The Ribbon Sign as a Radiological Indicator of Intramedullary Spinal Cord Subependymomas

Abstract

INTRODUCTION: Intramedullary spinal cord (IMSC) subependymomas are rare World Health Organization grade 1 ependymal tumors. The potential presence of functional neural tissue within the tumor and poorly demarcated planes presents a risk to resection. Recognition of an intramedullary subependymoma on preoperative imaging can assist in operative planning and factor into the decision-making for gross- or sub-total resection. However, no definitive pathognomonic features have been reported on magnetic resonance imaging (MRI). METHODS: We retrospectively reviewed preoperative MRIs of patients presenting with IMSC tumors at a large tertiary academic institution between April 2005 and January 2022. The diagnosis was confirmed histologically. The “ribbon sign” was defined as a ribbon-like structure of T2 isointense spinal cord tissue interwoven between regions of T2 hyperintense tumor. The ribbon sign was confirmed by an expert neuroradiologist. RESULTS: MRIs from 151 patients were reviewed, including 42 (28%) astrocytomas, 82 (54%) ependymomas, 8 (5.3%) gangliogliomas, and 19 (13%) hemangioblastomas. Of the 82 ependymomas, ten patients (12%) presented with intramedullary subependymomas. The ribbon sign was demonstrated on nine (90%) patients with histologically proven subependymomas. No other tumor types displayed the ribbon sign. CONCLUSIONS: The ribbon sign is a distinctive imaging feature of IMSC subependymomas and indicates the presence of spinal cord tissue between eccentrically located tumor. Recognition of the sign should prompt clinicians to consider a diagnosis of subependymoma. Unlike their intracranial counterparts, resection of these lesions can be technically difficult, particularly in cases with poor demarcation between cord and tumor. Therefore, the risks and benefits of gross- vs. sub-total resection should be carefully considered and discussed with patients.