Endometrial Polyps

Slide 1 · Endometrial Polyps

Pathologic anatomy, stromal biology, morphology, differential diagnosis, and clinical correlation

Pathology of a focal endometrial lesion

Dr Abu Suraih Sakhri

MBBS, MD (Pathology)

www.abusuraihsakhri.com

Slide 2 · Learning objectives

Locate a polyp within normal endometrial anatomy and the abnormal uterine bleeding differential.

Explain its predominantly stromal neoplastic interpretation and hormonal context.

Recognize characteristic tissue features and clinically relevant diagnostic pitfalls.

Apply pathology findings to bleeding, infertility, and postmenopausal presentations.

Slide 3 · What defines an endometrial polyp?

A localized exophytic mass projecting into the endometrial cavity.

A lesion of variable size and attachment, composed of endometrial tissue.

Usually benign; Uncommon examples harbor adenocarcinoma.

FOCAL · INTRACAVITARY

Slide 4 · The uterine corpus has two tissue compartments

Myometrium: Interwoven smooth-muscle bundles forming the uterine wall.

Endometrium: Glands embedded in cellular stroma lining the uterine cavity.

A polyp projects from the endometrial lining into that cavity.

Endometrial cavity

Slide 5 · The endometrium contains glands and stroma

Endometrial glands supply the epithelial compartment.

Stromal cells form the supporting cellular connective tissue.

For polyps, the stromal component is especially important in interpreting pathogenesis.

Schematic · not a histologic specimen

Slide 6 · Functionalis versus basalis

Functionalis: Superficial endometrium shed during menstruation.

Basalis: Deeper endometrium from which the lining regenerates.

Polypoid growth is a focal structural lesion, distinct from normal cyclic renewal.

Functionalis · cyclic shedding

Basalis · regeneration

Anatomical layers · schematic

Slide 7 · The proliferative endometrium is hormonally active

Estrogen promotes proliferation of glands and stroma.

Glands are usually relatively straight and tubular, lined by proliferating epithelium.

Stromal cells also proliferate during this phase.

Estrogen

Starting observation

Gland + stroma

Intermediate step

Proliferation

Interpretation / action

Normal endometrium · hormone sequence

Slide 8 · The secretory endometrium changes after ovulation

Progesterone induces glandular differentiation and stromal functional change.

It suppresses additional estrogen-driven endometrial proliferation.

Normal cyclic hormone responsiveness provides the comparison for a polyp.

Ovulation

Starting observation

Progesterone

Intermediate step

Differentiation

Interpretation / action

Normal endometrium · hormone sequence

Slide 9 · Gland–stroma signaling mediates hormone effects

Estrogen acts through nuclear receptors in both tissue compartments.

Stromal growth factors support epithelial proliferation.

Progesterone lowers estrogen receptor expression during the secretory phase.

Ovarian estrogen

Starting observation

Stromal signaling

Intermediate step

Gland + stroma growth

Interpretation / action

Normal endometrium · simplified mechanism

Slide 10 · Abnormal uterine bleeding has two broad contexts

Structural pathology: Polyps, submucosal leiomyomas, endometrial neoplasms, inflammation.

Nonstructural functional bleeding: Commonly hormonal or anovulatory.

Identifying a focal mass changes the pathologic differential.

Structural

Polyp · leiomyoma · neoplasia · inflammation

Functional

Anovulatory / endocrine disturbance

Simplified differential categories · not exhaustive

Slide 11 · Why a polyp belongs in the structural differential

The lesion is visible as a focal intracavitary growth, rather than only altered cycling.

It may produce abnormal bleeding, although some polyps remain silent.

Histologic assessment must also consider coexisting endometrial disease.

Focal tissue finding + clinical context

Slide 12 · Exophytic growth distinguishes a polyp

The base originates in the endometrium.

The bulk of the mass extends toward the uterine lumen.

A growth configuration is not, by itself, a diagnosis of benignity.

Endometrium

Uterine cavity

Schematic · endometrium and intracavitary projection

Slide 13 · Polyps may be solitary or multiple

A single localized mass is possible.

Several separate masses may coexist.

Multiplicity changes the gross appearance without redefining the lesion.

Endometrium

Uterine cavity

Schematic · endometrium and intracavitary projection

Slide 14 · Sessile polyps have a broad attachment

Most endometrial polyps are sessile.

The polyp merges with the endometrial surface through a relatively broad base.

Distinguish attachment shape from lesion size.

Endometrium

Uterine cavity

Schematic · endometrium and intracavitary projection

Slide 15 · A pedunculated polyp has a stalk

Larger lesions may project on a narrow pedicle.

The stalk connects the mass to its site of origin.

Both pedunculated and sessile forms qualify as endometrial polyps.

Endometrium

Uterine cavity

Schematic · endometrium and intracavitary projection

Slide 16 · Typical polyp dimensions are modest

Most as approximately 0.5–3 cm in diameter.

Exceptionally, polyps can become considerably larger.

Size varies; It is not a stand-alone benign-versus-malignant criterion.

Small

Typical

Variable

Usual diameter: 0.5–3 cm

Slide 17 · Gross description: Four separate observations

Count: Single or multiple.

Contour: Focal projection into the cavity.

Attachment: Sessile or pedunculated.

Dimensions: Measure the lesion rather than assuming a standard size.

Slide 18 · Focal growth differs from diffuse glandular proliferation

Focal polyp

Diffuse hyperplasia

Localized cavity projection

Gland crowding relative to stroma

Variable attachment and size

Microscopic endometrial architectural change

Evaluate lesion plus background

Evaluate distribution and cytology

Slide 19 · Characteristic histology uses multiple tissue clues

Recognize an endometrial-type epithelial surface and glands.

Assess the stromal composition and vascular structures.

Interpret the whole architecture, not one gland or vessel in isolation.

Schematic · not a histologic specimen

Slide 20 · Thick-walled blood vessels support the diagnosis

Prominent thick-walled vessels are a useful polyp-associated morphologic clue.

Look for them within the polyp stroma.

A single vessel is supportive, not proof by itself.

Thick wall

Schematic · not a histologic specimen

Slide 21 · Collagenous stroma is a key distinguishing clue

Endometrial polyp stroma is often more collagenous than ordinary cycling endometrial stroma.

Evaluate stroma alongside vessels and surface configuration.

Distinguish this from myometrial smooth-muscle fascicles.

Collagen-rich supporting stroma

Schematic · not a histologic specimen

Slide 22 · Glands can vary within benign polyps

Benign polyp glands may be irregularly spaced or cystically dilated.

Their epithelial lining may remain cytologically bland.

Gland shape alone must not be equated with endometrial carcinoma.

Irregular / cystically dilated glands

Schematic · not a histologic specimen

Slide 23 · The surface configuration aids histologic recognition

Epithelium on multiple sides of a tissue fragment supports a polypoid structure.

Orientation and fragmentation can obscure this feature.

Combine surface architecture with stromal and vascular clues.

Surface epithelium

Schematic · not a histologic specimen

Slide 24 · Read morphology as a composite pattern

Exophytic architectural context, where available.

Collagenous stroma and thick-walled vessels.

Endometrial glands with assessment of cytology and crowding.

Endometrial glands

Fibrous stroma

Thick vessels

Composite morphologic assessment

Slide 25 · Tissue sections may contain incidental epithelial change

Tubal metaplasia can be seen in an otherwise benign endometrial polyp.

Metaplasia does not by itself establish malignancy.

Evaluate epithelial atypia and architecture independently.

Tubal metaplasia can be a benign finding

Schematic · not a histologic specimen

Slide 26 · What is not established by a schematic?

Illustrations explain gland–stroma–vessel relationships, not measured tissue appearances.

A real H&E section is needed to assess cytology, mitoses, and diagnostic detail.

A linked CC0 authentic micrograph is listed in the presenter notes for teaching comparison.

Evaluate atypia and carcinoma, not only polyp architecture

Slide 27 · Cytogenetics points toward the stroma

Acquired chromosomal rearrangements occur in stromal cells of endometrial polyps.

The reported changes resemble those of some other benign mesenchymal tumors.

This supports a stromal neoplasm interpretation.

Acquired stromal change

Starting observation

Stromal tumor biology

Intermediate step

Focal polyp formation

Interpretation / action

Slide 28 · Acquired changes are not germline traits

Acquired lesion change

Inherited predisposition

Occurs in somatic lesional cells

Constitutional variant

Supports local neoplastic biology

Requires separate hereditary evidence

No specific rearrangement given here

No germline testing recommendation implied

Slide 29 · Why the term “stromal neoplasm” matters

A polyp is not merely a displaced fold of otherwise normal endometrium.

Stromal abnormalities explain why focal growth may persist.

Neoplasm does not mean carcinoma; Most polyps are benign.

STROMAL ORIGIN ≠ MALIGNANCY

Slide 30 · Do not confuse stromal origin with epithelial risk

Lesion biology

Clinical safety check

Stromal chromosomal rearrangements

Inspect epithelial glands and lining

Benign mesenchymal analogy

Exclude atypia/carcinoma if present

Not a statement of cancer risk

Do not ignore the background endometrium

Slide 31 · Normal endometrium responds to two major hormones

Estrogen promotes proliferation in glands and stroma.

Progesterone suppresses estrogen-driven growth and causes secretory differentiation.

Polyps differ from background endometrium in their response pattern.

Estrogen

Starting observation

Progesterone

Intermediate step

Cycle-dependent changes

Interpretation / action

Normal endometrium · hormone sequence

Slide 32 · Endometrial polyps respond to estrogen

Polyps are estrogen responsive.

This is consistent with their endometrial hormonal environment.

Do not infer a quantitative estrogen threshold from this description.

Estrogen signal

Response retained in polyp

Localized polyp tissue

Growth responsiveness

Qualitative response · no quantitative threshold implied

Slide 33 · Polyps respond little, if at all, to progesterone

Unlike ordinary secretory endometrium, polyp tissue shows little or no progesterone response.

The mismatch helps contextualize polyp persistence during normal cycles.

Responsiveness is a biologic observation, not a treatment algorithm.

Progesterone signal

Little / no polyp response

Localized polyp tissue

Secretory differentiation is limited

Qualitative response · no quantitative threshold implied

Slide 34 · Polyp versus background: A hormonal mismatch

Background lining

Polyp

Cyclic gland/stromal change

Focal persistent growth

Estrogenic proliferation

Estrogen responsiveness

Strong secretory progesterone effects

Little or no progesterone response

Slide 35 · Tamoxifen acts differently by tissue

Tamoxifen is used for its antiestrogenic effects in breast tissue.

In endometrium, weak proestrogenic activity.

This tissue-selective pattern explains the association with endometrial polyps.

Breast tissue

Antiestrogenic effect

Endometrium

Weak proestrogenic effect

Qualitative tissue selectivity · tamoxifen

Slide 36 · Tamoxifen exposure is a clinical clue

Endometrial polyps may occur during tamoxifen administration.

Medication history is therefore relevant when interpreting an intracavitary lesion.

Association should not be presented as a deterministic individual risk estimate.

Medication history + cavity lesion

Slide 37 · Do not assume every tamoxifen-associated lesion is benign

A polyp may coexist with epithelial abnormalities.

Clinical context and tissue assessment remain important.

Robbins documents rare adenocarcinoma arising within a polyp.

Evaluate atypia and carcinoma, not only polyp architecture

Slide 38 · Atrophic polyps occur after menopause

Atrophic polyps chiefly occur in postmenopausal patients.

Robbins interprets them as likely residual lesions formed before menopause.

Atrophy refers to tissue state, not guaranteed clinical harmlessness.

Premenopause

Menopause

Postmenopause

Atrophic polyp may persist

Slide 39 · Atrophy and persistence can coexist

A pre-existing localized polyp can remain after normal ovarian cyclic activity declines.

Its glands may show atrophic rather than proliferative features.

The patient’s life stage affects morphology and clinical interpretation.

Premenopause

Menopause

Postmenopause

Atrophic polyp may persist

Slide 40 · Clinical presentation spans a wide range

Some patients have no symptoms.

Others present with abnormal uterine bleeding.

Infertility may also be associated with polyps.

Asymptomatic

Incidental finding

Bleeding

Presenting symptom

Infertility

Possible association

Slide 41 · Bleeding is a symptom, not a histologic diagnosis

Polyps can cause abnormal bleeding.

Anovulatory endometrium, inflammation, leiomyomas, and neoplasia can also cause bleeding.

A focal finding must be interpreted with clinical and endometrial context.

Structural

Polyp · leiomyoma · neoplasia · inflammation

Functional

Anovulatory / endocrine disturbance

Simplified differential categories · not exhaustive

Slide 42 · Infertility may be part of the presentation

Infertility as a possible manifestation.

The presence of a polyp does not prove it is the sole cause of infertility.

A clinicopathologic conclusion should acknowledge alternative explanations.

Focal tissue finding + clinical context

Slide 43 · An asymptomatic polyp may be discovered incidentally

Absence of bleeding does not exclude a polyp.

Anatomic detection and symptom burden are separate dimensions.

Reporting should still characterize the tissue and assess concerning features.

ASYMPTOMATIC ≠ ABSENT

Slide 44 · Carcinoma may rarely arise within a polyp

Robbins explicitly identifies adenocarcinoma arising in endometrial polyps as rare.

The primary concern is an epithelial malignant focus, not a generalized claim that all polyps progress.

Carefully inspect lesions for atypical epithelial architecture or cytology.

Evaluate atypia and carcinoma, not only polyp architecture

Slide 45 · Histology must check beyond the benign polyp pattern

Confirm polyp-associated stromal, vascular, and epithelial features.

Survey for atypia, architecturally concerning glands, or carcinoma.

Review the background endometrium when available.

Endometrial glands

Fibrous stroma

Thick vessels

Composite morphologic assessment

Slide 46 · Polyp versus submucosal leiomyoma

Endometrial polyp

Submucosal leiomyoma

Endometrial origin

Myometrial smooth muscle

Glands + stroma

Interlacing smooth muscle fascicles

Variable stalk/broad attachment

Can protrude beneath endometrium

Slide 47 · Polyp versus endometrial hyperplasia

Polyp

Hyperplasia

Focal mass

Increased gland-to-stroma ratio

Stromal and vascular clues

Architectural gland crowding

Inspect lesion and lining

Assess cytologic atypia

Slide 48 · Polyp versus anovulatory bleeding

Polyp

Anovulatory endometrium

Localized projection

Often diffuse hormonal pattern

Stromal neoplastic interpretation

Failure of ovulation

May coexist with hormonal abnormalities

Stromal breakdown with proliferative glands

Slide 49 · Polyp versus chronic endometritis

Polyp

Chronic endometritis

Focal endometrial mass

Inflammatory endometrium

Thick vessels + collagenous stroma

Stromal plasma cells

May cause bleeding/infertility

May cause bleeding/infertility

Slide 50 · Polyp versus adenomyosis

A polyp projects into the cavity.

Adenomyosis consists of endometrial tissue within the myometrium.

Their abnormal endometrial tissue is located in different compartments.

Ectopic glands in muscle

Slide 51 · Diagnostic reasoning starts with focality

Question 1: Is there a discrete intracavitary lesion?

Question 2: Is the tissue endometrial gland-and-stroma or smooth muscle?

Question 3: Is epithelial atypia or carcinoma present?

Focal lesion?

Starting observation

Tissue identity?

Intermediate step

Epithelial safety check

Interpretation / action

Slide 52 · Hysteroscopy directly evaluates the cavity

ACOG describes hysteroscopy for diagnosis and treatment of intrauterine pathology.

It allows visual assessment of a suspected focal lesion.

The procedural context is supplementary clinical guidance, distinct histopathology.

Cavity visualization

Starting observation

Targeted tissue removal

Intermediate step

Histopathologic examination

Interpretation / action

Slide 53 · Targeted polypectomy supports definitive tissue review

ACOG favors direct hysteroscopic polyp removal over blind methods when removal is indicated.

A resected specimen can be evaluated for benign polyp features and focal malignancy.

Procedural choice remains individualized to clinical circumstances.

Identify lesion

Starting observation

Remove under visualization

Intermediate step

Review tissue

Interpretation / action

Slide 54 · Reasons for removal depend on clinical context

ACOG lists abnormal bleeding, infertility, and recurrent pregnancy loss among indications for polyp removal.

Expectant or surgical management depends on symptoms and malignancy risk factors.

No universal management rule follows from polyp size alone in these sources.

Bleeding

Abnormal uterine bleeding

Infertility

Relevant to fertility care

Pregnancy loss

Recurrent pregnancy loss

Slide 55 · Blind sampling has a focal-lesion limitation

ACOG notes that blind removal or curettage can inaccurately detect or incompletely remove an intracavitary lesion.

Direct visualization can improve target localization.

Histologic sampling must still evaluate any concerning tissue.

Focal tissue finding + clinical context

Slide 56 · A pathology report should answer clinical questions

Identify the lesion as an endometrial polyp when supported by morphology.

State whether atypia or malignancy is present.

Document any separate relevant background endometrial abnormality represented in the sample.

Slide 57 · Case 1 · Bleeding with a focal cavity mass

A premenopausal patient has abnormal uterine bleeding.

A focal lesion projects into the endometrial cavity.

What distinguishes a polyp from an anovulatory endometrial pattern?

Discussion prompt · explanation in presenter notes

Slide 58 · Case 2 · A patient receiving tamoxifen

A patient with prior breast cancer treatment is taking tamoxifen.

An endometrial cavity projection is detected.

What tissue-specific drug effect helps explain this association?

Discussion prompt · explanation in presenter notes

Slide 59 · Case 3 · A postmenopausal polyp

A patient after menopause has a small endometrial polyp with atrophic glands.

Which polyp subtype is compatible with this finding?

Does atrophy eliminate the need to assess epithelial abnormalities?

Discussion prompt · explanation in presenter notes

Slide 60 · Case 4 · A crowded glandular focus

A polyp contains areas of irregular and crowded glands.

What two different diagnoses must not be conflated?

What additional features must be assessed?

Discussion prompt · explanation in presenter notes

Slide 61 · Integrated interpretation: Four linked levels

Anatomic: Localized projection into the endometrial cavity.

Biologic: Acquired stromal rearrangements; Estrogen responsiveness with little progesterone effect.

Histologic: Integrate glandular, stromal, vascular, and epithelial findings.

Clinical: Correlate with bleeding, fertility, tamoxifen, menopausal state, and rare cancer.

Slide 62 · Six high-yield pathology statements

A polyp is a focal exophytic endometrial mass.

Most are small and sessile, but pedunculated and multiple lesions occur.

Stromal acquired rearrangements support a benign neoplastic process.

Estrogen responsiveness contrasts with weak progesterone responsiveness.

Bleeding, infertility, and asymptomatic detection are all possible.

Rare carcinoma requires diligent histologic examination.

Slide 63 · Selected sources

Robbins, Cotran & Kumar. Pathologic Basis of Disease, 11th ed. (2026), chapter 22, pp. 910–915.

Patholines. Endometrial polyp (M. Häggström): supplemental histologic recognition and reporting.

ACOG Committee Opinion No. 800 (2020): hysteroscopic diagnosis and removal.

Wikimedia Commons (M. Häggström, CC0): linked authentic H&E references in notes; not reproduced.