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Figure. FCDIIIb. Temporal neocortex adjacent to hippocampal sclerosis in a patient with TLE: a) shows
abnormal clustering of neurones with NeuN marker in layer II. b) shows a band of gliosis throughout a
gyrus in midlayers with GFAP marker which is shown at higher magnification in c).

Tumours and epilepsy
A wide variety of tumour types, particularly where there is cortical extension, can manifest
clinically with focal seizures (for review see Thom et al97). Within this group, patients with longer
histories of early onset, focal or partial epilepsy, neuroimaging and pathological studies more
often identify cortically-based, slow-growing tumours. These are also termed long-term epilepsy-
associated tumours (LEAT). In many of these cases the main aim of surgical treatment is seizure
control rather than to halt any tumour progression and low-grade glial or mixed glio-neuronal
tumours are common diagnosis in large surgical series.

Glioneuronal tumours
There are two main tumour types in this category, dysembryoplastic neuroepithelial tumours
(DNT) and gangliogliomas. Both tumour types have a predilection for the temporal lobe. Other
glial tumours associated with epilepsy may also have a minor neuronal component, including
pleomorphic xanthoastrocytoma, and pilocytic astrocytoma. In addition, newer forms of glial
tumours, such as the isomorphic astrocytoma98, the angiocentric neuroepithelial tumour or
glioma99 and rarer glioneuronal tumours such as the papillary glioneuronal tumour100, continue
to be recognised, some strongly associated with long-standing epilepsy101. DNT are typically
clinically associated with partial seizures. The pathological features of the classical DNT are
characterised by a multinodular, intracortical architecture composed of cells with mixed
cytological features102,103. The predominant cell type is the oligodendrocyte-like cell (OLC) but
regions with an astrocytic-piloid growth pattern, including eosinophilic granular bodies and
Rosenthal fibres, can be seen. Among the glial cells is a mature neuronal component and in some
cases single neurones suspended within a myxoid matrix between surrounding OLC (the
‘glioneuronal element’). These neurones display minimal cytological atypia and
immunophenotypically resemble neurones of adjacent cortex, including expression of mature
neuronal markers as MAP2 and NeuN and lack of expression of immature markers as nestin and
CD34. This classical form of DNT is readily recognised, particularly in large lobectomy
specimens in contrast to small biopsies where a precise pathological diagnosis is less feasible due
to the marked heterogeneity of these lesions. Other histological forms of DNT described are the
diffuse or non-specific forms103,104. The latter have a similar cytological composition but show
more diffuse infiltration of the cortex and white matter and lack a glio-neuronal element. All
DNT may show cystic degeneration, calcification, pigmentation, leptomeningeal extension and
nuclear pleomorphism of OLC, but mitotic figures and necrosis are rare. Resection typically