OBJECTIVE Incomplete hippocampal inversion (IHI) is a relatively frequent radiological finding at visual inspection in both epilepsy and healthy controls, but its clinical significance is unclear. Here, we systematically retrieve and assess the association between epilepsy and IHI using a meta-analytic approach. Additionally, we estimate the prevalence of IHI in patients with malformation of cortical development (MCD). METHODS We systematically searched two databases (Embase and PubMed) to identify potentially eligible studies from their inception to December 2019. For inclusion, studies were population-based, case-control, observational studies reporting on epilepsy and IHI. The risk of developing epilepsy in IHI (estimated with odds ratio [ORs]) and the frequency of IHI among patients with MCD are provided. RESULTS We screened 3601 records and assessed eligibility of 2812 full-text articles. The final material included 13 studies involving 1630 subjects. Seven studies (1329 subjects: 952 epileptic and 377 nonepileptic) were included for the estimation of the risk of developing epilepsy in the presence of IHI. The estimated OR of active epilepsy in IHI was 1.699 (95% confidence interval = 0.880-3.281), with moderate heterogeneity across studies (I2 = 71%). Seven studies (591 patients) provided information about the frequency of IHI in MCD. Up to one third of patients with MCD (27.9%) presented coexistent IHI. SIGNIFICANCE The present findings confirm that IHI is commonly observed in patients with MCD especially in periventricular nodular heterotopia or polymicrogyria. However, the estimated OR indicates overall weak increased odds of epilepsy in people with IHI, suggesting that the presence of isolated IHI cannot be considered a strong independent predictor for epilepsy development. Clear-cut neuroradiological criteria for IHI and advanced postprocessing analyses on structural magnetic resonance imaging scans are recommended to highlight differences between epileptogenic and nonepileptogenic IHI.

中文翻译：

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不完全海马倒置和癫痫：系统评价和荟萃分析

目的 不完全海马倒置 (IHI) 是癫痫患者和健康对照者肉眼检查中相对常见的放射学发现，但其临床意义尚不清楚。在这里，我们使用元分析方法系统地检索和评估癫痫与 IHI 之间的关联。此外，我们估计了皮质发育畸形 (MCD) 患者 IHI 的患病率。方法 我们系统地搜索了两个数据库（Embase 和 PubMed），以确定从开始到 2019 年 12 月期间可能符合条件的研究。为了纳入，研究是基于人群的病例对照观察性研究，报告癫痫和 IHI。提供了 IHI 中发生癫痫的风险（用比值比 [OR] 估计）和 MCD 患者中 IHI 的频率。结果 我们筛选了 3601 条记录并评估了 2812 篇全文文章的资格。最终材料包括 13 项研究，涉及 1630 名受试者。七项研究（1329 名受试者：952 名癫痫患者和 377 名非癫痫患者）被纳入评估 IHI 存在时发生癫痫的风险。IHI 中活动性癫痫的估计 OR 为 1.699（95% 置信区间 = 0.880-3.281），不同研究之间存在中等异质性（I2 = 71%）。七项研究（591 名患者）提供了有关 MCD 中 IHI 频率的信息。多达三分之一的 MCD 患者 (27.9%) 表现出共存的 IHI。意义 目前的研究结果证实 IHI 在 MCD 患者中很常见，尤其是在脑室周围结节性异位或多小脑回中。然而，估计的 OR 表明 IHI 患者癫痫发生几率整体微弱增加，这表明孤立性 IHI 的存在不能被视为癫痫发展的强有力的独立预测因素。建议使用明确的 IHI 神经放射学标准和对结构磁共振成像扫描的高级后处理分析，以突出致癫痫和非致癫痫 IHI 之间的差异。