Delayed Intradural Extramedullary Dissemination Following Vertebral Metastasis From a World Health Organization Type AB Thymoma:

Study Design: Case report. Objective: To report a rare case of intradural extramedullary (IDEM) dissemination following vertebral metastasis from a World Health Organization (WHO) type AB thymoma and to highlight its spine-specific clinical implications. Background: Thymomas are rare thymic epithelial tumors that generally follow an indolent course and rarely metastasize beyond the thoracic cavity. Spinal metastasis is uncommon, and IDEM dissemination associated with thymomas is rare. The clinical course and management of this progressive disease remain poorly characterized. Materials and Methods: A 51-year-old man underwent thymectomy for Masaoka stage II and World Health Organization (WHO) type AB thymoma, followed by postoperative radiotherapy. Seventy-one months later, biopsy-confirmed vertebral metastasis at T12 was treated with radiotherapy. At 110 months of age, progressive epidural spinal cord compression required decompression, vertebral reconstruction, and posterior fixation. At 127 months, recurrent gait disturbance and severe lower-extremity pain developed. Magnetic resonance imaging and computed tomography myelography revealed multiple IDEM lesions throughout the cauda equina. Intradural tumor resection was performed at 130 months of age. Results: Histopathologic examination of the intradural lesions revealed metastatic recurrent thymoma without evidence of thymic carcinoma. After surgery, the lower extremity pain markedly improved, analgesics were discontinued within one week, and ambulatory function recovered. Seven months after surgery, the patient was able to walk independently without a cane, although he still reported instability when descending stairs and was unable to run because of residual unsteadiness. Conclusion: WHO type AB thymoma rarely shows delayed vertebral metastasis followed by IDEM dissemination. Long-term surveillance should be considered when thymomas demonstrate spinal metastasis. New neurological symptoms or severe lower-extremity pain should prompt careful magnetic resonance imaging of the entire spine, including the cauda equina, and surgical treatment may help preserve neurological function when symptomatic intradural progression occurs.