Appearance of intracranial cottonoids on intraoperative magnetic resonance imaging.

To our knowledge, this is a unique report of intraoperative magnetic resonance imaging (iMRI) of an intracranial cottonoid. The current literature describes images of cottonoids as a post-operative finding in the setting of an unintentionally retained foreign body; however, the iMRI images we present are important as the use of iMRI in the resection of complex tumors and epilepsy foci increases. This series of images was obtained during a craniotomy for tumor resection of a patient with dysembryoplastic neuroepithelial tumor. To determine both the degree of tumor resection and the amount of residual tumor, cottonoids were left in our patient's resection cavity and underwent iMRI. The ability to distinguish cottonoids in these images is important for intraoperative localization of resection margins and to prevent the retention of cottonoids.