Diagnostic Imaging Europe
May 2003

Women's Health

MRI clarifies benign uterine disorders

Ultrasound fails to provide accurate diagnosis of gynecological disorders in many cases

By: Maite Villajos, M.D., Meleior Sentis, M.D., Lidia Tortajada, M.D., and M. Jesus Oses, M.D.

Although ultrasound is the preferred modality for assessing most benign uterine disorders, it is unable to provide an accurate diagnosis in a large number of cases. Diagnosis of common congenital or acquired benign uterine diseases frequently requires additional procedures, some of them aggressive.

MRI is an important adjunct to ultrasound, given its excellent soft-tissue visualization.1,2 It can improve diagnosis and management of gynecological disorders and preclude unnecessary invasive procedures. MRI can be used with confidence in pregnant patients and can add information about extrapelvic structures such as associated urological malformations.

Routine uterine MRI involves T2-weighted sequences in at least two planes using the major axis of the uterus as a reference. Additional fat-saturation pulses may also be used. Fat saturation improves contrast between structures and is useful to depict the external uterine contour and ovarian structures. Vascular contour and lymph nodes are more evident.

T1-weighted sequences, with associated fat-saturation pulses, are used to depict hemorrhagic content in lesions. Gadolinium-DTPA-enhanced T1-weighted sequences are applied in selected cases to evaluate the contrast behavior of solid lesions.

We perform most urinary tract studies with half-Fourier turbo spin-echo pulse sequences. A phased-array body coil is recommended, and an endocavitary coil is sometimes useful.3

DUCT EVALUATION

Women with mullerian duct anomalies (MDAs) have only slightly lower fertility than the general population, but they are more likely to have spontaneous abortion or preterm labor.

While MDAs are often identified on ultrasound or with a hysterosalpingogram, MRI can provide more complete information than either of these techniques. It can determine the type of anomaly with high accuracy using high tissue contrast and multiplanar imaging, involves no ionizing radiation, and can evaluate the entire genitourinary tract.

Correct classification of MDAs is vital to treatment planning.4-8 They should be classified according to the system established by the American Fertility Society:

  • Class I: agenesis or hypoplasia. Findings associated with class I vary. Mayer-Rokitansky-Kuster-Hauser syndrome is a complete or partial agenesis of the upper genital tract with associated skeletal and renal anomalies. No effective surgical therapy exists. The vagina can be partially or completely atretic. Differential diagnosis is an imperforate hymen or

    a vaginal septum. The uterus is dilated and filled with blood, revealed as high intensity on T1-weighted and T2-weighted MRI. Surgery is often performed to create a neovagina.

  • Class II: unicornuate uterus. Class II malformations result from hypoplasia or agenesis of one mullerian duct. Most patients have no fertility difficulties and do not suffer early pregnancy loss. MRI is excellent

    at demonstrating the characteristic elongated, banana-shaped hemiuterus as well as any associated contralateral rudimentary horn, which may be

    communicating or noncommunicating. Endometrial tissue within a noncommunicating rudimentary horn causes endometriosis-type symptoms and may require resection.

  • Class III: didelphic uterus. Lack of fusion of the mullerian ducts produces this malformation. Infertility and other reproductive dysfunctions are unusual. Didelphic uterus, characterized by the presence of two separate uterine horns and two cervices, can be difficult to distinguish from a uterus bicornis bicollis. A vertical vaginal septum is present in up to 75% of patients. No surgical therapy exists.

  • Class IV: bicornuate uterus. This malformation results from incomplete fusion of the mullerian ducts. Reproductive loss is greater in this group than in patients with unicornuate or didelphic anomalies. A bicornuate uterus typically shows a single cervix and two widely separate uterine horns (>75 degrees ) divided by an external fundal indentation deeper than 1 cm.

  • Class V: septate uterus. Resorption failure of the fibrous septum that separates the uterine horns accounts for this septate malformation, which has the highest rate of associated reproductive dysfunction. One reason for the high rate of early pregnancy loss is decreased blood supply to the septum. A fundal indentation <1 cm or a normal external fundal contour characterizes the septate uterus.

    Septal composition is important for surgical planning. Partial or complete septa are possible. The septum can be entirely fibrous, fibrous in the low portion and myometrial in the upper portion, or entirely myometrial. Most partial septa are composed primarily of myometrium.

    MRI is the only imaging modality that can reliably differentiate a bicornuate uterus from a septate uterus (Figures 1 and 2), an important distinction for preoperative surgical planning. Hysteroscopic septectomy is possible for a septate uterus, whereas a laparotomy is required for metroplasty when repairing the bicornuate uterus.

  • Class VI: arcuate uterus. Near-complete resorption of the fibrous uterine septum causes an arcuate uterus. Unlike septate uteri, the arcuate uterus has no effect on fertility.

  • Class VII: diethylstilbestrol- (DES) or drug-related. DES-related malformation is the only congenital uterine anomaly that is not associated with abnormal development of the genitourinary system. In utero exposure to DES may lead to several uterine anomalies, including uterine hypoplasia, T-shaped uterus, uterine cavity constrictions, and irregularity of the endometrial surface.

    Leiomyoma, the most common uterine mass, is present in about 20% of women over 35. The masses are estrogen-dependent and usually regress after menopause. Leiomyomas are benign smooth muscle tumors with varying amounts of connective tissue. They may undergo hyaline, myxomatous, cystic, fatty, or hemorrhagic degeneration. Complications such as torsion, infection, and sarcomatous degeneration are rare.

    Leiomyomas are classified according to their location within the uterus: submucosal, intramural, subserosal, and cervical. Known also as fibroids, the uterine tumors are usually asymptomatic. Symptoms that can occur include menorrhagia, dysmenorrhea, pressure effects, infertility, second trimester abortions, dystocia, and acute pain when the fibroids undergo torsion and cause infarction.

    MRI is more accurate than ultrasound for demonstrating the presence, number, and location of leiomyomas. This is particularly important in candidates hoping to have uterine-sparing surgery. Submucosal leiomyomas may be resected hysteroscopically, whereas intramural or subserosal leiomyomas may require a laparoscopic or transabdominal approach.

    The tumors have low signal intensity relative to the myometrium on T2-weighted images and are characteristically homogeneous, very well defined, and sharply demarcated from surrounding myometrium. Cellular leiomyomas, a specific subtype, are frequently isointense or hyperintense on T2-weighted images, appearing isointense on T1-weighted MRI. Hyperintense rims seen around leiomyomas on T2-weighted MRI represent a combination of dilated lymphatics, veins, and/or edema.

    Leiomyomas become heterogeneous on degeneration and have areas of increased signal. MRI cannot differentiate between the various types of degeneration, with the exception of the hemorrhagic type. This condition. which occurs most often during pregnancy and is associated with oral contraceptive use, is seen as areas of hyperintensity on T1-weighted MRI and as high or variable signal on T2-weighted images (Figure 3). A peripheral rim, hypointense on T2-weighted MRI and hyperintense on T1-weighted MRI, corresponds to obstructed veins at the periphery of the mass. Nearly complete hemorrhagic infarction and necrosis of the leiomyoma can occur in some cases, resulting in the appearance of a cystic cavity.9

    MRI has proved useful in differentiating leiomyomas from both adenomyosis and adenomyomas, from submucosal endometrial polyps, and from solid adnexal masses when they are subserosal or pediculated. Leiomyoma cannot be differentiated from sarcoma on signal characteristics alone. Rapidity of enlargement in postmenopausal women, irregular contours, and invasions of adjacent structures are the only clues suggesting malignant degeneration.

    DISEASE AND DISORDERS

    Uterine adenomyosis is a common disease resulting from the presence of heterotopic endometrial glands and stroma in the myometrium with adjacent myometrial hyperplasia. Clinical manifestations are variable and unspecific, including dyspareunia, secondary dysmenorrhea, and metrorrhagia.

    MRI may be more sensitive and specific than transvaginal ultrasound in diagnosing adenomyosis. It is less operator-dependent, provides standard images that are reproducible, and may prove useful in monitoring the disease when conservative hormonal therapy is instituted.

    Adenomyosis may be focal or diffuse. Characteristic MRI findings include diffuse or focal thickening of the junctional zone (>8 to 10 mm), ill-defined and homogeneous low signal intensity on T2-weighted masses within the myometrium (adenomyoma), and T2-weighted hyperintense striations radiating from the endometrium into the myometrium. Nonbleeding endometrial tissue is seen as hyperintense punctate foci on T2-weighted MRI and as isointense foci on T1-weighted imaging. Hyperintense foci on both T1-weighted and T2-weighted MRI correspond to bleeding endometrial tissue within the myometrium (Figure 4).

    MRI is highly accurate in differentiating adenomyosis from uterine leiomyoma. Features favoring diagnosis of adenomyoma include an ill-defined lesion, elongated shape, minimal or no mass effect, and punctate or linear areas of hyperintensity within the lesion. It is essential to differentiate between the two conditions. Uterine-conserving therapy is possible with leiomyomas, whereas hysterectomy is the traditional definitive treatment for debilitating adenomyosis.10.11

    Transvaginal ultrasound is the preferred modality for detecting endometrial anomalies. Endometrial biopsy is recommended if the endometrial thickness is more than 5 mm in postmenopausal women and more than 8 mm in postmenopausal women receiving hormonal therapy. Accurate measurement of endometrial thickness, however, may be difficult to perform in cases of vertically oriented uterus, morbid obesity, multiple leiomyomas, or marked adenomyosis. MRI may be helpful in determining which of these patients could benefit from further study.

    Endometrial hyperplasia usually presents as diffuse thickening of the endometrial stripe on T2-weighted MRI. Endometrial polyps are shown as slightly hypointense or isointense masses relative to the normal endometrium, as diffuse or focal thickening of the endometrial stripe, and as heterogeneous masses when they are large. Polyps show variable degrees of enhancement after gadolinium administration. These findings are nonspecific, and differentiation from early endometrial carcinoma is not possible. Patients taking tamoxifen are at increased risk of endometrial hyperplasia, polyps, and endometrial carcinoma. Neither MRI nor ultrasound can distinguish between these conditions, so endometrial sampling is indicated in all cases of thickening.12

    Intrauterine scarring or synechiae (Asherman syndrome) may follow endometritis or trauma, almost always related to pregnancy and surgical procedures. Symptoms depend on the degree and localization of intrauterine scarring.

    Dilated endocervical glands can produce nabothian cysts. Rarely symptomatic and requiring no treatment, they may be multiple, reach 2 to 4 cm in diameter, and enlarge the cervix markedly. MRI demonstrates well-defined margins, hyperintensity on T2-weighting imaging, low-intermediate signal on T1-weighted imaging, and lack of enhancement after gadolinium administration. These findings can help differentiate the cysts from carcinoma. Differential diagnosis includes adenoma malignum of the cervix and cervical endometriosis.

    Most cases of cervical stenosis, which involve the external os, are associated with surgical manipulation, radiation, and senile atrophy. Cervical stenosis prevents normal flow of uterine secretions, and patients usually present with uterine enlargement of indeterminate cause. MRI can demonstrate the presence and location of the cervical stenosis and exclude mechanical obstruction, which is most commonly endometrial or cervical carcinoma. When the cervix is completely obstructed, the uterine cavity is distended by material of variable signal intensity depending on its composition (serous, pus, or blood).

    Ultrasound remains a useful screening modality for benign uterine disorders. If scans are technically suboptimal or nondiagnostic, MRI should be the next step in the imaging assessment. MRI is a valuable problem-solving tool in diagnosing and managing benign uterine pathology that avoids additional diagnostic procedures.

    DR. VILLAJOS, DR. TORTAJADA, and DR. OSES are staff radiologists at the breast and gynecological radiology unit at UDIAT-CD, Sabadell, in Barcelona. DR. SENTIS is chief of the unit.

    References

    1. Silva A et al. Magnetic resonance imaging versus ultrasound in the assessment of benign uterine lesions. In: Lang EK, ed. Radiology of the female pelvic organs. Berlin: Springer-Verlag 1998:43-67.

    2. Schnall MD. Magnetic resonance evaluation of acquired benign uterine disorders. Semin Ultrasound CT MR 1994;15(1):18-26.

    3. Kinkel K, Vincent B, Balleyguier C, et al. Pathologie benigne de l' uterus: apport diagnostique de l'IRM. J Radiol 2000;81:773-779.

    4. Wagner BJ, Woodward PJ. Magnetic resonance evaluation of congenital uterine anomalies. Semin Ultrasound CT, MR 1994;15(1)4-17.

    5. Russ PD, Thickman DI, Schlaff WD, Harned RK. Magnetic resonance imaging of female Mullerian duct anomalies. J Women's Imaging 2000;2(4):185-194.

    6. Fielding JR. MR imaging of Mullerian anomalies: impact on therapy. AJR 1996;167:1491-1495.

    7. Carrington BM, Hricak H, Nuruddin RN, et al. Mullerian duct anomalies: MR imaging evaluation. Radiology 1990;176:715-720.

    8. Pellerito JS, McCarthy SM, Doyle MB, et al. Diagnosis of uterine anomalies: relative accuracy of MR Imaging, endovaginal sonography, and hysterosalpingography. Radiology 1992;183:795-800.

    9. Ueda H. et al. Unusual appearances of uterine leiomyomas: MR imaging findings and their histopathologic backgrounds. Radiographics 1999;19:S131-S145.

    10. Reinhold C, Tafazoli F, Mehio A, et al. Uterine adenomyosis: endovaginal US and MR imaging features with histopathologic correlation. Radiographics 1999;19:S147-S160.

    11. Byun JY, Kim SE, Choi BG, et al. Diffuse and focal adenomyosis: MR imaging findings. Radiographics 1999;19:S161-S170.

    12. Grasel RP, Outwater EK, Siegelman ES, et al. Endometrial polyps: MR imaging features and distinction from endometrial carcinoma. Radiology 2000;214:47-52.