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Uterus (excludes Cervix)

Stromal tumors

Endometrial stromal nodule

Reviewer: Mohamed Mokhtar Desouki, MD, PhD (see Reviewers page)
Revised: 21 August 2011, last major update August 2011
Copyright: (c) 2002-2011, PathologyOutlines.com, Inc.


● Benign tumor composed of cells reminiscent of proliferative-phase endometrial stroma


● Occur at any age during reproductive or later years (mostly in the 5th and 6th decades)

Clinical features

● May present with abnormal uterine bleeding, but most tumors are incidental findings in a hysterectomy specimen
● Prognostic significance of limited infiltration is unclear (Am J Surg Pathol 2002;26:567)


● Excellent prognosis; patients are cured by hysterectomy
● Conservative excision may be adequate, but usually limits ability to sample margins

Gross description

● Classically round, soft, yellow, solitary, sharply circumscribed neoplasm, confined to uterus, with no intravascular component
● Tumors are not encapsulated; they are usually solitary, ranging from 1 to 22 cm
● If located in endometrium, they are frequently polypoid
● Tumors may be located intramurally with no connection to the surface endometrium
● No whorled pattern characteristic of a leiomyoma
● Cysts may be present
● Tumors grow in an expansile, non-infiltrating pattern with a smooth margin

Micro description

● Usually uniformly well-circumscribed, monotonous proliferations of bland endometrial stromal cells
● Expansive growth pattern (not infiltration) at margin
● Infiltration, if present, should be at most one to three protrusions, 3 mm or less
● Usually prominent arterioles
● May have sex cord-like differentiation or infarct-like necrosis
● No angiolymphatic invasion, minimal mitotic activity (< 10 per 10 HPF)
● Note: foci of smooth muscle metaplasia within the tumor should NOT be interpreted as myometrial invasion at the edge of the tumor

Micro images

Circumscription with pushing margin

Small uniform cells closely resemble those of proliferative-phase endometrial stroma

Regularly distributed small blood vessels resemble spiral arterioles

Thick bands of hyalinized collagen

Starburst pattern of hyalinized collagen

Numerous cells with foamy cytoplasm

Note large focus (upper) of smooth muscle differentiation, well within the sharply circumscribed tumor border, distinguishing it from myometrium invaded by tumor

Silver reticulum stain demonstrates reticulin fibers wrapping around individual tumor cells and emphasizes the whorling pattern around the blood vessels

Positive stains

● CD10, ER, PR; also WT1, B-catenin, SMA, cytokeratin, androgen receptor, vimentin, muscle-specific actin

Negative stains

● Desmin, CD34 (rarely positive), h-caldesmin

Differential Diagnosis

Cellular leiomyoma: grossly soft and yellow, fascicular pattern, large, thick-walled blood vessels with muscular walls
Low-grade endometrial stromal sarcoma: infiltrative margin or angiolymphatic invasion
Uterine tumors resembling ovarian sex-cord tumors: tubules resembling ovarian sex-cord tumors, less cellular, often mature smooth muscle, no prominent arterioles

Additional references

Gynecol Oncol 2010;116:131

End of Uterus > Stromal tumors > Endometrial stromal nodule

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