Rare Lipomatous Neoplasm of the Thigh in A 13 Year Old Male With A Discussion of Imaging Features and Differential Diagnosis of A Fatty Extremity Mass - Rare Lipomatous Neoplasm of the Thigh in A 13 Year Old Male With A Discussion of Imaging Features and Differential Diagnosis of A Fatty Extremity Mass - Open Access Pub

Lipomatous tumors are among the most common primary musculoskeletal neoplasms affecting both pediatric and adult patient populations. Patient age, tumor location, and imaging features all contribute to the differential diagnosis of musculoskeletal tumors. Tumors identified outside of common patient demographics or in unusual locations may lead to preoperative misdiagnosis. We present an uncommon adipocytic tumor occurring at an uncommon age which was proven at surgery to represent a preoperatively unexpected diagnosis. A 13 year old male presented with a fatty anterior proximal thigh mass; age and magnetic resonance findings suggested lipoblastoma. However, following complete surgical resection, histopathology confirmed hibernoma, a benign lipomatous tumor characterized by the presence of white and multivacuolated brown fat cells, the vast majority of which occur in adult patients. DOI10.14302/issn.2639-1716.jn-18-1965 Lipomatous neoplasms comprise a large and diverse group of fat-containing musculoskeletal tumors ranging from purely benign to highly malignant with potential for distant metastatic disease 1, 2. Patient age, location of disease, and assessment of internal tumor composition at diagnostic imaging are important factors in the construction of a preoperative differential diagnosis 3. Common entities include simple lipoma, atypical lipomatous tumor (ALT), and liposarcoma. However, other benign adipocytic tumors including numerous lipoma variants and lipoblastoma more often affect pediatric and younger aged patients. Careful evaluation of the internal architecture and soft tissue elements within a musculoskeletal tumor at preoperative magnetic resonance imaging (MRI) often allows for accurate prediction of histopathology. However, unexpected etiologies may be diagnosed when rare tumors arise outside of common age ranges or typical sites of disease. The following report illustrates this point in describing a 13 year old male with a lipomatous thigh mass favored to represent lipoblastoma which proved to represent hibernoma. A 13 year old male presented to his local physician with a painless, slowly enlarging palpable mass of the proximal right thigh. Contrast-enhanced MRI was performed which raised concern for soft tissue sarcoma. We were consulted for a second opinion interpretation of the imaging study and recommendations for management. Outside multi-planar and multi-weighted MRI demonstrated a large lipomatous anterior compartmental thigh mass (Figure 1A-D). The mass was predominantly fatty with the majority of the tumor following the signal