Persistent collection of antibiotic ointment masquerading as a lipoma arising at a surgical site

Antibiotic ointments are often used to treat or prevent infections in surgical wounds. However, due to a dearth of reports on adverse effects, the complications of the use of such ointments, especially possible long-term effects, are largely unknown. We experienced a unique case of a cystic lesion that developed after surgical site infection treated with gentamicin ointment in a 62-year-old man who underwent subtotal glossectomy for tongue cancer. The antibiotic ointment that was applied following abscess drainage remained there, replacing the abscess cavity and forming an oval mass. The lesion was found incidentally on follow-up MR examination to monitor cancer recurrence. On both T1- and T2-weighted images, it showed high-intensity reflecting oily base material, constituting the ointment, which appeared to be a fat-containing tumor such as a lipoma that had arisen at the surgical site. Echo-guided drainage extracted the ointment, which was seemingly unaltered from the time it was applied 11 months before. We describe the clinical course and imaging findings to acknowledge this potential adverse effect associated with topical antibiotic treatment for surgical site infection.