Function and Assessment of the Human Hippocampus Szabo K, Hennerici MG (eds): The Hippocampus in Clinical Neuroscience. Front Neurol Neurosci. Basel, Karger, 2014, vol 34, pp 71–84 (DOI: 10.1159/000357925)
Conventional and Diffusion-Weighted MRI of the Hippocampus Kristina Szabo a · Alex Förster b · Achim Gass a
a
b
Departments of Neurology and Neuroradiology, UniversitätsMedizin Mannheim, University of Heidelberg, Mannheim, Germany
Abstract The human hippocampus is a highly complex structure located on the medial surface of the cerebral hemispheres as a part of the intralimbic gyrus. For clinical purposes, in addition to routine transverse MRI slices, acquisitions parallel and perpendicular to the long axis of the hippocampus need to be performed to fully appreciate its curved anatomy. Clinicians should be acquainted with the normal appearance of the hippocampus regarding size, shape, symmetry, and signal as well as with the width and form of the cerebrospinal fluid spaces surrounding the hippocampus to be able to recognize abnormalities. The human hippocampus can be affected in a variety of very different acute or chronic neurological diseases, such as stroke and certain forms of encephalitis or epilepsy and dementia. Many of these pathologies are associated with distinct lesion patterns on conventional MRI. In hippocampal sclerosis, the typical imaging features – T2 hyperintensity, atrophy on T1weighted images, and disturbed internal structures of the hippocampus – can be reliably diagnosed by visual analysis. Several visual rating scales exist for the evaluation of medial temporal lobe atrophy for the assessment of patients with cognitive disturbances; however, quantitative MRI-based volumetric analysis is increasingly being applied in research as well as clinical studies. In acute neurological disorders, diffusion-weighted imaging has the ability to demonstrate even minute and transient hyperintense hippocampal lesions. On the basis of distinct lesions patterns, diffusionweighted MRI can provide additional diagnostic information that may facilitate and support a final diagnosis, especially in those cases in which clinical symptoms are inconclusive.
In everyday clinical routine, special emphasis on imaging findings of the hippocampus is relevant in several typical settings. Basically, the hippocampus can be affected by very different pathologies in acute and chronic neurological disorders either in isolation or more commonly as a part of more extensive (visible) structural changes. In this chapter we will focus on clinically relevant aspects of MRI findings of the hippocampus using conventional and diffusion-weighted MRI sequences in common
Downloaded by: Siriraj Medical Library, Mahidol University 202.28.191.34 - 3/20/2015 1:05:40 PM
© 2014 S. Karger AG, Basel
Fig. 1. MRI performed in two planes, parallel to the long axis of the hippocampus (T2-weighted example) (a) and perpendicular to the long axis of the hippocampus (FLAIR example) (b), enables the best anatomical assessment of this complex structure.
neurological disorders. Knowledge of the characteristic features of these – in many cases specific – hippocampal changes may give diagnostic clues and thus aid the clinician in differentiating the underlying pathology.
The hippocampus is part of the limbic lobe, more precisely of the intralimbic gyrus on the medial surface of the cerebral hemispheres (medial temporal lobe), and can be subdivided into three segments: the anterior head, the body, and the posterior tail. Due to its curved structure, the hippocampus is not readily appreciated on routine transverse MRI slices. MRI performed in two planes, (1) parallel to the long axis of the hippocampus and (2) in a slightly oblique coronal plane (perpendicular to the long axis of the hippocampus), enables the best anatomical assessment of this complex structure (fig. 1). A slice thickness of
Conventional and Diffusion-Weighted MRI of the Hippocampus Kristina Szabo a · Alex Förster b · Achim Gass a
a
b
Departments of Neurology and Neuroradiology, UniversitätsMedizin Mannheim, University of Heidelberg, Mannheim, Germany
Abstract The human hippocampus is a highly complex structure located on the medial surface of the cerebral hemispheres as a part of the intralimbic gyrus. For clinical purposes, in addition to routine transverse MRI slices, acquisitions parallel and perpendicular to the long axis of the hippocampus need to be performed to fully appreciate its curved anatomy. Clinicians should be acquainted with the normal appearance of the hippocampus regarding size, shape, symmetry, and signal as well as with the width and form of the cerebrospinal fluid spaces surrounding the hippocampus to be able to recognize abnormalities. The human hippocampus can be affected in a variety of very different acute or chronic neurological diseases, such as stroke and certain forms of encephalitis or epilepsy and dementia. Many of these pathologies are associated with distinct lesion patterns on conventional MRI. In hippocampal sclerosis, the typical imaging features – T2 hyperintensity, atrophy on T1weighted images, and disturbed internal structures of the hippocampus – can be reliably diagnosed by visual analysis. Several visual rating scales exist for the evaluation of medial temporal lobe atrophy for the assessment of patients with cognitive disturbances; however, quantitative MRI-based volumetric analysis is increasingly being applied in research as well as clinical studies. In acute neurological disorders, diffusion-weighted imaging has the ability to demonstrate even minute and transient hyperintense hippocampal lesions. On the basis of distinct lesions patterns, diffusionweighted MRI can provide additional diagnostic information that may facilitate and support a final diagnosis, especially in those cases in which clinical symptoms are inconclusive.
In everyday clinical routine, special emphasis on imaging findings of the hippocampus is relevant in several typical settings. Basically, the hippocampus can be affected by very different pathologies in acute and chronic neurological disorders either in isolation or more commonly as a part of more extensive (visible) structural changes. In this chapter we will focus on clinically relevant aspects of MRI findings of the hippocampus using conventional and diffusion-weighted MRI sequences in common
Downloaded by: Siriraj Medical Library, Mahidol University 202.28.191.34 - 3/20/2015 1:05:40 PM
© 2014 S. Karger AG, Basel
Fig. 1. MRI performed in two planes, parallel to the long axis of the hippocampus (T2-weighted example) (a) and perpendicular to the long axis of the hippocampus (FLAIR example) (b), enables the best anatomical assessment of this complex structure.
neurological disorders. Knowledge of the characteristic features of these – in many cases specific – hippocampal changes may give diagnostic clues and thus aid the clinician in differentiating the underlying pathology.
The hippocampus is part of the limbic lobe, more precisely of the intralimbic gyrus on the medial surface of the cerebral hemispheres (medial temporal lobe), and can be subdivided into three segments: the anterior head, the body, and the posterior tail. Due to its curved structure, the hippocampus is not readily appreciated on routine transverse MRI slices. MRI performed in two planes, (1) parallel to the long axis of the hippocampus and (2) in a slightly oblique coronal plane (perpendicular to the long axis of the hippocampus), enables the best anatomical assessment of this complex structure (fig. 1). A slice thickness of
