Bilateral hippocampal atrophy in temporal lobe epilepsy: Effect of depressive symptoms and febrile seizures

Temporal lobe epilepsy (TLE) often is associated with mesial temporal sclerosis (MTS) on magnetic resonance imaging (MRI) (Cendes et al., 1993). MTS is characterized by neuron loss, gliosis, and hippocampal atrophy ipsilateral to seizure foci (Mathern et al., 1995). Because neuron loss and the extent of hippocampal atrophy vary among patients with TLE, comparing hippocampal volumes across diagnostic groups may reveal relationships among structural pathology, clinical features, and comorbidities. MTS and decreased hippocampal volume are associated with mood disorders in some but not all studies of TLE (Quiske et al., 2000; Shamim et al., 2009; Wrench et al., 2009). Measuring whole hippocampal volumes may overlook local shape and volume differences with potential clinical relevance, since MTS may be associated with restricted neuronal loss leading to local deformations in surface morphology (Lin et al., 2005). Identifying these patterns may help detect patients most at risk for affective symptoms and elucidate the epilepsy-depression link. Prolonged febrile seizures (FS) are associated with acute hippocampal injury (Van Landingham et al., 1998; Scott et al., 2002), increased risk for epilepsy (Verity & Golding, 1991), and MTS (Cendes et al., 1993; Van Paesschen et al., 1996; Kim et al., 1999; Theodore et al., 1999; Pittau et al., 2009). Histologic studies indicate loss of specific neuronal populations (Bluumcke et al., 1999; Crespel et al., 2002), and visualizing three-dimensional (3D) profiles of local hippocampal atrophy may elucidate pathology related to FS. Radial atrophy mapping (RAM) computes distances from a structure's center to reconstruct neuroanatomic surfaces and visualize local changes in surface anatomy. These distances can be averaged and compared across groups or covaried with other clinical data. Hippocampal RAM on patients with TLE predicted postsurgical outcome, with seizure-free patients displaying greater presurgical hippocampal asymmetry than those not seizure free after temporal lobectomy (Lin et al., 2005). A recent RAM study found a difference in hippocampal surface anatomy between two electrographically distinct forms of epilepsy (Ogren et al., 2009). We used RAM to investigate the effects of depressive symptoms, febrile seizure history, and epilepsy duration on hippocampal surface anatomy in 40 subjects with TLE.