A 38-year-old female is referred for imaging of a mass around the right iliac crest. She noticed the lump 5 years ago, progressive growing since 3 months. The mass is painless, but there are esthetical and psychological implications.
Radiography (Figure 1) shows an ill-defined lesion containing calcifications, projected over the right iliac bone. The exact relationship to the bone is difficult to evaluate.
CT scan (Figure 2) shows a pedunculated lesion, arising from the medial cortex of the spina iliaca anterior superior. There is continuity between the medullary and cortical bone of the lesion and the iliac wing. The lesion is surrounded by a cartilage cap containing ring-and-arc calcifications. There is contact between the cartilage cap and the lamina interna of the ala ossis ilii. Cortical disruption is absent.
MRI (Figure 3) shows a thick lobulated cartilage cap, compressing the overlying abdominal musculature and the psoas muscle. The lesion is predominantly hyperintense on T2-WI (WI) and iso-intense to muscle on T1-WI, except for the intralesional calcifications which are of low signal. Dynamic contrast MRI reveals lesion enhancement exceeding 1,5 x that of muscle.
Chondrosarcomas are malignant cartilaginous tumours accounting for about 25% of all primary malignant bone tumours. They can be divided into three grades based primarily on cellularity. Chondrosarcomas are either primary or secondary arising from a pre-existent cartilaginous lesion such as osteochondroma (aka cartilaginous exostosis) or enchondroma [1], [2].
Patients, typically in the 4th - 5th decade, may present with pain, pathological fracture, palpable lump or local mass effect. Chondrosarcomas are mostly seen in the long bones (45%) such as the femur (20-35%), tibia (5%) and proximal humerus (10-20%), as well as in the iliac bone (25%). Unfortunately, chondrosarcomas are usually large at the time of diagnosis (> 4 cm). Early detection hence, is mandatory to avoid mutilating surgery [1], [3].
Imaging is important to differentiate benign osteochondromas from chondrosarcomas and to identify hereditary multiple exostoses syndrome, who is more likely to become malignant. Malignant degeneration occurs in 1% of solitary osteochondromas and in 5-25% with hereditary multiple exostoses [4].
On plain radiography and CT, the cartilage cap may be thin and difficult to identify, or thick with rings-and-arcs calcifications and irregular subchondral bone. New cortical irregularity or continued growth after skeletal maturity, as well as frankly aggressive features (e.g. bony destruction, large soft tissue component, metastases) are all worrying for malignant transformation to chondrosarcoma.
MRI is the best imaging modality to assess malignant degeneration by evaluating the cartilage thickness. In adults, a cartilage cap of over 1.5 cm in thickness is suspicious for malignant degeneration, while the cartilage cap may be seen up to 3 cm in thickness in young patients [5].
In general, a chondrosarcoma arising in an osteochondroma is multilobulated with central high water content (chondroid matrix) accounting for the high T2 – low T1 signal. The peripheral enchondral ossifications result in the typical ring-and-arcs or popcorn calcifications. Gradient echo shows blooming of mineralized/calcified components. Enhancement of benign lesions is normally seen in the tissue that covers the cartilaginous cap which is fibrovascular in nature. The cartilaginous cap itself should not enhance.
If malignant transformation of an osteochondroma occurs, then the chondrosarcoma is usually of low grade (67-85% of cases), and surgery is usually curative (70-90%). Limb-sparing wide local excision usually suffices [2], [6].
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Degenerated osteochondroma of the iliac crest to low grade chondrosarcoma
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1. From the anteroposterior (AP) and lateral X-ray views of the pelvis, an irregular exophytic mass on the lateral margin of the right iliac bone can be seen, showing “popcorn-like” or “ring-and-arc” calcifications.
2. CT axial images indicate that the mass is in continuity with the iliac bone cortex locally, and multiple calcification/ossification foci can be observed in the main body of the tumor, which appears lobulated.
3. MRI reveals that the mass shows low to intermediate signal intensity on T1WI and high signal intensity on T2WI, with multiloculated partitions. These findings are characteristic of cartilaginous tissue. After contrast enhancement, mild to moderate enhancement is seen in the peripheral soft tissue capsule, while no obvious enhancement is observed in the main cartilaginous region of the tumor.
4. No prominent evidence of bone marrow cavity invasion is detected in the overall lesion extent; however, the tumor is relatively large, protruding beyond the cortical bone with an irregular local contour.
Combining the 5-year history of slow growth with accelerated enlargement in the past 3 months, the characteristic “ring-and-arc” calcifications within a cartilaginous matrix, a thickened cartilage cap, and the patient’s age and lesion location, the most likely diagnosis is:
“Malignant Transformation of Osteochondroma (Exostosis) to Chondrosarcoma” or “Primary Chondrosarcoma”
Distinguishing between secondary and primary chondrosarcoma can be challenging based on imaging alone. If clinical and imaging findings strongly suggest malignancy, a biopsy is recommended for definitive histopathological diagnosis.
1. Treatment Strategy:
- If pathology confirms chondrosarcoma, surgical resection is the primary treatment. Wide (en-bloc) resection is commonly performed to ensure clear margins and reduce recurrence.
- For low-grade chondrosarcoma, local wide resection often achieves cure, with a relatively low recurrence and distant metastasis rate.
- For high-grade chondrosarcoma or extensive lesions, further assessment of surgical approach is needed, with consideration of radiotherapy or adjuvant chemotherapy based on oncological parameters.
- If there is uncertainty regarding benign or malignant nature, a biopsy should be performed, followed by surgical intervention or regular follow-up, depending on the thickness of the cartilage cap and dynamic changes in the tumor.
2. Rehabilitation and Exercise Prescription:
After surgery or other therapeutic interventions, progressive and individualized rehabilitation exercises are recommended to restore function while protecting the stability of the surgical site:
This report is a reference analysis based on current imaging and clinical information and cannot replace an in-person medical consultation, further diagnostic evaluations, or professional medical advice. For specific treatment plans, please consult with specialized physicians or orthopedic oncology experts.
Degenerated osteochondroma of the iliac crest to low grade chondrosarcoma
