Intermediate metastatic risk lipomatous solitary fibrous tumor of the thigh (previously known as hemangiopericytoma): A rare case report with a literature review.

Rationale: Solitary fibrous tumor (SFT) is a rare mesenchymal tumor, which can arise at any anatomical location and exhibit a wide variety of histopathological characteristics. Lipomatous solitary fibrous tumor (LSFT) is a rare variant of SFT characterized by hemangiopericytoma-like vascular areas with a varying amount of adipocytic tissue. LSFT can be misdiagnosed with other tumors such as liposarcoma which can lead to unnecessary overtreatment for patients.

Patient concerns: A 48-year-old man presented to the hospital clinic with a painless swelling located on the medial area of the upper thigh near the femoral artery, he has not seen any change in its size since he has noticed it a year ago.

Diagnoses: Histological examination confirmed LSFT with an intermediate risk of metastasis.

Interventions: Three-dimensional imaging technology with intravenous injection of contrast material was made and revealed a mass with well-vascularity supplied from the deep femoral artery. The lesion was excised and showed an intramuscular well-circumscribed encapsulated mass.

Outcomes: The pathological findings LSFT with intermediate metastatic risk, and he is scheduled to receive radiotherapy for one and a half months. The majority of SFTs display benign histological characteristics and typically follow a slow clinical progression, leading to a favorable prognosis. To date, fewer than 20 cases of malignant LSFT have been documented. In our case, we utilized a recent tumor classification model that evaluates the metastatic potential of SFTs, and long-term follow-up is necessary because there is a chance of aggressive behavior.

Lessons: LSFTs are usually found incidentally and often present as painless, movable masses. Even though they mostly follow a benign course, long-term follow-up is essential due to the possibility of turning malignant.