Actinomycosis is an opportunistic infection which, in the pelvis, usually presents after the introduction of foreign devices or surgery (such as an IUD in our case). The radiological appearance of soft tissue actinomycosis can be quite impressive and aggressive-looking. This appearance might be mass-like or infiltrative and will demonstrate cellularity (restricted diffusion on MRI and contrast enhancement). It is important to consider Actinomycosis as a differential option in appropriate patients, without delaying confirmatory tissue sampling.

Fortunately for this patient, there was no need for partial or total cystectomy, and there was resolution of the "mass" after medical treatment.