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Objective:
Chondroid neoplasms are common imaging findings. Lesions with imaging characteristics of low-grade chondroid neoplasms located in axial skeleton and flat bones (i.e., pelvis, sternum, ribs) should be considered malignant. These lesions pose management challenges, especially in younger patients, whose expected lifespan renders imaging surveillance suboptimal. Alternatively, surgical excision is frequently accompanied by substantial morbidity. We present two cases in which low-grade periacetabular chondrosarcomas were managed with percutaneous cryoablation on an outpatient basis.

Materials and Methods:
Patient A (pt A), a 42-year-old female, and patient B (patient B), a 23-year-old female, were referred to orthopedic oncology after magnetic resonance imaging (MRI) demonstrated acetabular chondroid lesions. Biopsy was planned with immediate ablation if a frozen section specimen demonstrated chondrocytes. Both patients received intravenous moderate sedation with fentanyl and midazolam. Lesions were localized with CT, and biopsy was performed via a co-axial technique using a 10-gauge introducer needle and 12-gauge biopsy needle. Specimens were taken directly to pathology for frozen sectioning, which demonstrated chondroid cells. Next, cryoablation was performed. A cryoablation probe was placed through the introducer needle and two freeze-thaw cycles were performed until the ice ball margins were visualized beyond the lesion. Needles were removed and the patients were transferred to recovery prior to discharge home. Initial clinical follow-up with orthopedic oncology took place approximately 1 - 2 months following ablation. For pt A, initial pelvic MRI took place at approximately 2 weeks after the procedure. Due to ongoing hip pain, she underwent arthroscopic labral repair 7 months after cryoablation. Additional pelvic MRI took place 8, 12, 20, 24, and 37 months after ablation. Pt B underwent pelvic MRI at approximately 2 and 12 months after the procedure.

Results:
There were no postprocedural complications. In both cases, initial postablation MRI demonstrates findings of osteonecrosis surrounding the treated lesions. In subsequent follow up for Pt A, concentric healing is noted around the ablation zone with decreased diameter of the spherical high signal line. No recurrent central lesion or hyperintensity has been identified. Pt A underwent uncomplicated arthroscopic labral repair 7 months after the cryoablation. The arthroscopist noted that the acetabular cartilage near the ablation zone and fovea appeared normal. The patient’s pain resolved following labral repair, and she was asymptomatic at nearly 45 months after ablation. Pt B remained asymptomatic at 14 months after the procedure. Her follow up MRI also demonstrates no recurrent lesion or hyperintensity at the ablation zone.

Conclusion:
Percutaneous cryoablation may be an efficacious treatment strategy for low-grade chondrosarcoma, helping to avoid the morbidity associated with surgical excision and mitigating anxiety associated with conservative approaches.