Abstract

Oil cyst lesions are well-described radiologically in the breast as a consequence of trauma. The conglomeration of lipoid-material from adipocyte rupture, liquefactive necrosis and saponification induces formation of a dense fibrous capsule, which calcifies over time. They are rarely biopsied given their benign nature and classic appearance. However, explanation of the pathology findings is difficult to find, especially outside the breast and within the pediatric population. A 6-month-old girl presented with an erythematous, swollen area on the left buttock. The lesion resolved with antibiotic treatment. Months later, a distinct lump recurred within the same area. Ultrasound showed a simple, well-circumscribed, anechoic and avascular cyst measuring 2.0 x 1.9 x 0.9 cm within the superficial subcutaneous tissue, with no free fluid. During surgery for excision, a creamy fluid, inconsistent with pus, leaked from the incision. The excisional specimen was sent for pathology and microbiologic cultures. Histopathologic review showed a dense fibrous cyst wall with scattered calcifications and lacking epithelium located within the deep dermis. It was flanked by extensive fat necrosis, scattered multinucleated giant cells and an exuberant histiocytic response. GMS and Gram stains were negative; microbiologic cultures showed no growth. We share this interesting case of an oil cyst developing months after a presumed cellulitis infection within the gluteal fat of an infant to offer a pathological description to aid in accurate diagnosis. We also seek to remind clinicians to consider oil cysts outside the fibroadipose tissue of the breast, and in pediatric populations.