Abstract
Uterine fibroids (or leiomyomas) are the most common benign gynaecological tumours, formed by smooth muscle and connective tissue. Most are asymptomatic, but sometimes may cause pain, pressure symptoms, metrorrhagia, infertility due to implantation failure, miscarriage, preterm delivery, and puerperal haemorrhage. Fibroids can be single or multiple. Their size and location vary and they may undergo benign degenerative changes: atrophic and hyaline degeneration, calcification, infection, and infarction. Malignant degeneration towards leiomyosarcoma is extremely rare, occurring in less than 0.2 per cent of cases.
Introduction
Uterine fibroids (or leiomyomas) are the most common benign gynaecological tumours, formed by smooth muscle and connective tissue. Most are asymptomatic, but sometimes may cause pain, pressure symptoms, metrorrhagia, infertility due to implantation failure, miscarriage, preterm delivery, and puerperal haemorrhage. Fibroids can be single or multiple. Their size and location vary and they may undergo benign degenerative changes: atrophic and hyaline degeneration, calcification, infection, and infarction. Malignant degeneration towards leiomyosarcoma is extremely rare, occurring in less than 0.2 per cent of cases [1].
Adenomyosis is defined as the presence of endometrial tissue with its glands and stroma, implanted in the myometrium. Dysmenorrhoea and abnormal uterine bleeding in nulliparous women are the usual presenting symptoms associated with this condition. Adenomyosis is reportedly linked to infertility; however, the exact mechanism of this negative effect is unknown [2–8]. In addition, an association between this condition and various obstetric diseases (preterm delivery, growth retardation, recurrent bleeding, etc.) has also been found [9]. Ultrasound scans – two-dimensional (2D), power Doppler (PD) angiography and three-dimensional (3D) – are often adequate to make a definitive diagnosis and plan subsequent management. These investigations are the preferred diagnostic tools due to lower cost, accessibility, patient tolerability and minimal invasiveness of the procedure compared to other modalities [10].
The aim of this chapter is to provide an overview of the ultrasound diagnosis of uterine fibroids and adenomyosis and their sonographic appearance in typical and atypical cases, and to provide guidance when pitfalls are encountered.
Uterine Fibroids
Transvaginal ultrasound with high-frequency endocavitary transducers and wide angles of acquisition constitute the best diagnostic tool for describing uterine leiomyomas. On occasion, transabdominal ultrasound may provide better details, particularly in cases of large fibroids. The lower frequency of abdominal ultrasound transducers allows assessment of structures at a greater distance, and therefore, both routes can be combined for detailed analysis (Figure 4.1). Occasionally, application of abdominal pressure with the non-scanning hand may move the fibroid closer to the transvaginal transducer, allowing better visualization of the fibroid and surrounding structures.
(a) Uterus with eight fibroids.
(b) Uterus with four fibroids showing endometrium (e).
(c) Transvaginal ultrasound showing a large uterus with multiple myomas, partially visible.
(d) Abdominal ultrasound showing the same uterus allows for complete visualization and the measurement of all its diameters.
Figure 4.1 Transvaginal ultrasound showing two examples of a uterus with multiple myomas (arrows):
Modern ultrasound equipment is delivered with predefined technical settings for a gynaecological examination recommended by the manufacturer. In general, the preset parameters are very suitable and usually do not need to be modified. In 2D mode these parameters include frequency, power, gain, dynamic range and greyscale; in PD mode they include wall filter and the pulse repeated frequency (PRF); and in 3D/4D mode they include acquisition mode, volume angle, quality and various image display modalities including sectional planes and render modes. Nevertheless, in some cases these settings need to be modified depending on the patient’s characteristics (body mass index, uterine position, uterine size), the particular type of examination and the preferences of the examiner. Attenuation of ultrasound waves through fibroids is common and therefore assessment in ‘penetration mode’ (low frequency and better depth, but at the cost of resolution) may often be needed, especially in cases of an enlarged uterus with multiple fibroids.
Myomas appear on the ultrasound as rounded or oval structures, well defined and circumscribed nodular masses, usually hypoechogenic and homogeneous with respect to the surrounding myometrium. Occasionally, these fibroids are minimally echogenic, appearing as small cystic masses in the myometrial layer (Figure 4.2). The echogenicity depends on the amount of fibrous tissue present in the smooth muscle, in addition to vascular contribution and the presence of degenerative changes. Even the inner fibrous spiral architecture can sometimes be seen, since the fibres of the smooth muscle and connective tissue are arranged in a concentric pattern. It is essential to visualize the interface between the normal myometrium and the pseudocapsule surrounding the myoma, as this allows the examiner to differentiate fibroids from true adenomyosis.
Establishing the location and size of myomas [11] is necessary for a full assessment. This should be carried out in the longitudinal and transverse planes of the uterus and the fibroid location should be noted in relation to the anterior, posterior, right or left uterine walls, as well as to the endometrial cavity. This approach allows for measurement of the fibroids in three orthogonal planes. In cases of multiple fibroids and enlarged uterus, fibroid mapping can be difficult by ultrasound. Systematic scanning and identification of relevant landmarks (i.e. the bladder and cervical canal) is very helpful, especially when planning any surgical interventions. The assessment should follow the endometrial cavity from the cervical canal to the fundus (and vice versa), and systematically, the mapping of fibroid location is done. Assessment should be completed by scanning the uterus from one side to the other (operator preference dictates whether the start is on the right or the left side of the uterus). When multiple fibroids are mapped, a typed report should be supplemented by a graphic representation of the exact location of the myomas.
According to the location of the myomas with respect to the uterine layers, they are classified as intramural (confined within the myometrium), subserosal (greater than 50 per cent of the fibroid protrudes through the serosal surface) and submucosal (distorting the endometrial cavity). Multiple types of fibroids can co-exist at any time (Figures 4.3–4.9), and intramural types, when continuing to grow, may change and indent the endometrial or serosal surfaces, thus becoming submucosal or subserosal types, respectively. Fibroids may also be intraligamentous (i.e. within the broad ligament), pedunculated, cervical or within the uterine horn (Figures 4.3–4.9).
Figure 4.7 Large submucous myoma that occupies the entire endometrial cavity.
Subserous myomas deform the uterine contour. In the case of intraligamentous and pedunculated fibroids, locating the vascular connection with the uterus (‘bridge sign’) is very useful to accurately determine its uterine origin and avoid confusion with adnexal masses. Another way to determine the origin of the adnexal mass is to apply slight pressure on the fibroid with the vaginal transducer; if the mass moves with the uterus, its uterine origin is confirmed. As for intramural myomas, during a scan the normal myometrium can be clearly demonstrated surrounding the fibroid and separates them from the endometrium or the external surface of the uterus. The large leiomyomas can, however, deform the cavity or alter the uterine contour.
Submucous myomas can be confused with endometrial polyps, although polyps are usually more echogenic and most often contain one feeding vessel when visualized using Doppler sonography. It is very important, especially from the reproductive point of view, to delineate the exact relationship to the uterine cavity and to assess the degree of protrusion into it. There are several classifications, although the classical one belongs to Wamsteker and Blok and has been adopted by the European Society for Gynaecological Endoscopy (ESGE) [12], which defines them as follows: type 0 (100 per cent inside the cavity), type 1 (more than 50 per cent inside the cavity) and type 2 (less than 50 per cent inside the cavity). Other authors recently modified this classification for better management in subsequent hysteroscopy using the STEPW parameters, which include size, topography, extension of the base of the myoma, penetration of the fibroid into the myometrium, and wall [13]. Each factor is scored on a scale 0–1–2 according to predefined criteria, and in the multicenter study of 465 submucous myomas, fibroids with a score of ≤4 were resected completely and had a better sensitivity of 100 per cent (95 per cent CI 89.4–100.0 per cent) and specificity 74.1 per cent (95 per cent CI 69.7–78.1 per cent), compared to the ESGE system when using the type 1 fibroids as a cutoff (sensitivity 36.4 per cent (95 per cent CI 20.4–54.9 per cent) and specificity 84.0 per cent (95 per cent CI 80.2–87.3 per cent)) [13]. Hysterosonography or saline infusion sonography (SIS) may sometimes be very useful for reaching a definitive diagnosis of submucous myomas and to determine the extent of protrusion of the fibroid into the endometrial cavity [14] (Figure 4.10). For all types of myomas, it is essential to measure their diameter in three perpendicular planes, and for the large ones to measure at least two major perpendicular diameters (Figures 4.11–4.13).
It should be noted that myomas can undergo degenerative phenomena so their echogenicity may change over time depending on the type of degeneration that they are undergoing. The longstanding ones may become hyperechogenic, with intense circumferential acoustic shadowing suggesting calcifications, and may be in the form of small isolated foci or a complete border surrounding the entire fibroid, with other patterns in between also being common (Figures 4.14 and 4.15).
Figure 4.15 Large myoma on the right side of the uterus with a fully calcified surface and significant acoustic shadowing.
The vascular blood supply may become insufficient to supply the entire fibroid, hence leading to vascular, ischaemic necrosis. In the beginning of pregnancy, myomas can rapidly increase in size, leading to extensive necrosis affecting the entire fibroid, with sudden and intense pain; this situation is called red degeneration. Red degeneration on ultrasound scan may appear as hypoechogenic structures that may be confused with blood vessels or adenomyotic cysts. Prior knowledge of presence and location of fibroids may be of help when making the diagnosis. Using power Doppler modality or elastography is also useful to clarify the nature of the observed structure. The presence of Doppler signal indicates a blood vessel, whereas a red contour on elastography indicates a high-density structure (i.e. fibroid). Doppler imaging in early pregnancy should only be used if absolutely necessary.
In cases when the blood supply to the fibroid is reduced gradually, its degeneration may be in the form of hyaline, cystic, fat or myxomatous. This will present with a complex ultrasound appearance of a homogeneous hyperechogenic lesion without acoustic shadowing or occasionally with posterior reinforcement and irregular hyperechoic or anechoic areas inside the fibroid, representing fat or myxoid degeneration respectively. Hyaline degeneration is the most common and appears on ultrasound as anechoic foci within the myoma (Figure 4.16).
