Introduction Uterine fibroids (myoma or leiomyoma), with the prevalence between 70-80%, present the most common benign gynecologic tumours, which arise from smooth muscle cells of the myometrium.
Myomas are hormonally dependent tumours which usually increase in size in reproductive age.
They are often multiple and asymptomatic.
When they occur, symptoms include abnormal uterine bleeding, pain, dysmenorrhea, infertility, or symptoms related to mass effect (1,2).
Ultrasound presents an initial method, which can be sufficient especially in small and well defined masses.
However, MRI is the most effective imaging modality, which provides accurate location, type, number and potential complications of myomas (torsion, infarction).
Furthermore, MRI is effective in case of significant uterine enlargement and presents the problem-solving tool in case of fibroid mimics (leiomyosarcoma, adenomyosis, focal uterine contractions, adnexal pathology) (2).
Non-degenerated leiomyomas have typical MRI features which include well circumscribed lesions, homogenous iso- or mildly hypointense on T1W and hypointense on T2W MR images (relative to the myometrium).
They are hypointense on DWI and ADC maps.
However, hypercellular myomas can show restricted diffusion.
After administration of gadolinium, myomas often show early homogenous enhancement similar to the myometrium (2,3,4).
In case of indeterminate origin of the pelvic mass, recognizing the bridging vessels and claw sign indicates uterine origin of the lesion, particularly fibromas.
The bridging vessels sign presents as flow voids (hypointense on T2W), referring to the vessels extending from the uterus to the lesion.
The claw sign correlates with the uterine tissue surrounding the lesion (Fig 1) (5,6).
MRI examination Patient preparation include: 1.
Patients should fast 3 to 6 hours before the exam to reduce risk from vomiting and bowel movement artefacts. 2.
When not contraindicated, the use of antiperistaltic is recommended to improve image quality. 3.
Moderately filled bladder is optimal for the pelvic MRI. 4.
It is not necessary to schedule the patients according to the menstrual cycle.
MRI imaging sequences Basic protocol include: 1.
At least two T2W orthogonal oblique planes, including a sagittal plane of the uterine corpus – to evaluate uterus morphology and to survey the fibroids 2.
Axial T1W – to evaluate other pathology in pelvis as well as to depict high signal intensity lesions 3.
Fast T2W of upper abdomen – in case of large tumours, renal obstruction, potential metastases Additional sequences: 4.
T1W FS – to differentiate hemorrhagic from fatty lesions 5.
Oblique coronal T2W – to evaluate relationship to the uterine cavity, assessment of the uterine or adnexal origin of the lesion 6.
DWI – in case of T2W hyperintense myomas and rapidly growing lesions 7.
Postcontrast T1W (optimally DCE) – in case of rapidly growing lesions and lesions with T2W high signal intensity, assessment of the uterine or adnexal origin of the lesion, pre- and post-embolization evaluation. (7) FIGO classification The FIGO classification system for uterine fibroids provides uniform assessment and reporting of the localization of myomas which leads to optimal treatment for the patient (Fig 2).
FIGO subtypes: FIGO 0 – pedunculated intracavitary myoma FIGO 1 – ≥ 50% submucosal and < 50% intramural FIGO 2 – < 50% submucosal and ≥ 50% intramural FIGO 3 – 100% intramural fibroids in contact with the endometrium FIGO 4 – 100% intramural, without endometrial or serosal contact FIGO 5 – ≥ 50% intramural and < 50% subserosal FIGO 6 – < 50% intramural and ≥ 50% subserosal FIGO 7 – pedunculated subserosal myomas, without intramural component FIGO 8 – extrauterine fibroids (cervical, broad ligament) Hybrid form represents myoma with both submucosal and subserosal components.
The first number of the FIGO stage is addressed to the submucosal component and the second number to the subserosal component (e.g.
FIGO 2-5).
Submucosal fibroids (FIGO 0-2) can cause dysmenorrhea or metrorrhagia and infertility and often require treatment, which includes hysteroscopic myomectomy.
Patients with other fibroids (FIGO 3-8) can report symptoms related to mass effect on adjacent organs (bladder and colon).
Treatment for FIGO stage 3 and 4 includes laparotomy or laparoscopy, whereas UEA, laparoscopic or open myomectomy and targeted therapy are choices for myomas FIGO stage 5 – 7 (4,8).
Myomas subtypes 1.
Hyaline degeneration of leiomyomas is the most common type of degeneration, which occurs as a result of eosinophilic plaque forming in the extracellular space.
T1W and T2W signal intensity is similar to the non degenerated myomas, but they show decreased enhancement after contrast administration (Fig 3) (4,9). 2.
Lipoleiomyoma shows signal intensity similar to the fatty tissue on all sequences, with no restricted diffusion and no central enhancement of the lesion.
Lipoleiomyoma shows fat suppression on fat-saturated images.
Fatty component is a result of fatty metaplasia of smooth muscle cells (Fig 4) (2,10). 3.
Apoplectic leiomyomas represent red or hemorrhagic degeneration of fibroids.
MR imaging features depend on the age of haemorrhage.
They usually show a T1W high signal with variable T2W signal intensity.
Peripheral T1W hyper- and T2W hyposignal presents thrombosed vessels, which result in no enhancement on postcontrast images (Fig 5) (2,4). 4.
Hydropic leiomyomas represent cystic degeneration of the myomas which result in fluid signal intensity on T1W and T2W sequences, without contrast enhancement (4). 5.
Myxoid degeneration of leiomyomas is rare form of degeneration, often presented as a large T1W hypointense (compared to the muscle) and heterogeneous T2W hyperintense lesion with T2W lakes which presents mucinous lakes, with no restricted diffusion.
Heterogeneous enhancement of non-myxoid components of the mass is noted on postcontrast MR images (Fig 6) (2,4).