Extra Axial Chordoma of the Distal Femoral Metaphysis: A Case Report

Abstract

Background Chordomas are malignant bone tumors that are derived from remnant embryonic tissue of the notochord and are typically found in the axial midline. When they are found outside of the axial skeleton, the diagnosis can be challenging and elusive. Often, they are overlooked on initial presentation in lieu of other more common lesions, including cartilage tumors (eg, enchondroma, chondrosarcoma, osteochondromatosis) due to their overlapping features. Case Report A 30-year-old female with a four-year history of intermittent left knee pain presented for initial evaluation. Physical exam of the knee was unremarkable except for moderate tenderness on palpation. Radiographs showed a lucent lesion with peripheral sclerosis, eccentrically located within the anteromedial femoral diaphysis. The patient was subsequently lost to follow-up. She presented again two years later with similar symptoms. Her physical exam remained unchanged, and repeat radiographs showed interval growth. She underwent open biopsy of the left distal femur, with pathology revealing tumor consisting predominantly of epithelioid cells set in an abundant myxoid matrix. Immunohistology showed cells that stained strongly for EMA, CK19, and brachyury. These findings support the diagnosis of extra-axial chordoma. Discussion Extra-axial chordomas remain a challenging diagnosis for clinicians due to their extreme rarity and overlapping features with other more common lesions. They are often misdiagnosed as extraskeletal myxoid chondrosarcomas or myoepitheliomas. Our patient’s insidious presentation and radiologic findings present a learning opportunity for clinicians to recognize extra-axial chordomas as a potential early diagnosis in someone presenting with a long history of intermittent and worsening knee pain.