Microanatomic and vascular aspects of the temporomesial region

Anatomo-functional changes in neural substrates of cognitive memory in developmental amnesia: Insights from automated and manual MRI examinations

Despite bilateral hippocampal damage dating to perinatal or early-childhood period, and severely-impaired episodic memory that unfolds in later childhood, patients with developmental amnesia continue to exhibit well-developed semantic memory across the developmental trajectory. Detailed information on the extent and focality of brain damage in these patients is needed to hypothesize about the neural substrate that supports their remarkable capacity for encoding and retrieval of semantic memory. In particular, we need to assess whether the residual hippocampal tissue is involved in this preservation, or whether the surrounding cortical areas reorganise to rescue aspects of these critical cognitive memory processes after early injury. We used voxel-based morphometry (VBM) analysis, automatic (FreeSurfer) and manual segmentation to characterize structural changes in the brain of an exceptionally large cohort of 23 patients with developmental amnesia in comparison with 32 control subjects. Both the VBM and the FreeSurfer analyses revealed severe structural alterations in the hippocampus and thalamus of patients with developmental amnesia. Milder damage was found in the amygdala, caudate and parahippocampal gyrus. Manual segmentation demonstrated differences in the degree of atrophy of the hippocampal subregions in patients. The level of atrophy in CA-DG subregions and subicular complex was more than 40% while the atrophy of the uncus was moderate (-23%). Anatomo-functional correlations were observed between the volumes of residual hippocampal subregions in patients and selective aspects of their cognitive performance viz, intelligence, working memory, and verbal and visuospatial recall. Our findings suggest that in patients with developmental amnesia, cognitive processing is compromised as a function of the extent of atrophy in hippocampal subregions, such that the greater the damage, the more likely it is that surrounding cortical areas will be recruited to rescue the putative functions of the damaged subregions. Our findings document for the first time not only the extent, but also the limits of circuit reorganization occurring in the young brain after early bilateral hippocampal damage.

Anatomical Organization of the Amygdala: A Brief Visual Review

The amygdala consists of a collection of nuclei that are deep within the medial temporal lobe. Despite its small size, the amygdala is one of the most densely connected structures in the brain, and it plays a role in many superior neural functions, including neurovegetative control, motor control, memory processing, and neuromodulation. Advances in neuroimaging technology for examining brain activity have opened up new ways of understanding the functional contribution of this structure to emotions, learning, and related memories. Many studies have shown that the amygdala plays a key role in the pathophysiology of neuropsychiatric disorders, such as anxiety disorders, depression, aggression, and temporal epilepsy. This article reviews the anatomical structure of the amygdaloid complex and the connectivity among its subdivisions and with other brain structures, which will serve as a basis for understanding the clinical correlations.

Clipping of Unruptured Anterior Choroidal Artery Aneurysms Together with Small Branches: Safety Confirmation Using Intraoperative Indocyanine Green Video-Angiography and Intraoperative Neurophysiological Monitoring

BACKGROUND

In treating anterior choroidal artery (AChA) aneurysms, preserving the AChA main trunk is of course necessary to prevent postoperative ischemic complications. However, in practice, complete occlusions are often limited by small branches.

OBJECTIVE

We aimed to demonstrate that even in cases where complete occlusion of the AChA aneurysm is complex due to small branches, complete occlusion can be safely achieved using indocyanine green video-angiography and intraoperative neurophysiological monitoring (IONM).

METHODS

We performed a retrospective review of all unruptured AChA aneurysms surgically treated at our institution from 2012 to 2021. All available surgical videos were reviewed to find AChA aneurysms clipped with small branches; clinical and radiological data were collected for these cases.

RESULTS

Among 391 cases of unruptured AChA aneurysms treated surgically, 25 AChA aneurysms were clipped with small branches. AChA-related ischemic complications occurred in 2 cases (8%) without retrograde indocyanine green filling to the branches. These 2 cases had changes in IONM. There were no ischemic complications in the remaining cases with retrograde indocyanine green filling to the branches and no change in IONM. During an average follow-up of 47 months (12-111 months), a small residual neck was observed in 3 cases (12%) and recurrence or progression of the aneurysm was observed in only 1 case (4%).

CONCLUSIONS

The surgical treatment of AChA aneurysms carries the risk of devastating ischemic complications. Even in cases where complete clip ligation seems impossible due to small branches associated with AChA aneurysms, complete occlusion can be safely achieved using indocyanine green video-angiography and IONM.

Structural and functional alterations in cerebral small vessel disease: an ALE-based meta-analysis

 

Cerebral small vessel disease (CSVD) is one of the most important causes of stroke and dementia. Although increasing studies have reported alterations of brain structural or neuronal functional activity exhibited in patients with CSVD, it is still unclear which alterations are reliable. Here, we performed a meta-analysis to establish which brain structural or neuronal functional activity changes in those studies were consistent. Activation likelihood estimation revealed that changes in neuronal functional activity in the left angular gyrus, bilateral anterior cingulate cortex/left medial prefrontal cortex, right rolandic operculum, and alterations of gray structure in the left insular cortex/superior temporal gyrus/claustrum were reliable in sporadic CSVD. Decreased neuronal functional activity in the caudate head, anterior cingulate cortex, and reduced gray matter volume in the insular cortex/superior temporal gyrus/claustrum were associated with CSVD-related cognitive impairment. Furthermore, unlike sporadic CSVD, the reliable alterations of neuronal functional activity in cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy were concentrated in the left parahippocampal gyrus. The current study presents stable brain structural and neuronal functional abnormalities within the brain, which can help further understand the pathogenesis of CSVD and CSVD-cognitive impairment and provide an index to evaluate the effectiveness of treatment protocols.

Highlights

• Default mode network and salience network are reliable networks affected in sporadic CSVD in resting-state.

• Altered corticostriatal circuitry is associated with cognitive decline.

• Decreased gray matter volume in the insular cortex is stable “remote effects” of sporadic CSVD.

• The parahippocampal gyrus may be a reliable affected brain region in CADASIL.

Vascularization of the uncus - Anatomical study and clinical implications

Background:

The objective of this paper was to describe the arterial supply of the uncus and quantify the branches directed to the anteromedial aspect of the human temporal cortex.

Methods:

We studied 150 human cerebral hemispheres identifying main afferent arteries supplying the anteromedial temporal cortex with particular attention to the uncus, determining the territory supplied by each artery through either cortical or perforating branches.

Results:

The uncus was supplied by 419 branches of the anterior choroidal artery (AChA), 210 branches of the internal carotid artery (ICA), 353 branches of the middle cerebral artery (MCA), and 122 branches of the posterior cerebral artery (PCA). The total of supplying vessels was 1104 among the 150 hemispheres studied, which corresponds to 7.36 arteries per uncus. The average of branches per hemisphere was as follows: 2.79 from AChA, 1.40 from ICA, 2.35 from MCA, and 0.81 from PCA. The relative contribution of each artery for the total of specimens studied was as follows: 38% from AChA, 19% from ICA, 32% from the MCA, and 11% from the PCA. We identified cortical anastomoses mostly between the MCA and PCA (27 cases).

Conclusion:

We described and quantified the uncus’ vascularization, including anatomical variations. This updated, detailed description of the mesial temporal vascularization is paramount to improve the treatment of neurosurgical conditions.

Hippocampal vascularization patterns exert local and distant effects on brain structure but not vascular pathology in old age

The hippocampus within the medial temporal lobe is highly vulnerable to age-related pathology such as vascular disease. We examined hippocampal vascularization patterns by harnessing the ultra-high resolution of 7 Tesla magnetic resonance angiography. Dual-supply hemispheres with a contribution of the anterior choroidal artery to hippocampal blood supply were distinguished from single-supply ones with a sole dependence on the posterior cerebral artery. A recent study indicated that a dual vascular supply is related to preserved cognition and structural hippocampal integrity in old age and vascular disease. Here, we examined the regional specificity of these structural benefits at the level of medial temporal lobe sub-regions and hemispheres. In a cross-sectional study with an older cohort of 17 patients with cerebral small vessel disease (70.7  ±  9.0 years, 35.5% female) and 27 controls (71.1  ±  8.2 years, 44.4% female), we demonstrate that differences in grey matter volumes related to the hippocampal vascularization pattern were specifically observed in the anterior hippocampus and entorhinal cortex. These regions were especially bigger in dual-supply hemispheres, but also seemed to benefit from a contralateral dual supply. We further show that total grey matter volumes were greater in people with at least one dual-supply hemisphere, indicating that the hippocampal vascularization pattern has more far-reaching structural implications beyond the medial temporal lobe. A mediation analysis identified total grey matter as a mediator of differences in global cognition. However, our analyses on multiple neuroimaging markers for cerebral small vessel disease did not reveal any evidence that an augmented hippocampal vascularization conveys resistance nor resilience against vascular pathology. We propose that an augmented hippocampal vascularization might contribute to maintaining structural integrity in the brain and preserving cognition despite age-related degeneration. As such, the binary hippocampal vascularization pattern could have major implications for brain structure and function in ageing and dementia independent of vascular pathology, while presenting a simple framework with potential applicability to the clinical setting.

Brain arteriolosclerosis

Brain arteriolosclerosis (B-ASC), characterized by pathologic arteriolar wall thickening, is a common finding at autopsy in aged persons and is associated with cognitive impairment. Hypertension and diabetes are widely recognized as risk factors for B-ASC. Recent research indicates other and more complex risk factors and pathogenetic mechanisms. Here, we describe aspects of the unique architecture of brain arterioles, histomorphologic features of B-ASC, relevant neuroimaging findings, epidemiology and association with aging, established genetic risk factors, and the co-occurrence of B-ASC with other neuropathologic conditions such as Alzheimer's disease and limbic-predominant age-related TDP-43 encephalopathy (LATE). There may also be complex physiologic interactions between metabolic syndrome (e.g., hypertension and inflammation) and brain arteriolar pathology. Although there is no universally applied diagnostic methodology, several classification schemes and neuroimaging techniques are used to diagnose and categorize cerebral small vessel disease pathologies that include B-ASC, microinfarcts, microbleeds, lacunar infarcts, and cerebral amyloid angiopathy (CAA). In clinical-pathologic studies that factored in comorbid diseases, B-ASC was independently associated with impairments of global cognition, episodic memory, working memory, and perceptual speed, and has been linked to autonomic dysfunction and motor symptoms including parkinsonism. We conclude by discussing critical knowledge gaps related to B-ASC and suggest that there are probably subcategories of B-ASC that differ in pathogenesis. Observed in over 80% of autopsied individuals beyond 80 years of age, B-ASC is a complex and under-studied contributor to neurologic disability.

Hippocampal vascularization patterns: A high-resolution 7 Tesla time-of-flight magnetic resonance angiography study

Considerable evidence suggests a close relationship between vascular and degenerative pathology in the human hippocampus. Due to the intrinsic fragility of its vascular network, the hippocampus appears less able to cope with hypoperfusion and anoxia than other cortical areas. Although hippocampal blood supply is generally provided by the collateral branches of the posterior cerebral artery (PCA) and the anterior choroidal artery (AChA), different vascularization patterns have been detected postmortem. To date, a methodology that enables the classification of individual hippocampal vascularization patterns in vivo has not been established. In this study, using high-resolution 7 Tesla time-of-flight angiography data (0.3 mm isotropic resolution) in young adults, we classified individual variability in hippocampal vascularization patterns involved in medial temporal lobe blood supply in vivo. A strong concordance between our classification and previous autopsy findings was found, along with interesting anatomical observations, such as the variable contribution of the AChA to hippocampal supply, the relationships between hippocampal and PCA patterns, and the different distribution patterns of the right and left hemispheres. The approach presented here for determining hippocampal vascularization patterns in vivo may provide new insights into not only the vulnerability of the hippocampus to vascular and neurodegenerative diseases but also hippocampal vascular plasticity after exercise training.

•

First attempt to classify human hippocampal vascularization in vivo using 7Tesla Angiography

•

Good concordance between in vivo findings and autopsy studies

•

A new avenue to investigate interindividual variability in hippocampal vascular plasticity

•

A new avenue for linking individual vascular anatomical phenotypes to neurodegenerative and vascular pathology

Anatomical Variations of the Temporomesial Structures in Normal Adult Brain - A Cadaveric Study

BACKGROUND

Despite significant evolutional, functional, and clinical interest, the anatomical variations of the temporomesial structures in cadaveric samples have received little attention. This study was undertaken to document the anatomical variations observed in the temporal lobe of human brain with emphasis on the structures present in temporomesial region.

MATERIALS AND METHODS

Using 26 postmortem cadaveric cerebral hemispheres (13 right and 13 left hemispheres), several neurosurgically significant mesial structures were studied by blunt dissection under the operating microscope. The observed surface-based qualitative variations and right-left asymmetries were tabulated under well-defined, moderately defined, and ill-defined classification.

RESULTS

Among the areas, uncus (100%), limen insulae (88.4%), rhinal sulcus and hippocampus (81%), intralimbic gyrus (77%), Heschl's gyrus (73%), gyrus ambiens, semilunar gyrus, sulcus semiannularis, and calcar avis (69.2%) were well defined, and band of Giacomini (38.4%) was found to be distinctly ill-defined areas in the list. Further, our analysis confirmed the presence of consistent left-greater-than-right asymmetry in all the areas of interest in temporal region under well-defined category. Rightward asymmetry was noticed in moderately defined and ill-defined classification. However, no asymmetry was detected in the uncal region. P value for all the obtained results was >0.05.

CONCLUSION

Our study offers a preliminary anatomic foundation toward the better understanding of temporal lobe structures. These variations may prove valuable to neurosurgeons when designing the appropriate and least traumatic surgical approaches in operating the temporomesial lesions.

Anterior Choroidal Artery Aneurysms: Influence of Regional Microsurgical Anatomy on Safety of Endovascular Treatment

Several anatomical variables critically influence therapeutic strategizing for anterior choroidal artery (AChA) aneurysms, and specifically, the safety of flow diversion for these lesions. We review the microsurgical anatomy of the AChA, discussing and detailing these considerations in the treatment of AChA aneurysms, theoretically and in the light of our recent findings.

The Amygdala as a Locus of Pathologic Misfolding in Neurodegenerative Diseases

Over the course of most common neurodegenerative diseases the amygdala accumulates pathologically misfolded proteins. Misfolding of 1 protein in aged brains often is accompanied by the misfolding of other proteins, suggesting synergistic mechanisms. The multiplicity of pathogenic processes in human amygdalae has potentially important implications for the pathogenesis of Alzheimer disease, Lewy body diseases, chronic traumatic encephalopathy, primary age-related tauopathy, and hippocampal sclerosis, and for the biomarkers used to diagnose those diseases. Converging data indicate that the amygdala may represent a preferential locus for a pivotal transition from a relatively benign clinical condition to a more aggressive disease wherein multiple protein species are misfolded. Thus, understanding of amygdalar pathobiology may yield insights relevant to diagnoses and therapies; it is, however, a complex and imperfectly defined brain region. Here, we review aspects of amygdalar anatomy, connectivity, vasculature, and pathologic involvement in neurodegenerative diseases with supporting data from the University of Kentucky Alzheimer's Disease Center autopsy cohort. Immunohistochemical staining of amygdalae for Aβ, Tau, α-synuclein, and TDP-43 highlight the often-coexisting pathologies. We suggest that the amygdala may represent an "incubator" for misfolded proteins and that it is possible that misfolded amygdalar protein species are yet to be discovered.

Microsurgical anatomy of the cisternal anterior choroidal artery with special emphasis on the preoptic and postoptic subdivisions

Object

The object of this study was to delineate the microsurgical anatomy of the cisternal segment of the anterior choroidal artery (AChA). The authors also propose a new classification of this segment on the basis of its complicated course within the carotid and crural cisterns in relation to important neurovascular structures, and the site of origin, course, and areas of supply of perforating arteries.

Methods

Thirty cadaveric cerebral hemispheres injected with colored latex were dissected under surgical magnification to view the cisternal segment of the AChA and its perforators. Fiber dissections using the Klingler technique were performed in two additional latex injected hemispheres to follow the penetration points, courses, and terminal areas of supply of perforating branches that arise from the cisternal segment of the AChA.

Results

The cisternal segment of the AChA was divided into pre- and postoptic parts that meet at the artery's genu, the most medial extension point of the cisternal segment where the artery makes an abrupt turn after passing under the optic tract. The preoptic part of the AChA extended from its origin at the inferomedial side of the internal carotid artery to the artery's genu, which is commonly located just inferomedial to the initial part of the optic tract. The postoptic part coursed within the crural cistern and extended from the genu to the inferior choroidal point. The genu of the AChA was 8 mm medial to the artery's origin and was located medial to the optic tract in 13% of the hemispheres. The postoptic part was longer than the preoptic part in all hemispheres and had more perforating arteries supplying critical deep structures (preoptic 3.4 per hemisphere vs postoptic 4.6 per hemisphere), and these results were statistically significant (p = 0.01). At the preoptic part, perforating arteries arose from the superolateral portion of the artery and coursed laterally; at the postoptic part, perforators arose from the inferomedial portion of the artery and coursed medially. Perforating arteries from both segments passed most commonly to the optic tract, followed by the anterior segment and apex of uncus in the preoptic part and the cerebral peduncle in the postoptic part.

Conclusions

Both parts of the cisternal segment of the AChA come into surgical view during surgeries for different pathologies in and around the perimesencephalic cisterns. However, attending to the artery's genu and defining pre- and postoptic parts during surgery may help the surgeon locate the origin and eventual course of these perforators, and even estimate the terminal areas of supply of most of the perforating arteries. The proposed classification system can prove helpful in planning any operative procedure along the crural cistern and may reduce the probability of inadvertent injury to perforating branches of the cisternal segment.

Differential connectivity of perirhinal and parahippocampal cortices within human hippocampal subregions revealed by high-resolution functional imaging

Numerous studies support the importance of the perirhinal cortex (PRC) and parahippocampal cortex (PHC) in episodic memory. Theories of PRC and PHC function in humans have been informed by neuroanatomical studies of these regions obtained in animal tract-tracing studies, but knowledge of the connectivity of PHC and PRC in humans is limited. To address this issue, we used resting-state functional magnetic resonance imaging to compare the intrinsic functional connectivity profiles associated with the PRC and PHC both across the neocortex and within the subfields of the hippocampus. In Experiment 1, we acquired standard-resolution whole-brain resting-state fMRI data in 15 participants, and in Experiment 2, we acquired high-resolution resting-state fMRI data targeting the hippocampus in an independent sample of 15 participants. Experiment 1 revealed that PRC showed preferential connectivity with the anterior hippocampus, whereas PHC showed preferential connectivity with posterior hippocampus. Experiment 2 indicated that this anterior-posterior functional connectivity dissociation was more evident for subfields CA1 and subiculum than for a combined CA2/CA3/dentate gyrus region. Finally, whole-brain analyses from Experiment 1 revealed preferential PRC connectivity with an anterior temporal and frontal cortical network, and preferential PHC connectivity with a posterior medial temporal, parietal, and occipital network. These results suggest a framework for refining models of the functional organization of the human medial temporal lobes in which the PRC and PHC are associated with distinct neocortical pathways that, in turn, may differentially interact with regions along the anterior-posterior axis of the hippocampus.

Zygomatic anterior subtemporal approach for lesions in the interpeduncular cistern

The interpeduncular cistern is a difficult region to approach through conventional methods due to its deep location and important adjacent neurovascular structures. Therefore, it is usually difficult to expose the region sufficiently. Technical problems associated with various surgical approaches have led to emergence of combined approaches and their modifications (i.e., the removal of the zygomatic arch). In addition, a frontotemporal craniotomy is reported to provide a wide exposure of the anterior temporal base, thus allowing oblique access to the interpeduncular cistern with minimal brain retraction. This study describes clinicians' experience and the surgical results of 24 patients who underwent a zygomatic anterior subtemporal approach.

Through the choroidal fissure: a quantitative anatomic comparison of 2 incisions and trajectories (transsylvian transchoroidal and lateral transtemporal)

BACKGROUND

We compared the transsylvian transchoroidal (TSTC) approach with the lateral transtemporal (LTT) approach. Both approaches proceed through the choroidal fissure but through different incisions and along different trajectories.

METHODS

Four fixed, silicon-injected heads (8 sides) were used. Nine strategic anatomic points within the dissections were compared between the TSTC and LTT approaches in 7 other silicon-injected heads (14 sides). Neuronavigation was used to gather coordinates from selected points of both approaches to calculate surgical angles and distances to common targets.

RESULTS

The surgical angle of the TSTC approach for the inferior choroidal point was wider compared with the LTT approach (P < .05). The surgical angles for the P2a-P2p point were similar for both approaches. In the TSTC approach, the P2-P3 point angle was smaller than in the LTT approach (P < .05). The TSTC approach provided (except for the P2-P3 point) significantly shorter distances to all defined anatomic targets compared with the LTT approach. When the posterior cerebral artery was the target in the TSTC approach, the hippocampus was retracted 3 to 8 mm compared with 8 to 13 mm in the LTT approach.

CONCLUSION

We quantitatively described anatomic features of the TSTC approach and compared them with the LTT approach. For approaching the mesial temporal region, the TSTC approach offers an adequate surgical angle and shorter or similar distances proximal to P2-P3 and requires less temporal lobe and hippocampal retraction than the LTT approach. Such information can help surgeons select the optimal approach to the mesial temporal lobe and its surrounding structures. The TSTC approach should be considered for lesions located in the medial temporal region.

Microvascular anatomy of the medial temporal region: part 1: its application to arteriovenous malformation surgery

BACKGROUND

The medial temporal region (also called the temporomesial or mediobasal temporal region) is the site of the most complex cortical anatomy.

OBJECTIVE

To investigate the anatomic variability of the arterial supply and venous drainage of each segment of the medial temporal region (MTR), and to discuss and illustrate the implications of the findings for surgery of arteriovenous malformations (AVM) of the MTR.

METHODS

Forty-seven cerebral hemispheres and 10 silicon-injected cadaveric heads were examined using x3 to x40 magnification. Illustrative surgical cases of MTR AVMs were selected.

RESULTS

The anterior choroidal artery (AChA) gave rise to an anterior uncal artery in 83% of hemispheres and a posterior uncal or unco-hippocampal artery in 98%. The plexal segment of the AChA gave off neural branches in 38%. The MCA was the site of origin of anterior uncal, unco-parahippocampal, or anterior parahippocampal arteries in 94% of hemispheres. An anterior uncal artery arose from the internal carotid artery (ICA) in 45% of hemispheres. The posterior cerebral artery (PCA) irrigated the entorhinal area through its anterior parahippocampal or hippocampo-parahippocampal branches in every case. A PCA bifurcation was identified in 89% of hemispheres, typically at the middle segment of the MTR. The most common pattern of bifurcation was by division into posteroinferior temporal and parieto-occipital arterial trunks. The anterior segment of the basal vein had a predominant anterior drainage in 35% of hemispheres, and the middle segment had a predominant inferior drainage in 16%.

CONCLUSION

An understanding of the vascular variability of the MTR is essential for accurate microsurgical resection of MTR AVMs.

Integrity of the hippocampus and surrounding white matter is correlated with language training success in aphasia

Aphasia after middle cerebral artery (MCA) stroke shows highly variable degrees of recovery. One possible explanation may be offered by the variability of the occlusion location. Branches from the proximal portion of the MCA often supply the mesial temporal lobe including parts of the hippocampus, a structure known to be involved in language learning. Therefore, we assessed whether language recovery in chronic aphasia is dependent on the proximity of the MCA infarct and correlated with the integrity of the hippocampus and its surrounding white matter. Language reacquisition capability was determined after 2weeks of intensive language therapy and 8months after treatment in ten chronic aphasia patients. Proximity of MCA occlusion relative to the internal carotid artery was determined by magnetic resonance imaging (MRI) based on the most proximal anatomical region infarcted. Structural damage to the hippocampus was assessed by MRI-based volumetry, regional microstructural integrity of hippocampus adjacent white matter by fractional anisotropy. Language learning success for trained materials was correlated with the proximity of MCA occlusion, microstructural integrity of the left hippocampus and its surrounding white matter, but not with lesion size, overall microstructural brain integrity and a control region outside of the MCA territory. No correlations were found for untrained language materials, underlining the specificity of our results for training-induced recovery. Our results suggest that intensive language therapy success in chronic aphasia after MCA stroke is critically dependent on damage to the hippocampus and its surrounding structures.

Posterior parahippocampal gyrus pathology in Alzheimer's disease

The posterior parahippocampal gyrus (PPHG) of the non-human primate brain has a distinct dual role in cortical neural systems. On the one hand, it is a critical link in providing the entorhinal cortex and hippocampal formation with cortical input, while on the other hand it receives output from these structures and projects widely by disseminating the medial temporal lobe output to the cortex. Layer III of TF and TH areas largely mediate the former (input) while layer V mediates the latter (output). We have examined areas TF and TH in the normal human brain and in Alzheimer's disease (AD) using pathological stains (Nissl, Thioflavin S) and phenotype specific stains non-phosphorylated neurofilament protein (SMI32) and parvalbumin (PV). Seven clinically and pathologically confirmed AD cases have been studied along with six age-compatible normal cases. Our observations reveal that neurofibrillary tangles (NFTs) heavily invest the area TF and TH neurons that form layers III and V. In both cortical areas, the large pyramids that form layer V contain a greater number of NFTs. These changes, and possibly, pyramidal cell loss, greatly alter the cytoarchitectural picture and diminish SMI32 staining patterns. Layer III of area TH loses the majority of SMI32 immunoreactivity, whereas this change is more conspicuous in layer V of area TF. PV-staining in both areas is largely unaffected. Normal cases contained no evidence of pathology or altered cytoarchitecture. These observations reveal a further disruption of memory-related temporal neural systems in AD where pathology selectively alters both the input to the hippocampal formation and its output to the cortex.

The selective amobarbital test in the anterior choroidal artery: perfusion pattern assessed by intraarterial SPECT and prediction of postoperative verbal memory

To screen for patients at risk for memory decline after temporal lobe epilepsy (TLE) surgery, selective amobarbital procedures, such as injection into the anterior choroidal artery (ACA-IAT), are sometimes used. We investigated the extent of the territory affected during ACA-IAT and its predictive value with respect to postoperative memory. Seventeen patients with TLE underwent ACA-IAT. In 9 of 17 patients, intraarterial SPECT co-registrated to MRI allowed delineation of amobarbital-perfused structures. Another subgroup of 9 of 17 patients underwent anterior temporal lobectomy. Verbal memory was tested pre- and postoperatively and during ACA-IAT. Major variations in the ACA-IAT perfusion pattern occurred and were not correlated with the verbal memory scores during ACA-IAT. Postoperatively, no patient experienced a severe verbal memory decline, but individual postoperative performance was not correlated with results during ACA-IAT. Our study suggests that ACA-IAT can be used to screen for severe postoperative amnesia in inconclusive cases, but cannot predict individual outcome, even when the perfusion pattern is taken into account.

A case of hippocampal laminar necrosis following complex partial status epilepticus

Cortical laminar necrosis (CLN) is a metabolic injury pattern usually observed after cerebral hypoxia, hypoglycemia, or ischemia. We report serial magnetic resonance imaging findings in a patient with complex partial status epilepticus (SE) developing a band-like, T1-hyperintense lesion consistent with CLN along the surface of the left hippocampus without concurrent other causes of CLN. This observation suggests a direct pathogenetic link between SE and CLN involving combined damage to neurons and glia.

Neural regions essential for distinct cognitive processes underlying picture naming

We hypothesized that distinct cognitive processes underlying oral and written picture naming depend on intact function of different, but overlapping, regions of the left hemisphere cortex, such that the distribution of tissue dysfunction in various areas can predict the component of the naming process that is disrupted. To test this hypothesis, we evaluated 116 individuals within 24 h of acute ischaemic stroke using a battery of oral and written naming and other lexical tests, and with magnetic resonance diffusion and perfusion imaging to identify the areas of tissue dysfunction. Discriminant function analysis, using the degree of hypoperfusion in various Brodmann's areas--BA 22 (including Wernicke's area), BA 44 (part of Broca's area), BA 45 (part of Broca's area), BA 21 (inferior temporal cortex), BA 37 (posterior, inferior temporal/fusiform gyrus), BA 38 (anterior temporal cortex) and BA 39 (angular gyrus)--as discriminant variables, classified patients on the basis of the primary component of the naming process that was impaired (defined as visual, semantics, modality-independent lexical access, phonological word form, orthographic word form and motor speech by the pattern of performance and types of errors across lexical tasks). Additionally, linear regression analysis demonstrated that the areas contributing the most information to the identification of patients with particular levels of impairment in the naming process were largely consistent with evidence for the roles of these regions from functional imaging. This study provides evidence that the level of impairment in the naming process reflects the distribution of tissue dysfunction in particular regions of the left anterior, inferior and posterior middle/superior temporal cortex, posterior inferior frontal and inferior parietal cortex. While occipital cortex is also critical for picture naming, it is likely that bilateral occipital damage is necessary to disrupt visual recognition. These findings provide new evidence that a network of brain regions supports naming, but separate components of this network are differentially required for distinct cognitive processes or representations underlying the complex task of naming pictures.

Probabilistic map of blood flow distribution in the brain from the internal carotid artery

Brain single photon emission computed tomographic (SPECT) images acquired after injecting Tc-99m-HMPAO into the internal carotid artery (ICA) during an intracarotid amobarbital procedure (IAP SPECT) provide anatomical information on the blood flow distribution from the ICA. In this study, probabilistic maps of the distribution of blood supply from the ICA were developed using the IAP SPECT images. Twenty-two sets of basal and IAP SPECT were collected from an existing database. IAP SPECT images were coregistered to basal SPECT images, and spatial normalization parameters used for basal SPECT images were reapplied to IAP SPECT for anatomical standardization. Pixel counts of IAP SPECT images were then normalized, and the probabilistic map of cerebral perfusion distribution (perfusion probabilistic map) for each hemisphere was determined by averaging the spatial/count-normalized IAP SPECT images. Population-based probabilistic maps representing the extent of ICA territory (extent probabilistic map) were also composed by averaging the binary images obtained by thresholding the spatially normalized IAP SPECT images. The probabilistic maps were used to quantify cerebral perfusion and reserve change after arterial bypass surgery in 10 patients with ICA stenosis. In the probabilistic maps, blood supply from the ICA was found to be most likely in the dorsolateral frontal lobe, the anterosuperior portion of the temporal lobe, and in the frontoparietal area. Of the subcortical regions, the striatum was found to be most likely to derive its blood supply from ICA. In patients with cerebral occlusive disease, improvements in basal perfusion and perfusion reserve in the bypass-grafted ICA territory were well identified and were increased by 6.2% and 4.6%, respectively, on average. The probabilistic maps developed in this study illustrate the perfusion distribution and extent of vascular territory for ICA and would be useful for objective evaluations of perfusion status in cerebrovascular disease.

Physiology of cerebral venous blood flow: from experimental data in animals to normal function in humans

In contrast to the cerebroarterial system, the cerebrovenous system is not well examined and only partly understood. The cerebrovenous system represents a complex three-dimensional structure that is often asymmetric and considerably represent more variable pattern than the arterial anatomy. Particular emphasis is devoted to the venous return to extracranial drainage routes. As the state-of-the-art-imaging methods are playing a greater role in visualizing the intracranial venous system at present, its clinically pertinent anatomy and physiology has gain increasing interest, even so only few data are available. For this reason, experimental research on specific biophysical (fluid dynamic, rheologic factors) and hemodynamic (venous pressure, cerebral venous blood flow) parameters of the cerebral venous system is more on the focus; especially as these parameters are different to the cerebral arterial system. Particular emphasis is devoted to the venous return to extracranial drainage routes. From the present point of view, it seems that the cerebrovenous system may be one of the most important factors that guarantee normal brain function. In the light of this increasing interest in the cerebral venous system, the authors have summarized the current knowledge of the physiology of the cerebrovenous system and discuss it is in the light of its clinical relevance.

Early development destructive brain lesions and their relationship to epilepsy and hippocampal damage

Fifty-one consecutive adult patients with epilepsy and early development destructive brain lesions were divided into three main groups according to the topographic distribution of the lesion on magnetic resonance imaging: hemispheric (H) (n=9); main arterial territory (AT) (n=25) and arterial borderzone (Bdz) (n=17). Eight (89%) patients from group H presented status epilepticus in the first 5 years of life, five of them associated with fever. Seventeen of the 25 patients from group AT (76%) had an obvious hemiparesis observed early in life. In addition, major prenatal events were significantly more common in the group AT compared with the other two groups. Among patients from group Bdz, prenatal or postnatal events were not identified, except for one patient. Conversely, nine patients from group Bdz (60%) showed a history of perinatal complications. Hippocampal atrophy (HA) was determined by visual analysis in 74.5% of all patients and by volumetry in 92%. The frequency of HA was comparable among groups, but patients from group H presented the most severe atrophy and more frequent hyperintense T2 hippocampal signal. In conclusion, these three groups of patients with early destructive lesions and epilepsy (H, AT and Bdz), appear to have distinct pathogenic mechanisms. Our data show that there is a striking association of HA with different patterns of neocortical destructive lesions of early development. This association seems to be related to a common and synchronic pathogenic mechanism. The recognition of the pattern and degree of HA among these patients with intractable seizures may influence the surgical rationale.

Surgical anatomy of the temporal lobe for epilepsy surgery

Performing temporal lobe epilepsy (TLE) surgery needs secure knowledge of the surgical anatomy. As regards morphological anatomy, the required knowledge includes ability to identify the temporal sulci and gyri with their posterior landmarks, the opercula and borders of the insula on the convexity surfaces, as well as the mesial structures. The anatomical structures delineating the temporal horn have also to be well-recognized by the surgeon from inside the ventricle, namely: the hippocampus with its tiny fimbria bundle, the choroidal fissure and its velum with the attached choroid plexus, fed by the anterior and postero-lateral choroidal arteries. As TLE surgery also consists of disconnections, knowledge has to include 1) the (fronto-temporal) uncinate fascicle which is divided by doing limen insulae incision, 2) the (intertemporal) anterior commissure which is laterally interrupted when doing total removal of amygdala and entorhinal cortex, 3) the (fornical) bihippocampal commissure, and more generally the ipsilateral limbic system, which are disconnected when sectionning posteriorly the hippocampal tail and the parahippocampal gyrus, 4) the interhemispheric fibers passing through the corpus callosum via the tapetum when dividing the temporal stem, and 5) many other associative fibers... Functional anatomy has to be perfectly known because the temporal lobe plays a major role, especially in language and memory. Also of paramount importance are the visual and auditory pathways; they are in close relationships with the temporal horn; then they project to the occipital calcarine banks and the temporal operculum, respectively. Surgery in the temporal lobe entails risks of vascular complications; almost all the targets have "dangerous" vascular relationships. Therefore good knowledge in vascular anatomy and regular and intensive training in microsurgery are important prerequisitives for being allowed to perform epilepsy surgery.

Effects of subcortical ischemic vascular dementia and AD on entorhinal cortex and hippocampus

OBJECTIVE

To determine the effects of subcortical ischemic vascular dementia (SIVD) and AD on entorhinal cortex (ERC) and hippocampus.

METHODS

Thirty-eight cognitively normal subjects, 18 patients with SIVD, and 22 patients with AD were included. Volumes of ERC and hippocampus were manually measured based on MRI. Global cerebral changes of cortical gray matter, subcortical gray matter, white matter, sulcal CSF, ventricular CSF (vCSF), and white matter signal hyperintensities (WMSH) were assessed.

RESULTS

Patients with SIVD had 21.7% (p < 0.01) smaller ERC and 18.2% (p < 0.01) smaller hippocampi than cognitively normal subjects and 24.4% (p < 0.01) larger ERC and 11.1% (p < 0.05) larger hippocampi than patients with AD. In addition, patients with SIVD had less cortical gray matter and white matter and more vCSF and WMSH (all p < 0.01) than cognitively normal subjects and more vCSF and WMSH (p < 0.01) than patients with AD. The volumes of ERC and hippocampus were positively correlated to similar extents (p < 0.01) in SIVD and AD. Cortical gray matter loss was positively correlated (p < 0.01) with hippocampal atrophy, but not with ERC atrophy, in SIVD and AD. Hippocampal volume alone could classify 82% of patients with SIVD from cognitively normal subjects and 63% of patients with SIVD from subjects with AD. Adding global cerebral changes to hippocampus substantially improved the classification to 96% between patients with SIVD and cognitively normal subjects and 83% between subjects with SIVD and those with AD, whereas adding ERC change to hippocampus did not significantly improve the discrimination.

CONCLUSIONS

The entorhinal cortex and hippocampus are less affected by subcortical ischemic vascular dementia than by AD.