Abstract
Long-acting reversible contraceptives like intrauterine devices (IUDs) and systems (IUSs) and subdermal implants (SDIs) are widely used contraceptive devices in the world today. Intrauterine devices and systems together are referred to as intrauterine contraception (IUC). In the UK, IUCs and SDIs constitute approximately 38 per cent of the contraceptives used by women of reproductive age. Imaging plays an important role in a contraceptive clinic in ensuring IUDs/IUSs are correctly sited, locating them in case of missing threads and aiding in their removal or insertion. Of the imaging methods available, ultrasound is the most commonly used due to ease of availability, lack of exposure to radiation and cost-effectiveness. The transducers used to locate IUCs are usually a transvaginal probe and a curved transabdominal probe. The latter proves to be very useful in performing ultrasound-guided procedures.
Introduction
Long-acting reversible contraceptives like intrauterine devices (IUDs) and systems (IUSs) and subdermal implants (SDIs) are widely used contraceptive devices in the world today [1]. Intrauterine devices and systems together are referred to as intrauterine contraception (IUC). In the UK, IUCs and SDIs constitute approximately 38 per cent of the contraceptives used by women of reproductive age [2]. Imaging plays an important role in a contraceptive clinic in ensuring IUDs/IUSs are correctly sited, locating them in case of missing threads and aiding in their removal or insertion. Of the imaging methods available, ultrasound is the most commonly used due to ease of availability, lack of exposure to radiation and cost-effectiveness. The transducers used to locate IUCs are usually a transvaginal probe and a curved transabdominal probe. The latter proves to be very useful in performing ultrasound-guided procedures. Other imaging methods such as x-rays are used only when a translocated coil is not seen within the uterine cavity on scan. A plain x-ray of the abdomen and pelvis will then help identify whether the coil is intra-peritoneal and extra-uterine or has been expelled. Magnetic resonance imaging (MRI) or computed tomography (CT) are very rarely used when assessing IUDs, but coils may be seen when these modalities are used for other indications.
Intrauterine Contraception: Types
When performing an ultrasound in a case with an IUC in situ it is always best to note the type of coil inserted from the history. Coils in general can be classified into three types.
Inert. These are rarely seen nowadays. It is a historic ring, seen sometimes in patients from China, where it was once quite popular. They are easily seen on ultrasound, lack a thread and are best removed under local anaesthesia as an ultrasound-guided procedure. If this approach fails, a hysteroscopy under general anaesthesia with direct visualization of the device may be the only option for removal of these coils.
Copper coils. These have evolved over the years from a first-generation device, through to the second generation and then to the third-generation coils (T Safe Cu 380A) that we see today. The current third-generation coils used in contraception clinics generally have a straight shaft with a horizontal arm in the shape of a T. The denseness of the shaft along with the copper coil makes it easily identifiable on a scan. The newer versions of the coils also have barium incorporated into them, which makes them easily identifiable on scans and x-rays. On ultrasound, both the horizontal and vertical stems of the copper IUD appear very echogenic (Figures 15.1–15.3).
Figure 15.3 Longitudinal view of the uterus with a copper IUD. The IUD is displaced down slightly from the fundus (by 0.58 cm).
Hormonal coils. Hormonal coils available in the UK market are the Mirena®, Levosert® or Jaydess®. The Mirena is composed of a T-shaped polyethylene frame with a 32 mm vertical stem and 32 mm horizontal arm containing barium sulphate. The stem has a reservoir containing a mixture of levonorgestrel and silicone covered by a silicone membrane [3]. On ultrasound the appearance of the Mirena IUD is characteristic, with acoustic shadowing between the echogenic proximal and distal ends (Figure 15.4), unlike copper IUDs, which are more or less completely echogenic [4]. While the early versions of the Mirena IUD were very difficult to visualize sonographically, recent versions have an easily identifiable shaft appearance with a slightly less echogenic but readily identifiable string.
Complications of IUCs
It is when complications of IUCs develop that they become radiologically relevant. These include malposition, uterine perforation, pelvic inflammatory disease and pregnancy.
Malposition of the IUC
For an IUC to be effective it is expected to be as close to the fundus of the uterus as possible. There is no real consensus as to how much below the fundus the IUC must be before it can be deemed ineffective. For a copper IUD, if it is >3 mm below the fundus it is considered misplaced, with adequate contraceptive protection not guaranteed [5]. In theory, the hormonal coils (e.g. Mirena IUD) may remain effective in low positions. However, the guideline from the Faculty of Sexual and Reproductive Health is that if the IUC is at a distance of 2 cm from the fundus the contraceptive effect cannot be guaranteed [6].
On ultrasound, the malpositioned IUC can be visualized with the tip in the mid or lower uterus or in the cervix. However, for a hormonal IUD, as long as it is completely within the uterine cavity it will continue to be effective, unlike the copper IUD. Malpositioned IUCs can be a cause of pain, especially during intercourse. When positioned low they are also at risk of expulsion spontaneously, though they are sometimes known to migrate into a normal position 2–3 months later [7]. However, the recommendation is that malpositioned IUCs should be removed and replaced unless it is an IUS that is completely within the uterine cavity. Three-dimensional transvaginal sonography has been shown to be more accurate in identifying the type and location of the IUC than 2D transvaginal sonography [8]. However, in clinical practice this is rarely necessary. Three-dimensional sonography is especially useful in accurate evaluation of misplaced IUCs as, with this type of scanning, structures that are not located in the same plane can be imaged simultaneously, thus giving a much clearer picture of the displacement [9].
There is evidence that in patients with prior uterine surgery it is possible that the IUC will migrate into the scar and be a cause of pain [1]. In patients with previous Caesarean section deliveries there may be extension of the lower end of the IUC into the scar. While the clinical importance of such migration is uncertain, removal is recommended only in the presence of pain.
Malposition can also occur when the shaft or crossbar of an IUC extends into the myometrium. It could be an incidental finding or the patient may complain of pain. Clues to this diagnosis are when the crossbars are low in the uterus or when they extend in an antero-posterior direction rather than the typical transverse position in the uterine fundus (Figures 15.1 and 15.2). Extension into the myometrium typically occurs at the time of insertion. Therefore, when scanning it is important to assess for extension of the echogenic portion of the IUC outside the endometrium into the myometrium. Sometimes this can be a subtle finding, seen only on a single image.
Uterine Expulsion
Incidence of this complication is somewhere around 1 in 20 [6] and occurs within the first three months of insertion, especially around menstruation. Clinically the string of the IUC cannot be felt either by the patient or by the clinician. The possibilities are as follows: (1) the IUC has been ejected from the uterus; (2) the IUC is in the uterus (in either a normal or an abnormal location), but the string is broken or misplaced; or (3) the uterus has been perforated, and the IUC has translocated into the uterine cavity. The expulsion rate is highest when the IUC is placed in the immediate postpartum period after a vaginal delivery [10].
Uterine Perforation
The perforation rate for IUCs is quoted as less than 1 per 1000 and is increased in the following instances: (1) with placement by inexperienced operators; and (2) when the IUC is placed less than six months postpartum. When the IUD migrates outside the uterus, it can lead to additional complications, such as bowel or bladder perforation. In addition, in a hormone-containing IUC, the serum hormone levels can be up to 10 times higher when the IUC is in a peritoneal location than when it is intrauterine. When an IUC cannot be visualized within the uterine cavity using ultrasound, a plain radiograph of the abdomen and pelvis can help in localizing the IUC.
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