Diffusion-Weighted Imaging for the Differential Diagnosis of Disorders Affecting the Hippocampus

Abstract

Background: The human hippocampus can be affected in a large variety of very different neurological diseases, of which acute ischemic stroke, transient global amnesia, epilepsy, and limbic encephalitis are the most common. Less frequent etiologies include various infections and encephalopathy of different origins. Clinical presentation notably comprises confusional state, altered vigilance, memory deficits of various extent and seizures. While in hypoxic or hypoglycemic encephalopathy, clinical presentation and surrounding circumstances provide some clues to reach the correct diagnosis, in the above-listed more common disorders, signs and symptoms might overlap, making the differential diagnosis difficult. This review presents recent studies using the diffusion-weighted imaging (DWI) technique in diseases involving the hippocampus. Methods: References for the review were identified through searches of PubMed from 1965 to January 2011. Only papers published in English were reviewed. Full articles were obtained and references were checked for additional material where appropriate. Results: All pathologies affecting the hippocampus are associated with distinct lesion patterns on magnetic resonance imaging, and especially DWI has the ability to demonstrate even minute and transient hippocampal lesions. In acute ischemic stroke in the posterior cerebral artery territory, involvement of the hippocampal formation occurs in four distinct patterns on DWI that can be easily differentiated and correspond to the known vascular anatomy of the hippocampus. In the subacute phase after transient global amnesia (TGA), dot-like hyperintense lesions are regularly found in the lateral aspect of the hippocampus on DWI. The DWI lesions described after prolonged seizures or status epilepticus include unilateral or bilateral hippocampal, thalamic, and cortical lesions of various extent, not restricted to vascular territories. In limbic encephalitis, DWI lesions are only infrequently found and usually affect the hippocampus, uncus and amygdala. Furthermore, in some rare cases DWI lesions of different etiology may coexist. Conclusion: In patients with diseases affecting the hippocampus, DWI appears to be useful in differentiating between underlying pathologies and may facilitate a definite diagnosis conducive to an optimal treatment. With a careful clinical examination, experience with the interpretation of DWI findings and knowledge of associated phenomena, it is indeed possible to differentiate between ischemic, ictal, metabolic, and TGA-associated findings.

Recognizing Autoimmune-Mediated Encephalitis in the Differential Diagnosis of Limbic Disorders

“…Abnormal vessels on angiography and cytotoxic edema on DWI that usually extends throughout the compromised vascular territory and is not restricted to the limits of the limbic system are helpful to confirm imaging suspicions. 9 Transient global amnesia also affects the hippocampal formation, but its clinical and imaging presentation is rather typical. …”

“…In addition, symptoms can precede the diagnosis of cancer, and T2/FLAIR hyperintensity in the medial aspect of the TL may mimic several other disorders. [4][5][6][7][8][9][10][11][12] MR imaging plays a key role in the management of patients with suspected LE and is used as part of the LE diagnostic criteria to rule out differential diagnoses. Certain imaging and clinical peculiarities may narrow the list of possible diagnoses; however, a complete list of differential diagnoses remains beyond the scope of this article.…”

“…9,61 Imaging follow-up with typical clinical and electroencephalographic features may aid diagnosis. This condition is potentially reversible or can result in atrophy with mesial temporal sclerosis (Fig 8).…”

Inappropriate treatments for patients with cognitive decline

“…The hippocampus and its limbic circuits can be altered, therefore causing related amnesia symptoms in patients affected by trauma or surgery, or patients with anoxia, ischaemia, herpesviral encephalitis, tumours, hypothyroidism, and autoimmune diseases (for example, neurological lupus or autoimmune limbic encephalitis). [56][57][58][59] Therefore, AD diagnosis cannot be based solely on neuropsychological examination. On the other hand, hippocampal atrophy shown by MRI does not necessarily point to underlying AD.…”

Transient global amnesia

“…The current hypothesis is that it is associated with lesions within the mediobasal temporal region, hippocampus and the para-hippocampus. 17 Magnetic resonance imaging (MRI) has demonstrated lesions in the hippocampal formation and memory circuits in the mesiotemporal region 18,19 and analysis of the functional anatomy of these lesions has shown selective distribution within the CA1 subfield of the hippocampal cornu ammonis. 20,21 Some images have demonstrated that cellular mechanisms may play a role in developing the lesions, suggesting that a cascade initiated by the selective vulnerability of CA1 neurons to metabolic stress causes a temporary disturbance to the memory pathways.…”