Soft tissue chordoma of the right thigh demonstrated on 18F-FDG PET/CT and MRI: A case report

RATIONALE: Chordoma is a malignant bone tumor that typically affects structures along the midline. Soft tissue chordoma of the right thigh is an extremely rare entity but significant, as it can create diagnostic challenges and increases the risk of misdiagnosis, making accurate identification essential. This report introduces a diagnostic strategy of fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) for a huge chordoma. PATIENT CONCERNS: A 45-year-old man presented with a painless, gradually growing mass on his right thigh for 6 years without weight loss. Imaging studies revealed a huge mass in his soft tissue of the right thigh, raising concerns about pathology. DIAGNOSES: Magnetic resonance imaging demonstrated a mass with cystic mixed components, in the middle of the right thigh region with irregular shape and a poorly defined local boundary, measured 267 × 119 × 102 mm, leading to a presumptive diagnosis of malignancy. INTERVENTIONS: 18F-FDG PET/CT showed a huge area of heterogeneously increased 18F-FDG uptake (SUVmax, 4.4), and pathology and immunohistochemistry confirmed the diagnosis of conventional chordoma. OUTCOMES: He was treated with Imatinib Mesylate (400 mg) orally twice daily. There was no recurrence during the 6-month follow-up, with plans for continued long-term surveillance. LESSONS: This case highlights the diagnostic challenge posed by chordoma of the soft tissue in the thigh, as its radiological appearance can closely resemble other soft tissue tumors. Clinicians should ensure exhaustive assessment including CT, magnetic resonance imaging, and 18F-FDG PET/CT imaging. Pathological confirmation is essential. Despite the rarity of soft tissue chordoma, careful treatment planning including consideration of targeted therapy and long-term follow-up is important to address the risk of late recurrence.