Why the Hippocampus Matters: A Radiologist’s
Guide to Its Role in Brain MRI

A Small Structure with a Big Role

The hippocampus is a small, curved structure deep within the brain that plays a central role in memory, learning, and spatial orientation. Despite its size, it is one of the most studied regions of the brain because changes here often precede changes elsewhere.

In brain MRI, the hippocampus is more than a landmark; it is a region where radiologists can gather valuable, quantifiable information about brain health. Understanding its anatomy and function helps professionals and neurologists.

Where and What Is the Hippocampus

The hippocampus lies deep in the medial temporal lobe of each hemisphere, arching along the inner edge of the lateral ventricle. On a coronal MRI image, it appears as a distinct, curved structure just above the brainstem, adjacent to the amygdala and parahippocampal gyrus.

The name “hippocampus” means “seahorse” in Greek, reflecting its shape. This shape follows the natural curve of the temporal lobe and places it at a hub of connections linking the cortex, thalamus, and limbic system.

Internal organisation:

The hippocampus is composed of several interconnected regions known as subfields, each with a specific role in information processing:

• CA1 – important for consolidating memories.
• CA2 & CA3 – involved in associating spatial and contextual information.
• Dentate gyrus – receives incoming signals from the cortex and contributes to forming new memories.
• Subiculum – relays processed information back to other cortical areas.

Because of this layered structure, even small changes in one area can influence memory and navigation. This is why precise imaging is so valuable.

Why the Hippocampus Matters Beyond the Scan

The hippocampus performs several crucial tasks:

• Memory formation and recall: converting experiences into long-term memories.
• Learning: integrating new information into existing knowledge.
• Spatial navigation: creating mental maps to orient within environments.
• Emotion–memory link: connecting events with emotional context.

In everyday life, these functions translate into remembering faces, navigating a new city, or recalling where something was placed. When radiologists examine the hippocampus on MRI, they are looking at a structure central to everyday human abilities.

The Hippocampus in Brain MRI — What Radiologists Look For

On high-resolution MRI scans, the hippocampus appears as a well-defined structure whose morphology can vary slightly with age, domicile and individual anatomy. Radiologists evaluate:

• Volume: whether the size is within expected limits
• Symmetry: whether both sides are similar in size and shape
• Signal intensity: whether there are abnormal brightness or dark areas on T1, T2, or FLAIR sequences
• Contours and internal structure: whether the normal layered appearance is preserved.

Changes in these features may indicate an underlying process or provide clues in longitudinal monitoring.

Why Measurement Matters — From Research to Routine

Hippocampal volumetry, the measurement of hippocampal volume was once confined to research. Advances in MRI quality and computing now make it feasible in everyday practice. Quantitative measurements help to:

• Establish baselines for individual patients
• Provide objective evidence alongside visual impressions
• Enable consistent monitoring over time
• Support multi-site and multi-scanner consistency in larger studies

Objective data enhances the precision of radiology reports and can improve communication with referring physicians and researchers.

Challenges of Manual Measurement

Manual delineation of the hippocampus is technically demanding:

• It requires time; often 20–30 minutes per scan
• It suffers from inter-rater variability; two experts may draw slightly different boundaries
• It is affected by scanner and protocol differences; slice thickness and orientation can alter apparent volume

These challenges have historically limited volumetric analysis to specialized research settings rather than routine practice.

Automated and Standardized Measurement

Standardized volumetric tools now allow hippocampal volume to be derived quickly and reproducibly. Such tools use consistent anatomical criteria to produce comparable measurements across sites and time points. This allows larger studies, longitudinal tracking, and more routine use in busy clinical environments.

Looking Ahead: Quantitative Imaging in Everyday Practice

The hippocampus represents a natural starting point for quantitative brain imaging because of its clear boundaries and clinical relevance. As methods mature, the same principles will be applied to other structures, enabling whole-brain volumetry, cortical thickness mapping, and integration with cognitive or laboratory data. This will shift radiology from a primarily qualitative discipline to one that combines visual interpretation with reliable, objective metrics.

Conclusion: Why the Hippocampus gets attention

The hippocampus is a small but essential region of the brain. Understanding its anatomy, function, and appearance on MRI helps radiologists and Neurologists. Precise measurement of its structure bridges the gap between research and clinical care, opening the way for more standardized and informative reports.

Contact Us to Learn More

Find out how Alzevita’s hippocampal volumetry solutions can support your practice or research. Contact us to discuss your needs or request further information.

FAQ

References

• A computational atlas of the hippocampal formation using ex vivo, ultra-high resolution MRI: Application to adaptive segmentation of in vivo MRI.” NeuroImage. 2015.
• Automated volumetry and regional thickness analysis of hippocampal subfields and medial temporal cortical structures in mild cognitive impairment.” Hum Brain Mapp. 2015.

Common hippocampal-segmentation toolkits/documentation:

• FreeSurfer — hippocampal subfields & related documentation
• FSL (FIRST) — subcortical/hippocampal segmentation docs and how-to