Large Epileptogenic Type IIIb Dysplasia: A Radiological and Anatomopathological Challenge

Background: Type IIIb dysplasia is a subtype of focal cortical dysplasia associated with a tumor, most frequently with gangliogliomas then with dysembryoplastic neuroepithelial tumors (DNETs). Their preoperative diagnosis often remains equivocal since specific features are missing. The functional results (i.e., seizure free) is good with 81%-87% of Engel Ia at 5-year follow-up.

Case description: A 4-year-old boy presented with a 1-year history of severe, invalidating, drug-resistant epilepsy. Imaging workup demonstrated a huge left limbic lesion, of which diagnosis remained speculative. Because of worsening neurological status, resective surgery was recommended after multidisciplinary discussion. The resection was performed through left transtemporal approach under neuronavigation (C.R.). Postoperative magnetic resonance imaging assessed uncomplicated near-total resection. Histopathological analysis showed combined features of a DNET of nonspecific type and a focal cortical dysplasia.

Conclusion: We describe a rare condition of type IIIb dysplasia combining a focal cortical dysplasia with a DNET. Preoperative diagnosis of the lesion was of utmost difficultly, thereby rendering mandatory a thorough histopathological examination of resected specimen in the vast majority of cases. Increased recognition of the condition brings up the hypothesis of a genetic continuum or linkage between the 2 conditions. Functional results on seizure activity after ablative surgery are good and maximal safe resection should be the goal.