Abstract
Uterine fibroids are perhaps the commonest benign tumours a gynaecologist will encounter, with an estimated lifetime prevalence of approximately 30%; however, approximately three-quarters of cases are thought to be asymptomatic [1]. Given that the majority of fibroids are asymptomatic, they are likely to be encountered for the first time within the context of infertility investigations, assuming that couples will undergo a baseline screening which will invariably include an ultrasound scan of the female pelvis.
2.1 Introduction
Uterine fibroids are perhaps the commonest benign tumours a gynaecologist will encounter, with an estimated lifetime prevalence of approximately 30%; however, approximately three-quarters of cases are thought to be asymptomatic [1]. Given that the majority of fibroids are asymptomatic, they are likely to be encountered for the first time within the context of infertility investigations, assuming that couples will undergo a baseline screening which will invariably include an ultrasound scan of the female pelvis.
The question therefore arises: do fibroids require intervention, and if so, in which cases? In women with symptomatology, such as pressure symptoms and menorrhagia, the accurate diagnosis of fibroids is of utmost importance since it will determine whether indeed the symptoms can be attributed to the fibroid detected. For example, a 2 cm subserosal fibroid is not likely to be the culprit in significant menorrhagia, whereas a 2 cm submucosal fibroid may well be. Even more subtle differences become of increasing importance in women with infertility, where meta-analyses have shown that submucosal, intramural and subserosal fibroids affect fertility in reducing order of significance [2]. In such cases, further characterization of – for example – intramural fibroids (i.e. size, exact location, distance from the endometrium/junctional zone) may determine whether a woman may benefit from intervention or not.
It therefore becomes apparent that the correct evaluation (i.e. diagnosis and characterization) of fibroids is pivotal in the modern management of these tumours. This depends wholly on the classification models that are available, but also on the correct use and interpretation of diagnostic methodology, both of which will be examined in the present chapter.
2.2 Classifications
The traditional classification of fibroids is dependent on where the fibroids are located with respect to two anatomical planes: the uterine endometrium and the uterine serosa. The terms submucosal, intramural and subserosal have therefore been coined for several decades. Historically, however, there was no consensus as to what precisely constituted each category, and this was proving to be particularly confusing in borderline cases. A classification was therefore suggested by Bajekal and Li in 2000 which helped distinguish three diagnostic categories [3]:
1. Submucosal: A fibroid that distorts the uterine cavity. Subdivisions included type 0 (pedunculated fibroid with no intramural extension); type 1 (with intramural extension of <50%); type 2 (with intramural extension of >50%).
2. Intramural: A fibroid that does not distort the uterine cavity and with <50% extension beyond the serosal surface.
3. Subserosal: A fibroid that extends >50% beyond the serosal surface and can be either sessile or pedunculated.
This classification was later expanded by the International Federation of Gynecology and Obstetrics (FIGO) Menstrual Disorders Working Group, which devised the classification of causes of abnormal uterine bleeding in the reproductive years, otherwise known as the PALM-COEIN (Polyp, Adenomyosis, Leiomyoma, Malignancy and Hyperplasia, Coagulopathy, Ovulatory Disorders, Endometrial Disorders, Iatrogenic Causes, and Not Classified) classification system [4]. It included a total of nine types of myomas (types 0–8) with a view to being able to further characterize the intramural and subserosal types. Therefore, in this classification, fibroids are classified as follows (schematically presented in Figure 2.1):
1. Type 0: Pedunculated intracavitary (i.e. submucosal) fibroid.
2. Type 1: Intracavitary fibroid with intramural extension of <50%.
3. Type 2: Intracavitary fibroid with intramural extension of >50%.
4. Type 3: Intramural fibroid in contact with the endometrium but with no extension into the uterine cavity or serosal surface.
5. Type 4: Intramural fibroid not in contact with the endometrium and with no extension into the uterine cavity or serosal surface.
6. Type 5: Fibroid of which >50% is intramural and <50% is subserosal (intramural in the previous classification)
7. Type 6: Fibroid of which <50% is intramural and >50% is subserosal (subserosal in the previous classification)
8. Type 7: Pedunculated subserosal fibroid
9. Type 8: Other types of fibroids (e.g. cervical, parasitic)
10. Hybrid type [2–5]: Combined submucosal–subserosal with <50% indentation into the cavity and also into the serosal surface.
By devising this classification, the working group hoped to create a system that would be universally accepted and would allow for both effective and accurate communication between clinicians and patients, and also aid in the conduction of appropriately designed trials.
Figure 2.1 A schematic representation of the different types of fibroids in accordance with the FIGO classification (Munro et al. [4]). Small fibroids have been used here to facilitate the representation of the classification in a single uterine image.
2.3 Diagnosis
2.3.1 Two-Dimensional Ultrasound
The next logical step after the acceptance of an appropriate classification is ascertaining an accurate diagnostic modality to apply the given classification. Indeed most classifications, systematic reviews and international consensuses advocate the use of two-dimensional (2D) ultrasound (US) as an accurate means of diagnosing and characterizing uterine fibroids [3–7]. This has been consistently supported by data from the last few decades that has shown 2D US to have sensitivities of 90–100%, specificities of 87–98%, positive predictive values (PPV) of 81–93% and negative predictive values (NPV) of 98–100% [5, 8–11]
Interestingly, irrespective of the FIGO anatomical classification, until recently, there was no universally accepted consensus on how specifically to scan, characterize and report uterine fibroids. This is something the MUSA (Morphological Uterus Sonographic Assessment) group attempted to achieve with the publication of their long and comprehensive consensus [7]. This suggested a systematic approach to assessing and reporting the myometrium and associated fibroids, including the following parameters (examples shown in Figure 2.2):
1. Uterine corpus: Measurement of length, anteroposterior diameter, transverse diameter and volume
2. Serosal contour: Regular versus lobulated
3. Myometrial walls: Symmetrical versus asymmetrical
4. Myometrial echogenicity: Homogeneous versus heterogeneous
5. Myometrial lesions:
a. Well-defined versus ill-defined
b. Number
c. Location (anterior, posterior, fundal, right or left lateral, global)
d. Site (type according to FIGO classification)
e. Size (three perpendicular diameters)
f. Outer lesion-free margin (distance from the serosal surface)
g. Inner lesion-free margin (distance from the endometrial surface)
h. Echogenicity (homogeneous versus heterogeneous; hypo-, iso-, hyper-echogenic)
i. Shadowing (edge, internal, fan-shaped)
j. Myometrial cysts (size, number, echogenicity)
k. Hyperechogenic islands (outline, number, size)
l. Subendometrial echogenic lines/buds
Indeed, for the majority of fibroids, the MUSA consensus for characterizing and reporting fibroids can be applied via use of 2D transvaginal ultrasound. However, for large-volume uteri this may require complementation using transabdominal 2D ultrasound, where the penetration achieved may be higher [12]. Furthermore, for fibroids in which the anatomical relations to the endometrial cavity and tubal ostia cannot be adequately ascertained, three-dimensional (3D) US and saline-infusion (SI) US may have a role, as described below.
Figure 2.2 Schematic representation of the commonest fibroid characteristics as described by the MUSA group (Van den Bosch et al., [7]): (1) hypoechogenic; (2) hyperechogenic; (3) heterogeneous echogenicity; (4) ill-defined outline; (5) echogenic areas; (6) cystic area; (7) internal shadowing; (8) fan-shaped shadowing.
2.3.2 Three-Dimensional Ultrasound
Assessment of fibroids using 3D ultrasound appears to be an upcoming and promising prospect [13]. To date, however, the data with regards to 3D ultrasound and the diagnosis of fibroids are relatively sparse. Two well-designed prospective studies compared 3D versus 2D ultrasound and found the former to be superior [14, 15]. In particular, it was thought that 3D ultrasound could provide a clearer visualization of the endometrial cavity and an overall better estimation of the size, outline and fibroid characteristics. The authors of the first study considered this to be of benefit in terms of preoperative planning [14]. The authors of the second study reported that 3D ultrasound corrected the diagnosis in many cases where 2D ultrasound had suggested that a fibroid was distorting the endometrial cavity. In fact, they reported that the rate of normal endometrial cavity examinations increased from 7.2% to 30.1% when 3D ultrasound was employed compared with 2D ultrasound alone [15]. Despite the lack of robust evidence to date, these advantages of 3D US in the assessment of uterine fibroids have been supported by subsequent expert authors in their systematic reviews [16, 17]. Most characteristically, Salim et al. commented that 3D ultrasound enables the assessment of the uterus from any angle and in any arbitrary plane, making it possible to assess both the size and the extent of cavity indentation of each individual fibroid perpendicularly to the endometrium, in a way which cannot be achieved with any other conventional diagnostic technique [18]. Examples of such fibroid mapping with 3D ultrasound are shown in Figures 2.3–2.6.
Figure 2.3 Example of a FIGO type 2–5 fibroid (i.e. intramural fibroid with <50% extension into the endometrial cavity and <50% extension beyond the serosal surface). The precise relation between the fibroid and the endometrial cavity is not so apparent on 2D US alone (a). However, with 3D US mapping, this becomes very clear as the fibroid can be seen protruding beyond the serosal surface by approximately 25% and abutting to the right lower third of the uterine cavity with a minor indentation of approximately 5%. The arrows (a) and callipers (b) are used to denote the fibroid.
Figure 2.4 In addition to the coronal plane, 3D US can also prove to be useful in the sagittal plane. In this example, a bulky uterus with no distinct fibroids was seen on 2D US (a); when applying 3D US rendering on the same sagittal plane, it is possible to see clearly a number of hypoechogenic intramural fibroids (as indicated by the arrows) (b).
Figure 2.5 An interesting case of a FIGO type 2 fibroid co-existing with a complete septate uterus. Surgical treatment may involve a two-step procedure consisting of an initial resection of the fibroid followed by resection of the residual septate tissue.
Figure 2.6 Fibroid mapping with 3D US can also be used during early pregnancy, particularly in those with known uterine fibroids. In this particular case, an intramural fibroid can be seen millimetres away from the implantation site. The fibroid did not distort the gestational sac and the outcome of this case was good.
2.3.3 Saline-Infusion Ultrasound (SI US)
Saline-infusion ultrasound (SI US) has long been thought to enhance the diagnostic accuracy of ultrasound due to the ability to clearly delineate the uterine cavity [9, 11]. This claim has now been substantiated by a recent systematic review and meta-analysis that has demonstrated a pooled sensitivity and specificity for diagnosing submucosal fibroids of 82% (95% CI: 69–92) and 100% (98–100), respectively, with positive and negative likelihood ratios of 44.14 (95% CI: 17.77–109.64) and 0.26 (95% CI: 0.15–0.45), respectively [19]. The authors concluded that SI US is a highly sensitive investigative modality and comparable to the gold-standard tool, hysteroscopy, in the detection of intrauterine abnormalities, including submucosal fibroids. With regards to 3D SI US, the authors concluded that 3D SI US may replace 2D SI US altogether owing to improved accuracy rates for preliminary studies. Furthermore, they went on to comment that 3D SI US may become a confirmatory test rather than a screening tool and may overtake diagnostic hysteroscopy as the gold-standard imaging method of choice [19]. Examples of fibroid mapping with 3D SI US are shown in Figures 2.7 and 2.8.
Figure 2.7 An example of a presumed intramural fibroid that was detected on 2D US (a). As the relation to the endometrial cavity could not be clearly delineated, 2D SI US was performed, which demonstrated a significant extension into the cavity and therefore a type 2 submucosal fibroid (b). Subsequently, 3D SI US was performed to further map out the location of the fibroid. Incidentally, and within a single coronal plane, an additional small polyp was identified near the right ostium, while a further intramural fibroid (type 4) was found to be adjacent to the left lateral cavity wall outline (c).
Figure 2.8 A case of multiple fibroids in which 2D US could not delineate the uterine cavity (a). 2D SI US demonstrated FIGO type 1 fibroid on the posterior wall of the uterine cavity (b). 3D SI US mapping demonstrated that the fibroid of 8.2 mL volume was occupying the entire right mid to ostial region of the uterine cavity while the remaining cavity was surrounded by type 2–3 fibroids (c).
2.3.4 Magnetic Resonance Imaging
Although not within the remit of the present chapter, MRI is becoming increasingly available, with an increasing role in the assessment of uterine fibroids. The pertinent question is: when is MRI evaluation of uterine fibroids required? Overall, authors appear to support that US is as efficient as MRI in the diagnosis and evaluation of fibroids in the majority of cases, particularly when they are fewer than five in number and they measure less than 375 mL in volume [20]. However, in larger and more numerous fibroids (i.e. >4 in number of >375 mL in volume), MRI appears to have an advantage, as it is not limited by acoustic shadowing and reduced penetration, and appears to suffer less inter-observer variability [21].
2.4 Special Considerations
2.4.1 Adenomyosis
Although adenomyosis is outside the remit of the present chapter, in clinical practice there can occasionally be a discrepancy or difficulty in distinguishing adenomyosis from fibroids when performing US. Therefore, it is important to distinguish both the histological and the US features of adenomyosis from those of fibroids. Adenomyosis is defined as the benign invasion of ectopic endometrial glands within the myometrium, either diffusely (adenomyosis) or in a localized manner (adenomyoma) [22, 23]. Conversely, fibroids consist of a collection of disorganized proliferated smooth muscle cells, commonly surrounded by an extracellular matrix and presenting in varying shapes, sizes, numbers and forms [24]. As the implications and management of each condition are different, the correct US differentiation and diagnosis is pivotal. The distinguishing appearances of each entity are therefore presented clearly in this chapter in Table 2.1.
Table 2.1 Features that aid the differentiation of fibroids versus adenomyosis
| Features | Fibroids | Adenomyosis |
|---|---|---|
| Contour of uterus | Lobulated or regular | Globular |
| Symmetry of uterine walls | Dependent on lesions | Anteroposterior asymmetry |
| Junctional zone | Regular and/or thin | Irregular and/or thickened |
| Outline of lesion | Well-defined | Ill-defined |
| Shape of lesion | Round, oval, lobulated | Ill-defined |
| Contour of lesion | Smooth | Ill-defined |
| Rim of lesion | Hypo-, hyper-echogenic | Ill-defined |
| Shadowing of lesion | Edge, internal, fan-shaped | Mostly fan-shaped |
| Echogenicity of lesion | Uniform or mixed echogenicity | Mixed echogenicity |
| Vascularity | Circumferential flow | Translesional flow |
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