Epilepsy is among the most commonchronicneurological disease and one of the major health problems in developing countries with the incidence of almost (7.5%) (1). Magnetic Resonance Imaging (MRI) is typically used as a noninvasive medical test for the evaluation of patients with epilepsy. After thediagnosisof epilepsy,in order tofind the cause of seizures, prognosisand treatment plans, brain structure shouldbe evaluated with MRI (2).

Previously, the relationship between the hippocampus and epilepsy has been studied. Temporal lobe epilepsy is the most common form of partial epilepsy in which the hippocampal sclerosis is the most common radiologic findings (1). It is suggested that developmental abnormalities of the hippocampus may lead to seizures or may be the main cause of epilepsy (2). Hippocampal folding in temporal lobe occurs at 18 weeks of fetal development, and in week 21, the folding pattern is similar to those in adults (3, 4).

Because hippocampus has many role in cognition and memory processes (5); hence, every malrotation during hippocampal folding may be responsible for most of hippocampus related complications including cardiac and respiratory dysfunction (6), loss of cognitive function, learning and memory impairment (7) and other complications such as incidence of seizure (8). Incomplete Hippocampal Inversion (IHI) which is traditionally known as Hippocampal Malrotation (HIMAL) is the incomplete inversion of the hippocampus to abnormally round shape (9). In other word, the shape of hippocampus in malrotated form is round or pyramidal than oval. Incomplete rotation rate of the hippocampus in both healthy subjects and patients with epilepsy are not clear. In addition, there are different estimations on the relationship between incomplete rotation of hippocampus and partial seizures. But, it is not yet clear whether this partial rotation as a structural disorder is the underlying cause for seizure, or it is a common finding in asymptomatic population.

Although the role of hippocampus anomalies in onset of seizures is accepted (6); yet, the exact role of incomplete hippocampus inversion in patients with epilepsy is not fully understood. Hence, finding relationship between incomplete inversion of hippocampus and epilepsy can help to predict the incidence of seizures or other structural abnormalities in the fetus. This study aimed tosystematically review the frequency of reported incomplete rotation ofthe hippocampusinepilepsy patientscompared tohealthy individuals based on MRI findings.

Materials and Methods

Literature search strategy

PubMed and Scopuswere searched for evaluation of incomplete hippocampal inversion with magnetic resonance imaging in patient with epilepsy on words in the title, keywords, and abstract. First these databases searched for incomplete inversion of hippocampus or hippocampal malrotation. Then the search was limited to patients with epilepsy, and finally the results were restricted to those in which MRI has been used for brain structural evaluation. Relevant articles with the following search terms: (incomplete hippocampal inversion or hippocampal malrotations) and epilepsy and MRI were selected and reviewed with the last update on February2015.

Nonrelevant articles were omitted as we reviewed the abstract of the articles. Subsequently, the full text of the relevant papers was studied. To minimize the possibility of missing relevant data, and in order to find further potentially relevant studies, the reference list of related articles was also scanned.

Study selection

There was no time limitation for the included articles, but we excluded the articles to those in English language. All types of the articles including the case series, clinical trials and cohort studies in which the study has been conducted on at least two patients were selected. But, we did not include review articles,meta-analysis and book chapters. Inclusion criteria for study selection were patients with verified hippocampal malrotation with or without epilepsy. Those papers with duplicated data were omitted. Exclusion criteria for this review were articles in which the patients with epilepsy had not been studied for incomplete inversion of hippocampus, or studies in which the incidence of seizure was due to hippocampal sclerosis or neuropathology of the temporal lobe. In order to avoid selection bias, we included all studies in which the incomplete hippocampal inversion had been investigated in patients with or without epilepsy, or studies in which the patients with epilepsy were studied for the presence of hippocampal abnormalities.

Data extraction

Data about authors, country of origin, publication date, study design and the concluded results were extracted. The data regarding hippocampal malrotation obtained in each study were compared. Total number of patients and controls were identified and structural features of hippocampus were compared between the groups. All information from included articles were tabulated. Results were organized based on the association between hippocampal abnormalities, specifically incomplete hippocampal inversion with the incidence of epilepsy. The quality assessment of selected papers was performed based on recommendations of CONSORT checklist 2010 by two independent reviewers (10).

Results

From overall 645 article found in PubMed and 12 in Scopus, only 33 articles seemed to be relevant to the purpose of this study in the first step. After carefully reviewing the articles, only 11 papers met the inclusion criteria for further assessment. Therefore, full texts of these articles were collected and the data were extracted based on the main purpose of this study.