The Classical Pathways of Occipital Lobe Epileptic Propagation Revised in the Light of White Matter Dissection

Figure 5

Artistic illustration of the white matter connectivity underlying the occipital region. The illustration shows a schematic reconstruction from a posterior coronal view the occipital region with all the major white matter bundles dissected and shown with different colours through the cortical layer. This illustration serves to summarize the complex subcortical organization, which can be significantly correlated to the semiology of the seizures involving each sublobar occipital region. A lesion on the lateral surface of the occipital lobe or at the temporo-occipital/parieto-occipital junction would probably spread to the parietal and frontal regions. The vertical component of the superior longitudinal fasciculus (vSLF/red), arcuate fasciculus or the horizontal superior longitudinal fasciculus (AF/yellow, hSLF/light green), and the vertical occipital fasciculus (VO/gray) can support this direction of propagation. Deep lesions may involve different pathways within the sagittal stratum of Sachs (SSS) such as inferior longitudinal fasciculus (ILF/orange), middle longitudinal fasciculus (MLF/pink), inferior fronto-occipital fasciculus (IFOF/light blue), or even the optic radiation (OR/dark green). According to the hierarchical segregation of the fibres, the epileptic propagation would spread to temporo-lateral areas, temporo-mesial areas, and/or frontal lobe. Moreover, a possible epileptic lesion in a dorsal-mesial location with respect to the OR and calcarine fissure would involve fibres of the cingulum (Ci/dark red) and callosal fibres of the forceps major-tapetum (Ta/dark blue) with a resultant ipsilateral and/or contralateral epileptic propagation. Finally, ventral-mesial deep lesions located below the calcarine fissure can involve the ventral portion of the IFOF (light blue) with a fast propagation to the frontal lobe or can recruit the ventral portion of the ILF (orange) and Li-Am bundle (LiAm/purple) with a fast temporo-mesial involvement (see the text for the functional considerations). Ag: angular gyrus; Cc: corpus callosum; Cu: cuneus; Li: lingula; PreCu: precuneus; Op: occipital pole.