1409 imaging the endometrium: disease and normal...

EDUCATION EXHIBIT 1409

Imaging theEndometrium: Diseaseand Normal Variants1

LEARNINGOBJECTIVESFOR TEST 2After reading thisarticle and takingthe test, the reader

will be able to:

� Recognize the nor-mal and pathologicappearances of theendometrium at US,CT, and MR imag-ing.

� Discuss causes andpatterns of endome-trial thickening.

� Understand theroles of US and MRimaging in the evalu-ation of the post-menopausal endome-trium.

Kenneth M. Nalaboff, MD ● John S. Pellerito, MD ● Eran Ben-Levi, MD

The endometrium demonstrates a wide spectrum of normal and patho-logic appearances throughout menarche as well as during the prepu-bertal and postmenopausal years and the first trimester of pregnancy.Disease entities include hydrocolpos, hydrometrocolpos, and ovariancysts in pediatric patients; gestational trophoblastic disease duringpregnancy; endometritis and retained products of conception in thepostpartum period; and bleeding caused by polyps, submucosal fi-broids, endometrial hyperplasia, or endometrial adenocarcinoma.Other findings include tamoxifen-associated changes, intrauterine fluidcollections, and endometrial adhesions. Although ultrasound (US) isalmost always the first modality used in the radiologic work-up of en-dometrial disease, findings at sonohysterography, hysterosalpingogra-phy, magnetic resonance imaging, and computed tomography are oftencorrelated with US findings. It is important to understand that the ap-pearance of the endometrium is related to multiple factors, includingthe patient’s age, stage in the menstrual cycle, and pregnancy statusand whether she has undergone hormonal replacement therapy or ta-moxifen therapy. Accurate diagnosis requires that these factors betaken into account in addition to clinical history and physical examina-tion findings.

Abbreviations: IUD � intrauterine device, IUP � intrauterine pregnancy, RPOC � retained products of conception

Index terms: Uterus, CT, 854.1211 ● Uterus, diseases, 854.20, 854.30 ● Uterus, endometrium, 854.1478, 854.1495, 854.31, 854.324, 854.82Uterus, hemorrhage ● Uterus, MR, 854.1214 ● Uterus, myometrium ● Uterus, US, 854.1298

RadioGraphics 2001; 21:1409–1424

1From the Department of Radiology, North Shore University Hospital, 300 Community Dr, Manhasset, NY 11030. Presented as a scientific exhibit atthe 1999 RSNA scientific assembly. Received November 17, 2000; revision requested January 17 and received August 1; accepted August 8. Addresscorrespondence to J.S.P. (e-mail: [email protected]).

©RSNA, 2001

CME FEATURESee accompanying

test at http://www.rsna.org

/education/rg_cme.html

IntroductionEndometrial abnormalities are common diagnos-tic challenges facing the radiologist and referringgynecologist. Ultrasound (US) is the primary im-aging modality in this setting, but findings at sono-hysterography and magnetic resonance (MR) im-aging are often correlated with US findings. Inthis article, we review the current approach toendometrial imaging and demonstrate the spec-trum of normal and pathologic findings in pediat-ric, premenopausal, pregnant, postpartum, andpostmenopausal patients.

Pediatric Endometrium

Normal AppearanceCharacteristic morphologic changes take place inthe uterus and endometrium over time. At birth,the uterus is similar in size to the cervix (2.3–4.6cm), and the endometrium generally appears as athin, echogenic line (Fig 1) (1). Approximatelyone-fourth of neonates will have fluid collectionswithin the endometrial cavity (1). Once puberty isreached, the appearance of the endometrium be-gins to approximate that seen in adulthood andvaries with the stage of the menstrual cycle.

Pathologic AppearancesThe most common pelvic masses in neonates in-clude hydrocolpos, hydrometrocolpos, and ovar-ian cysts. Hydrocolpos is characterized by disten-tion of the vagina. Hydrometrocolpos is charac-terized by dilatation of both the uterus and vagina(with the vagina usually being distended to a

greater extent [2]) with serous fluid and possiblyurine if there is a urogenital sinus. The endome-trium is intrinsically normal, but the endometrialcavity is distended with fluid. Both hydrocolposand hydrometrocolpos result from vaginal or cer-vical stenosis, hypoplasia, or agenesis (Meyer-Rokitansky-Kuster-Houser syndrome), which isoften associated with congenital anomalies (1).US demonstrates a cystic midline mass with inter-nal echoes representing mucoid material and cel-lular debris.

On the other hand, hematocolpos and hema-tometrocolpos in adolescent girls are generallyassociated with an imperforate hymen without anincrease in associated congenital anomalies. USdemonstrates an echogenic, tubular, cystic mid-line mass with internal echoes representing fluidand debris (Fig 2) (3).

Premenopausal Endometrium

Normal AppearanceDuring menstruation, the endometrium appearsas a thin, echogenic line 1–4 mm in thickness(Fig 3) (4,5). The endometrium is usually bestseen on endovaginal scans. Endometrial thicknessis measured from echogenic border to echogenicborder across the endometrial cavity on a sagittalmidline image. Intraluminal blood or sheets ofsloughed endometria may be identified. Once theproliferative phase of the menstrual cycle (days6–14) begins, the endometrium becomes thicker(5–7 mm) and more echogenic relative to themyometrium, reflecting the development ofglands, blood vessels, and stroma (5). In the lateproliferative (periovulatory) phase, the endome-trium develops a multilayered appearance with anechogenic basal layer and hypoechoic inner func-

Figure 1. Normal pediatric endometrium. SagittalUS image of the uterus in a 2-year-old girl demon-strates a thin endometrium (arrow).

Figure 2. Hematometrocolpos in a 12-year-old girlwith abdominal pain. Sagittal US image demonstrates amarkedly distended vagina (straight arrow) and uterinecavity (curved arrow).

1410 November-December 2001 RG f Volume 21 ● Number 6

tional layer, separated by a thin echogenic medianlayer arising from the central interface or luminalcontent (Fig 4). In this stage, the endometriummay measure up to 11 mm in thickness. The lay-ered appearance usually disappears 48 hours afterovulation. During the secretory phase, the endo-metrium becomes even thicker (7–16 mm) andmore echogenic (Fig 5) (4,5). This increasedechogenicity is thought to be related to stromaledema and glands distended with mucus and gly-cogen. Stromal edema also accounts for the in-creased posterior acoustic enhancement that maybe seen (5). The endometrium typically reaches a

maximum thickness during the midsecretoryphase (4). The appearances of normal and abnor-mal endometrium, such as in the setting of endo-metrial hyperplasia, may overlap. Cyclic ovarianchanges parallel the endometrial changes in thefollicular and luteal phases.

The MR imaging appearance of normal endo-metrium is best demonstrated on T2-weightedimages because the uterus has homogeneous in-termediate signal intensity with T1-weighted se-quences. T2-weighted images delineate the uter-ine zonal anatomy. The normal endometrium isof uniformly high signal intensity, and the innermyometrium, or junctional zone, is of uniformlylow signal intensity (Fig 6).

Figure 3. Normal premenopausal endometrium.Sagittal US image of the uterus obtained during men-struation shows a thin endometrial lining (arrow) witha trace of fluid.

Figure 4. Normal premenopausal endometrium.Sagittal US image of the uterus obtained during thelate proliferative phase of the menstrual cycle demon-strates the endometrium with a multilayered appear-ance (arrows).

Figure 5. Normal premenopausal endometrium.Sagittal US image of the uterus obtained during thesecretory phase of the menstrual cycle shows a thick-ened, echogenic endometrium (cursors).

Figure 6. Normal premenopausal endometrium. T2-weighted MR image shows the normal endometrium(straight arrow) and junctional zone (curved arrow).

RG f Volume 21 ● Number 6 Nalaboff et al 1411

Appearance during PregnancyTransvaginal US is the primary modality forevaluation of an early intrauterine pregnancy(IUP). The appearance of an IUP depends ongestational age. The normal gestational sac can beseen at 4.5 weeks gestation and should be visual-ized when greater than 5 mm in length (6,7). Theyolk sac should be visualized between 5 and 6weeks gestation, and an embryo may be seen be-fore 6 weeks gestation (8). The normal gesta-tional sac appears as an oval or rounded anechoicspace within the endometrium surrounded by ahyperechoic rim at least 2 mm in thickness, andthe sac should grow at a rate exceeding 1.2 mmper day (8). It should be located in the upper ormiddle uterine segment, midway between the twoapposed uterine walls (6). A low position in theendometrial cavity suggests an impending or on-going miscarriage, a cervical ectopic pregnancy,or a fundal fibroid compressing the sac downward(8). The presence of placental flow in a cervicalectopic pregnancy or low-lying sac is useful indistinguishing these entities from an abortion inprogress.

Prior to visualization of a yolk sac or embryo,two US signs assist in the diagnosis of a normalIUP. The intradecidual sign occurs before 5

weeks gestational age, when the sac is too small toindent or deform the central endometrial echo(9). The sac appears as a rounded, hyperechoicarea surrounding a small anechoic area within thethickened decidua. After 5 weeks gestational age,the double decidual sac sign may be seen (Fig 7)(10). The double decidual sac sign appears as ahyperechoic ring about the sac surrounded by asecond hyperechoic ring, with a hypoechoic lineinterposed between the two echogenic rings dueto apposition of the endometrial walls.

Although many findings suggestive of or diag-nostic for an ectopic pregnancy can be seen out-side the uterine cavity (eg, living embryo, tubalring sign, fluid in the cul-de-sac, adnexal mass),various endometrial changes may also be seen. Apseudogestational sac is an intrauterine findingthat is seen in 10%–20% of ectopic pregnancies(11). It may range in appearance from anechoicfluid to echogenic material (in which case it iscalled a decidual cast) in the uterine cavity (Fig 8)and is related to the hormonal effects of the preg-nancy. Apparent endometrial thickening in thesetting of a positive pregnancy test may in factrepresent an echogenic decidual cast in the endo-metrium, although retained products of concep-tion (RPOC) may have a similar appearance.There is no associated double decidual sign.

The double decidual and intradecidual signsmay not be seen in early abnormal IUPs, andtheir absence does not exclude a normal IUP. A

Figure 7. Double decidual sac sign. US image of anearly IUP demonstrates two hyperechoic rings (ar-rows). The inner ring represents the combined cho-rion-decidua capsularis, and the outer ring representsthe decidua parietalis.

Figure 8. Decidual cast. Transabdominal US imagereveals echogenic material within the endometrium(cursors).


thin decidual reaction of less than 2 mm, an ab-normally shaped sac, or a gestational sac in a lowuterine location suggests an abnormal pregnancy.An empty gestational sac may represent a blightedovum (mean gestational sac diameter, �10 mm[6,12]) (Fig 9), an early IUP, or the pseudogesta-

tional sac of an ectopic pregnancy (Fig 10). Ab-sent fetal cardiac activity when the crown-rumplength is greater than 5 mm is indicative of em-bryonic demise (13). RPOC may appear as anill-defined intrauterine collection with mixedechogenicity.

Gestational trophoblastic disease is a prolifera-tive disease of the trophoblast that may manifestas a complete or partial hydatidiform mole, inva-sive mole, or choriocarcinoma. A hydatidiformmole, the most common form of gestational tro-phoblastic disease, is noninvasive and usuallymanifests in the second and third trimesters. Thistype of mole distends and fills the endometrialcavity without invading the myometrium. USdemonstrates a uterus that is enlarged for gesta-tional age and filled with multiple small, hyper-echoic areas 3–10 mm in diameter with good pos-terior acoustic enhancement (Fig 11). The cystsrepresent grossly swollen villi from trophoblastichyperplasia. During the first trimester, the molartissue may appear as a homogeneously echogenicendometrial mass. In cases of partial molar preg-nancy, part of the fetus will be identified. DopplerUS of the tissue may reveal trophoblastic flowgreater than 21 cm/sec (14).

Figure 9. Blighted ovum. US image shows the gesta-tional sac with no visible embryo or yolk sac. A smallsubchorionic hematoma is noted (arrow).

Figure 10. Pseudogestational sac. Transvaginal colorDoppler US image demonstrates an irregular saclikestructure in the endometrial canal (arrows), normalflow in the myometrium, and decreased vascularity ad-jacent to the pseudogestational sac.

Figure 11. Molar pregnancy. US image demon-strates an echogenic mass in the uterine cavity withmultiple small, hyperechoic areas (arrowheads).


Postpartum Endometrium

Normal AppearanceThe normal US appearance of the postpartumpelvis includes uterine enlargement and an endo-metrial cavity less than 2 cm in anteroposteriordiameter (15). The cavity wall has a variable ap-pearance ranging from smooth, well-defined bor-ders to irregular, heterogeneous linings, with con-siderable overlap between normal and abnormalcases (15). Small echogenic foci within the endo-metrial cavity may not be pathologic, instead rep-resenting retained membranes and clots not com-pletely expelled with the placenta (15). Althoughthe presence of intrauterine air, as demonstratedby tiny internal echoes at US or foci of very lowattenuation at computed tomography (CT), isconsistent with endometritis in the appropriateclinical setting, it may also be seen in up to 21%of healthy patients in the postpartum period (16).Clot and debris are seen in 24% of cases after de-livery (17). The thickness of the endometrialstripe decreases with involution of the uterus dur-ing puerperium, and if the endometrial cavity re-mains thickened, complications such as RPOC orhypotonic uterus should be suspected.

Pathologic AppearancesEndometritis, the most common cause of fever inthe postpartum period, complicates 2%–3% ofvaginal deliveries and up to 85% of cesarean sec-tions (18). It is also associated with prolonged

labor, premature rupture of membranes, retainedclots, and RPOC. Although the US appearanceof the uterus and endometrium may be normal,findings may include a thickened, heterogeneousendometrium, intracavitary fluid, and intrauterineair (Fig 12).

Postpartum hemorrhage is most often causedby uterine atony and RPOC and complicates1%–2% of vaginal deliveries (19). There can beconsiderable overlap in the US appearance ofthese two entities. They can be distinguishedclinically because uterine atony is seen in the im-mediate postpartum period and RPOC usuallycauses hemorrhage or infection at a later date. Anormal-appearing uterus and endometrial cavity

Figure 12. Endometritis. US image demonstratesmultiple echogenic foci within the endometrium (ar-row) representing gas.


in the presence of postpartum hemorrhage indi-cates uterine atony, whereas an echogenic intra-cavitary mass is suggestive of RPOC (Fig 13a)(20). If the mass remains attached to the endome-trium, a finding of high-velocity, low-resistanceflow at color Doppler US is suspicious for RPOC.A peak systolic velocity of 21 cm/sec is used as theminimum threshold for the diagnosis of residualtrophoblastic tissue (Fig 13b) (14). It should benoted that the lack of increased flow does not

eliminate the possibility of RPOC. RPOC that areseen late after delivery may contain calcifications(Fig 14). MR imaging depicts RPOC as an eccen-tric, enhancing intrauterine mass. CT may nothelp distinguish between RPOC and intrauterineclot because both processes can appear as densemasses (21).

Postmenopausal Endometrium

Normal AppearanceThe postmenopausal examination should takeinto consideration the patient’s clinical history(eg, vaginal bleeding) and whether she has under-gone hormonal replacement therapy. The normalpostmenopausal endometrium should appearthin, homogeneous, and echogenic. There is con-troversy regarding endometrial thickness withmenopause. Although some authors have found

Figures 13, 14. (13) RPOC. (a) US image shows echo-genic material within the endometrial canal (arrows).(b) Color Doppler US image (shown in black and white)demonstrates low-resistance arterial flow within RPOC.Peak systolic velocity was 22 cm/sec. (14) RPOC with cal-cifications. US image shows echogenic material with pos-terior acoustic shadowing (arrow), a finding that is consis-tent with calcified RPOC.


that endometrial thickness decreases with age(22,23), others believe there is no statistically sig-nificant change during menopause (24). In gen-eral, a double-layer thickness of less than 5 mmwithout focal thickening excludes significant dis-ease and is consistent with atrophy (25–27). Ho-mogeneous, smooth endometria measuring 5 mmor less are considered within the normal rangewith or without hormonal replacement therapy(28). The endometrium in a patient undergoinghormonal replacement therapy may vary up to 3mm if cyclic estrogen and progestin therapy isbeing used (22). The endometrium will appearthickest prior to progestin exposure and thinnestafter the progestin phase. Imaging should be per-formed at the beginning or end of a cycle of treat-ment, when the endometrium will be at its thin-nest and any pathologic thickening will be mostprominent. A patient undergoing unopposed es-trogen therapy with endometrial thickening ex-ceeding 8 mm should be considered for biopsy,whereas patients receiving progesterone in addi-tion to estrogen can be rescanned at the begin-

ning or end of the following cycle to determine ifthere has been a change in endometrial thickness(22).

Postmenopausal BleedingCauses of postmenopausal bleeding include en-dometrial atrophy (approximately 75% of cases),endometrial polyps, submucosal fibroids, endo-metrial hyperplasia, endometrial carcinoma (ap-proximately 10%), and estrogen withdrawal (5).Imaging should take place immediately afterbleeding has stopped, when the endometrium ispresumed to be thinnest and any disease entitywill be most prominent. Endometrial thicknessless than 4–5 mm at transvaginal US generallyexcludes cancer (Fig 15) (27). The atrophic post-menopausal endometrium may also be appreci-ated at MR imaging (Fig 16). Any thicknessgreater than 5 mm in the setting of postmeno-pausal bleeding or any endometrial heterogeneityor focal thickening seen at transvaginal US shouldbe investigated further with sonohysterography,biopsy, or hysteroscopy. Endometrial sampling inthe gynecologist’s office can lead to false-negativeresults if a focal abnormality is not sampled.

Figures 15, 16. Postmenopausal endometrial atrophy. (15) Transvaginal US image demonstrates a postmeno-pausal endometrium with thin walls and outlined with fluid. (16) T2-weighted MR image demonstrates an atrophicpostmenopausal endometrium (arrows).


Endometrial Polyps.—Endometrial polyps area common cause of postmenopausal bleeding andare most frequently seen in patients receiving ta-moxifen. Although endometrial polyps may bevisualized at transvaginal US as nonspecific endo-metrial thickening, they are frequently identifiedas focal masses within the endometrial canal. Pol-yps are best seen at sonohysterography and ap-

pear as echogenic, smooth, intracavitary massesoutlined by fluid (Fig 17) (29,30). Cystic spacescorresponding to dilated glands filled with pro-teinaceous fluid may be seen within the polyp(31). The polyp may be broad-based and sessileor pedunculated. The point of attachment shouldnot disrupt the endometrial lining (30). Polypsmay also be seen at hysterosalpingography as pe-dunculated filling defects within the uterine cavity(Fig 18) or at T2-weighted MR imaging as low-signal-intensity intracavitary masses surroundedby high-signal-intensity fluid and endometrium(Fig 19). Color Doppler US may be used to im-age vessels within the stalk. Fibroids or foci ofendometrial hyperplasia or carcinoma can mimica sessile polyp, and foci of atypical hyperplasia aresometimes found within polyps (30,32).

Submucosal Fibroids.—Uterine leiomyomasare benign soft-tissue tumors that occur in pa-tients of all ages. Although their size and fre-quency increases with age, they may grow untilmenopause and then involute and are a causeof premenopausal uterine bleeding. They arecommonly identified at US as hypoechoic solid

Figure 17. Endometrial polyp. Sonohysterogramreveals a small polyp attached by a stalk to the endome-trium (black arrow). An echogenic focus in the endo-metrial cavity (white arrow) represents injected air.

Figure 18. Endometrial polyp. Anteroposterior (left)and oblique (right) hysterosalpingograms demonstratea pedunculated filling defect within the uterine cavity(arrows).

Figure 19. Endometrial polyp. T2-weighted MR im-age demonstrates a low-signal-intensity lesion withinthe endometrial canal (arrow).


masses, but they may be heterogeneous or hy-perechoic, depending on the degree of degenera-tion and calcification. Fibroids tend not to inter-rupt the endometrium unless they are submucosal

in location. Submucosal fibroids may distort theuterine cavity with varying degrees of intracavi-tary extension and are best visualized at sonohys-terography (Fig 20). Hysteroscopy can depictonly the intracavitary portion of the fibroid (33).

Figure 20. Submucosal fibroid. (a) Transvaginal US image reveals a uterine mass (arrows) with posterior acousticshadowing. (b) Sonohysterogram reveals that the mass is submucosal in location, a finding that is consistent with anechogenic fibroid.

Figures 21, 22. Submucosal fibroids. (21) Oblique (left) and anteroposterior (right) hysterosalpingograms demon-strate smooth filling defects distorting the uterine cavity and representing submucosal fibroids. (22) T2-weighted MRimage shows a hypointense submucosal fibroid splaying the endometrium (arrows).


Determining the intracavitary extent of a leiomy-oma is important for surgical management be-cause hysteroscopic myomectomy can be per-formed if over one-half the volume of the mass iswithin the endometrial canal (34).

At hysterosalpingography, submucosal fibroidsare seen as filling defects with enlargement or de-formity of the uterine cavity (Fig 21). At T1-weighted MR imaging, fibroids appear iso- to hy-pointense relative to the myometrium, whereas atT2-weighted imaging they appear homogeneouslyhypointense or heterogeneously hyperintensewhen degeneration is present (Fig 22).

Endometrial Hyperplasia.—Endometrial hy-perplasia is an abnormal proliferation of endome-trial stroma and glands and represents a spectrumof endometrial changes ranging from glandularatypia to frank neoplasia. A definitive diagnosiscan be made only with biopsy, and imaging can-not reliably allow differentiation between hyper-plasia and carcinoma. Up to one-third of endo-metrial carcinoma is believed to be preceded byhyperplasia (35).

All types of endometrial hyperplasia (cystic,adenomatous, atypical) can cause diffuselysmooth or, less commonly, focal hyperechoic en-dometrial thickening (Fig 23). The US appear-ance can simulate that of normal thickening dur-ing the secretory phase, sessile polyps, submuco-sal fibroids, cancer, and adherent blood clots,yielding potentially false-positive results (32). En-dometrial hyperplasia is considered whenever theendometrium appears to exceed 10 mm in thick-ness, especially in menopausal patients (36), al-though it can be reliably excluded in these pa-tients only when the endometrium measures lessthan 6 mm. Endometrial hyperplasia may alsocause asymmetric thickening with surface irregu-larity, an appearance that is suspicious for carci-noma. Because endometrial hyperplasia has anonspecific appearance, any focal abnormalityshould lead to biopsy if there is clinical suspicionfor malignancy.

Endometrial Adenocarcinoma.—Endometrialadenocarcinoma is the most common invasivegynecologic malignancy, but thanks to early de-tection and treatment, it is not a leading cause ofcancer deaths. US signs of endometrial carcinomainclude heterogeneity and irregular endometrialthickening (Fig 24a). These signs are nonspecificand can be seen in endometrial hyperplasia aswell as polyps, leading to biopsy of almost anyirregularity in the setting of postmenopausalbleeding. However, polypoid tumors tend tocause more diffuse and irregular thickening than apolyp and more heterogeneity than endometrialhyperplasia (37). A more specific US sign is ir-regularity of the endometrium-myometrium bor-der, a finding that indicates invasive disease. Asmall amount of fluid in the endometrial canal islikely related to benign cervical stenosis and doesnot require further evaluation. An intrauterinefluid collection in a postmenopausal patient, al-though possibly related to cervical stenosis,should raise concern for endometrial (or cervi-cal) carcinoma.

Figure 23. Endometrial hyperplasia. US imageshows an endometrium with diffuse thickening (maxi-mum thickness, 1.74 cm) due to hyperplasia (cursors).This finding was confirmed at biopsy.


The value of Doppler and color Doppler US indistinguishing benign from malignant endome-trial disease is controversial. It has been suggestedthat low-impedance blood flow at Doppler UScan be associated with malignancy (38). In-creased focal vascularity may be seen at colorDoppler US in both benign and malignant dis-eases of the endometrium. Significant overlap inDoppler indices (ie, peak systolic velocity, resis-tive index, pulsatility index) in benign and malig-nant endometrial processes reduces the valueof Doppler US in characterizing endometrialmasses. Color and power Doppler US may occa-sionally aid in determining the presence and ex-tent of tumor invasion and ensuring that biopsiesare directed toward regions with increased bloodflow (5).

MR imaging is valuable in the evaluation ofendometrial cancer. Endometrial carcinoma usu-ally manifests as a mass that, relative to normalendometrium, is hypo- to isointense on T1-weighted images and hyperintense or heteroge-neous on T2-weighted images. Although MR im-aging is not helpful in differentiating endometrialcarcinoma from hyperplasia, it is helpful in cancerstaging. Tumors are staged on the basis of depthof myometrial invasion. T1-weighted gadolinium-

enhanced MR imaging is helpful in demonstrat-ing myometrial invasion because a carcinoma willenhance less than normal endometrium. Superfi-cial invasion involves only the inner half of themyometrium, whereas deep invasion involves theouter half of the myometrium and beyond (Fig24b). If the normal low-signal-intensity junction-al zone is intact, myometrial invasion can mostlikely be excluded. If the junctional zone isthinned due to atrophy or distention from clot,fluid, or polypoid tumor and is not well visual-ized, the presence of myometrial invasion is indi-cated by loss of the normal endometrium-myo-metrium interface. An irregular interface suggestsinvasion. Both MR imaging and CT (Fig 24c) areuseful in demonstrating extrauterine spread andlymphadenopathy.

Figure 24. Endometrial adenocarcinoma. (a) US imagereveals a heterogeneous endometrial mass (arrows) that isdifficult to distinguish from the myometrium. Cursors in-dicate the entire transverse width of the uterus. (b) T2-weighted MR image shows a large, heterogeneous tumordistending the endometrial canal (arrows). (c) CT scanalso reveals a heterogeneous tumor (arrowheads).


Tamoxifen-associated ChangesTamoxifen has proestrogenic effects on the endo-metrium and is associated with an increasedprevalence of endometrial hyperplasia, polyps,and carcinoma (39,40). Up to one-half of breastcancer patients who are treated with this medica-tion may develop an endometrial lesion within6–36 months (40). Therefore, any patient who

develops bleeding while taking tamoxifen requiresevaluation. Tamoxifen causes the endometriumto appear thickened, irregular, and cystic at US(Fig 25). The punctate cystic spaces may be sec-ondary to reactivation of adenomyosis within theinner myometrium or to obstructed glands in theendometrium due to the drug’s weak estrogeniceffects (41). It has also been reported that the de-gree of endometrial thickening corresponds to theduration of tamoxifen therapy (42).

Two MR imaging patterns associated with ta-moxifen have been described (43). The first pat-tern manifests as homogeneous high signal inten-sity on T2-weighted images, contrast materialenhancement of the endometrium-myometriuminterface, and signal void within the endometriallumen on T1-weighted images. This pattern wasfound to be associated with endometrial atrophyor proliferative changes. The second patternmanifests as heterogeneous signal intensity onT2-weighted images (Fig 26) and lattice-like en-hancement traversing the endometrial canal onT1-weighted images. This pattern was found tobe associated with polyps, and it is believed thatthe lattice-like appearance may represent enhanc-ing interstices between cysts within a polyp. Inaddition, an enhancing stalk may be seen if thepolyp is pedunculated.

Figure 25. Endometrial thickening associated with tamoxifen therapy. (a) US image reveals marked endometrialthickening (arrowheads) associated with subendometrial cysts (arrows) resulting from tamoxifen therapy. (b) Sono-hysterogram demonstrates that the endometrial thickening is secondary to a large polyp (arrows).

Figure 26. Endometrial thickening associated withtamoxifen therapy. T2-weighted MR image shows athickened endometrium (straight arrows) with focalareas of decreased signal intensity (curved arrow) asso-ciated with polyps resulting from tamoxifen therapy.


Intrauterine Fluid CollectionsAlthough a tiny amount of fluid within the post-menopausal endometrial canal may be considerednormal (44), any significant fluid collection is ab-normal and requires careful evaluation of theuterus and adnexal structures for associated find-ings. Intrauterine fluid collections are associatedwith both endometrial and cervical cancers (45–47). An obstructing tumor must be excluded evenwhen cervical stenosis has been identified clini-cally. In premenopausal patients, fluid collectionsare most commonly associated with menstrua-tion, early IUP, or the pseudogestational sac in anectopic pregnancy. In prepubertal patients, fluidin the endometrial canal may be related to hema-tometrocolpos. Other benign causes of obstruc-tion leading to intrauterine fluid production in-clude polyps, infection, and submucosal fibroids.The fluid may range in appearance from hypo-echoic to hyperechoic depending on whether it iscomposed of serum, mucin, or blood.

Endometrial AdhesionsEndometrial adhesions are posttraumatic or post-surgical in nature and can cause Asherman syn-drome, which includes infertility, recurrent preg-nancy loss, and amenorrhea. Adequate distentionof the endometrial cavity seen at sonohysterogra-phy or hysterosalpingography is necessary for ra-diologic diagnosis. Sonohysterography may dem-onstrate synechiae as echogenic bands bridgingthe uterine cavity. If the bands are thick and fi-brotic, they may prevent complete uterine disten-tion. Hysterosalpingography will demonstrate

similar findings, with incomplete filling of the en-dometrial cavity and numerous irregular fillingdefects (Fig 27). Sonohysterography or hystero-salpingography may also be used to documentresolution following hysteroscopic lysis.

Intrauterine Contraceptive DevicesIntrauterine contraceptive devices (IUD) shouldlie within the endometrial cavity and serve to pre-vent implantation of the embryo. IUDs should bereadily detected at US as highly echogenic struc-tures with distal acoustic shadowing (Fig 28). En-dovaginal US is useful when distinction betweenthe IUD and normal endometrial stripe cannot bemade transabdominally. Penetration of the myo-metrial wall by the IUD may also be seen at US.If US cannot help identify an IUD within the en-dometrial canal, conventional radiography or CTmay be performed to determine whether it lieswithin the peritoneal cavity. If so, the diagnosis ofperforation of the uterine wall can be made (4).

ConclusionsThere are many different imaging appearances ofthe normal and abnormal endometrium. Al-though US is almost always the first modalityused in the radiologic work-up of endometrialdisease, the use of multiple imaging modalities iscommon. Whether using US, MR imaging, sono-hysterography, or hysterosalpingography, radiolo-gists must understand that the appearance of theendometrium is dynamic. They must take intoaccount the patient’s age, stage in the menstrualcycle, and pregnancy status and whether she hasundergone hormonal replacement therapy or ta-moxifen therapy, in addition to clinical historyand physical examination findings, to make anaccurate diagnosis.

Figure 27. Endometrial adhesions. Hysterosalpingo-gram reveals irregular filling defects in the endome-trium (arrows) representing adhesions.

Figure 28. IUD. US image shows a hyperechoic lin-ear structure within the endometrial canal (arrow) rep-resenting an IUD.


Acknowledgments: The authors acknowledge theinvaluable assistance of Catherine D’Agostino, MD,George Autz, MD, and Alan Wecksell, MD.

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This article meets the criteria for 1.0 credit hour in category 1 of the AMA Physician’s Recognition Award. To obtaincredit, see accompanying test at http://www.rsna.org/education/rg_cme.html.

1409 imaging the endometrium: disease and normal...

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