A 3D navigation-guided surgical resection of a rare case of sacral spine mesenchymal chondrosarcoma: a case report.

Background: Chondrosarcomas are a group of heterogeneous malignant cartilaginous neoplasms that arise from preexisting benign precursors. They can be divided into conventional (primary) chondrosarcomas, which account for 90% of cases, and nonconventional chondrosarcomas, which account for the remaining 10%. Mesenchymal chondrosarcoma (MCS) is a rare high-grade soft tissue tumor variant of nonconventional chondrosarcoma that is histologically characterized by a biphasic pattern of atypical cartilage with small round cells.

Case description: A 23-year-old female known case of ovarian cyst presented with a two-year history of low back pain and constitutional symptoms. Pelvic magnetic resonance imaging (MRI) with contrast showed a well-defined lesion with intermediate to high signals located at the right wing of the upper sacrum, at the level of S1-S2. The patient underwent a combined ultrasound and computed tomography-guided biopsy under local anesthesia and the immunochemical profile was positive for CD99 and S100 biomarkers. The patient underwent a two-stage procedure for a wide marginal tumor resection. Stage 1 was performed with an anterior approach; identification of the tumor margins was done followed by designing the cuts of the sacrum to achieve wide margins around the tumor. Stage 2 was performed with a posterior approach exposing L3 vertebrae down to the sacrum. Utilizing O-Arm Navigation for posterior margin allocation in addition to instrumentation. After 12 months post-operation, follow up revealed no evidence of recurrence.

Conclusions: Limitation in accessibility to the axial skeleton and the neurovascular component, poses a challenge to treatment. Therefore, using neuro-navigation system and optimal adjuvant therapy should be studied further to improve the prognosis.