Focal Cortical Dysplasia Type IIIb with Oligodendroglioma in a Seizure-Free Patient

• Published in: Canadian journal of neurological sciences 2018-05, Vol.45 (3), p.360-362
• Main Authors: MacLean, Mark A., Easton, Alexander S., Pickett, Gwynedd E.
• Format: Article
• Language: English
• Subjects: Brain cancer; Brain Neoplasms - complications; Brain Neoplasms - diagnostic imaging; Brain Neoplasms - surgery; Classification; Convulsions & seizures; Craniotomy; Epilepsy; Epilepsy - complications; Epilepsy - diagnostic imaging; Humans; Letters to the Editor; Magnetic Resonance Imaging; Male; Malformations of Cortical Development, Group I - complications; Malformations of Cortical Development, Group I - diagnostic imaging; Oligodendroglioma - complications; Oligodendroglioma - diagnostic imaging; Oligodendroglioma - surgery; Patients; Tumors; Young Adult
• ISSN: 0317-1671; 2057-0155
• DOI: 10.1017/cjn.2017.295

Focal cortical dysplasia (FCD) refers to malformation of cortical development with abnormalities of cortical layering, neuronal differentiation, and maturation.1 Focal cortical dysplasia is responsible for most cases of medically refractory epilepsy in the paediatric population, and medically intractable seizures in adults.2 The coexistence of FCD and low-grade glial tumours such as ganglioglioma (GG) and dysembryoplastic neuroepithelial tumour (DNT) have been classified by the International League Against Epilepsy (ILAE) as FCD Type IIIb.3 Patients with FCD Type IIIb generally present with increased seizure frequency compared with isolated FCD or brain tumours.4 Herein, we describe the first report of FCD Type IIIb discovered incidentally in a seizure-free patient, which is the fifth reported case associated with oligodendroglioma.4,5 A 20-year-old male with suspected arteriovenous malformation of the right pinna underwent MRI. Focal cortical dysplasia Type III cortical lamination abnormalities usually affect the same lobe as the principal lesion and are most common in the frontal and temporal lobes.3,4 As many as 25% of patients undergoing epilepsy surgery have an underlying epileptogenic neoplastic lesion, whereas ~50% of patients with brain tumours have seizures.8 Chronic focal epilepsy associated with benign glioneuronal tumours mostly relates to GG and DNT.8 Only 2.7% of epileptic patients with brain tumours are attributed to oligogendroglioma.9 The primary clinical manifestation of FCD is epilepsy.3 Glioneuronal tumours may be surrounded by cortical disorganization in up to 80% of cases; such coexistence adds to their epileptogenicity, having only been described in the epileptic patient.5 Although FCD is commonly associated with GG and DNT, the coexistence of FCD with oligodendroglioma has been reported in four previous cases.4,5 The histological characteristics of FCD Type IIIb include cortical dyslamination and hypoplasia without six-layered structure and/or hypertrophic neurons of the neocortex, occurring adjacent to tumours (e.g., GG or DNT).3 The mechanism(s) by which glioneuronal tumours and perilesional cortical tissue develop and contribute to epileptogenicity have not been clearly defined.3 The lack of seizure activity in this case may suggest that FCD is not inevitably associated with epilepsy, or point to a reduced risk of seizures when combined with oligodendroglioma, rather than other tumours, many of which also have neuronal components