[Sonographic localization of non-palpable implanon hormone implants]

Implanon is a rod-shaped hormone implant which leads to reliable contraception. The rod is implanted in the subcutis of the upper arm and is usually removed easily after its effective period. In the scenario where the rod is not palpable, the removal of the rod can be difficult or impossible. The purpose of this study was to evaluate the reliability of US in locating non-palpable Implanon implants and to investigate the optimal technical parameters for determining the location.

In a prospective study we evaluated 21 women between June 2004 and June 2008. In 14 patients previous examinations with US, radiography, CT and/or MRI were non-diagnostic. The US evaluation followed a standardized protocol in transverse and longitudinal sections. The technical parameters US frequency, position and number of focal zones and compound imaging were varied to define the optimal parameters for the visualization of the Implanon implant.

The Implanon implant was detected in all 21 patients. Reasons for negative palpability were mainly an intramuscular or subfascial location as well as a significant migration of the Implanon implant in 2 patients. The use of a high US frequency, the position of the focal zones in the near field and the deactivation of compound imaging all facilitate visualization of the characteristic US morphology of the plastic rod.

High resolution US is the method of choice for determining the location of non-palpable Implanon implants. Knowledge of US morphology and optimal technical settings as well as the use of high-resolution scan heads are essential for determining the correct location.