Cerebral edema following iodine-131 therapy for thyroid carcinoma metastatic to the brain

Brain metastases are rare in well-differentiated thyroid carcinoma but when present they can lead to the patient's death. Iodine-131 therapy for intracerebral thyroid carcinoma metastases causes radiation-induced acute cerebral edema that can lead to CNS complications and even death. We present a case in which a patient with intracerebral 131I uptake developed seizures, slurred speech, and muscle weakness 12 hr following 131I therapy. The patient's CT scan, post-therapy, confirmed an intracranial metastasis with a significant amount of surrounding edema. Radiotherapists, when using external beam radiation to treat intracerebral metastases, commonly place these patients on steroids, glycerol, or mannitol prior to instituting therapy, to prevent complications from radiation-induced cerebral edema. This technique could be applied to 131I therapy of intracranial thyroid carcinoma metastases as well.