Reversible and multiphasic parenchymal changes in MRI after coil embolization for a ruptured cerebral aneurysm

BACKGROUND: Reversible and multiphasic parenchymal changes in magnetic resonance imaging (MRI) are exceedingly rare. The authors experienced a case of reversible and multiphasic parenchymal changes in MRI after coil embolization for a ruptured cerebral aneurysm. CASE DESCRIPTION: A 48-year-old woman had a sudden onset of severe headaches and was referred to us for coil embolization. She was alert-oriented and had no neurologic deficits. Her medical history was atopic dermatitis and metal allergy. A head computed tomography (CT) scan demonstrated subarachnoid hemorrhage, and three-dimensional-CT angiography revealed a left internal carotid artery-posterior communicating artery aneurysm. Coil embolization was performed on the next day and seven coils made by three different manufacturers were used for the embolization. Despite no neurologic deficits after the surgery and no abnormal findings in MRI 7 days after the coil embolization, an MRI 2 weeks after embolization demonstrated delayed multiple white matter high intense lesions on T2-weighted image and fluid-attenuated inversion recovery in the left hemisphere. Repeat MRI scans showed multiple high intense lesions at various locations and at different timings. The blood test revealed the elevation of the proportion of EOS up to 9.7%, strongly indicating some allergic response. The MRI scan obtained 3 months after the onset confirmed the complete disappearance of the lesions. CONCLUSION: Given her history of metal allergy, and the reversible and multiphasic lesions in the non-vascular territories of the treated aneurysm, metal allergic encephalitis was most likely despite no clear evidence.