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Topic

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Hippocampus

The hippocampus is a curved, elongated structure located within the mesial temporal lobe, forming part of the limbic system. It lies in the floor of the temporal horn of the lateral ventricle and extends from the amygdala anteriorly to the splenium of the corpus callosum posteriorly. The hippocampus is divided into distinct subfields: CA1–CA4 (cornu ammonis), dentate gyrus, and subiculum, each with specialized roles in memory processing. It is highly susceptible to ischemia, hypoxia, and neurodegenerative disorders, making it an important focus in radiology and clinical neuroscience.

Synonyms

  • Cornu ammonis

  • Mesial temporal lobe hippocampus

  • Archicortex component of limbic system

Function

  • Critical for memory formation and consolidation

  • Involved in spatial navigation and learning

  • Integrates sensory input with emotional responses (via connections with the amygdala)

  • Plays a role in stress regulation and neuroplasticity

  • Dysfunction implicated in epilepsy, Alzheimer’s disease, and psychiatric disorders

MRI Appearance

T1-weighted images:

  • The hippocampus appears as a gray matter structure of intermediate signal intensity

  • Surrounded by hyperintense white matter tracts and the CSF of the temporal horn

  • Good for assessing hippocampal volume, atrophy, and internal architecture

T2-weighted images:

  • Hippocampal formation shows intermediate to slightly hyperintense signal relative to white matter

  • Provides better visualization of internal subfields and adjacent CSF

  • Pathologies such as hippocampal sclerosis appear as volume loss and hyperintensity

FLAIR sequences:

  • Suppress CSF, highlighting subtle parenchymal hyperintensities

  • Useful for detecting hippocampal gliosis, sclerosis, or edema in temporal lobe epilepsy

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • Normal hippocampus demonstrates no significant enhancement

  • Abnormal enhancement may indicate encephalitis, tumors, vascular malformations, or active inflammation

Diffusion-weighted imaging (DWI):

  • Normal hippocampus shows no restricted diffusion

  • Restricted diffusion seen in acute ischemia, encephalitis, or seizure-related changes

CT Appearance

  • On non-contrast CT, the hippocampus appears as a soft tissue density structure in the medial temporal lobe

  • Difficult to delineate from adjacent cortex without contrast

  • Best visualized indirectly through the contour of the temporal horn of the lateral ventricle

  • CT is useful for detecting calcifications, hemorrhage, gross atrophy, or mass effect but lacks fine detail compared to MRI

MRI images

Hippocampus Anatomy MRI IMAGE

MRI images

Hippocampus Anatomy