Rare chest wall chondrosarcoma masqueraded as benign mediastinal tumor in 66-year-old woman

A tumor that surgeons believed was a harmless fatty growth in the chest of a 66-year-old woman turned out to be a rare, low-grade cancer of the costal cartilage, according to a case report published in General Thoracic and Cardiovascular Surgery Cases. Only when the specimen reached the pathology laboratory did the true identity emerge: a grade 1 chondrosarcoma arising from the costal cartilage, a cancer so uncommon at this site that only a handful of similar cases have ever been described.

The woman had no symptoms at all. An abnormal shadow appeared incidentally on chest imaging, and she had no relevant medical history or exposure to carcinogens. Contrast-enhanced computed tomography revealed a well-defined, poorly enhancing, calcified mass in the anterior mediastinum, lying adjacent to the left costal arch near the epigastric region. Critically, bone-window images together with coronal and sagittal reformats failed to demonstrate any continuity between the mass and the adjacent costal cartilage, the single clue that might have revealed its true origin. Magnetic resonance imaging showed T1-weighted hyperintensity with signal loss on fat-suppressed sequences, a pattern consistent with fat, and no invasion of surrounding structures. T2-weighted imaging showed low signal within the calcified portion and high signal elsewhere.

Further workup reinforced the impression of a benign teratoma. Positron emission tomography-computed tomography showed only low fluorodeoxyglucose uptake within the mass and no distant metastasis, arguing against an aggressive malignancy. Tumor markers were all within normal limits: carcinoembryonic antigen measured 2.8 nanograms per milliliter against a reference threshold of 6.0, alpha-fetoprotein was 4.3 nanograms per milliliter against a threshold of 10.0, and squamous cell carcinoma antigen was 0.5 nanograms per milliliter against a threshold of 1.5. Well-defined borders, absence of invasion, low metabolic activity and normal markers collectively argued against cancer, and the team made a confident preoperative diagnosis of mature teratoma and planned resection.

Because the tumor occupied the narrow space between the heart and the sternum, the surgeons judged a median sternotomy too invasive for a lesion presumed benign, while conventional video-assisted thoracoscopic surgery offered inadequate maneuverability in so confined a corridor. They instead chose robot-assisted thoracoscopic surgery, performed under general anesthesia with one-lung ventilation in the left semi-lateral decubitus position. Three 1-centimeter ports were placed at the fifth intercostal space in the midaxillary line, the third intercostal space in the anterior axillary line, and the sixth intercostal space anterior to the anterior axillary line, with carbon dioxide insufflation at 5 millimeters of mercury.

The tumor was not visible from the right thoracic cavity until the mediastinal pleura was incised; dissection of its cranial aspect entered the left pleural cavity, where part of the mass was exposed without adhesions. Intraoperatively, the tumor contacted the left fifth through seventh costal cartilages and showed direct continuity with the sixth, strongly suggesting a chest wall rather than mediastinal origin. Because the boundary between tumor and normal cartilage could not be identified, the sixth costal cartilage was divided with bipolar energy applied through robotic Maryland forceps, following the plane in which division was possible, and the specimen was removed in one piece through a sixth intercostal incision extended to 3 centimeters. Operative time was 90 minutes with blood loss of just 2 milliliters.

The postoperative course was uneventful and the patient was discharged on postoperative day 4. Gross examination showed a well-circumscribed, firm mass with a glistening cartilaginous cut surface and focal calcification. Hematoxylin and eosin staining revealed chondrocyte-like tumor cells with mild nuclear atypia meeting the histological criteria for grade 1 chondrosarcoma of the costal cartilage. No uninvolved costal cartilage was identified in the specimen and the tumor-cartilage boundary was indistinct; although no definite tumor was seen at the inked margin, sectioning and crush artifact precluded reliable assessment, so residual tumor could not be excluded, categorized as Rx, and the resection was at most marginal rather than the wide excision that is standard for this disease.

Chondrosarcoma is the most common primary malignant tumor of the chest wall, yet its annual incidence is below 0.5 per million, and origin from the costal cartilage is rarer still. A previous review found eight reported anterior mediastinal chondrosarcomas, only three arising from the sternum or costal cartilage; with subsequent reports, five chest wall-derived cases presenting as anterior mediastinal masses have been described, a group that now includes this patient. The imaging overlap with teratoma is genuine and well documented: calcification on computed tomography is a recognized feature of mature teratoma, T1 hyperintensity interpreted as fat is a hallmark of teratoma, and high T2 signal can reflect chondroid matrix in chondrosarcoma but equally fluid or myxoid content within a teratoma, making it non-specific. On retrospective review, even bone-window and reformatted computed tomography still did not demonstrate continuity with the costal cartilage.

Misdiagnosis in similar cases has been reported before. One previously described costal chondrosarcoma was strongly suspected to be a thymoma, in which low fluorodeoxyglucose uptake and absent calcification precluded a confident malignant diagnosis, and another case, arising in a patient with hereditary multiple exostoses, required differentiation from teratoma, lymphoma and chondroblastoma. The role of frozen section analysis during surgery emerged as a cautionary theme in the discussion. In one prior case, surgeons obtained frozen section when a presumed thymoma proved adherent to the sternum and proceeded to en bloc sternal and costal cartilage resection; in another, frozen section of a costal chondrosarcoma was read as benign, with grade 1 chondrosarcoma confirmed only on final pathology, forcing a second operation with wider chest wall resection. Frozen section is therefore neither reliably conclusive nor dispensable, the authors conclude, and preoperative suspicion remains the more dependable safeguard. In the present case, conversion to a wider resection guided by frozen section was considered but not undertaken, which the authors describe in retrospect as a missed opportunity.

The decision about further treatment rested on evidence from a population-based series of 106 chest wall chondrosarcomas, in which margins were classified as wide, meaning over 2 centimeters, marginal, meaning tumor-free but under 2 centimeters, or intralesional. In that series, local recurrence occurred in 4 percent of patients after wide resection and 73 percent after intralesional resection, with margin and grade serving as independent predictors. Grade 1 outcomes were not confined to wide margins, which were achieved in only 28 percent of cases: local recurrence occurred in 2 of 19 grade 1 tumors, none metastasized, and 13 of 44 tumors recurred after marginal resection versus 19 of 26 after intralesional resection. The 4 percent figure reflects the margin obtained at the first operation, and no data show that re-resection restores it. Local recurrence nonetheless proved lethal in that series, with nearly half of patients recurring without metastases dying of local progression.

Weighing the absence of residual disease on imaging one month after surgery, the grade 1 histology, and the extensive chest wall and diaphragmatic resection and reconstruction that a wide margin would have required, a multidisciplinary tumor board elected surveillance, and the patient agreed. The follow-up regimen comprises computed tomography every three months, magnetic resonance imaging every six months, and a low threshold for intervention. No recurrence has been observed at 18 months postoperatively, but the authors are explicit that this falls far short of the interval over which recurrence typically emerges: in the population-based series, the mean time to local recurrence was 3.5 years, ranging to 14 years, with four recurrences occurring beyond 10 years. Imaging cannot exclude microscopic residual disease, and wide resection remains the standard of care.

The authors also acknowledge the limits of their own diagnosis. Costal cartilage origin rests on the intraoperative finding alone; neither imaging nor the specimen demonstrated the interface between tumor and cartilage. The right-sided robot-assisted approach provided favorable visualization and maneuverability in the confined retrosternal space, but its oncological safety cannot be generalized from a single case. Their conclusion is a practical warning for clinicians: 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 never compromise the surgical margin when malignancy is suspected. Robot-assisted surgery may prove feasible in carefully selected patients in whom an adequate margin can be secured, they write, but larger series will be needed to validate that claim.

Subject of Research: A case report of robot-assisted thoracoscopic resection of a costal cartilage chondrosarcoma preoperatively misdiagnosed as a mature anterior mediastinal teratoma.

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

Article References: Takemoto, T., Murakami, J., Yoshimine, S., Tanaka, T., & Mikamo, A. (2026). Robot-assisted thoracoscopic resection of a costal cartilage chondrosarcoma mimicking anterior mediastinal teratoma: a case report. General Thoracic and Cardiovascular Surgery Cases, 5(1), Article 41. https://doi.org/10.1186/s44215-026-00279-w

Image Credits: AI Generated

DOI: 10.1186/s44215-026-00279-w

Keywords: chondrosarcoma, costal cartilage, anterior mediastinal mass, mature teratoma, robot-assisted thoracoscopic surgery, case report, chest wall tumor, misdiagnosis, surgical margins, mediastinal tumor, thoracic surgery, surveillance