European Society of Urogenital Radiology (ESUR) Guidelines: MR Imaging of Leiomyomas

Neither optimal scheduling according to the menstrual cycle nor a clinical questionnaire before MRI of uterine benign disease is covered in the recent literature. It is recommended that institutions do not schedule their patients according to their menstrual cycle, but obtain clinical information at the time of the scan (e.g., time of menstruation, clinical symptoms, hormonal medication, prior surgical procedures). This regimen obtained consensus among the ESUR Female Pelvic Imaging Working Group (Table 1).

Despite lack of substantial evidence to support fasting for pelvic MRI examinations, there was agreement that patients should fast (3-6 hours), especially when intravenous (iv) gadolinium injection is considered. This is also supported by previous ESUR guidelines [3, 7, 8]. The rationale behind fasting is to reduce the risks from vomiting occurring as a reaction to the contrast medium injection as well as to reduce bowel motion artifacts.

There are no new data regarding the use of antispasmodic agents for the reduction of bowel artefacts. Its supporting evidence has also been extensively discussed in previous ESUR guidelines [3, 7‐10]. The committee recommends the use of antiperistaltic agents for the improvement of image quality of pelvic MR (20 mg butyl-scopolamine im/iv or 1mg of glucagon iv), unless it is contraindicated.

There is consensus that a moderately filled bladder is optimal for pelvic MRI. The literature only sparsely addresses this issue. Previous ESUR guidelines recommend patients should empty their bladder 1h prior to examination to achieve a moderately filled bladder [8, 11‐15].

Although there are no studies comparing 3 Tesla versus 1.5 Tesla or pelvic array coils versus multi channel body coils in benign uterine lesions, all these options seem valuable.

It is recommended that institutions routinely include at least one fast T2WI sequence of the upper abdomen. This strategy allows exclusion of complications in patients with large leiomyoma, e.g. signs of compression such as hydronephrosis, or to rule out lymphadenopathy or metastases in patient with suspected malignancy.

We recommend a basic MRI examination protocol with at least two T2WI orthogonal planes of the uterus, including a sagittal sequence of the uterine corpus. Doing the sagittal sequence first allows subsequent scan planes to be aligned to the axis of the uterus rather than just aligned to the body. An oblique sequence aligned along the long axis of the uterus is optional, but provides useful information for anatomic localization of leiomyomas, particularly in the work-up of infertility, as it best displays the relationship of the leiomyomas to the endometrial cavity. A 3D T2W sequence may be an alternative in selected cases, e.g. mapping in multiple myomas. In the work-up of an adnexal mass of indeterminate origin, a T2W plane selected across the maximum point of contact between the mass and the uterus is advised [10, 13, 16, 17] (Tables 2 & 3).

Besides the T2W sequences, the basic protocol should include an axial T1W sequence in order to assess other pelvic pathologies and to depict high-signal intensity lesions. In this scenario, a fat-supressed T1W sequence in the same plane allows characterization of haemorrhagic from fatty uterine pathologies (lipoleiomyomas vs leiomyomas with haemorrhagic degeneration; haematometra; endometriosis and adenomyosis), adnexal masses (teratomas or endometriomas) or other pelvic fat or blood-containing masses [10, 13, 16, 17] (Table 3).

Major indications for iv gadolinium include: characterization of a rapidly growing leiomyoma; characterization of a leiomyoma with areas of high signal intensity on T2W images; differentiation from an adnexal mass; pre-embolization assessment including vascularization and viability of leiomyomas; post-embolization assessment to define treatment response in persistence of clinical symptoms or post-embolization complications [12, 17‐23] (Table 3).

Gadolinium is optimally administered in a dynamic acquisition in the plane that best depicts the morphology of the lesion to be characterized, as determined based on the T2W sequence.

Especially for radiologic interpretation of therapeutic response, image subtraction can be helpful in distinguishing enhancing areas from T1W hyperintense material such as haemorrhage or debris.

Different types of benign degenerating leiomyomas show T2W hyperintense areas and can rapidly grow (cystic, myxoid, hydropic and cellular degeneration) [23‐25]. In these settings, an intravenous contrast medium is imperative to identify solid components of leiomyosarcomas, which may also show rapid growth and T2W hyperintensity due to necrosis (Fig. 1). Unfortunately, differentiation between benign degenerating cellular leiomyomas and leiomyosarcomas is challenging due to considerable overlap [12, 13, 23] (Table 4). Lakhman et al recently reported four discriminitative features: nodular borders, haemorrhage, T2W dark areas and central unenhanced areas. Combination of >3 MR features allowed specificity of >95% [26].

In a T2W hypointense solid mass of indeterminate origin, studies have shown that ovarian fibromas enhance late and less compared to the myometrium, whereas typical subserosal leiomyomas tend to have a similar enhancement pattern [18, 19].

3D-reconstructed contrast-enhanced MR angiography, has proven to be valuable in determining details of the pelvic vasculature and the optimal image intensifier C-arm obliquity before embolization, thus reducing the fluoroscopy time, the radiation dose and the contrast medium volume (Fig. 2) [20‐22]. Currently, MR angiography is not part of the routine protocol. Twelve of the participating institutions perform MR angiography in selected cases.

Based on the current literature DWI is not mandatory for assessing leiomyomas in a clinical routine setting. However it might have a potential for characterization of T2W hyperintense leiomyomas or in rapid growth (Fig. 3). Both leiomyosarcomas and benign cellular leiomyomas display restricted diffusion. Thus, restricted diffusion in a leiomyoma is a pitfall of which radiologists should be aware [11, 27‐29]. Two publications found significantly lower mean ADCs in leiomyosarcomas than in degenerated leiomyomas (Fig. 3) [30, 31]. As reported previously by our working group, for gynaecological imaging, the optimal b value is usually 800–1000 s/mm², but may be increased up to 1200 or 1400 s/mm² [10].

DWI has also been shown to be useful in pre- and post-embolization evaluation of uterine leiomyomas. Persistent decrease of the ADC values of the dominant leiomyoma 6 months following embolization is reported, which also correlates with its volume reduction [32‐37]. Therefore, a high pre-embolization ADC value seems related with a greater volume reduction and to be useful in predicting the response of a dominant leiomyoma to embolization [33‐35].

Although standardized pro forma reporting was used in only a few institutions, there was consensus that this will become an issue in the future and that the written report has to include mandatory findings (Table 5).

Leiomyomas are typically multiple and are classified according to their location as submucosal, intramural and subserosal (Figs. 4 and 5). To standardize the nomenclature in patients with abnormal bleeding, regardless of their number and size, they can be further subdivided into 8 categories according to the FIGO classification (PALM-COEIN) (Table 5) [38, 39].

Size and MR features, e.g. signs of necrosis or degeneration as well as enhancement patterns, must be described (Table 5) [1].

Unusual variants, such as diffuse leiomyomatosis characterized by symmetrical enlargement of the uterus due to innumerable small ill-defined leiomyomas, lipoleiomyomas, and parasitic leiomyomas should be mentioned in the report [1, 2].

Inclusion of any differential diagnosis is mandatory in every report. These include myometrial contractions, adenomyosis (Fig. 6), and, most importantly, uterine malignancy or adnexal fibromas.

Depending on the planned procedure other imaging information may be required (Table 5).

While (as corroborated by our survey) currently laparoscopic or open surgery is still the mainstay of operative intervention, minimal invasive interventions, such as Uterine Leiomyoma/Fibroid Embolization (UFE) and Magnetic Resonance guided Focused Ultrasound (MRgFUS) are emerging techniques that are likely to gain increasing acceptance. In 14 of the participating institutions, embolization is offered to patients, while only one institution had experience with MRgFUS.

Although not mandatory for pre-UFE evaluation using high-quality ultrasonography, MRI may change diagnosis and treatment plan in about 20% of patients with symptomatic leiomyomas [4‐6]. Patients with leiomyomas and coexisting adenomyosis are potential candidates for uterine artery embolization. The coexistence of adenomyosis should be reported, as it may require changes in the embolization protocol and might have a negative impact on long term results [4, 40‐42]. Further, the size, number and location of leiomyomas are important for choosing treatment options for the individual patient. Though not contraindicated for UFE, it is valuable to visualize pedunculated leiomyomas for pre-treatment planning [4, 43, 44]. Cervical leiomyomas may not have a beneficial outcome after UFE [45]. Finally, it is crucial for the outcome of UFE that leiomyomas are vascularized, since a treatment response cannot be expected in a degenerated leiomyoma. MR-angiography (MRA) identifies major arteries supplying the leiomyomas. Usually the uterine arteries are the dominant suppliers, but blood supply by ovarian arteries may be a concern [4]. In these cases, the ovarian arteries are visualized as enlarged winding vessels on the MR angiogram (Fig. 2), while they are not clearly visualized under normal circumstances [46].

After UFE, leiomyomas usually undergo degeneration, although some observations contradict this [33, 47, 48]. If enhancement persists, repeat embolization of collateral blood supply or other treatment options may be considered [34, 45].

Post UFE problems may be identified by MRI. Persistent vaginal discharge may indicate a necrotic remnant or, rarely, expulsion and transvaginal sloughing of a necrotic leiomyoma may occur [4, 49].

MRgFUS induces focal heating and coagulative necrosis within a leiomyoma under real-time MRI monitoring using thermal maps [50, 51]. Ideally, leiomyomas should be limited in number and size (<10cm in largest diameter), show homogenously low-signal on T2W and no calcifications. Pre-treatment MRI in prone position allows targeting of a safe pathway during MRgFUS. Abdominal scars or pedunculated leiomyomas are relative contraindications, and intestine along the acoustic pathway is an absolute contraindication. Post treatment predictor of success is the non-perfused volume of the leiomyoma. Treatment typically achieves around 50–55% non-perfused volume, based on post contrast imaging after the completion of treatment [52].