Endometrial stromal sarcoma (ESS) is a rare uterine sarcoma arising from endometrial stromal cells, accounting for <1% of all uterine malignancies. It has two main subtypes: low-grade (LG-ESS) and high-grade (HG-ESS). LG-ESS typically occurs in premenopausal or early postmenopausal women (mean age 40-55) and shows an indolent course. HG-ESS occurs at a more advanced age with aggressive behavior. The pathognomonic imaging finding is the worm-like extension of the tumor within the myometrium and intravascular extension into parametrial/uterine veins/gonadal veins/IVC. This intravascular extension is the most specific finding differentiating ESS from other uterine malignancies. It is hormonally sensitive (estrogen/progesterone receptor positive) and responds to hormonal therapy.
Age Range
40-65
Peak Age
50
Gender
Female predominant
Prevalence
Rare
Endometrial stromal sarcoma is a mesenchymal neoplasm arising from endometrial stromal cells. In LG-ESS, the JAZF1-SUZ12 (JJAZ1) fusion gene is characteristic (50-75%) — this genetic alteration leads to low-grade malignant transformation of normal endometrial stromal cells. In HG-ESS, YWHAE-NUTM2A/B fusion or BCOR genetic alterations are seen — associated with more aggressive biology. The most striking feature of the tumor is its infiltrative growth pattern: the tumor sends worm-like extensions between smooth muscle fibers of the myometrium — these extensions also advance into myometrial vessels, showing intravascular growth. This intravascular extension can progress from parametrial veins to uterine veins, gonadal veins, and even the IVC — resembling 'intravenous leiomyomatosis' but is a malignant process. Imaging findings reflect this pathology: T2 shows multiple high-signal nodular/linear extensions within the myometrium (worm-like pattern). Intravascular extension is detected as filling defect and enhancing tissue within vessels on contrast-enhanced MRI. LG-ESS expresses estrogen receptor (ER) and progesterone receptor (PR) — this hormonal sensitivity is used in treatment and produces adenomyosis/endometriosis-like symptoms. Diffusion restriction reflects cellular density — less pronounced in LG-ESS, more pronounced in HG-ESS.
The combination of worm-like T2-hyperintense extensions within the myometrium + intravascular tumor extension in parametrial/uterine veins on T2-weighted MRI is pathognomonic for ESS. No other uterine neoplasm demonstrates both findings together.
On T2-weighted MRI, ESS appears as T2-hyperintense nodular/linear extensions extending from the endometrial cavity into the myometrium — the 'worm-like' infiltrative pattern is pathognomonic. Extensions branch between smooth muscle fibers of the myometrium, making the myometrium heterogeneous. LG-ESS usually shows homogeneous T2 hyperintense signal (similar to normal endometrial stroma). HG-ESS may show more heterogeneous signal (necrosis areas). The mass usually shows continuity with the endometrial cavity — polypoid component in the cavity and infiltrative component in the myometrium coexist.
Report Sentence
Worm-like T2 hyperintense extensions are identified within the myometrium showing continuity with the endometrial cavity on T2-weighted sequences, a pathognomonic finding consistent with endometrial stromal sarcoma.
The most specific finding of ESS on contrast-enhanced MRI is intravascular extension. The tumor can extend from parametrial veins to uterine veins, gonadal veins, and even the IVC — detected as enhancing tumor tissue or filling defect within vessels. Intravascular extension is particularly common in LG-ESS and may also be seen as a recurrence pattern. Intravascular extension is best evaluated with contrast-enhanced MR venographic sequences (MRV) or dynamic contrast-enhanced sequences. This finding directly affects surgical planning — vascular surgeon involvement may be needed.
Report Sentence
Enhancing tumor tissue is identified within the [parametrial vein / uterine vein / gonadal vein / IVC] on contrast-enhanced MRI with intravascular extension detected, a pathognomonic finding consistent with endometrial stromal sarcoma.
ESS shows grade-dependent diffusion restriction on DWI. LG-ESS shows mild-to-moderate restriction due to lower cellularity — ADC values are generally between 1.0-1.4 x 10-3 mm2/s. HG-ESS shows more pronounced restriction due to higher cellularity — ADC values may be <1.0 x 10-3 mm2/s. DWI is also valuable in addition to T2 for detecting myometrial infiltrative extensions — DWI may show extensions more prominently, especially in LG-ESS. Intravascular extension may also be detected with DWI.
Report Sentence
Mild-to-moderate / marked] diffusion restriction is identified in the myometrial mass and infiltrative extensions on DWI; ADC values are consistent with [low-grade / high-grade] endometrial stromal sarcoma.
Contrast-enhanced CT shows ESS as a heterogeneously enhancing mass in the uterine cavity and/or myometrium. CT's most important contribution is in detecting intravascular extension — filling defect or enhancing tumor tissue is detected in parametrial veins, uterine veins, gonadal veins, and IVC. CT also evaluates pelvic/para-aortic lymph nodes, peritoneal spread, and distant metastasis (lung most common). Worm-like myometrial extensions are not as clearly seen on CT as on MRI — due to soft tissue contrast limitations.
Report Sentence
A filling defect is identified within the [parametrial/uterine/gonadal vein / IVC] along with a uterine mass on contrast-enhanced CT with intravascular tumor extension detected, consistent with endometrial stromal sarcoma.
Transvaginal US shows ESS as a heterogeneous echogenicity myometrial mass — irregular margins, cystic areas (necrosis/hemorrhage), and increased Doppler flow may be seen. Worm-like myometrial extensions may appear as fine infiltrative structures difficult to demonstrate on US. US is limited in differentiating from adenomyosis or leiomyoma. Intravascular extension may be detected with Doppler US — seen as filling defect or solid vascular content in parametrial/uterine veins.
Report Sentence
A heterogeneous mass is identified in the myometrium on US with irregular margins and increased Doppler flow; endometrial stromal sarcoma should be considered in the differential diagnosis, MRI characterization is recommended.
Criteria
Most common subtype. JAZF1-SUZ12 fusion gene (50-75%). Low mitotic activity (<5 mitoses/10 HPF). Minimal necrosis. ER/PR positive. Homogeneous cells similar to normal endometrial stroma. In premenopausal/early postmenopausal women.
Distinct Features
Indolent course, late recurrence (even 10-20 years later), intravascular extension common, responsive to hormonal therapy (aromatase inhibitors, megestrol), homogeneous hyperintense on T2, good prognosis (80-90% 5-year survival).
Criteria
YWHAE-NUTM2A/B fusion or BCOR alterations. High mitotic activity (>10 mitoses/10 HPF). Necrosis common. ER/PR negative or weakly positive. Round cell morphology or fusiform cells. Older age.
Distinct Features
Aggressive course, early recurrence, unresponsive to hormonal therapy, marked restriction on DWI, heterogeneous T2 signal (necrosis), poor prognosis (30-50% 5-year survival), chemotherapy (doxorubicin/ifosfamide) may be needed.
Criteria
Previously classified as 'high-grade ESS' but now a separate entity. High-grade sarcoma showing no specific differentiation. Pleomorphic, high mitotic activity, extensive necrosis. No specific genetic alteration identified.
Distinct Features
Most aggressive subtype, markedly heterogeneous signal on T2 (extensive necrosis), very pronounced restriction on DWI, worst prognosis (20-30% 5-year survival), indistinguishable from leiomyosarcoma and carcinosarcoma on imaging.
Distinguishing Feature
Leiomyosarcoma grows as an intramural mass, does not show worm-like infiltrative extension, intravascular extension is not seen (rarely), coagulative necrosis T1 hyperintense, T2 heterogeneous but not infiltrative.
Distinguishing Feature
Adenomyosis shows JZ thickening (>12 mm), may be diffuse or focal, small cystic areas on T2 (ectopic endometrial glands), small hyperintense foci on T1 (hemorrhage), no DWI restriction, no intravascular extension.
Distinguishing Feature
Endometrial carcinoma invades from the endometrial cavity into myometrium but does not show worm-like extension — recognized by JZ disruption, intravascular extension not seen (rarely LVSI), is an epithelial tumor.
Distinguishing Feature
Leiomyoma is well-defined, T2 homogeneous hypointense, pushes but does not infiltrate the myometrium with mass effect, no intravascular extension, no DWI restriction.
Urgency
urgentManagement
surgicalBiopsy
NeededFollow-up
specialist-referralWhen worm-like infiltrative pattern and/or intravascular extension is detected on preoperative MRI, ESS should be strongly considered. Standard treatment is total hysterectomy + bilateral salpingo-oophorectomy. Ovarian preservation in LG-ESS is controversial (oophorectomy is preferred due to estrogen sensitivity). Vascular surgeon involvement is needed in the presence of intravascular extension — cardiovascular surgery collaboration may be required in cases extending to the IVC. Adjuvant hormonal therapy (aromatase inhibitors: letrozole/anastrozole, or megestrol/medroxyprogesterone) is applied long-term in LG-ESS — ER/PR positivity guides treatment selection. Chemotherapy (doxorubicin/ifosfamide) may be needed in HG-ESS. Long-term follow-up is mandatory — LG-ESS can recur even 10-20 years later. Recurrence is usually pelvic (local) or lung metastasis.
Low-grade ESS has a relatively good prognosis but late recurrence is common (even after 10-20 years). It is hormone-sensitive — ovarian preservation is controversial. High-grade ESS is aggressive with poor prognosis. Surgery is the primary treatment. Hormonal therapy can be used for recurrences in low-grade disease.