Robot-assisted thoracoscopic resection of a costal cartilage chondrosarcoma mimicking anterior mediastinal teratoma: a case report.

BACKGROUND: Chondrosarcoma arising from the costal cartilage is extremely rare. When such a tumor extends toward the mediastinum, it may present as a well-defined mass that is difficult to distinguish from a primary anterior mediastinal tumor. We report a case diagnosed preoperatively as a mature teratoma but later proven to be a grade 1 chondrosarcoma of the costal cartilage.

CASE PRESENTATION: A 66-year-old asymptomatic woman was incidentally found to have an abnormal shadow on chest imaging. Contrast-enhanced computed tomography revealed a well-defined, calcified mass measuring 37 × 31 × 21 mm in the anterior mediastinum, adjacent to the left costal arch; bone-window and reformatted images did not clearly demonstrate continuity with the adjacent costal cartilage. Magnetic resonance imaging demonstrated T1-weighted hyperintensity with signal loss on fat-suppressed imaging, consistent with a fatty component, and no invasion of surrounding structures. Positron emission tomography-computed tomography showed low fluorodeoxyglucose uptake and no distant metastasis, and tumor markers were normal. A preoperative diagnosis of mature teratoma was made, and resection was planned. Robot-assisted thoracoscopic surgery was performed via a three-port right-sided approach. Intraoperatively, the tumor lay in the narrow space between the heart and the sternum, with direct continuity with the left sixth costal cartilage suggesting its origin; the tumor-cartilage boundary could not be identified, and the cartilage was divided at the tumor interface. The postoperative course was uneventful. Pathological examination revealed chondrocyte-like tumor cells with mild nuclear atypia, consistent with a grade 1 chondrosarcoma of the costal cartilage; residual tumor could not be excluded (Rx). A multidisciplinary tumor board elected surveillance, and no recurrence has been observed at 18 months postoperatively.

CONCLUSIONS: Costal cartilage chondrosarcoma belongs in the differential diagnosis of a calcified anterior mediastinal mass because preoperative recognition determines whether a wide or marginal resection is planned, and a minimally invasive approach must not compromise the surgical margin when malignancy is suspected. The right-sided robot-assisted thoracoscopic approach provided favorable visualization and maneuverability in this confined retrosternal location, but its oncological safety cannot be generalized from a single case.