A) Position of the patient and technical considerations (Figure 2):

For the study of IUD and ITD, sonographic acquisition can be obtained via a transabdominal or transvaginal approach, however, the transvaginal approach has become the most useful for reconstruction of the coronal plane with 3DUS. The operator holds the transducer in place while the probe sweeps across the obtained volume with images being electronically stored. 3D images are then processed and modified, and can then be displayed in multiple planes and orientations, such as sagittal, coronal, and axial planes and rendered images. They are obtained in addition to selected 2D transvaginal and transabdominal images.

The coronal view of the uterus is one of the most important benefits of 3DUS. [1]

The study of the pelvic floor is performed by placing the vaginal probe in a neutral position in the vaginal introitus with no excess compression on the urethral complex or surrounding structures. This allows a mid-sagittal image: visualizing pubic symphysis pubic, the entire length of the urethra, bladder, vagina, anal canal, rectum and levator ani muscle. 

B) Type of devices and normal positioning:

B1. Intrauterine device (IUD):

Most IUD are “T shaped, and hyperechoic, with associated extensive shadowing, that can limit evaluation on 2DUS.

There are two types of IUD (Figure 3,4,5): 

1- Copper IUD: the central stem is uniformly echogenic due to its copper coils. 

2- Levonorgestrel-releasing intrauterine system (LNG-IUS): consists of a plastic sleeve that contains the progestin and surrounds a central stem. This configuration causes acoustic shadowing and has a characteristic “laminated” sonographic appearance with parallel lines. The arms are only echogenic at the proximal and distal ends, with characteristic central posterior acoustic shadowing on transverse images. 

Properly-placed IUD (Figure 6) may be visualized as a straight hyperechoic structure in the uterine cavity and the arms of the IUD extending laterally at the uterine fundus. The main longitudinal axis of the IUD should align with the uterine cavity. On 3DUS we can better visualize the device without the acoustic shadow. [2]

B2. Intratubal device (Essure) (Figure 7):

These devices, no longer commercialized, are a permanent form of contraceptive that consists in two coils. On US they are echogenic metallic coils extending from the cornual portion into the proximal tubes. The device is introduced by hysteroscopy, and a coil anchors the device in the region of the cornua and into the fallopian tube, stimulating a benign fibrotic reaction that progressively occludes the tubes. 

3DUS with coronal reconstruction allows improved visualization of the device over 2DUS because the device can be seen in a single plane along its long axis. [3]

B3. Suburethral slings for urinary incontinence:

Slings for incontinence are seen as highly echogenic structures easily visualized by 2DUS being superior to clinical examination and MRI. 

Whether a retropubic (RP-TVT) or transobturator (TOT) approach has been used can be ascertained by the position of the arms and overall shape appearance (Figure 8,9):

- TOT classically has the arms going laterally towards the obturator foramen with a “sea-gull” shape. 

- RP-TVT is U-shaped with the arms traversing caudally towards the pubic bone.

Normal positioning criteria are depicted in Figures 10-13.

C) Complications:

C1. IUD:

Structural abnormalities:

IUDs may, rarely, broke during expulsion or removal. Few data are available on the long-term effects of retained strings or pieces of devices. 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.

Malposition:

The IUD is considered malpositioned if any part of it extends into the myometrium or cervix. Some patients have a small endometrial cavity or anatomic variant that causes abnormal IUD positioning. 3DUS allows precise determination of the amount of myometrial embedment. 

 There are 4 types of IUD malpositioning described in Figures 14-18:

- Expulsion is the passage either partially or completely through the

external cervical os.

- Displacement is the rotation or inferior positioning in the lower uterine segment or cervix. At evaluation of fundal placement of the IUD, the distance from the top of the uterine cavity to the IUD should be 3 mm or less. A distance greater than 4 mm is more often associated with a higher risk of expulsion. 

- Embedment results from myometrial penetration, without extension through the serosa, by the arm or stem of the IUD. In cases of subtle arm embedment, 3D coronal images allow for better detection.

- Perforation is the penetration through both the myometrium and the serosa, partially or completely. It can occur at the time of insertion in 1-2 cases per 1,000 or later [4].

C2. Intratubal device (Figure 19):

Structural Abnormalities:

Include a fractured or stretched coil. These have been reported on placement of the device at the time of initial device deployment into the fallopian tube. 

Malpositioning:

The coronal plane obtained with 3DUS is particularly helpful in showing coils that are too proximal in position, extending within the uterine cavity, or when they are in satisfactory position crossing the uterotubal junction. The perfect position includes an intrauterine portion, a cornual portion and an isthmic portion. A proximal position includes an intrauterine and a cornual portion (suboptimal) and a distal position does not include the intracavitary portion (suboptimal). A very distal position corresponds to the location in the isthmic portion of the fallopian tube. Only the very distal position showed a significant association with failed tubal occlusion [5].

C3. Suburethral slings for urinary incontinence:

The main complications regarding slings for incontinence are [6]:

- Sling failure – increased distance sling-urethra, sling-pubic symphysis, low or high position of the sling relative to urethral length and lack of dynamic compression on imaging;

- Folding;

- Obstructive sling – common findings are angulation and kinking of the urethra by the sling, short distance between the sling and the urethra/pubic symphysis and abnormalities of sling configuration around the urethra;

- Infection;

- Urethral perforation/erosion – can be readily apparent on US although the definitive diagnosis requires cysto‐urethroscopy.

3DUS is of particular value in the assessment of complex patients with several sling procedures [7].