphangiectasia present
  • Category may improve with proper treatment

Category III

  • ≤10% foaling rate, even with optimal management
  • Greatly decreased conception rate and pregnancy maintenance
  • Histologic changes are prominent, diffuse, and severe:
    • Cellular infiltration
    • Fibrotic glandular nests with ≥5 nests/LPF
    • Lymphangiectasia with palpable “jelly-like” texture
    • Endometrial glandular atrophy during the breeding season

Risk Factors!!navigator!!

  • Age
  • Parity
  • Anatomic abnormalities causing inflammation, e.g. pneumovagina or urovagina
  • Repeated inflammation from coitus, DUC, infectious endometritis

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Imaging!!navigator!!

US for presence of intraluminal uterine fluid, edema, lymphatic cysts, foreign body, or other.

Other Diagnostic Procedures!!navigator!!

Breeding Soundness Examination

  • Endometrial biopsy is performed as part of a complete examination, not as a sole diagnostic
  • Swab or brush culture and cytology precede biopsy to avoid contamination
  • Sterile biopsy forceps are carried through the cervix into the uterus, sampling at the caudal portion of the horn or junction of horn/body, preferably when the mare is cycling and in estrus. TRP guides placement of forceps, tissue is pressed into the opened forceps, which are closed to obtain tissue
  • One sample is representative of the entire endometrium. If gross abnormality is present additional samples are obtained (pathologists prefer 2 or 3 samples)
  • Preferred to fix in Bouin's solution for 4–24 h, then transfer into 70% ethanol or 10% BNF until processed. If Bouin's is unavailable, use 10% BNF
  • Routine stain—H&E may request others
  • Include history, stage of cycle, TRP, and US findings on day of examination
  • If performing cytology, roll biopsy specimen onto sterile slide, air dry, stain
  • If performing culture from biopsy specimen, guarding the biopsy forceps is required
  • Culture and cytology from biopsy may be more accurate than swab method

Endoscopy

Evaluate for intraluminal adhesions, endometrial cysts, focal lesions, and foreign body.

Pathologic Findings!!navigator!!

See I, IIA, IIB, and III category descriptions.

Treatment ⬆ ⬇

Outline

TREATMENT

Category I!!navigator!!

  • Exclude bacterial endometritis
  • Focus on estrus detection, timing of breeding and insemination with respect to ovulation, semen quality and type, mare anatomic or behavioral abnormalities
  • Evaluate health—manage lameness or systemic disease; reproduction is a luxury

Categories IIA and IIB!!navigator!!

  • Direct therapy at problems identified on biopsy, to improve category and prognosis
  • Minimize contamination and inflammation at and after breeding
  • Caslick's vulvoplasty for pneumovagina
  • Bacterial or fungal infections—local/systemic antibiotic/antifungal
  • Treat DUC with uterine lavage and oxytocin
  • Impaired lymphatics and edema managed with cloprostenol (PGF2α analog) at 12–24 h before and after breeding
  • P + E improves uterine tone and may enhance vascular perfusion and lymphatic drainage
  • Urethral extension surgery, if vulvo- or perineoplasty does not adequately improve urovagina
  • Fibrosis and angiosis are irreversible

Category III!!navigator!!

  • May conceive, but EED or fetal loss at ≤90 days of gestation
  • Aggressive therapy directed at problems identified on biopsy
  • Extensive fibrosis—irreversible, category will not improve
  • If no improvement is achieved, reproductively retire mare
  • If allowed by breed registry, consider mares for embryo transfer or as oocyte donor

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Antibiotic based on culture and sensitivity
  • Normal saline or lactated Ringer's solution for uterine lavage
  • Cloprostenol 100–250 μg IM
  • P + E:
    • Combined P4 (150 mg) + E (5–10 mg) IM daily for 10 days or 10 mL bio-release P + E IM once
    • Day 10 administer PGF2α 10 mg IM
    • Day 5 after ovulation, if no fluid is in the uterus (indicating inflammation or infection), may resume treatment
    • If pregnant at 14 days, may continue to day 45 of gestation

Contraindications!!navigator!!

  • Do not administer P4 or progestins if mare is infected, as endometritis will worsen
  • Cloprostenol or PGF2α is generally not recommended post ovulation as it may harm luteal growth and P4 production
  • PGF2α or cloprostenol is contraindicated during pregnancy

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Repeat biopsy ≌2 weeks after treatment, as a means to determine effectiveness.

Possible Complications!!navigator!!

  • Rarely uterine perforation or excessive hemorrhage
  • Pregnancy is a contraindication to biopsy

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Synonyms!!navigator!!

Uterine biopsy

See Also!!navigator!!

Endometritis

Abbreviations!!navigator!!

  • BNF = buffered neutral formalin
  • DUC = delayed uterine clearance
  • EED = early embryonic death
  • LPF = low-power field (5.5 mm)
  • P4 = progesterone
  • P + E = P4 + estradiol-17β
  • PGF2α = prostaglandin F2α (dinoprost tromethamine; Lutalyse®)
  • PMN = polymorphonuclear leukocyte
  • TRP = transrectal palpation
  • US = ultrasonography, ultrasound

Suggested Reading ⬆ ⬇

Love CC. Endometrial biopsy. In: McKinnon AO, Squires EL, Vaala WE, Varner DD, eds. Equine Reproduction, 2e. Ames, IA: Wiley Blackwell, 2011:1929–1939.

McCue PM. Endometrial biopsy. In: Dascanio J, McCue P, eds. Equine Reproductive Procedures. Hoboken, NJ: Wiley Blackwell, 2014:68–70.

Snider TA, Sepoy C, Holyoak GR. Equine endometrial biopsy reviewed: observation, interpretation, and application of histopathologic data. Theriogenology2011;75:1567–1581.

Wolfsdorf KE. How to utilize endometrial culture, cytology, and biopsy to manage the sub-fertile mare. Proc Am Assoc Equine Pract 2016;62:164–168.

Author(s) ⬆

Authors: Audrey A. Kelleman and Maria E. Cadario

Consulting Editor: Carla L. Carleton