Internal mammary lymph node siliconoma in absence of prosthesis rupture: a case series that raises concern for potential risk of overdiagnosis.

Background: Silicon migration after rupture is an adverse event of breast implant, whose risk increases with the aging of prosthesis. The exact prevalence of this complication remains unclear and reported data are inconsistent. In addition, microscopic diffusion of silicone gel through intact implant, known as gel bleeding, might verify thus complicating diagnosis. Although high cohesive gel has reduced the occurrence of gel bleeding, this phenomenon is still possible and its occurrence rate remains underestimated. If silicon droplets migrate in locoregional lymph node, a swelling that mimics recurrence can arise. Therefore, a risk of overdiagnosis is possible when clinicians rely only on imaging techniques. The aim of this study is to evaluate the actual prevalence of metastasis in internal mammary lymph node (IMLN) in presence of PET positive uptake and no prosthesis rupture.

Methods: We retrospectively evaluated our patient's records and selected those with intact breast implants and suspected relapse in IMLN that underwent biopsy, either surgical or imaging guided. All patients performed PET/CT scan showing pathological uptake in IMLNs. A breast magnetic resonance (MRI) or ultrasound (US) imaging confirmed a suspicious adenopathy and excluded prosthesis rupture. From 2015 to 2019 a total of nine patients underwent biopsy of the IMLN and only six of them met inclusion criteria.

Results: Four biopsies were CT-guided, two were surgical. Three patients (50%) were diagnosed with breast cancer relapse while two (33.3%) were found with siliconoma and one (16.7%) was inflammatory.

Conclusions: Siliconoma can occur even without evidence of capsule rupture, challenging the clinicians and leading to a risk of relapse over diagnosis. Echographic, MRI and nuclear medicine imaging criteria may be not sufficient in differential diagnosis. To overcome the issue, we suggest introducing into the clinical practice the biopsy of suspicious enlarged IMLN with minimally invasive technique.