Relationship between focal cortical dysplasia and epilepsy‐associated low‐grade tumors: an immunohistochemical study

We retrospectively analyzed 29 seizure‐associated temporal lobe low‐grade tumors to evaluate the utility of CD34 and bcl‐2 expression in clarifying the relationship of these tumors with different classes of focal cortical dysplasia (FCD). CD34 immunostained 75% of gangliogliomas (GG) and 60% of pleomorphic xanthoastrocytomas. FCD type IIIb i.e. abnormal cortical layering associated with a glioneuronal tumor, according to the new International League Against Epilepsy (ILAE) classification] presented CD34‐immunopositive cells in 2/9 (22.2%) cases, whereas FCD type II in 6/7 (85.7%) cases, a difference statistically significant (p = 0.0117). Bcl‐2 immunostained 9/12 (75%) gangliogliomas and 2/3 (66.6%) gangliocytomas. The cases of FCD type IIIb resulted negative for Bcl‐2, whereas 4/7 cases (57.1%) of FCD type II showed immunopositive cells. These differences in Bcl‐2 expression between FCD type IIIb and FCD type II resulted statistically significant (p = 0.0088). Abnormal cortical layering, overall, represents the kind of FCD more commonly associated with seizure‐related low‐grade tumors, whereas FCD type II is more frequently associated with GG. The profile of CD34 and Bcl‐2 expression exhibited by GG is more similar to that observed in FCD type II. Such immunoprofile suggests the existence of a common pathogenesis linking glioneuronal tumors and FCD type II.