Giant Subcortical Heterotopia Mimicking a Brain Tumor: A Case Report

Background Giant subcortical heterotopia is a rare neuronal migration disorder characterized by ectopic gray matter forming a mass-like subcortical lesion. Its imaging appearance, particularly on computed tomography, may closely resemble that of a brain tumor, leading to potential misdiagnosis and unnecessary invasive procedures. The rarity of this entity, especially in the neonatal period, and its atypical clinical presentation make early recognition challenging. This case highlights the importance of magnetic resonance imaging in establishing the correct diagnosis and expanding awareness of this uncommon malformation of cortical development. Case presentation: We report the case of a 13-day-old term newborn referred for evaluation of right facial palsy and a history of poor adaptation to extrauterine life requiring neonatal intensive care support. Clinical examination revealed hypotonia without respiratory or peripheral compromise. Brain computed tomography demonstrated a non-enhancing left hemispheric pseudomass exerting mass effect on the ipsilateral ventricle, initially raising suspicion of a brain tumor or subependymal heterotopia. Subsequent magnetic resonance imaging confirmed the diagnosis of giant subcortical heterotopia, showing a large subcortical lesion isointense to cortical gray matter, without contrast enhancement or diffusion restriction, associated with cortical thinning, ventricular asymmetry, and ipsilateral basal ganglia hypoplasia. Antiepileptic therapy was initiated. At one-month follow-up, facial palsy persisted without seizure occurrence, and repeat imaging at three months demonstrated stable findings. Conclusions Giant subcortical heterotopia is an uncommon but important differential diagnosis of neonatal intracranial mass-like lesions. Magnetic resonance imaging plays a crucial role in distinguishing this malformation from neoplastic processes by demonstrating gray matter signal characteristics and the absence of enhancement or diffusion restriction. Early and accurate diagnosis can prevent unnecessary surgical interventions and guide appropriate medical management. Increased awareness of this entity may improve diagnostic confidence in atypical pediatric neuroimaging presentations.