MRI findings in low grade tumours associated with focal cortical dysplasia

Magnetic resonance imaging (MRI) is mandatory to identify the epileptogenic zone in refractory temporal lobe epilepsy (TLE). The correct identification of lesions is essential to obtain good post-surgery seizure control. Low grade tumours (LGT) and focal cortical dysplasia (FCD) are common findings in symptomatic TLE, and frequently coexist. The aim of this study was to identify the MRI characteristics in the diagnosis of FCD associated with LGT. We analyzed 24 subjects with TLE who underwent tailored surgery. They all had LGTs. Two expert neuroradiologists analyzed the imaging data and compared them with histological results, hypothesizing the causes of diagnostic errors in the identification of FCD. We selected three exemplary cases to report the most important causes of errors. In the diagnosis of FCD we reported false positives and false negatives due to different causes. An incomplete MRI protocol, the large dimensions of the tumour, infiltration and related oedema were the most important factors limiting MRI accuracy. MRI can be limited by an incomplete protocol. In addition, the presence of an LGT may limit the neuroradiological diagnosis of FCD in the temporal lobe. Advanced MRI techniques could help reveal subtle lesions that eluded a previous imaging inspection.