Spontaneous Resolution of a Confounding Insular Lesion

Insular gliomas were previously considered inoperable lesions and were typically treated via biopsy, chemotherapy and/or radiation, if not observation alone. Stereotactic biopsies of low grade insular gliomas can underestimate tumor grade or fail to establish malignancy. Moreover, the survival advantages of maximal safe resection for insular lesions are increasingly being recognized. As such, early surgical resection is increasingly being performed. As with most lesions, a differential diagnosis exists for apparent insular gliomas, with definitive diagnosis generally obtained upon resection. We report an illuminating case that presented similarly to an insular glioma undergoing malignant transformation, but resolved spontaneously following a nondiagnostic biopsy. A 53-year-old female patient presented with aphasia and dizziness, followed by syncope and a 30-minute loss-of-consciousness. Imaging findings included a 12 mm region of contrast enhancement and central necrosis within a larger 3.5 cm expansile, T2-hyperintense lesion involving most of the left insula and extending into the anterior left temporal lobe. Imaging was felt most consistent with high-grade glioma. Stereotactic biopsy demonstrated nonspecific gliosis without definitive neoplastic tissue. A systemic workup was unrevealing, and thus an open procedure was subsequently planned in the intraoperative magnetic resonance imaging (MRI) suite. Preoperative MRI demonstrated interval resolution of the original lesion, despite profound T2 hyperintensity along the needle tract; thus, the planned resection was aborted. Subsequent imaging and systemic studies failed to establish a definitive infectious, neoplastic, autoimmune, or other diagnosis. However, poor dentition, history of a recent dental procedure, and the tiny central focus of diffusion restriction on the index MRI rendered abscess the most parsimonious explanation. On follow-up imaging, the lesion was noted to have further resolved without intervention. Our case illustrates the complexity of managing insular lesions and highlights the potential for alternate pathologies that can mimic insular glioma. Additionally, it provides a humbling reminder that, even in the presence of seemingly pathognomonic imaging findings, a differential diagnosis of insular lesions must be thoughtfully considered in patient counseling and presurgical planning.