Isolated hippocampal infarcts: Vascular and neuropsychological findings

A Case With Bilateral Hippocampal Infarction Resembling Transient Global Amnesia

Transient global amnesia (TGA) is a benign and transient condition with a sudden short-term amnesia. One of the conditions resembling TGA is hippocampal infarction, which requires relapse prevention treatments. In this report, we present a case with bilateral hippocampal infarction in whom distinguishing these two conditions was difficult for up to 1 week from the onset. A 60-year-old female visited our hospital with sudden onset retrograde and anterograde amnesia. Thin-slice magnetic resonance imaging (MRI) with 2-mm thickness revealed hyperintense signals on diffusion-weighted imaging (DWI) with signal loss on apparent diffusion coefficient (ADC) on both sides of the hippocampus. MRI with 5-mm thickness on day 7 revealed persistent restricted diffusion on both sides, one of which was still with decreased ADC values. Based on this finding, the diagnosis of bilateral hippocampal infarction was reached, and the relapse-preventive antiplatelet was continued. This case implied the potential difficulty of distinguishing cases with TGA and those with hippocampal infarction based on MRI findings within the first several days after onset. Thin-slice brain MRI, careful search of potential cardiovascular risks, and follow-up MRI ≥ 7 days after onset will be helpful to reach a correct diagnosis in cases with sudden amnesia.

Unveiling the Effects of Left Hemispheric Intracerebral Hemorrhage on Long-term Potentiation and Inflammation in the Bilateral Hippocampus: A Preclinical Study

OBJECTIVE

Changes in cognition and memory are common complications of intracerebral hemorrhage (ICH), although the exact cause of this phenomenon is still unknown. The objectives of our project were to assess the changes in long-term potentiation, inflammation, and cell damage in the bilateral hippocampus following striatal intracerebral hemorrhage at different time points.

MATERIALS AND METHODS

Unilateral ICH was induced in the striatum of 96 Wistar rats (6 control groups and 6 ICH groups). We measured changes in synaptic inputs in the bilateral hippocampus using the field potential recording method on days 3, 7, and 14 after ICH. After staining the section with hematoxylin, the volume and number of hippocampal cells were measured. The number of NF-κB positive cells was evaluated using the immunohistochemistry method.

RESULTS

There was a significant change in the amplitude and slope of the hippocampal excitatory potential in the ICH group compared to the sham group, but only on the 7th day after surgery. Specifically, the ipsilateral hippocampus in the ICH-7 group showed an increase in stimulation recording in 90 minutes compared to the sham-7 group (p<0.0001), while the contralateral hippocampus in the ICH-7 group exhibited a decrease in potential recording compared to the sham-7 group (p<0.0001). By day 14, the ICH group had a lower cell density in both the ipsilateral (p<0.05) and contralateral hippocampus (p<0.05) compared to the sham group, but there was no significant change in the hippocampal volume between the groups at any time interval. Furthermore, our immunohistochemical analysis revealed that the number of NF-kB-positive cells in both hemispheres of the ICH groups was significantly greater than that of the sham groups across all time intervals.

CONCLUSIONS

These findings suggest that striatal injury may lead to inflammation and cell death in the bilateral hippocampus, which can impair cognitive function after ICH.

Nasu-Hakola Disease With Stroke-like Attack: A Case Report

Homozygous mutations in the triggering receptor expressed on myeloid cells 2 (TREM2) gene are known to cause Nasu-Hakola disease, which is a rare cause of progressive presenile dementia. A 36-year-old woman presented with repetitive seizures, a 5-year history of progressive behavioral and cognitive changes, and an affected sibling. Magnetic resonance imaging of the brain revealed an ischemic lesion in the left medial temporal lobe. Extensive evaluation of juvenile stroke revealed that viral and autoimmune encephalitides, serum lactate and pyruvate levels, and cerebrospinal fluid composition were all normal. Brain magnetic resonance imaging was notable of thinning of the corpus callosum and caudate and frontotemporal cortical atrophy, in addition to the ischemic lesion. Whole exome sequencing revealed a homozygous mutation (c.A257T; p.D86V) in TREM2. The present case expands the clinical phenotype of Nasu-Hakola disease and further suggests that TREM2 pathway might have role in vessel wall health.

Forgetting the Unforgettable: Transient Global Amnesia Part II: A Clinical Road Map

Transient global amnesia (TGA) is a clinical syndrome characterized by the sudden onset of a temporary memory disorder with profound anterograde amnesia and a variable impairment of the past memory. Usually, the attacks are preceded by a precipitating event, last up to 24 h and are not associated with other neurological deficits. Diagnosis can be challenging because the identification of TGA requires the exclusion of some acute amnestic syndromes that occur in emergency situations and share structural or functional alterations of memory circuits. Magnetic Resonance Imaging (MRI) studies performed 24–96 h after symptom onset can help to confirm the diagnosis by identifying lesions in the CA1 field of the hippocampal cornu ammonis, but their practical utility in changing the management of patients is a matter of discussion. In this review, we aim to provide a practical approach to early recognition of this condition in daily practice, highlighting both the lights and the shadows of the diagnostic criteria. For this purpose, we summarize current knowledge about the clinical presentation, diagnostic pathways, differential diagnosis, and the expected long-term outcome of TGA.

The Amnestic Syndrome of Posterior Cerebral Artery Infarction

OBJECTIVE

Little is known about the character and underlying lesions of ischemic amnesia. We therefore studied episodic memory functions and brain lesions in 84 patients with acute ischemic infarcts in the supply territory of the posterior cerebral artery (PCA). We also aimed to learn how the neural memory systems are organized.

METHODS

Standard neuropsychological tests were used to assess verbal and figural memory. Patients were split in memory-impaired and memory-intact. Lesions were demarcated, normalized and anatomically labeled, using standard mapping procedures.

RESULTS

Of the 84 patients more than 80% had an amnestic syndrome, mostly with combined, less often with figural or verbal memory impairment. Amnesia in subjects with left hemispheric lesions was more frequent and more severe, with significantly lower scores on the verbal memory test. Normal performance or figural amnesia were prevalent after right hemispheric lesions. However, no amnesia subtype was strictly tied to left- or right-sided brain damage. Hippocampal and thalamic lesions were common, but 30% of lesions were extrahippocampal located in the ventral occipito-temporal cortex and long occipital white matter tracts. Most amnestic-patients lacked awareness for their memory impairment.

CONCLUSIONS

Memory impairment is a key clinical manifestation of acute PCA stroke. Amnesia is more frequent and more severe after left stroke, suggesting a left hemisphere dominance of the two memory systems. Domain specific memory appears not strictly lateralized, since deficits in verbal and figural memory were found after lesions of both sides. Extrahippocampal lesions may also cause memory impairment.

Acute-onset amnesia: transient global amnesia and other causes

Acute-onset amnesia is a dramatic neurological presentation that can cause considerable concern to both patient and clinician. The patient typically presents with an inability not only to retain new memories but also to access previously acquired memories, suggesting disturbance of hippocampal function. Transient global amnesia (TGA) is the most common cause of acute-onset amnesia, and is characterised by a profound anterograde and retrograde amnesia that typically lasts for up to 24 hours. Although TGA has a strikingly stereotypical presentation, it can be challenging to distinguish from other causes of acute-onset amnesia, including posterior circulation strokes, transient epileptic amnesia, psychogenic amnesia, post-traumatic amnesia, and toxic/drug-related amnesia. Here, we describe the general approach to the patient with acute amnesia; summarise the clinical and neuropsychological differences between the potential causes; and, provide practical recommendations to aid diagnosis and management of acute amnesia. Regardless of cause and the dramatic presentation, non-ischaemic acute-onset amnesia generally has a favourable prognosis.

Sensitivity of diffusion-weighted magnetic resonance imaging in transient global amnesia as a function of time from symptom onset

BACKGROUND

The objective was to systematically evaluate the sensitivity of diffusion-weighted magnetic resonance imaging (DW-MRI) for transient global amnesia (TGA) across various time frames compared to the reference-standard clinical criteria.

METHODS

All indexed publications related to TGA and MRI through June 2020 were retrieved by a medical librarian. Two independent reviewers identified original research studies of adults with a clinical diagnosis of TGA using Caplan and Hodges and Warlow criteria (reference standard) who were evaluated with DW-MRI. Pooled estimates and its 95% confidence intervals (CI) for the proportion of acute TGA patients with positive DW-MRI (i.e., sensitivity) were obtained using random-effects meta-analysis for various time frames. Quality assessment was performed using the revised Quality of Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool.

RESULTS

After screening 665 reports, we identified 81 potentially relevant studies. Twenty-three studies representing 1688 patients met eligibility criteria, but not all studies had data available for meta-analysis. The pooled sensitivity (also described as positivity rate) of DW-MRI was 15.6% (95% CI = 2.6%-35.0%) between 0 and 12 h from symptom onset, 23.1% (95% CI = 6.1%-45.7%) at 0-24 h, 72.8% (95% CI = 40.8%-96.3) at 12-24 h, 68.8% (95% CI = 44.8%-88.8%) at 24-36 h, 72.4% (95% CI = 59.8%-83.5%) at 36-48 h, 82.8% (95% CI = 54.7%-99.6%) at 48-60 h, 66.9% (95% CI = 47.5%-83.9%) at 60-72 h, and 72.0% (95% CI = 30.1%-100.0%) at 72-96 h. There was significant concern for risk of bias in the QUADAS-2 domains of patient selection and index test, yielding a low level of certainty in the pooled estimates.

CONCLUSION

DW-MRI lesions are uncommon in patients with TGA early after symptom onset, but the sensitivity (i.e., positivity rate) of DW-MRI increases with time. Despite the limited quality of existing evidence, obtaining an early DW-MRI in patients with clinical diagnosis of TGA in the acute setting is likely a low-yield test.

Altered consciousness with transient abnormal signals in the hippocampus: A case report

Hippocampal infarction is relatively rare. Many different diseases can mimic hippocampal infarction including transient global amnesia, Alzheimer’s disease, epilepsy, encephalitis, and encephalopathies. An 89-year-old man was transported to our hospital for altered consciousness. Diffusion-weighted magnetic resonance imaging revealed slightly intense signals in the hippocampus with a mildly decreased apparent diffusion coefficient. Serial magnetic resonance imaging revealed features of hippocampal infarction. Symptoms and cognitive function gradually improved with rehabilitation, and he was transferred to a rehabilitation facility on Hospital Day 38. Hippocampal infarction is rare in patients with altered mental status, but should be considered when magnetic resonance imaging shows findings suggestive of this condition. Other differential diseases should be ruled out by serial magnetic resonance imaging and observation of the clinical course.

Lesion topography of posterior cerebral artery infarcts

This study analyzed the topography of acute ischemic stroke in the posterior cerebral artery (PCA) territory. We studied 84 patients with unilateral ischemic PCA stroke. Patients were classified according to lesion levels as cortico-subcortical (superficial), combined (cortical and mesodiencephalic) or isolated thalamic. To receive a lesion map, data from acute MR and CT imaging were normalized and labelled automatically by mapping to stereotaxic anatomical atlases. Cortical lesions accounted for 41.7%, combined for 36.9%, and isolated thalamic lesions for 21.4%. The maximum overlay of ischemia and, thus, highest occurrence of PCA ischemic stroke was found in the ventral and medial occipito-temporal cortex and adjacent white matter association tracts. Dorsal and peripheral segments of the occipito-temporo-parietal region were only rarely lesioned. This configuration was similar in both hemispheres. Consistent with this lesion pattern, visual field defects (VFD) were the most frequent signs, followed by sensorimotor signs, dizziness and sopor, cognitive and oculomotor deficits, and ataxia. The three vascular subgroups differed not only by their anatomical lesion profile and lesion load, but also by their clinical manifestation; although patients with combined and thalamic lesions were sigificantly younger, they were more disabled than participants with cortical lesions. VFD were only found in cortical and combined, and oculomotor deficits only in mesodiencephalic lesions. White matter lesions were common in the cortico-subcortical and the combined group. Basal occipito-temporal and calcarine regions, and neighbouring white matter tracts have the highest risk of ischemia in acute PCA stroke.

Positive psychotic symptoms are associated with divergent developmental trajectories of hippocampal volume during late adolescence in patients with 22q11DS

Low hippocampal volume is a consistent finding in schizophrenia and across the psychosis spectrum. However, there is a lack of studies investigating longitudinal hippocampal development and its relationship with psychotic symptoms. The 22q11.2 deletion syndrome (22q11DS) has proven to be a remarkable model for the prospective study of individuals at high risk of schizophrenia to unravel the pathophysiological processes predating the onset of psychosis. Repeated cerebral MRIs were acquired from 140 patients with 22q11DS (53 experiencing moderate-to-severe psychotic symptoms) and 135 healthy controls aged from 6 to 35 years and with up to 5 time points per participant. Hippocampal subfield analysis was conducted using FreeSurfer-v.6 and FIRST-FSL. Then, whole hippocampal and subfield volumes were compared across the groups. Relative to controls, patients with 22q11DS showed a remarkably lower volume of all subfields except for CA2/3. No divergent trajectories in hippocampal development were found. When comparing patients with 22q11DS exhibiting psychotic symptoms to those without psychosis, we detected a volume decrease during late adolescence, starting in CA1 and spreading to other subfields. Our findings suggested that hippocampal volume is consistently smaller in patients with 22q11DS. Moreover, we have demonstrated that patients with 22q11DS and psychotic symptoms undergo a further decrease in volume during adolescence, a vulnerable period for the emergence of psychosis. Interestingly, CA2/3, despite being affected in patients with psychotic symptoms, was the only area not reduced in patients with 22q11DS relative to controls, thus suggesting that its atrophy exclusively correlates with the presence of positive psychotic symptoms.

Insulin-Like Growth Factor 2 (IGF-2) Regulates Neuronal Density and IGF-2 Distribution Following Hippocampal Intracerebral Hemorrhage

BACKGROUND

The insulin-like growth factor 2 (IGF-2) is a growth factor and anti-inflammatory cytokine that plays a crucial role in memory consolidation. However, the precise role of this factor in acute brain damage is still unclear. The present study aimed to evaluate the variations in hippocampal IGF-2 distribution on different days and investigate the effect of recombinant IGF-2 on memory cell density, and IGF-2 distribution following acute hippocampal damage resulting from intracerebral hemorrhage (ICH).

METHODS

ICH was induced by injection of 100 μL of autologous blood into the left hippocampus of 72 male Sprague-Dawley rats. Recombinant IGF-2 was injected into the damaged hippocampus 30 min post-induction of ICH in the ICH-IGF-2 group. Then, on postoperative days 1, 3, 7, and 14, samples of brain tissue were collected to perform histopathological and immunohistochemical examinations.

RESULTS

The stereological study indicated that the volume of the hippocampus and the number of neurons had a significant reduction, and the infarct volume had a significant increase following ICH. Following the injection of IGF-2, a significant improvement was observed in stereological studies. Immunohistochemical data showed that IGF-2 distribution increased in the hippocampus on different days after ICH, and IGF-2 injection led to a dramatic reduction in this distribution.

CONCLUSIONS

In summary, the gradual increase of endogenous IGF-2 as growth and anti-inflammatory factor following hemorrhagic stroke reveals a critical role of this factor in brain recovery after injury. Moreover, the injection of IGF-2 can prevent cell death and alleviate the damage caused by the hemorrhagic stroke.

Which Neural Tract Plays a Major Role in Memory Impairment After Multiple Cerebral Infarcts? A Case Report

Injury to the thalamocortical tract (one in the Papez circuit) that leads to memory impairment following brain injury is very rare. In this study, we present a case of partial injury to the thalamocortical tract that causes memory impairment after concurrent thalamic and hippocampal infarct. A 20-year-old male complained of memory impairment 1 month after partial injury to the thalamocortical tract. Using a probabilistic diffusing tensor tractography, it was found that the right thalamocortical tract was thinner than the left thalamocortical tract. However, all other neural tracts including the fornix, cingulum, and mammillothalamic tract were intact on both hemispheres. Therefore, the memory impairment in this patient was considered as being due to thalamic infarct based on the observation that the fornix from hippocampal infarct was intact. This case suggests that the assessment of lesions in the neural tracts of the Papez circuit might be useful for understanding the mechanism of memory impairment following cerebral infarction.

Transient global amnesia: current perspectives

Transient global amnesia (TGA) is a clinical syndrome characterized by the sudden onset of an extraordinarily large reduction of anterograde and a somewhat milder reduction of retrograde episodic long-term memory. Additionally, executive functions are described as diminished. Although it is suggested that various factors, such as migraine, focal ischemia, venous flow abnormalities, and epileptic phenomena, are involved in the pathophysiology and differential diagnosis of TGA, the factors triggering the emergence of these lesions are still elusive. Recent data suggest that the vulnerability of CA1 neurons to metabolic stress plays a pivotal part in the pathophysiological cascade, leading to an impairment of hippocampal function during TGA. In this review, we discuss clinical aspects, new imaging findings, and recent clinical-epidemiological data with regard to the phenotype, functional anatomy, and putative cellular mechanisms of TGA.

Posterior hippocampal stroke presenting with transient global amnesia

The acute onset of isolated amnesia is an intriguing challenge for neurologist, because the lack of associated signs can be misleading for diagnosis. The most common cause is transient global amnesia (TGA), a benign condition, but rarely it results from abuse of substance/alcohol or cerebrovascular diseases. In the latter, the brain region involved is the hippocampus. We describe a patient with presenting symptoms of TGA, but affected by an ischemic hippocampal stroke. The computed tomography angiography helped the etiologic diagnosis showing an hemodynamic stenosis of the posterior P2P segment. Interestingly, neuropsychological features were consistent with those found in patients suffering TGA.

Isolated punctuate hippocampal infarction and transient global amnesia are indistinguishable by means of MRI

Background Small punctuate lesions in the hippocampus on diffusion-weighted images are a typical finding in transient global amnesia. Consequently, it has been suggested that diffusion-weighted images findings might corroborate the diagnosis of transient global amnesia. However, isolated punctuate hippocampal infarction might be a differential diagnosis of transient global amnesia. Aim Evaluation of isolated punctuate hippocampal infarction frequency and comparison of its clinical presentation and MRI findings to transient global amnesia. Methods From an MRI database, we identified 10 patients with isolated punctuate hippocampal infarction and compared these to 12 patients with transient global amnesia with diffusion-weighted images lesion with regard to clinical symptoms and MRI findings. Results Disorientation and memory deficits were more common in transient global amnesia patients, whereas dysphasia/aphasia and vertigo were more common in hippocampal infarction patients. MRI findings in isolated punctuate hippocampal infarction and transient global amnesia did not differ significantly, neither regarding the affected hemisphere, lesion distribution, size, nor relative ADC values. Conclusions Differentiation of isolated punctuate hippocampal infarction and transient global amnesia based on neuroimaging findings is not possible. Thus, in the case of isolated punctuate hippocampal diffusion-weighted images lesions the final diagnosis of hippocampal infarction or transient global amnesia should be based on the clinical presentation.

Complete, bilateral hippocampal ischemia: a case series

Acute and complete ischemia of the hippocampi represents a rare cause of amnesia. This paper describes the features of four such cases presenting to a single tertiary care center over a 3-year period. Interestingly, in three instances, toxicology screening was positive for opioids at the time of presentation, while in the fourth, there was a known, reportedly remote, history of heroin use. Taken together with the known literature on the topic, complete hippocampal ischemia appears at least highly suggestive of a toxic exposure. Further case finding is necessary to better understand the etiology, nature, and prevalence of this unusual clinico-radiologic entity.

Vascular cognitive impairment and dementia

Vascular contributions to cognitive impairment are receiving heightened attention as potentially modifiable factors for dementias of later life. These factors have now been linked not only to vascular cognitive disorders but also Alzheimer's disease. In this chapter we review 3 related topics that address vascular contributions to cognitive impairment: 1. vascular pathogenesis and mechanisms; 2. neuropsychological and neuroimaging phenotypic manifestations of cerebrovascular disease; and 3. prospects for prevention of cognitive impairment of later life based on cardiovascular and stroke risk modification. This article is part of a Special Issue entitled: Vascular Contributions to Cognitive Impairment and Dementia edited by M. Paul Murphy, Roderick A. Corriveau and Donna M. Wilcock.