Non-palpable contraceptive implants localization: review of imaging techniques and algorithm proposal

Contraceptive arm implants provide long-acting contraception through a subdermal rod. The device is intended to be placed on the medial side of the non-dominant upper arm. There are two main types of implants: etonogestrel (ENG)-releasing devices, such as Implanon NXT^®/Nexplanon^®, and levonorgestrel (LNG)-releasing devices, including Sino-implant II^® and Jadelle^®. Since the rods are not biodegradable, the implants must be removed after the device's licensed duration. When the implant is palpable and located in subcutaneous tissue, it can be removed with a small skin incision, without the need for imaging. If the implant is not palpable, imaging techniques must be used for precise localization. Ultrasound (US) is the first-line imaging modality for non-palpable implants, allowing quick and accurate localization in the vast majority of cases. The patient can usually indicate the implant insertion site, which speeds up the localization process. If the implant cannot be located using US, other imaging techniques should be used. X-ray can also be useful for a quick localization assessment of radiopaque implants. Magnetic resonance imaging (MRI) is valuable for locating deep or migrated implants, especially if the device has not been locatable through US or X-ray. In case of suspected pulmonary migration, a thoracic computed tomography (CT) should be performed for arterial implant detection. In this article, we review the imaging techniques used for implant localization. We also present an algorithm that recommends a sequential approach to implant localization, integrating imaging modalities based on implant characteristics and patient presentation.