Peripheral Chondrosarcoma

Clinical History

A 26-year-old female presented with a painful mass in the left buttock, with slow growth during the last six months.

Imaging Findings

A 26-year-old female presented with a painful mass in the left buttock, which worsened at night, nonresponsive to nonsteroid anti-inflammatory treatment, with slow growth during the last six months. Physical examination confirmed a hard mass adherent to the left iliac wing with slight tenderness.
Radiographs of the pelvis (Fig. 1) showed a large soft-tissue mass with a lobulated structure and chondroid matrix mineralisation located in the lateral aspect of the left iliac wing.
Computed tomography (CT) of the pelvis (Fig. 2) confirmed a large, well-defined soft-tissue mass with chondroid matrix and lower density than the muscle (Fig. 2a).The tumour seemed to arise from a pedunculated osseous stalk continuous with iliac wing, pointing to a precursor osteochondroma (Fig. 2b). Notice also the associated irregular cortical erosion. There was no evidence of sacroiliac joint involvement or ganglionar metastasis.
Magnetic resonance imaging (MRI) of the pelvis (Fig. 3) confirmed a large well-defined, lobulated soft-tissue mass with low signal in T1-weighted images (WI) (Fig. 3 a), high signal in T2-WI (Fig. 3 b), and the typical septal-nodular and peripheral enhancement pattern (Fig. 3 c). The pedunculated stalk (arrow) continuity and the thick cartilaginous cap (*) suggestive of malignancy are clearly demonstrated. T2-WI showed predominantly high signal intensity with peripheral areas of low signal corresponding to calcification. The large central areas without enhancement can relate to cartilage, necrosis, or myxoid tissue. The patient underwent an uneventful wide-resection and its pathology demonstrated a grade I chondrosarcoma.

Discussion

Chondrosarcoma (CS) corresponds to a heterogeneous group of malignancies with cartilaginous differentiation, being the third most common primary bone malignancy.
The most frequent forms of CS are called conventional (85% of CS), encompassing primary central (85%) and secondary peripheral CS (10-15%). Primary CS (62-86%) arises without a previous lesion whereas secondary CS develops from pre-existing benign cartilaginous neoplasm; malignant transformation occurring in 1-2% of solitary osteochondromas and in 5-25% of multiple osteochondromas.
CS can be categorised according to location within bone as central (intramedullar) and peripheral, as well as tissue distribution (extraskeletal) and histology (clear cell, myxoid, mesenchymal, and dedifferentiated). Juxtacortical CS is a rare surface primary CS (1-4%) with better prognosis than secondary peripheral CS.
CS has a predilection for the male gender and the 2nd-4th decades. Symptoms are nonspecific and include a slow enlarging mass and occasionally pain with or without pathologic fracture (3–17%). CS can involve any bone, with a propensity for the metaphysis long tubular bones (45%). Peripheral CS has a predilection for pelvic (22-39%) and shoulder girdle.
Imaging directly reflects the process of peripheral enchondral ossification and high water content of CS.
Radiograph is usually the first modality employed and allows confident diagnosis in the majority. It typically reveals a mixed lytic and sclerotic, chondroid matrix mineralisation (punctuate, flocculent or ring-and-arc patterns) combined with aggressive growth. Higher-grade CSs often contain less pronounced mineralisation and more extensive osteolysis. Continued growth may lead to lobulated endosteal scalloping.
CS’s only treatment is carcinological exeresis, as it is radio- and chemoresistant. The majority of CS is low-grade and local recurrence rather than metastasis is the main problem. Up to 13% of recurrent CS exhibit a higher grade and may dedifferentiate into a higher grade. Accordingly, survival after treated pelvic CS remains lower than for other locations due to lesser success rate in obtaining healthy margins.
CT and MR further evaluate these neoplasms, being helpful for staging and surgical planning. In large or peripheral CS with complex anatomic locations, CT is particularly useful in identifying the stalk, the pattern of bone destruction, and matrix mineralisation. MR provides the best method to preoperatively delineate the extent of intraosseous and soft tissue involvement. The thickness and enhancement of the cartilaginous cap can reliably assess malignancy likelihood.
The spectrum of surface lesions is broad and includes developmental, traumatic, infectious, primary and secondary neoplasms, as well as systemic and metabolic disorders. While biopsy can establish the cartilaginous nature, it may not provide proof of malignancy and can be obviated when radiological diagnosis is certain. Whenever there is uncertainty, biopsy is indisputable and should be generous and planned to optimise tissue sampling.
Histology remains the best prognostic determinant (survival at 10 years: Grade I - 83%; grade II - 64%; grade III - 29%). The distinction between low-grade CS and benign cartilage lesions can be difficult, benefiting from integrated interpretation of clinical, radiological, and pathological data. New molecular markers are promising as predictors of clinical behaviour and potential targets for directed therapy.

Differential Diagnosis List

Final Diagnosis

Peripheral chondrosarcoma

URL:	https://www.eurorad.org/case/8073
DOI:	10.1594/EURORAD/CASE.8073
ISSN:	1563-4086