Preperitoneal Myelolipoma Occurring after Video-Assisted Thoracoscopic Surgery for Thymoma: A Case Report

Myelolipoma is a benign tumor composed of mature adipose tissue and hematopoietic elements that typically arises in the adrenal glands, and involvement of the anterior abdominal region is extremely uncommon. We report a rare case of myelolipoma arising in the subxiphoid preperitoneal region adjacent to the site where a sternum-lifting device had been placed during previous surgery.

A 62-year-old man had undergone extended thymectomy for thymoma associated with myasthenia gravis at the age of 39. The procedure was performed via bilateral video-assisted thoracoscopic surgery using a sternum-lifting technique. The tumor was classified as Masaoka stage III, and postoperative radiotherapy was administered. No recurrence was observed during 13 years of follow-up. Ten years after completion of follow-up, CT performed for an unrelated condition incidentally revealed a slowly enlarging 65 × 40-mm mass in the preperitoneal space, adjacent to the previous surgical site where a sternum-lifting device had been placed. MRI demonstrated a fat-containing component within the lesion, and the differential diagnosis included liposarcoma and teratoma. Complete surgical resection was therefore planned. A midline incision extending caudally from the xiphoid process was made, and en bloc resection of the tumor with the involved peritoneum was performed via laparotomy. Histopathological examination revealed mature adipose tissue admixed with hematopoietic elements, confirming the diagnosis of myelolipoma.

This unique case of extra-adrenal myelolipoma highlights the importance of MRI-based qualitative assessment for tumors arising at unusual sites and underscores the need to include extra-adrenal myelolipoma in the differential diagnosis of fat-containing lesions occurring at previous surgical sites.