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

Introduction

Contraceptive arm implants are a reversible form of long-acting contraception, providing an extended release of progestin into the body through a subdermal implant (1). The implant is intended to be placed subcutaneously on the non-dominant upper arm’s medial side, using a pre-loaded trocar. Nowadays, there are two main types of globally available implants: levonorgestrel (LNG)-releasing devices, which include Sino-implant II^® (Dahua Pharmaceutical, Shanghai, China) and Jadelle^® (Bayer, Berlin, Germany), and etonogestrel (ENG)-releasing devices, which include Implanon NXT^® and Nexplanon^® (Merck, Kenilworth, NJ, USA), which are the same product with a different trade name (2,3).

In addition to the difference in the type of progestin released, both models of LNG-releasing implants are composed of two rods. In contrast, ENG-releasing contraceptive implants are composed of a single rod. Also, it is worth noting that Implanon NXT^®/Nexplanon^® is a new iteration of the product previously called Implanon^®. This latest model shares the same dimensions and progestin content as Implanon^®, but incorporates 15 mg of barium sulfate for visibility in case it becomes non-palpable at the insertion site, facilitating visualization through X-ray imaging (1). ENG implants are composed of an ethylene vinyl acetate (EVA) copolymer encased by a rate-controlling EVA membrane (4). The semi-rigid consistency of the EVA co-polymer base aids in the removal of the implant rod (5). LNG implants are also made of flexible material but, unlike ENG implants, they do not have a barium coating. Therefore, their radiopacity is significantly lower, and they also exhibit less echogenicity on ultrasound (US). The main differences between commercially available types of implants are summarized in Table 1.

The implants need to be removed when they reach the device’s licensed duration. Frequent or prolonged menstrual bleeding, pregnancy planning, and no longer needing the contraceptive method are common circumstances that require the removal of the implant before its maximum duration of action.

When the implant is palpable and located in the subcutaneous tissue, its removal can be performed in primary care centers or sexual health clinics with a small skin incision, without the need for imaging. The non-palpability of the implant may be due to inadvertent deep placement, which is estimated to occur once in every 1,000 insertions (6). Non-palpability can also be due to implant migration, defined as a movement of 2 cm or more beyond the insertion site, on which numerous case studies have been published over the years (7). If the implant is not palpable, imaging techniques must be used for its localization. Apart from the arm, the axillary region is the most frequent migration site for the implant, making it the initial area to examine if the implant cannot be found in the upper limb (8). On rare occasions, complications such as nerve injury, migration, and intravascular insertion leading to pulmonary embolization have been documented (9,10).

In this article, we will discuss imaging techniques that allow localization of the non-palpable contraceptive implant and we will propose an algorithm for its localization.

Imaging techniques for non-palpable contraceptive implant localization

US

US is the first-line imaging modality for a non-palpable implant (11). The patient usually can indicate the location of the implant insertion site, speeding up the localization process. It is advisable to use a high-frequency linear transducer (9–18 MHz or even higher) to accurately locate the implant (12).

It is recommended to perform the US with the patient’s arm in 90° abduction and external rotation, with elbow flexion, which allows exposing the postero-medial aspect of the arm, where the implant is usually located (replicating the position used for its insertion) (13).

The US appearance of the implant will depend on the orientation of the transducer plane relative to the implant. In the longitudinal plane, current ENG implants appear as an echogenic 40-mm linear structure, casting a posterior acoustic shadow (Figure 1A). If the transducer is in a transverse plane relative to the implant, the implant rod will be visualized as a small yet distinct 2-mm-diameter highly echogenic spot with a strong posterior acoustic shadow (Figure 1B) (14). Unlike the previously mentioned ENG implants, Jadelle^® implants present as a hypoechoic tubular image on US and also generate a weaker posterior acoustic shadow. (Figure 1C,1D).

Figure 1 Ultrasound characteristics of contraceptive implants. (A) A subcutaneous Implanon NXT^® implant is observed in the longitudinal plane, with the total length of the implant indicated by the dotted double arrow. The implant shows a strong posterior acoustic shadow. (B) The Implanon NXT^® implant (blue arrow) is shown in the transverse plane, where it appears as a highly echogenic spot with a posterior acoustic shadow. (C) A Jadelle^® implant (dotted double arrow) is observed in the longitudinal plane. Note the weaker acoustic shadow compared to the Implanon NXT^®. (D) The Jadelle^® implant (white arrow) is observed in the transverse plane, where it appears as a tubular hypoechoic image, also with a weaker posterior acoustic shadow than the Implanon NXT^®.

Due to the presence of echogenic fibrous septae in the arm, false-positive diagnoses, indicating the apparent detection of a rod, can occasionally occur. The linear condensations of fibrous septae can often resemble the appearance of an implant rod. Therefore, it is crucial that during US, the rod is observed in both sagittal and transverse imaging planes, ensuring clear end-points and the presence of acoustic shadowing (15).

The main objective of US is to determine the depth and location of the implant. The supra or subfascial (intramuscular) location of the implant should be reported (Figure 2A), along with its relationship with adjacent nervous and vascular structures (Figure 2B). In some cases, the implant may be in close contact with the fascia, making it challenging to confidently determine a supra or subfascial position.

Figure 2 Implant ultrasound localization and relationship with adjacent structures. (A) An Implanon NXT^® rod (white arrow) is clearly identified, located intramuscularly in the muscle belly of the triceps. (B) The close relationship of this Jadelle^® implant rod (asterisk) with the ulnar nerve (red arrow) and median nerve (blue arrow) can be appreciated.

X-ray

To determine if the contraceptive implant can be correctly located using X-ray, it’s necessary to know the type of implant that has been inserted. The type of implant will influence the possibility of its visualization through X-ray and the number of rods that need to be located. In some instances, patients may have carried their contraceptive implant for many years, so it may be necessary to locate implants that are no longer commercially available today. The ENG implants currently on the market are radiopaque and can be easily identified on X-ray and computed tomography (CT) (16). The absence of this barium coating in LNG implants or older ENG implants makes their visualization on X-ray and CT scans more difficult.

For their localization, the most recommended approach is to perform X-rays of the upper arm in anteroposterior views, both in neutral and internal or external arm rotation. Lateral projections can also be conducted to facilitate visualization in case of difficulty locating the implant. The implant will appear as one (or two, depending on the implant) radio-opaque bands (Figure 3A,3B). If the patient is unsure about which arm the implant was placed in, it is advisable to perform a bilateral X-ray.

Figure 3 X-ray characteristics of an Implanon NXT^®-type implant rod. Shown in AP humeral view (A) and AP view with external arm rotation and abduction (B). The arrows point to the implant, shown as a radiopaque band. This implant was located in the biceps brachii muscle belly (confirmed by US). AP, anteroposterior; US, ultrasound.

In some cases, the subcutaneous location of the implant can be confirmed with X-ray imaging. Additionally, arm X-rays may, in rare occasions, reveal axillary migration of the implant (8).

However, X-ray might, in certain instances, raise doubts about the intramuscular localization of the implant, requiring further investigation with other imaging techniques, primarily US (Figure 4A,4B).

Figure 4 Implanon NXT^® implant rod through X-ray. Anteroposterior projection of the humerus (A) and anteroposterior projection of the humerus with internal rotation (B) showing an implant apparently located at the intramuscular level on the medial margin of the biceps muscle. A subsequent ultrasound demonstrated that the implant was actually in a subcutaneous location but in close contact with the fascia of the biceps muscle.

Magnetic resonance imaging (MRI)

In uncommon instances, when implants are migrated or deep positioned within the muscle or just beneath the muscle fascia, they can be difficult to detect, even with the use of high frequency transducers (17).

In these relatively infrequent scenarios, MRI can function as a suitable secondary imaging method, particularly in cases involving deeply inserted, non-palpable implants (18). Since contraceptive implants are made of plastic and do not include any metallic parts, using MRI to locate them is completely safe. When used effectively, MRI is a fast and precise technique for locating misplaced rods that may not be visible during US examination. However, caution is necessary when distinguishing blood vessels and fibrous septae from implant rods as they have similar appearance (15). The usual orientation of the implant is parallel to the humerus. It can be helpful to initiate the MRI study with broad coronal or sagittal images that enable the craniocaudal localization of the implant, followed by acquiring axial images centered on that location.

In transverse MRI scans, the implant manifests as a highly hypointense 2-mm spot (Figure 5A,5B). This black spot can be tracked through sequential scan layers, adding up to 40 mm (the total length of the implant) (18). As the device lacks free water or free protons, it will appear hypo-intense on all sequences. Avoiding fat suppression is crucial, as it could decrease the chances of detecting the implant in subcutaneous fat and, by reducing the overall signal, hinder detection if it lies in deep muscle (15) (Figure 6A,6B). Both fibrous septae and vessels in fat and muscle can complicate accurate visualization. Thoroughly reviewing images in at least two planes is necessary (15).

Figure 5 MRI characteristics of intramuscular contraceptive implant. T1-weighted spin-echo images in axial (A) and coronal (B) planes. Both white arrows indicate the position of the contraceptive implant, in this case, incorrectly positioned at the intramuscular level in the biceps brachii, visualized in T1 as a markedly hypointense tubular image. MRI, magnetic resonance imaging.

Figure 6 Jadelle^® implant MRI localization and relationship with neurovascular structures. In this figure, we present a two-rod implant (Jadelle^®) located by MRI with axial T1-weighted sequence (A) and axial STIR-weighted sequence (B), at the subcutaneous level. The white arrows indicate the position of the two rods of the implant. The posterior rod is close to the basilic vein (red asterisk). Note how the image in T1 without fat saturation (A) allow a better visualization of the implant and a more precise assessment of adjacent neurovascular structures: median nerve (green arrow), medial cutaneous nerve (yellow arrow), ulnar nerve (blue arrow) and brachial artery (white asterisk). MRI, magnetic resonance imaging.

The use of MRI-contrast agents can be helpful if the implant is located in close contact with the vascular and nervous bundle, allowing for easier differentiation and more precise localization in relation to vessels and nerves before a potential removal.

CT

CT should be considered as a secondary imaging test for the localization of non-palpable contraceptive implants, due to its ionizing radiation exposure. In CT images, a radiopaque implant is visualized as a hyperdense band, attributed to its coating with barium sulfate. The primary utility of CT in locating non-palpable contraceptive implants lies in the case of pulmonary embolism due to vessel implant migration from arm veins to pulmonary arteries, an infrequent complication but with multiple reported cases (19-21). In the event of such suspicion, it is necessary to perform a contrast-free thoracic CT to facilitate the visualization of the implant in the arterial lumen, since arterial contrast opacification would hinder the proper visualization of the implant. Following localization, the patient can be referred for the removal of the device in interventional radiology (22).

Measurement of serum ENG levels

X-ray, US and MRI are expected to locate the vast majority of non-palpable implants. It is necessary to confirm that the implant was indeed initially inserted into the patient if imaging methods are unable to identify it, given that there have been cases of technical issues during the insertion procedure. These errors can result in the implant remaining in the insertion device and not having been truly introduced into the patient at any point (23). Measuring serum ENG levels can confirm whether the implant is in place but cannot determine its specific location. A negative serum ENG level verifies the absence of the implant by indicating undetectable levels of the active component of the implant, ENG (14,18). This detection method can only be employed with ENG implants.

Localization algorithm proposal

The first step for localization is palpation of the implant in the arm. If the implant is clearly in a subcutaneous location through the palpation technique, there will be no need for any imaging test. In cases where the implant is not palpable or only slightly palpable, raising doubts about a possible subfascial location, an US should be performed to determine its exact position.

In rare instances where the implant cannot be located through US, it should be considered whether the device is radiopaque. If the implant is radiopaque, the next step for its localization is an X-ray of the arm. Through this imaging technique, it is possible to quickly and easily assess whether the implant is indeed in the arm and determine its approximate location. The implant may have migrated proximally, even in some cases toward the axillary region, which could have hindered its US localization. Once its approximate location in the arm is determined through X-ray, the US can be repeated, focusing on the area where the implant is located, to pinpoint its position easily.

If the implant is not radiopaque, its visualization through X-ray is challenging. In such cases, it is advisable to perform an MRI of the arm. Through MRI, the implant can be precisely located in the arm or, in cases of proximal migration, even in the axillary region (it is advisable to obtain wide coronal sequences to increase the explored area in the MRI).

When the implant has not been located through US, X-ray, and MRI, it may be due to two main causes: either the implant was never placed in the patient or the implant has migrated from the arm veins to the pulmonary region. If the implant is trackable through serum ENG levels, this blood test should be conducted to determine if the implant is indeed present in the patient’s body. Once its presence is confirmed, or if the implant is not trackable, a chest X-ray should be obtained (although it may be difficult to locate the implant due to the overlap of structures) or, preferably, a chest CT to help determine if there has been migration of the implant to the pulmonary arteries. The algorithm for the localization of deep contraceptive implants that we propose is depicted in Figure 7.

Figure 7 Algorithm proposal for the localization of contraceptive implants. US, ultrasound; MRI, magnetic resonance imaging; ENG, etonogestrel; CT, computed tomography.

When the implant is subcutaneous and palpable, the removal procedure (“pop out” technique) is usually quick and done without the need for imaging guidance, through a small skin incision. In cases where the implant is in a deep subcutaneous or subfascial location, or in proximity to vascular or nervous structures in the arm, its removal is recommended with US guidance, also through a skin incision (24). The US-guided procedure enables the removal of the implant at the very moment of its US localization. In cases where this option of US-guided percutaneous removal is not available, open surgery will be necessary for its safe removal after marking the implant location on the skin or through intraoperative US guidance. In the event of an extremely rare pulmonary migration of the implant, the possibility of percutaneous removal should be assessed by an interventional radiology team, or other surgical options should be explored (22,25).

Conclusions

Non-palpable contraceptive implants can be accurately located using imaging techniques. US is the primary imaging technique that should be used for implant localization because of its simplicity and quickness when it comes to precisely locating non-palpable contraceptive implants. In rare instances where US fails to locate the implant, alternative imaging techniques such as X-ray, MRI, or CT can be employed, following the algorithm suggested in this article.

Acknowledgments

Funding: None.

Footnote

Provenance and Peer Review: With the arrangement by the Guest Editors and the editorial office, this article has been reviewed by external peers.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-24-353/coif). The special issue “Advances in Diagnostic Musculoskeletal Imaging and Image-guided Therapy” was commissioned by the editorial office without any funding or sponsorship. X.T. served as the unpaid Guest Editor of the issue. The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

References

1. Zhang S, Batur P, Martin C 3rd, Rochon PJ. Contraceptive Implant Migration and Removal by Interventional Radiology. Semin Intervent Radiol 2018;35:23-8. [Crossref] [PubMed]
2. Thaxton L, Lavelanet A. Systematic review of efficacy with extending contraceptive implant duration. Int J Gynaecol Obstet 2019;144:2-8. [Crossref] [PubMed]
3. Bahamondes L, Bahamondes MV. New and emerging contraceptives: a state-of-the-art review. Int J Womens Health 2014;6:221-34. [Crossref] [PubMed]
4. Croxatto HB, Urbancsek J, Massai R, Coelingh Bennink H, van Beek A. A multicentre efficacy and safety study of the single contraceptive implant Implanon. Implanon Study Group. Hum Reprod 1999;14:976-81. [Crossref] [PubMed]
5. Mascarenhas L. Insertion and removal of Implanon: practical considerations. Eur J Contracept Reprod Health Care 2000;5:29-34. [Crossref] [PubMed]
6. Mansour D. Nexplanon(®): what Implanon(®) did next. J Fam Plann Reprod Health Care 2010;36:187-9. [Crossref] [PubMed]
7. Ismail H, Mansour D, Singh M. Migration of Implanon. J Fam Plann Reprod Health Care 2006;32:157-9. [Crossref] [PubMed]
8. Uwagbai ON, Wittich AC. Migration of a Subcutaneous Contraceptive Device. J Am Osteopath Assoc 2016;116:627. [PubMed]
9. Ohannessian A, Levy A, Jaillant N, Tanguy Le Gac Y, D'Journo X, Vidal V, Agostini A. A French survey of contraceptive implant migration to the pulmonary artery. Contraception 2019;100:255-7. [Crossref] [PubMed]
10. Rivera F, Bianciotto A. Contraceptive subcutaneous device migration: what does an orthopaedic surgeon need to know? A case report and literature review. Acta Biomed 2020;91:232-7. [PubMed]
11. Herzog J, Walker L, Sutter C, Azar N, Nakamoto D. Ultrasound First for Removal of Nonpalpable Contraceptive Implants. J Ultrasound Med 2021;40:1479-83. [Crossref] [PubMed]
12. James P, Trenery J. Ultrasound localisation and removal of non-palpable Implanon implants. Aust N Z J Obstet Gynaecol 2006;46:225-8. [Crossref] [PubMed]
13. Biskamp C, Kauffman RP. Arm flexion during ultrasound assists localization of an intramuscular etonogestrel contraceptive implant. Contraception 2016;93:273-5. [Crossref] [PubMed]
14. Kapstein M, Ganpat R. Localisation of nonpalpable single-rod contraceptive implants using ultrasound sonography. Eur J Contracept Reprod Health Care 2002;7:86.
15. Westerway SC, Picker R, Christie J. Implanon implant detection with ultrasound and magnetic resonance imaging. Aust N Z J Obstet Gynaecol 2003;43:346-50. [Crossref] [PubMed]
16. Schnabel P, Merki-Feld GS, Malvy A, Duijkers I, Mommers E, van den Heuvel MW. Bioequivalence and x-ray visibility of a radiopaque etonogestrel implant versus a non-radiopaque implant: a 3-year, randomized, double-blind study. Clin Drug Investig 2012;32:413-22. [Crossref] [PubMed]
17. Merki-Feld GS, Brekenfeld C, Migge B, Keller PJ. Nonpalpable ultrasonographically not detectable Implanon rods can be localized by magnetic resonance imaging. Contraception 2001;63:325-8. [Crossref] [PubMed]
18. Shulman LP, Gabriel H. Management and localization strategies for the nonpalpable Implanon rod. Contraception 2006;73:325-30. [Crossref] [PubMed]
19. Gao GT, Binder W. Embolization of a contraceptive implant into the pulmonary vasculature in an adolescent female. Am J Emerg Med 2018;36:1122.e1-2. [Crossref] [PubMed]
20. Hindy JR, Souaid T, Larus CT, Glanville J, Aboujaoude R. Nexplanon migration into a subsegmental branch of the pulmonary artery: A case report and review of the literature. Medicine (Baltimore) 2020;99:e18881. [Crossref] [PubMed]
21. Rowlands S, Mansour D, Walling M. Intravascular migration of contraceptive implants: two more cases. Contraception 2017;95:211-4. [Crossref] [PubMed]
22. Akhtar MM, Bhan A, Lim ZY, Akhtar MA, Sekhri N, Bharadwaj P, Mullen M. Percutaneous extraction of an embolized progesterone contraceptive implant from the pulmonary artery. Open Access J Contracept 2018;9:57-61. [Crossref] [PubMed]
23. de Leeuw M, Oostenbroek RJ, Pijpers L, Plaisier PW. Two patients with a non-palpable, subcutaneously implanted contraceptive. Ned Tijdschr Geneeskd 2004;148:1785-8. [PubMed]
24. Jacques T, Brienne C, Henry S, Baffet H, Giraudet G, Demondion X, Cotten A. Minimally invasive removal of deep contraceptive implants under continuous ultrasound guidance is effective, quick, and safe. Eur Radiol 2022;32:1718-25. [Crossref] [PubMed]
25. Cerato A, Luyckx M, Ghaye B. Migration of implanon contraceptive implant into the pulmonary artery. Diagn Interv Imaging 2019;100:59-60. [Crossref] [PubMed]