Amnesia due to the Injury of Papez Circuit Following Isolated Fornix Column Infarction

Acute amnestic syndrome in fornix lesions: a systematic review of reported cases with a focus on differential diagnosis

Introduction

Acute amnestic syndrome is an uncommon clinical presentation of neurological disease. Differential diagnosis encompasses several syndromes including Wernicke-Korsakoff and transient global amnesia (TGA). Structural lesions of the fornix account for a minority of cases of acute amnestic syndromes. Etiology varies from iatrogenic injury to ischemic, inflammatory, or neoplastic lesions. A prompt diagnosis of the underlying pathology is essential but challenging. The aim of this review is to systematically review the existing literature regarding cases of acute amnestic syndrome associated with non-iatrogenic lesions of the fornix.

Methods

We performed a systematic literature search on PubMed, Scopus, and Web of Science up to September 2023 to identify case reports and case series of patients with amnestic syndrome due to fornix lesions. The systematic review was conducted according to PRISMA guidelines. The research was limited to articles written in English. Cases of fornix damage directly ascribable to a surgical procedure were excluded.

Results

A total of 52 publications reporting 55 cases were included in the review. Focusing on acute/subacute onset, vascular etiology was highly prevalent, being responsible for 78% of cases, 40/55 (74%) of which were due to acute ischemic stroke. The amnestic syndrome was characterized by anterograde amnesia in all patients, associated with retrograde amnesia in 27% of cases. Amnesia was an isolated presentation in most cases. Up to two thirds of patients had persistent memory deficits of any severity at follow-up.

Discussion

Acute amnestic syndrome can be rarely caused by fornix lesions. In most cases of acute/subacute presentation, the etiology is ischemic stroke, mainly caused by strokes involving the subcallosal artery territory. The differential diagnosis is challenging and a distinction from common mimics is often difficult on a clinical basis. A high index of suspicion should be maintained to avoid misdiagnosis and provide adequate acute treatment to patients with time-dependent disease, also employing advanced neuroimaging. More research is needed to better understand the outcome and identify prognostic factors in patients with amnestic syndrome due to fornix lesions.

Increased fiber density of the fornix in patients with chronic tinnitus revealed by diffusion-weighted MRI

Up to 45% of the elderly population suffer from chronic tinnitus - the phantom perception of sound that is often perceived as ringing, whistling, or hissing "in the ear" without external stimulation. Previous research investigated white matter changes in tinnitus patients using diffusion-weighted magnetic resonance imaging (DWI) to assess measures such as fractional anisotropy (a measure of microstructural integrity of fiber tracts) or mean diffusivity (a measure for general water diffusion). However, findings overlap only minimally and are sometimes even contradictory. We here present the first study encompassing higher diffusion data that allow to focus on changes in tissue microstructure, such as number of axons (fiber density) and macroscopic alterations, including axon diameter, and a combination of both. In order to deal with the crossing-fibers problem, we applied a fixel-based analysis using a constrained spherical deconvolution signal modeling approach. We investigated differences between tinnitus patients and control participants as well as how cognitive abilities and tinnitus distress are related to changes in white matter morphology in chronic tinnitus. For that aim, 20 tinnitus patients and 20 control participants, matched in age, sex and whether they had hearing loss or not, underwent DWI, audiometric and cognitive assessments, and filled in questionnaires targeting anxiety and depression. Our results showed increased fiber density in the fornix in tinnitus patients compared to control participants. The observed changes might, reflect compensatory structural alterations related to the processing of negative emotions or maladaptive changes related to the reinforced learning of the chronic tinnitus sensation. Due to the low sample size, the study should be seen as a pilot study that motivates further research to investigate underlying white matter morphology alterations in tinnitus.

A Case Report of Transient Amnesia Following Spontaneous Intracerebral Hemorrhage of the Fornix

In this report, we share the case of a 65-year-old male with a remote history of brain concussion who presented to the emergency department for evaluation of transient amnesia that lasted 30 minutes to one hour. He was found to have spontaneous intracerebral hemorrhage of the fornix as a cause of his amnesic episode. To date from the creation of this case report (January 2023), spontaneous hemorrhage of the fornix resulting in transient amnesia has not been previously described in the literature. The fornix is an unusual location for spontaneous hemorrhage to occur. The differential diagnosis of transient amnesia is broad and includes, but is not limited to, transient global amnesia, traumatic injury, hippocampal infraction, and various metabolic derangements. Determination of the etiology of transient amnesia can result in changes in treatment decisions. Because of this unique patient presentation, we propose that spontaneous hemorrhage of the fornix should be considered in patients who present with transient amnesia.

Like a rolling stone: Psychotherapy without (episodic) memory

People with profound amnesia still retain the capacity to learn about the emotional value of experiences, which is crucial in developing and sustaining interpersonal relationships. In a 2017 paper, we demonstrated for the first time (with patient JL) that transferential feelings develop across the therapeutic process, despite profound episodic memory impairment after medial temporal lesions. This paper reports a second case (GA) of a profoundly amnesic patient in psychotherapy, this time after lesions to the anterior fornix. The work with GA opens issues such as the differences and similarities to the previous case, counter-transference phenomena, and the effects of hyperphagia. The findings make it clear that many phenomena are common to both GA and JL, such as forgetfulness, various types of repetition, the importance of the therapeutic alliance, and the ability to make therapeutic gain. However, there were differences between the cases, for example as regards confabulation, which may relate to either pre-morbid personality or lesion site. The paper also discusses the way in which patients of this type bear the very status of psychotherapeutic work with profoundly amnesic patients. Where others have seen barriers and in principle problems in working with such patients, we see many opportunities.

Structural and functional alterations within the Papez circuit in subacute stroke patients

Beyond causing local injury, stroke disrupts structural and functional organization of the brain networks, exposing patients to a high risk of cognitive impairment by affecting the neural network activity. However, the impact of these pathological changes on cognition-related neural circuits is not well understood. In this study, we mainly focused on structures and directed functional connectivity within the Papez circuit in subacute stroke patients. Forty-five stroke patients and thirty-four age-, sex-matched healthy controls were included in our study. The Papez circuit gray matter were measured to explore ischemia-induced structural alterations. And Granger causality analysis with the hippocampus as seed regions was performed to identify alterations of directional functional connectivity within the neural circuit. We also explored the associations between cerebral changes with cognitive status. Compared with healthy controls, stroke patients revealed marked atrophy in gray matter of the Papez circuit, including ipsilateral hippocampus, amygdala, thalamus, and caudal anterior cingulate gyrus. Additionally, there are alterations in the directed functional connections between the bilateral hippocampus and cingulate gyrus within the Papez circuit. These altered effective connectivities were correlated with cognitive function after cerebrovascular event. Taken together, in the early post-stroke period, disruptions of the Papez circuit in both architecture and directed functional connectivity have already occurred and might affect the cognitive function. These findings have prompted researchers to better understand the potential mechanisms underlying vascular cognitive impairment and to investigate new therapeutic targets that could reduce cognitive burden.

Time to retire the serial Papez circuit: Implications for space, memory, and attention

After more than 80 years, Papez serial circuit remains a hugely influential concept, initially for emotion, but in more recent decades, for memory. Here, we show how this circuit is anatomically and mechanistically naïve as well as outdated. We argue that a new conceptualisation is necessitated by recent anatomical and functional findings that emphasize the more equal, working partnerships between the anterior thalamic nuclei and the hippocampal formation, along with their neocortical interactions in supporting, episodic memory. Furthermore, despite the importance of the anterior thalamic for mnemonic processing, there is growing evidence that these nuclei support multiple aspects of cognition, only some of which are directly associated with hippocampal function. By viewing the anterior thalamic nuclei as a multifunctional hub, a clearer picture emerges of extra-hippocampal regions supporting memory. The reformulation presented here underlines the need to retire Papez serially processing circuit.

The temporal lobes and memory

Since the first description of the case of H.M. in the mid-1950s, the debate over the contribution of the mesial temporal lobe (MTL) to human memory functioning has not ceased to stimulate new experimental work and the development of new theoretical models. The early demonstration that despite their devastating memory loss patients with hippocampal damage are still able to learn a number of visuo-motor and visuo-perceptual skills at a normal rate and to be normally primed by verbal and visual material suggested that the term "memory" is actually an umbrella concept that includes very different brain plasticity phenomena and that MTL damage actually impairs only one of these. Subsequent research, which capitalized on a detailed anatomical description of MTL structures and on the close analysis of memory-related phenomena, tried to define the unique role of the MTL structures in brain plasticity and in the government of human behavior. A first hypothesis identified this role in the conscious forms of memory as opposed to implicit ones. In the last two decades, the emphasis has moved to the relational role of the hippocampus in binding together different pieces of unimodal information to provide unitary, multimodal representations of personal experiences.

Acute Amnestic Syndrome and Ischemic Stroke: A Case Series

Purpose of Review

Stroke is an uncommon cause of amnesia. We describe in detail 3 cases of anterograde amnesia and confabulation secondary to acute ischemic stroke and review the available literature.

Recent Findings

In our case series, all 3 patients presented with anterograde amnesia and 2 of 3 copresented with prominent confabulation. These symptoms were recognized in delayed fashion, and no patients received IV tissue plasminogen activator (tPA). Although stroke infarct topology was variable, all 3 patients had infarction of the fornix. Long-term follow-up was obtained in 2 of 3 patients: both had persistent memory impairment and were no longer functionally independent.

Summary

Acute onset anterograde amnesia and confabulation may uncommonly represent acute ischemic stroke. Delays in this diagnosis typically exclude patients from emergent stroke treatment or timely diagnostic stroke evaluation. Clinicians should maintain a high degree of suspicion for ischemic stroke in this setting, especially in patients with comorbid vascular risk factors. Memory impairment secondary to ischemic stroke can produce considerable long-term disability.

Fornix Integrity Is Differently Associated With Cognition in Healthy Aging and Non-amnestic Mild Cognitive Impairment: A Pilot Diffusion Tensor Imaging Study in Thai Older Adults

Damage to the fornix leads to significant memory impairment and executive dysfunction and is associated with dementia risk. We sought to identify if fornix integrity and fiber length are disrupted in mild cognitive impairment (MCI) and how they associate with cognition. Data from 14 healthy older adult controls (HCs) and 17 subjects with non-amnestic MCI (n-aMCI) were analyzed. Diffusion tensor imaging (DTI) at 1.5 Tesla MRI was performed to enable manual tracing of the fornix and calculation of DTI parameters. Higher fractional anisotropy of body and column of the fornix was associated with better executive functioning and memory, more strongly in the HC than in the n-aMCI group. Fornix fiber tract length (FTL) was associated with better executive function, more strongly in the n-aMCI than in the HC group, and with better memory, more strongly in the HC than in the n-aMCI group. These results highlight a decline in the contributions of the fornix to cognition in n-aMCI and suggest that maintenance of fornix FTL is essential for sustaining executive functioning in people with n-aMCI.

Diffusion tensor imaging findings in children with sluggish cognitive tempo comorbid Attention Deficit Hyperactivity Disorder

Objective: The construct of Sluggish Cognitive Tempo (SCT) is characterized by daydreaming, mental confusion, staring blankly and hypoactivity. Our main goal was to explore neuropsychological differences in Attention Deficit Hyperactivity Disorder-Inattentive presentation (ADHD-IA) groups with and without SCT symptoms compared to healthy controls. After detecting specific neuropsychological differences, we examined white matter microstructure using Diffusion Tensor Imaging (DTI) data obtained from 3.0 Tesla MRI scans of the cases with SCT symptoms comparing to Typically Developing (TD) controls.Method: In this study, we included 24 cases in the ADHD-IA group with SCT symptoms, 57 cases in the ADHD-IA group without SCT symptoms and, 24 children in the TD group. We applied tract-based spatial statistics to the DTI measures for obtaining fractional anisotropy (FA), axial, radial and mean diffusivity (AD, RD, MD) to explore white matter differences for the whole brain.Results: Omission error scores and longer reaction time scores were specifically associated with inattention symptoms. Commission error scores were significantly and specifically related to SCT symptoms. Cases with SCT symptoms presented increased FA in the bilateral anterior and posterior limb of the internal capsule, bilateral cerebral peduncle, and the fornix than TD group.Conclusions: Neurobiological differences in ADHD cases are still relatively unexplored. We suggest that including an assessment for SCT in the neuropsychological and neuroimaging studies of ADHD may provide more consistent results.

Ischemic stroke in the combined territories of the septum pellucidum and the cingulate gyrus: A case report and literature review

INTRODUCTION

Cases of isolated septum pellucidum infarction have not yet been reported. To date, there are only 2 stroke reports involving septum pellucidum infarction. The etiology of septum pellucidum infarction was subcallosal artery (ScA) injury. The abnormalities were strictly confined to the septum pellucidum and the right cingulated gyrus, making this the first case to report such confined abnormalities.

PATIENT CONCERNS

In this report, we present a case of ischemic stroke confined to the septum pellucidum and cingulated gyrus in a 48-year-old male patient who presented with transient ischemic attack-like paroxysmal lower left limb weakness.

DIAGNOSIS

Even no obvious abnormalities were revealed by an emergency computed tomography, the infarction in the combined territories of the septum pellucidum and the cingulate gyrus was detected on magnetic resonance imaging.

INTERVENTIONS

Aspirin with clopidogrel was administered for 3 weeks as a secondary preventive drug. Clopidogrel was selected as a long-term antiplatelet drug based on a thromboelastogram.

OUTCOMES

The patient showed no positive signs related to the nervous system in the hospital, and there was no recurrence during the 3-month follow-up.

CONCLUSIONS

Infarction in the septum pellucidum and cingulate gyrus is rare and has atypical clinical manifestations. Physical examination may not yield obvious positive signs. False-negative computed tomography findings of the head may result in misdiagnosis. Thus, it is necessary to perform whole-brain magnetic resonance imaging in time. Moreover, ScA protection should be paid attention to during surgery for anterior communicating artery aneurysm.