Findings:

Intrauterine device is malpositioned with arms embedded in the myometrium near right cornu.

Malposition on gray scale is suspected by inability to image the stem in entirely in sagittal plane.

Embedment on gray scale is suspected by end of the stem surrounded only by myometrium and not by endometrium.

The correctly positioned IUD is shown within the uterine cavity near the fundus. The two arms are fully unfolded, reaching laterally toward the uterine cornua. The stem extends inferiorly with the retrieval strings exiting through the cervix.

USG:

The stem is usually easily identified on standard two-dimensional (2D) transvaginal ultrasonography (TVUS) as a linear echogenic structure (Fig. 3A–D). While the arms of the copper IUD are also fully echogenic, the arms of the levonorgestrel-releasing IUD are only echogenic at the proximal and distal ends, with characteristic central posterior acoustic shadowing on transverse images (Fig. 3D) [11]. Three-dimensional (3D) reconstructions are increasingly being used, particularly in the coronal view, which allows for a more careful evaluation of the arm positioning 

Other imaging modalities can be accessory in select cases. When the IUD cannot be seen on pelvic ultrasonography, abdominal radiographs can be used to evaluate IUD positioning, as all IUDs are radiopaque. Positioning on an abdominal radiograph varies with normal uterine positions, but the IUD should be located near the midline low in the pelvis and orientated with the arms superior to the stem (Fig. 4A, B). In cases where complications such as perforations or abscesses are suspected, computed tomography (CT) or magnetic resonance imaging (MRI) may be a helpful adjunctive modality given their larger field of view. 

Types of malpositioned intrauterine devices

Expulsion

The expelled IUD has passed inferiorly, either partially or completely through the external cervical os. The expulsion risk is greatest in the first year of use and the expulsion rate is highest with immediate postpartum placement after vaginal delivery.

When the expelled device has been identified or is seen on physical exam, expulsion can be managed without imaging. However, in cases of absent retrieval strings without witness of the expelled device, pelvic ultrasonography should be performed to evaluate the IUD position. If no IUD is identified by ultrasonography, an abdominal radiograph is recommended to exclude perforation and intraperitoneal migration.

Displacement

 A displaced copper IUD has decreased efficacy; however, a displaced hormone-releasing IUD is equally effective as a properly positioned one [22]. 

Because of the pregnancy risk and the differences in efficacy, some researchers advocate for the removal of displaced copper IUDs but not hormone-releasing devices in asymptomatic patients [9]. Regardless, findings of a malpositioned IUD should be communicated to the referring physician.

Embedment

When involving the stem, this may be obvious on standard 2D TVUS, but in cases of more subtle arm embedment, 3D coronal images allow for better detection. With the added sensitivity of 3D techniques, the incidence of embedment was found to be as high as 16.8%.

Extension into the myometrium is thought to occur at the time of insertion. When these findings are associated with symptoms of pain or abnormal bleeding, IUD removal is recommended. Often, embedment occurs in combination with displacement, which also leads to the same management decisions based on efficacy as those previously discussed.

Perforation

As with embedment, perforation occurs at the time of insertion. Perforation through the serosa occurs in one to two cases per 1,000 and is more often seen with inexperienced operators, with early postpartum placement, and in women with either few prior pregnancies or multiple miscarriages.

Adhesions that form as a result of a foreign body reaction to the perforated IUD can involve the fallopian tubes and result in decreased fertility. Cases of complete perforation can also rarely be associated with injury to adjacent structures, most often the bowel. If an IUD cannot be identified on initial ultrasonography, abdominal radiographs are required to locate the IUD. Cross-sectional imaging can be used for surgical planning and to evaluate for complications such as abscess formation or bowel injury. 

Uncommon IUD Complications and Mimics

Fragmentation

IUDs may, rarely, be broken during expulsion or removal, including embedded retrieval strings

Calcification

Incrustation, the formation of calcium carbonate deposits on or near the IUD, is a well-described phenomenon that can be demonstrated as uneven echoes surrounding the normal IUD echoes

Mimics

• Retained fetal bone fragments are rare sequelae of spontaneous or induced abortions. Ultrasonography findings include linear or angular echogenic shadowing structures within the uterine cavity or myometrium [27]. In the absence of a clear history, this finding may be misinterpreted as an IUD on ultrasonography [28]. In fact, the retained fetal part is thought to act like an IUD, causing secondary infertility, which may be the only presenting symptom. 
• Endometrial osseous metaplasia is a related and equally rare phenomenon, with the development of a mature bone in the endometrium, whose pathogenesis is controversial. Prevailing theories include development from retained fetal bone or true metaplasia of the endometrial tissue secondary to chronic inflammation. This can also be the cause of secondary infertility and be mistaken for an IUD [29].