Purpose or Case Report: Lipoblastomas are rare benign soft tissue tumors (6% of all pediatric soft tissue tumors) that are composed of immature lipoblasts and mature adipocytes. Lipoblastomas primarily occur in infants and children younger than three years of age and most frequently occur in the extremities. Less than 10 case reports exist of pelvic lipoblastomas. We report two children with pelvic lipoblastoma with the typical presentation of a rapidly enlarging, painless, fat-containing mass.

A 30-month-old girl presented with an enlarging gluteal mass over a period of four months. CT performed at an outside institution showed a large fat-containing intra-pelvic lesion anterior to the sacrum that extended to the perineum. An atypical sacrococcygeal teratoma was suspected. Subsequently, MRI demonstrated a large fairly-well-circumscribed intra-pelvic lesion that followed fat on all sequences with the exception of a few thin, enhancing septations.

A 14-year-old boy presented with a large firm scrotal/inguinal mass during a wellness visit. The child reported the lesion had been rapidly increasing in size over the past two months. Ultrasound showed a >15 cm inguinal mass that extended both into the pelvis and left hemiscrotum. The mass was homogeneous in echotexture and displaced but did not involve the epididymis and testicle. Based on concern for a malignant lesion, subsequent evaluation with PET-CT showed the lesion to be predominantly composed of fat with only low level F-18-FDG uptake in a few internal septations.

In both cases, lipoblastoma was confirmed after surgical excision with pathologic examination and immunohistochemistry.

Imaging serves to demonstrate the macroscopic fat content of lipoblastomas but cannot reliably differentiate lipoblastoma from liposarcoma. Therefore, imaging primarily contributes information about size and anatomic relationships relevant to surgical approach. Surgical excision is the treatment of choice; however, the lack of a capsule makes complete excision difficult and local recurrence is common. Close clinical follow-up is recommended for a minimum of five years, with imaging follow-up by MRI or CT utilized when the tumor’s anatomic location precludes or limits detection by physical examination.
Methods & Materials:
Results:
Conclusions: