Case of incidental thoracic spinal dumbbell hemorrhagic arachnoid cyst and tentorial metastasis from breast carcinoma.

Background: Spinal arachnoid cysts (SACs) in adults are typically acquired dural defects following trauma, inflammation, or infection. Brain metastases from breast cancer account for 5-12% of all CNS metastases and are mostly leptomeningeal. Here, the authors reported a 50-year-old female treated for a tentorial metastasis from breast carcinoma that underwent chemotherapy and radiotherapy. Three months later, she presented with a thoracic spinal extradural dumbbell hemorrhagic arachnoid cyst. Case Description: A 50-year-old female underwent a left retrosigmoid suboccipital craniectomy for microsurgical removal of a tentorial metastasis attributed to poorly differentiated breast carcinoma (i.e., comedonic pattern). The patient subsequently underwent both chemotherapy and radiotherapy for accompanying bony metastases. Three months later, she experienced the onset of severe posterior thoracic pain. When the thoracic magnetic resonance imaging revealed a hyperintense "dumbbell" extradural T10-T11 lesion, she underwent a T10-T11 laminectomy for marsupialization and excision of the hemorrhagic lesion. The histological examination revealed blood and arachnoid tissue within a benign SAC, without accompanying tumor. Her postoperative course was uneventful, and she was discharged on postoperative day 3. Conclusion: A 50-year-old female underwent a left retrosigmoid suboccipital craniectomy for removal of a tentorial metastasis from breast carcinoma, followed by radiation/chemotherapy. Three months later, she hemorrhaged into an MR-documented T10-T11 dumbell extradural SAC that was successfully treated with laminectomy, marsupialization, and excision.