Ultrasound has changed the practice of gynaecology over the past decades (Bau and Atri, 2000; Papp and Fekete, 2003). In fact it has become the main imaging tool and the first line of diagnostic investigation in gynaecologic examinations. Supported by the fact that it is noninvasive (Okaro and Valentin, 2004) and produces real time, immediate results, it helps to triage patients into appropriate management protocols. Pelvic ultrasound scans are also frequently performed in community sexual health and reproductive clinics and this reduces referrals to hospitals (Frates, 2008). Moreover, portable ultrasound machines can be brought to site of use in emergencies and in the hands of a well-trained Sonographer ultrasound scanning is a safe procedure without hazard to the patient (Barnett et al, 2000). In this essay, the author aims to discuss and evaluate the role of ultrasound and its potentials and limitations in assessing the female pelvis.
The standard gynaecology ultrasound examination involves transabdominal (TAS) and transvaginal (TVS) approaches, if there are no contraindications (Levi, et al 2008). A curvilinear 3.5-5MHz probe and a transvaginal high frequency probe usually a 7.5MHz are required. TAS done with a full urinary bladder gives a wider field of view providing better visualization of structures high up in the pelvis such as a large fibroid uterus or adnexal masses (Bates, 2006). As Bates points out, TAS is also useful in locating ovaries in relation to uterus, picking up uterine anomalies such as bicornuate uterus and scanning the iliac fossae and bladder. Levi et al, 2008 argue that this is limited by patients’ body habitus; in addition the full bladder itself in addition to displacing the organs to the far field thereby decreasing
resolution may produce reverberation artefacts0 (Bates 2006a). A further disadvantage of TAS is the fact that some patients cannot tolerate the distended bladder or else because of coexisting morbidities cannot reach adequate bladder filling (Bates 2006a). TVS on the other hand allows detailed examination of pelvic organs without requiring the bladder to act as an acoustic window. Therefore TVS should be performed in all situations when there are no contraindications such as virgo intacta patients, patients with narrow introitus or patients that do not consent (Levi et al, 2008). As pointed out by Bates (2006a) TVS disadvantages include narrower field of view, decreased probe flexibility during scanning, acceptability by patients who may regard it as invasive and uncomfortable, however this is generally overcome by the sonographer’s good communication skill and ensuring patients’ privacy and dignity (Bates, 2006a).In the normal examination TAS is performed initially to assess the pelvic view for large masses, then after emptying the bladder, TVS is done to obtain detailed study of the pelvic organs (Levi et al, 2008).
The indications to perform pelvic ultrasound include, but are not limited to these:-
- Pelvic pain
- Abnormal uterine bleeding, menorrhea, metrorrhagia, menometrorrhagia
- Follow up of abnormalities e.g. ovarian cysts
- Evaluation of infertility
- Delayed menses or precocious puberty
- Post-menopausal bleeding
- Evaluation of the congenital anomalies
- Localization of intrauterine contraceptive devices
- Screening for malignancy in patients with increased risk
The Guideline was issued by AIUM to outline the role of ultrasound in gynaecology
NORMAL PELVIC ANATOMY
The normal female reproductive system comprises of vagina, uterus, fallopian tubes and ovaries and on ultrasound their appearance is dependent on patients’ age and hormonal status at the time of imaging (Bates, 2006). The vagina, which is a thin walled muscular structure lies midline and appears as a hyperechoic midline echo. From the vagina, the uterus, a pear shaped muscular organ can be followed. This also lies in the midline and can be anteverted, retroverted or retroflexed (Bates, 2006b, Levi et al, 2008). The uterus is divided into a fundus, corpus, isthmus and cervix, however because no acoustic difference is evident between the parts, delineation is not always possible. The uterine wall is composed of three layers, each exhibiting its own characteristics on ultrasound (Alty and Hoey, 2006). The outer the innermost layer changes its thickness (pre menopause <15mm, post menopause <5mm) and reflectivity according to hormonal status of the patient. The ovaries are small oval shaped organs lying posterolateral on either side of uterus. Ovarian follicles are seen as well defined echofree areas that change in size with the menstrual cycle, varying from 2mm-20mm in diameter (Levi et al, 2008). The fallopian tubes, peritoneal recesses and ligaments are not visualized on ultrasound unless surrounded by, or contain fluid (Levi et al,2008). Pelvic floor musculature, however can be seen on ultrasound and appear as homogenous, hypoechoic linear structures.
ROLE OF ULTRASOUND IN COMMON GYNAECOLOGICAL PROBLEMS
– Asymptomatic palpable masses
Manypathologies may present as palpable masses on gynaecology ultrasound. Pelvic ultrasound is the primary diagnostic test used to characterize palpable pelvic masses (Langer and Arger, 2008). It differentiates between physiological masses which are usually only followed up and pathological masses which require further investigation and management. Typical physiological cysts arising from unruptured follicles appear as well defined, thin walled anechoic cysts with acoustic enhancement. Cysts <3cm usually don’t require further evaluation, however when larger may need re-evaluation after two menstrual cycles by which time most will have resolved (Tolan and Weston, 2006). Lesions >5cm raise concern for malignancy even in premenopausal women and therefore need to be correlated with CA125, though most are likely to be benign (Modesitt et al, 2003). Haemorrhagic cysts vary in appearance, however typically they show ‘lacelike reticular echoes’ with no vascularity on doppler ultrasound and this differentiates them from possible malignant lesions which may have similar appearance (Langer and Arger, 2008). Polycystic ovaries are quite distinguishable on ultrasound and appear as enlarged ovaries with bright stroma and show 12 or more follicles between 3-6mm. Paraovarian cysts may mimic ovarian cysts but confident diagnosis may be made if a band of tissue is seen between the cyst and ovary (Tolan and Weston, 2006). Endometriomas and dermoid cysts are also common. Endometriomas appear as cystic lesions with hypoechoic homogenous echotexture with no internal vascularity. Dermoids vary in appearance depending on their contents from cystic/complex to hyperechoic tumors with fluid levels, mural nodules, dots or lines containing hair, bone or teeth (Langer and Arger, 2008). In general, the lesions that raise concern for malignancy include, predominantly solid echotexture, cystic lesions with non-echogenic solid component, thick septations, mural nodules, internal vascularity and irregular outline (Valentin and Callen, 2008)
– Abnormal uterine bleeding
This may be classified as premenopausal or post menopausal uterine bleeding (Goldstein, 2008). Causes of bleeding excessive in flow and duration (menorhagia) are usually adenomyosis, submucous fibroids or dysfunctional uterine bleeding. Fibroids are usually assymptomatic and may vary in size and location, including intramural, subserosal, pedunculated and submucosal fibroids. Adenomyosis is another common cause of menorrhagia and dyspareunia and appears as ill-defined areas of hypo/hyperechogenicity varying from a few millimetres to large infiltrative masses with central vascularity producing streaky shadows as compared to the shadows produced by fibroids. Focal tenderness on palpation with TVS probe is also a typical finding (Lyons,2008:Goldstein, 2008). Metrorrhagia (intermenstrual bleeding) is most commonly caused by ovulation followed by endometrial polyps, carcinoma of the cervix or endometrium. For endometrial evaluation, scanning must be done before day 7 of menstrual cycle when the endometrium is thin. On ultrasound, polyps appear as echogenic masses with thin feeding stalk. Saline hysterosonography is helpful in detecting small polyps (Goldstein, 2008). For postmenopausal bleeding (PMB), causes include, endometrial atrophy, hyperplasia, carcinoma and polyps. Further studies of postmenopausal endometrium show that endometrial thickness is related to endometrial pathology (Langer et al, 1997, Goldstein, 2008). Endometrial echotexture and doppler indices are not conclusive, however saline hysterosonography is excellent to identify risk of carcinoma especially in patients where biopsy is needed. The cut off for endometrial thickness in postmenopause is <5mm.
– Investigation of infertility
Causes of infertility detectable on ultrasound include; congenital uterine anomalies, fibroids, polyps, hydrosalpinx as well as ovarian pathologies such as polycystic ovaries. Evaluation of fallopian tubes is essential in infertility, with normal fallopian tubes not visualized on
sonography. A fluid filled serpiginous adnexal structure suggests a non patent tube (Frates, 2008). Ovarian assessment to detect any possible pathologies and to visualize and document the number of follicles in each ovary is essential in evaluation of infertility (Kelly et al, 2001, Frates, 2008). In monitoring fertility treatment, ultrasound is essential to assess endometrial receptivity for implantation in vitro fertilization, monitor ovarian stimulation, facilitating transvaginal ovum retrieval, embryo transplant and identification of early pregnancy (Kelly et al, 2001).
– Acute pelvic pain
Acute pelvic pain (APP) is common with common gynaecological causes being ovarian cysts, torsion, pelvic inflammatory disease (PID), ectopic pregnancy, fibroids, endometrioma, ovarian carcinoma (Pellerito, 2008). PID caused by ascending infection from the cervix may
appear as a wide spectrum of disease with signs of inflammation such as endometritis, salpingitis, oophoritis or tubo-ovarian abscess. The main feature on ultrasound is usually a thick serpiginous adnexal structure representing the inflamed fallopian tube. Tubo-ovarian
abscesses appear as complex masses with fluid levels and echogenic debris (Pellerito, 2008). Ultrasound appearance of torsion depends on the degree of infarction and duration therefore diagnosis is mostly clinical (Tang and Ong, 2008). Ectopic pregnancy may be seen as an extra-uterine sac or tubal ring with an embryo or fetal activity. If this is not seen, examination for a pseudo gestational sac associated with decidual reaction and correlation with beta HCG may suggest the diagnosis.
LIMITATIONS OF ULTRASOUND IN GYNAECOLOGY
Pitfalls arise both during imaging and interpretation for example where some physiological structures mimic pathology. Some pathologies may also show overlapping ultrasound characteristics making diagnosis harder (Ong, 2004). Bowel gas obscures structures and may sometimes mimic cysts when overly distended. The production of good quality imaging is very much dependent on the skills of the sonographer. Standards of practice for pelvic ultrasound examinations have been set up by professional bodies and the sonographer should be aware of such guidelines and protocols. Clinical skills and knowledge should be kept up to date by means of continuous CPD.
From the discussion above, one can see that ultrasound is a valuable tool in gynaecology diagnosis and management with benefits outweighing risks if performed by well trained professionals. A combination of technical abilities, clinical knowledge and skills is required
to reach accurate diagnosis. A well prepared cooperative patient also contributes to successful outcome. Regular quality control procedures and auditing are a must for upkeep of good quality service. Considering the above evidence, the author concludes that to provide good safe practice, a sonographer should;
- Acquire recognized training, keeping skills updated with continuous practice and CME
- Use ultrasound as an extension of clinical practice not as replacement
- Perform each examination appropriately making an informed choice for patient preparation, procedure and equipment
- Perform regular quality control procedures and audit
- Use protocols and guidelines
- Respect the ALARA principle, as the basic safety principle to protect patients from over exposure