Camping Out in the Hippocampus: Imaging Spectrum of Etiologies That Affect the Hippocampi and Tips for Honing the Differential Diagnosis

The hippocampus is a complex anatomic structure characterized by interlocking folds of gray matter situated within the medial temporal lobes. As a crucial structure within the limbic system, it plays a vital role in memory formation and emotional decision-making. The hippocampi are susceptible to a heterogenous spectrum of pathologies related but not limited to degenerative, ischemic, drug-related, infectious, metabolic, autoimmune-mediated, and neoplastic etiologies. These include hippocampal sclerosis, Alzheimer disease and frontotemporal dementia, transient global amnesia, herpes simplex encephalitis, mitochondrial encephalopathy with lactic acidosis and strokelike episodes, ischemic and hemorrhagic infarction, seizure-related edema, autoimmune and paraneoplastic limbic encephalitis, and gliomatous lesions. Although imaging findings for some of these entities often overlap, which renders them potentially difficult to distinguish from one another, attention to both the imaging and clinical findings is important in narrowing the differential diagnosis.

Learning Objectives: To (1) review the normal hippocampal anatomy, function, and development; (2) recognize common hippocampal pathologies by reviewing original cases that illustrate the spectrum of hippocampal disease; and (3) become aware of the potential pitfalls, variants, and developmental anomalies related to the hippocampus that may confound evaluation for pathology.