Abstracts

Rationale: Focal cortical dysplasia type IIB (FCDIIB) according to Palmini and Lueders are highly epileptogenic lesions and often associated with medically intractable focal epilepsy. Due to improvements of MRI techniques FCDIIB are increasingly recognized as an underlying cause of formerly MRI-negative epilepsy. However, the appearance of FCDIIB on MRI is variable concerning the size and morphology of the cortical and subcortical abnormality. In this study we classified FCDIIB according to their appearance on MRI and correlated this to the postoperative outcome. Methods: We retrospectively analyzed 67 patients with histologically proven FCDIIB. The following classification based on the size and morphology of the cortical and subcortical abnormality on MRI was applied: if the cortical and subcortical abnormality was limited to one sulcus or one gyrus, the FCDIIB was classified as circumscribed. FCDIIB reaching the crown of two adjacent gyri were classified as extended. The third group, containing FCDIIB with their cortical and subcortical abnormality extending over three or more gyri, was classified as diffuse (Figure 1). Seizure outcome was determined according to Engel's classification and correlated with these different subtypes. Results: According to our classification 37 (55%) FCDIIB were circumscribed, 21 (31%) were extended, and 9 (14%) were diffuse. Circumscribed FCDIIB had the best postoperative outcome, achieving Engel Ia in 81% and Engel I total in 92%. In comparison to this, extended FCDIIB had a less favorable postoperative outcome, achieving Engel Ia in 71% and Engel I total in 81%. Patients with diffuse FCDIIB had a significant worse postoperative outcome compared to the circumscribed FCDIIB group, achieving Engel Ia and Engel I total in 44% (p = 0.039 for Engel Ia, and p = 0.004 for Engel I total). The difference between the extended FCDIIB group and the diffuse FCDIIB group did not reach statistical significance (p = 0.161 for Engel Ia, and p = 0.061 for Engel I total). Results are summarized in Figure 2. Conclusions: FCDIIB may appear very heterogeneously on MRI. We classified these lesions according to their size and morphology into three groups. This classification correlates significantly with the postoperative outcome and facilitates the early identification of good surgical candidates. Furthermore, our findings allow a better assessment of the chance for postoperative seizure freedom individually for each patient depending on the morphology of the FCDIIB on MRI.