Conventional chondrosarcoma of the sternum presenting as a chest wall mass with multilobulated intra- and extra-thoracic extension

Abstract

Chondrosarcomas are rare malignant tumors, comprising 20% of all primary bone tumors. They are classified as primary or secondary based on their origin and as conventional or nonconventional based on histology. While conventional chondrosarcomas are the most common form, their occurrence in the chest, and more specifically in the sternocostal joints, is extremely infrequent. We present a case of a 61-year-old female with a longstanding history of a small stable-appearing anterior chest chondrosarcoma for well over a decade, which required surgical intervention after rapid and spontaneous growth. The unique growth pattern extending both extra-thoracically and intra-thoracically is a rare occurrence. Common radiological findings of chondrosarcomas that were appreciated in this case includes lytic lesions with matrix calcifications, endosteal scalloping, and soft tissue masses. Modern imaging techniques, like computed tomography (CT), are excellent for identifying and preoperative planning of chondrosarcomas, however, histology remains the gold standard for confirming the diagnosis.

Introduction

Chondrosarcomas are rare malignant tumors arising from cartilage-producing cells and are mostly found in the pelvis or at the ends of long bones. As of 2020, the World Health Organization (WHO) stratifies chondrogenic bone tumors as benign, locally aggressive, or malignant, also separating atypical cartilaginous tumors (ACTs) and chondrosarcoma grade 1 (CS1) as intermediate and malignant tumors. Chondrosarcomas can be classified as primary or secondary lesions based on their origin, with primary chondrosarcomas being the third most common primary bone malignancy [1,2]. Secondary chondrosarcomas arise from preexisting benign bone lesions, such as osteochondromas, but histologically they resemble primary chondrosarcomas [3]. There are roughly 15,000 new sarcomas diagnosed each year, with approximately 3,000 being primary bone tumors. Of those bone tumors, roughly 20% will be chondrosarcomas [4]. Like many connective tissue tumors, chondrosarcomas are divided into distinct histologic subtypes, including conventional and nonconventional neoplasms. Conventional chondrosarcomas are the most common subtype, accounting for 85%-90% of new lesions, and are mostly low to intermediate-grade and rarely metastasize [5]. Nonconventional chondrosarcomas include histological variants that display slight morphological differences, such as clear cell, mesenchymal, and dedifferentiated chondrosarcoma [4]. Conclusive diagnosis can often times be determined by imaging studies alone due to chondrosarcoma’s distinct radiological features, but pathological coordination is typically included for robustness [4,6]. We present the unusual case of a 61-year-old female diagnosed with a large atypical conventional chondrosarcoma of the left sternum that penetrated the anterior mediastinum. This case presents a unique clinical challenge given its uncommon location arising from the sternocostal joints and its unusual intra-thoracic and extra-thoracic character. We focus on the use of computed tomography (CT), for accurate and timely diagnosis and the utility of radiological imaging in preoperative planning for effective management of this malignant disease.

Case presentation

A 61-year-old female was referred to our hospital for consultation for management of a previously diagnosed chondrosarcoma located in her left anterior mediastinum. She presented with no reported symptoms and upon examination was found to have a small, nontender, and immobile lump protruding from the left side of her sternum that she reported had grown significantly in the past couple of months. Her past oncological history was significant for right nasal Basel cell carcinoma and cervical dysplasia. The mass had been discovered approximately 13 years prior by her gynecologist, measuring roughly 1 cm in diameter at the time, protruding from the anterior left chest at the junction of the sternum and second and third ribs. A chest radiography and CT performed shortly after discovery suspected the mass to be a chondrosarcoma. However, the mass had recently shown rapid growth, measuring 4 × 4 × 3 cm. After another chest CT following presentation with and without intravenous contrast, a sternal biopsy was performed, which was then followed by an excisional biopsy. Both biopsies reported fragments of a low-grade (I-II/III) hyaline cartilage neoplasm, consistent with conventional chondrosarcoma. The CT was shared with our hospital for a second interpretation, displaying the known sternal chondrosarcoma with an extra-thoracic component of 2.2 × 2.9 × 3.3 cm and an intrathoracic extension measuring 9.1 × 5.1 × 6.9 cm, abutting the right side of the heart (Fig. 1 A-E). No evidence of metastatic disease was visualized in the chest or abdomen. The patient was immediately referred to surgery for resection of the remaining portion of the chondrosarcoma and the radiological studies were used to correlate surgical planning. Surgical pathology described a destructive 10.2 cm conventional chondrosarcoma, now grade II/III, completely excised with negative margins. In addition, right cartilaginous margins were excised, and the adjacent mediastinal lymph node was dissected—both negative for residual and metastatic tumor (Fig. 2 A-F).

Fig. 1.

A 61-year-old female with a chondrosternal junction chondrosarcoma. Axial (A and B), Sagittal (C and D), and Coronal (E) CT imaging demonstrated an anterior mediastinal soft tissue mass arising from the left chondrosternal junction with an extra-thoracic component (yellow arrow – B and C) and intrathoracic extension via the third and fourth anterior intercostal space, abutting the mediastinal structures including left brachiocephalic vein, aorta (orange arrow – D), pulmonary artery and the right heart border (white arrow – D). However, there was no evidence of direct invasion of the heart or the great vessels. Ring and arc calcifications representing chondroid matrix are also visualized (white arrows – E). No other osseous lesion was seen.

Fig. 2.

A 61-year-old female with a sternal chondrosarcoma. (A-B) Gross examination of the resection specimen reveals a destructive cartilaginous tumor with an epicenter in the sternal body with bulky soft tissue extension and central cystic dropout (blue stars). (C-D) Low-power histologic sections demonstrate the permeative growth of the chondrosarcoma arising within the sternum (C) and grows in a lobular pattern with extraosseous extension. One can appreciate the non-neoplastic native sternal cartilage at the top center (yellow star) which is encased by the chondrosarcoma. At high-power, the tumor is moderately cellular hyaline cartilage neoplasm composed of small, lymphocyte-like nuclei (E) which reside in lacunae with occasional bi-nucleation (F) designating this lesion as intermediate grade II.

Discussion

We present the highly unusual case of chondrosarcoma arising from the sternum in an atypical bidirectional growth pattern in both the intra- and extra-thoracic space. The etiology is largely sporadic, however, some secondary chondrosarcomas may develop from more common benign bone lesions, such as osteochondromas or enchondromas [7]. The incidence of chondrosarcomas is relatively low as they are observed in roughly 3 cases per million population per year, ranking fifth among all bone tumors, with the most common being enchondromas at 10 cases per million population per year [8,9]. Chondrosarcomas are generally found in or around the pelvic region or at the ends of long bones, such as the femur or humerus, however, roughly 15% of cases occur in the chest wall [10,11]. Diagnosis of conventional chondrosarcomas is usually highest between 50 and 70 years old, and slightly favors males over females [12]. The nonconventional variants, including clear cell, mesenchymal, and dedifferentiated chondrosarcomas, are less common and thought to be morphological expressions of different points of differentiation found in normal chondrogenesis [13]. While most conventional chondrosarcomas are slow-growing malignancies, there is a significant concern for skeletal and pulmonary metastases in advanced-grade tumors, necessitating timely and coordinated efforts to diagnose and treat [5,14].

Clinically, patients with chondrosarcomas present with localized pain and swelling of the affected areas, mostly at the proximal or distal portions in long bones and cartilaginous joints of flat bones. Soft tissue masses are irregularly seen but are usually discovered by imaging studies [4,7]. Imaging studies are essential for staging and diagnosing chondrosarcomas, as they often portray distinct features on radiographs, CTs, and MRIs. Radiographs generally show lytic and sclerotic degradation, including distinct low-grade chondroid matrix mineralization, endosteal scalloping, cortical expansion, and penetration [2,6,15]. The case we present is unique in the way that not only does it incorporate extensive soft tissue neoplastic growth, but its growth pattern extends outwardly and also penetrates the intrathoracic cavity, giving it a unique appearance.

While radiographs may guide initial staging of the lesion, CTs and MRIs are typically required to fully investigate the extent of the disease and differentiate between low and high-grade lesions. CT features may better display the previously mentioned bony destruction, such as endosteal scalloping and cortical destruction [1]. In addition, calcification is well appreciated on CT, and its common ring and arc appearance is helps rule out similar lesions [16]. The CT of our patient revealed extensive calcification in both the intrathoracic and extra-thoracic portions of the lesion. Like calcification, soft tissue masses are better appreciated on contrast-enhanced CT, where septal and rim enhancement can be seen along with overall uniform enhancement of the lesion [12]. MRI excels at demonstrating the extent of intraosseous tumor, demonstrating low to intermediate intensity on T1-weighted images, and punctate areas of signal void due to classical matrix mineralization, which also contributes to areas of heterogeneous low signal intensity. Noncalcified areas demonstrate high intensity on T2-weighted images due to elevated water content. As with CTs, MRIs better display the depth and extent of endosteal scalloping, extraosseous extension, and cortical changes. Specifically, high-grade chondrosarcomas and dedifferentiated chondrosarcomas show cortical destruction, bone edema, soft tissue edema, tumor necrosis, intermediate T2-weighted signal intensity, and joint invasion. Sternal chondrosarcomas are not considered to have unique or well-defined imaging features in comparison to other chondrosarcomas, however, due to their location, the possibility of bidirectional growth pattern can contribute to their unique character—a defining feature of this case [2,6,12,16]. Normally, MRIs would be useful for assessing sternal chondrosarcomas, however, MRI was not used for this case as it was the lesion was clearly defined by CT and there was no evidence of other thoracic soft tissue interaction. Technetium 99m-methyl diphosphonate bone scintigraphy, or bone scans, are useful in showing irregular focal activity and differentiating chondrosarcomas from their benign counterparts like enchondromas. However, bone scans have only been able to differentiate activity in certain regions of the body, rendering their conclusions not definitive [12,14]. Even though imaging has proven satisfactory for solely identifying chondrosarcomas, coordination with pathology remains the gold standard for further delineating between the various subtypes and precise grading.

Management of conventional chondrosarcomas may slightly vary between cases depending on tumor grade and surrounding anatomical involvement, but the mainstay of treatment is surgical resection, as both radiation and chemotherapy have little to no effect. Resection may be supplemented by radiation if the tumor access is limited surgically [1,17,18]. Conventional chondrosarcomas resistance to traditional chemotherapy is attributed to their characteristic slow mitotic division and growth, and poor vascularity, limiting drug accessibility within the tumor [19]. Prognosis of conventional chondrosarcomas is generally good, as most are low to intermediate-grade lesions. Local recurrence and metastasis are uncommon and often coincide with histological grade [7]. The 5-year survival rate of grade I chondrosarcomas is 83%, meanwhile, survival for high-grade II or III lesions drops to 53% [20,21]. Significant differences in mortality emphasize the importance of timely diagnosis and surgical resection.

Conclusion

This case highlights an uncommon presentation of a large, multilobulated conventional chondrosarcoma originating from the sternum and extending both extra-thoracically and intra-thoracically, invading the anterior mediastinum. Despite its atypical location, accurate diagnosis and effective surgical management were achieved through coordination between advanced imaging modalities and histopathologic evaluation. Complete resection with negative margins underscores the importance of early recognition, comprehensive radiological assessment, and multidisciplinary planning in achieving favorable outcomes. Given the known resistance of chondrosarcomas to adjuvant therapies, continued follow-up is essential to monitor for potential recurrence or malignancy, particularly in the case of higher-grade lesions.

Patient consent

The patient reported in the manuscript signed the informed consent/authorization for participation in research, which includes the permission to use data collected in future research projects such as the presented case details and images used in this manuscript.