Due to their high prevalence and related morbidity, uterine myomas constitute a group of gynecological pathologies largely studied in all clinical, diagnostic, and therapeutic aspects. They have been widely evaluated with a large series of imaging techniques. In fact, ultrasound (also saline infusion sonohysterography) and magnetic resonance imaging (MRI) are considered the optimal methods to assess uterine fibroids in terms of number, volume, echostructure, location, relation with endometrial cavity and uterine layers, vascularization, and differential diagnosis with other benign (adenomyosis) and malignant myometrial pathologies. Nevertheless, further studies are required to fill some gaps such as the absence of a common and sharable sonographic terminology and methodology to scan the myometrium, as well as imaging parameters for differentiation of typical myomas from smooth tumors of unknown malignant potential (STUMP) and leiomyosarcomas.
Highlights
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Ultrasound can be considered as the first diagnostic tool in the evaluation of uterine fibromatosis.
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Magnetic resonance imaging can be considered as a secondary technique for evaluation of uterine fibromatosis, though more accurate than ultrasound.
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The identification of imaging parameters able to differentiate benign from malignant myometrial pathology are still required.
Symptoms
Uterine myomas are benign tumors rarely associated with mortality but cause significant morbidity. Due to their high prevalence, the incidence of leiomyoma-associated symptoms would be high, but in reality, the majority of fibroids (estimated to be >50%) are asymptomatic. When women with fibroids present with symptoms, it is not always possible to be certain that the actual fibroids are causing the symptoms. The multitude of symptoms can include abnormal uterine bleeding and anemia, feeling of pelvic pressure or pain, urinary incontinence or retention, constipation, and reproductive dysfunction ( Table 1 ) .
| Asymptomatic |
|---|
| Abnormal uterine bleeding Menorragia Anemia |
| Pelvic pressure Urinary frequency Urinary incontinence Difficulty with urination Hydronephrosis Constipation Tenesmus |
| Pelvic mass |
| Pelvic pain |
| Infertility |
| Obstetric complications |
| Pregnancy related Myoma growth Red degeneration and pain Spontaneous miscarriage |
| Malignancy |
| Rare association Ascites Polycythemia Familiar syndromes, renal cell carcinoma |
| Benign metastasing |
| Adapted from Sabry and Al-Hendy 2012 (4) |
Black women have a threefold higher incidence of fibroids than white women . The prevalence of clinically significant myoma peaks in the perimenopausal years and declines after menopause .
The presence and severity of symptoms have traditionally been thought to be largely dependent on the size and location of the myomas (subserosal, intramural, or submucosal), although emerging evidence suggests that molecular mechanisms play an important role in the negative effects of fibroids .
The presenting symptoms are crucial for proposing the appropriate treatment. Management strategies are usually individualized based on the severity of symptoms, size and location of the fibroid, patient’s age, chronological proximity to menopause, and the patient’s desire for future fertility .
Imaging techniques
Imaging techniques are crucial for the planning of medical or surgical treatment; the procedures indicated in the work-up of uterine fibroids include ultrasound examination, saline infusion sonography, and magnetic resonance imaging (MRI) . The goals of imaging include localization, measurement, characterization of fibroids, and differential diagnosis from other myometrial pathologies such as adenomyosis, smooth tumors of unknown malignant potential (STUMP), and leiomyosarcomas.
Imaging techniques
Imaging techniques are crucial for the planning of medical or surgical treatment; the procedures indicated in the work-up of uterine fibroids include ultrasound examination, saline infusion sonography, and magnetic resonance imaging (MRI) . The goals of imaging include localization, measurement, characterization of fibroids, and differential diagnosis from other myometrial pathologies such as adenomyosis, smooth tumors of unknown malignant potential (STUMP), and leiomyosarcomas.
Ultrasound and uterine myomas
Ultrasound is an easy, accessible, harmless, and inexpensive diagnostic procedure; it can indeed be considered the first tool in the assessment of uterine myometrial pathology. Both transabdominal and transvaginal/transrectal (endocavitary) approach may be used, depending on the field of view desired. Transabdominal imaging offers a wide field of view, increased depth of signal penetration, flexibility in transducer movement, and the ability to examine other organs. Transabdominal ultrasound is more effective than endocavitary ultrasound for the visualization of subserosal or parasitic myomas extending into the abdominal cavity. It is also more effective in the presence of very large tumors.
Endocavitary ultrasound provides detailed images of the myoma as the probe is positioned close to the tumor, indicating that high-frequency ultrasound can be used. Endocavitary ultrasound is reliable, and a high level of interobserver agreement has been recorded for measurement of uterine size and endometrial thickness . Combined transabdominal ultrasound and endocavitary ultrasound is the most widely used technique for detection, mapping, and characterization of myomas . Fibroids produce uterine enlargement, lobularity of the outline (if subserosal), and distortion of the endometrial cavity (if submucosal). Intramural fibroids are most commonly found and may cause uterine enlargement without contour changes.
Ultrasound and uterine myomas: imaging findings
Morphological appearance of typical myomas
At ultrasound examination, uterine fibroids appear as solid, well-defined, round lesions within the myometrium or attached to it. In general, they have an inhomogeneous “stripy” or “fasciculate” echostructure, characterized by radial shadowing ( Fig. 1 ).
Echogenicity varies according to the different components in its context: muscle cells, fibrous stroma, calcification, and lipomatous or hyaline degeneration. When fatty tissue is overrepresented, myomas may appear hyperechoic ( Fig. 2 ) ; calcification or hyperechoic capsule, caused by deposition of calcium salts, is more frequent in postmenopausal women ( Fig. 3 ). When an acute myoma necrosis occurs, “complex heterogeneous internal structures” or “internal sonolucent areas” usually characterize fibroids at ultrasound examination .
Diameters
Fibroid diameters are usually measured in three orthogonal planes.
Number
The higher the number of uterine fibroids, the greater the disruption of the uterine structure. In the case of a low number of fibroids, it is recommended to describe each single lesion. On the contrary, in the case of a very high number of myomas, it is important that the report describes the uterus as “completely subverted,” thus conveying to the clinician the lack of a normal myometrium for a conservative surgery.
Location (relation with myometrium and endometrial cavity)
Uterine fibroids are usually located in the corpus uteri (95%) and rarely in the cervix (5%) .
According to their position and association with the uterine wall, fibroids are classified as intramural, subserous, or submucous. Intramural fibroids develop within the myometrial wall and are more commonly found (50%) . Intramural myomas are usually well demarcated due to the compression of the myometrium and subsequent formation of a pseudocapsule. When the growth of these masses involves another uterine layer, fibroids may be classified as subserous or submucous myoma.
* Subserosal myomas: They are located beneath the peritoneal covering of the uterus. When they extend into the peritoneal cavity, they may become sessile or pedunculated. Pedunculated myomas are connected to the uterus via a stalk containing vessels. The pedicle of a subserous leiomyoma can be very thin and frequently invisible at ultrasound examination.
When subserosal myomas extend into the peritoneal cavity, they may be described as parasitic or broad ligament. Parasitic myoma is a rare type of pedunculated subserosal myoma that is partially or completely separated from the uterus and receives an alternative blood supply from other sources such as the omentum and mesenteric vessels .
Broad ligament fibroids originate from hormonally sensitive smooth muscle elements and extend laterally from the uterus and are often confused with adnexal masses. In some cases, they can detach from the uterus and become mobile within the peritoneal cavity .
The differential diagnosis for this type of fibroids includes masses of ovarian origin (both primary neoplasms and metastases), broad ligament cysts, and lymphadenopathy. Ultrasound examination may facilitate diagnosis of broad ligament leiomyomas because it allows clear visual separation of the uterus and ovaries from the mass and mapping of the vascular supply of the tumor.
* Submucosal myomas: They are located in close proximity to the endometrium. Submucosal myomas are estimated to represent 5–10% of all leiomyomas, although this may be an underestimated proportion due to diagnostic difficulties. They tend to be the most bothersome clinically, causing symptoms that may include menorrhagia and infertility due to distortion of the endometrium. Submucosal myomas that extend into the uterine cavity while being attached to the myometrium by a pedicle are classified as pedunculated. A pedunculated submucosal myoma is at risk of torsion or expulsion through the cervical os. Infection and necrosis are common in submucosal leiomyomas due to inadequate blood supply. Myomas extending into the uterine cavity may be classified according to the depth of protrusion.
The European Society of Hysteroscopy classifies submucosal myomas as follows:
type 0: fibroid polyp (the mass is located entirely within the uterine cavity);
type I: >50% contained within the uterine cavity or <50% contained within the myometrium;
type II: <50% contained within the uterine cavity or >50% contained within the myometrium .
Type III of submucosal myomas was included by Donnez et al. and corresponds to multiple (>2) submucosal fibroids (myofibromatous uterus with submucosal fibroids and intramural fibroids) .
Submucosal myomas can be easily studied by sonohysterography, a simple and well-tolerated procedure with saline solution as the contrast medium. Results published in the literature show that this procedure presents the same accuracy as hysteroscopy in terms of location, breadth of attachment, and extent of protrusion into the uterine cavity of submucous myomas .
In the case of submucosal fibroids, minimal free myometrial margin, that is, the distance between the outer margin of the fibroid and the uterus surface, has to be measured ( Fig. 4 ). The myometrial free margin has to be evaluated before performing hysteroscopic resection; in fact, some studies documented the possibility to remove submucosal myoma with a minimal free margin <5 mm, but the recommended margin ranges between 5 and 10 mm .
Cervical fibroids may grow supravaginally or intravaginally; they are located very close to the uterine artery and ureter. Sometimes, they can be confused with other cervical pathology such as cervical carcinoma ( Figs. 5–6 ). In these cases, transvaginal ultrasound enables performing a guided biopsy of the lesion, thus avoiding invasive surgery ( [CR] ).
The following is the Supplementary data related to this article: Video 1
Transvaginal ultrasound-guided biopsy of a cervical myoma.
Vascularization
Color or power Doppler imaging shows myomas without rich vascularization; circumferential flow around the lesion is often visible (perifibroid plexus), while central flow is not very well represented ( Fig. 7 ). Centripetal branches reach the center of the tumor via peripheral arteries. The peripheral vascularity of fibroids is increased compared to that of normal myometrium and the center of the tumor . Doppler ultrasound may facilitate in distinguishing an endometrial polyp with a single feeding vessel from an intracavitary submucosal fibroid tumor and adenomyosis, where vascularization is characterized by diffusely spread vessels .
Doppler velocimetry usually attests a decreased resistance index in the perifibroid plexus in comparison with the surrounding normal myometrium. Doppler findings and velocimetry indices have been largely evaluated to predict proliferative status of the tumors and to differentiate benign from malignant lesions , but inconclusive results have been obtained .
In the study of Testa et al., even if intratumoral resistance index values did not provide predictive information of the proliferative status of the neoplasm, a significant negative correlation with the myoma volume was found .
Variants of fibroids and other uterine smooth muscle tumors
Morphological appearance of atypical myomas
A typical leiomyoma is easily recognized by imaging. However, degenerative changes may cause a leiomyoma to assume an atypical appearance that can cause diagnostic confusion. As leiomyomas enlarge, they may outgrow their blood supply, thus resulting in various types of degeneration. These include hyaline, myxoid, or cystic degeneration, dystrophic calcification, and red degeneration. Of these, hyaline degeneration is most common, occurring in up to 60% of cases. Spontaneous degeneration may occur in pregnancy, and red degeneration is an initial manifestation . No typical aspects of infarcted lesions (red or hyaline degeneration) have been observed: fibroids are often uniform, hypoechogenic, with a hyperechoic rim and acoustic shadows, without detectable flow inside . Only in the later phase of infarction, edema and necrosis may determine a mixed echogenicity or hypoechoic cystic areas within fibroids ( Fig. 8 ) easily recognizable by ultrasound examination.
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