Superior frontal gyrus

Superior frontal gyrus

The superior frontal gyrus(SFG) makes up about one third of the frontal lobe of the human brain. It is bounded laterally by the superior frontal sulcus.

The superior frontal gyrus, like the inferior frontal gyrusand the middle frontal gyrus, is more of a region than a true gyrus.

Function

While the functional role of many subregions has been elucidated using neuroimaging studies, the role of superior frontal gyrus (SFG) is not yet clear. Alagapan et al. combined electrocorticography and direct cortical stimulation in three patients implanted with subdural electrodes to assess if superior frontal gyrus is indeed involved in working memory. They found left SFG exhibited task-related modulation of oscillations in the theta and alpha frequency bands specifically during the encoding epoch. Stimulation at the frequency matched to the endogenous oscillations resulted in reduced reaction times in all three participants. The results provide evidence for SFG playing a functional role in working memory and suggest that SFG may coordinate working memory through low-frequency oscillations thus bolstering the feasibility of using intracranial electric stimulation for restoring cognitive function 1).


The supplementary motor area syndrome is a characteristic neurosurgical syndrome that can occur after surgery in the superior frontal gyrus.

The superior frontal gyrus (SFG) is thought to contribute to higher cognitive functions and particularly to working memory (WM), although the nature of its involvement remains a matter of debate. To resolve this issue, methodological tools such as lesion studies are needed to complement the functional imaging approach.

du Boisgueheneuc et al have conducted the first lesion study to investigate the role of the SFG in WM and address the following questions: do lesions of the SFG impair WM and, if so, what is the nature of the WM impairment? To answer these questions, they compared the performance of eight patients with a left prefrontal lesion restricted to the SFG with that of a group of 11 healthy control subjects and two groups of patients with focal brain lesions prefrontal lesions sparing the SFG (n = 5) and right parietal lesions (n = 4)] in a series of WM tasks. The WM tasks (derived from the classical n-back paradigm) allowed us to study the impact of the SFG lesions on domain (verbal, spatial, face) and complexity (1-, 2- and 3-back) processing within WM. As expected, patients with a left SFG lesion exhibited a WM deficit when compared with all control groups, and the impairment increased with the complexity of the tasks. This complexity effect was significantly more marked for the spatial domain. Voxel-to-voxel mapping of each subject’s performance showed that the lateral and posterior portion of the SFG (mostly Brodmann area 8, rostral to the frontal eye field) was the subregion that contributed the most to the WM impairment. These data led us to conclude that (i) the lateral and posterior portion of the left SFG is a key component of the neural network of WM; (ii) the participation of this region in WM is triggered by the highest level of executive processing; (iii) the left SFG is also involved in spatially oriented processing.

The findings support a hybrid model of the anatomical and functional organization of the lateral SFG for WM, according to which this region is involved in higher levels of WM processing (monitoring and manipulation) but remains oriented towards spatial cognition, although the domain specificity is not exclusive and is overridden by an increase in executive demand, regardless of the domain being processed. From a clinical perspective, this study provides new information on the impact of left SFG lesions on cognition that will be of use to neurologists and neurosurgeons 2).


Superior frontal gyrus tumor.

Quiz

The superior frontal gyrus (SFG) makes up about two thirds of the frontal lobe of the human brain

Y/N


The role of the superior frontal gyrus (SFG) is not yet clear

Y/N


The superior frontal gyrus (SFG) plays a functional role in working memory

Y/N

References

1)

Alagapan S, Lustenberger C, Hadar E, Shin HW, Frӧhlich F. Low-frequency direct cortical stimulation of left superior frontal gyrus enhances working memory performance. Neuroimage. 2019 Jan 1;184:697-706. doi: 10.1016/j.neuroimage.2018.09.064. Epub 2018 Sep 27. PubMed PMID: 30268847; PubMed Central PMCID: PMC6240347.
2)

du Boisgueheneuc F, Levy R, Volle E, Seassau M, Duffau H, Kinkingnehun S, Samson Y, Zhang S, Dubois B. Functions of the left superior frontal gyrus in humans: a lesion study. Brain. 2006 Dec;129(Pt 12):3315-28. Epub 2006 Sep 19. PubMed PMID: 16984899.

MATLAB

MATLAB is a multi-paradigm numerical computing environment and proprietary programming language developed by MathWorks.


Miller et al., from the Department of Neurosurgery of Stanford and Kaiser Permanente Redwood City Medical Center, proposed and presented a novel stereotactic coordinate system based on mesial temporal anatomical landmarks to facilitate the planning and delineation of outcomes based on extent of ablation or region of stimulation within mesial temporal structures.

The body of the hippocampus contains a natural axis, approximated by the interface of cornu ammonis (CA4) and the dentate gyrus. The uncal recess of the lateral ventricle acts as a landmark to characterize the anterior-posterior extent of this axis. Several volumetric rotations are quantified for alignment with the mesial temporal coordinate system. First, the brain volume is rotated to align with standard anterior commissureposterior commissure (AC-PC) space. Then, it is rotated through the axial and sagittal angles that the hippocampal axis makes with the AC-PC line.

Using this coordinate system, customized MATLAB software was developed to allow for intuitive standardization of targeting and interpretation. The angle between the AC-PC line and the hippocampal axis was found to be approximately 20°-30° when viewed sagittally and approximately 5°-10° when viewed axially. Implanted electrodes can then be identified from CT in this space, and laser tip position and burn geometry can be calculated based on the intraoperative and postoperative MRI.

With the advent of stereotactic surgery for mesial temporal targets, a mesial temporal stereotactic system is introduced that may facilitate operative planning, improve surgical outcomes, and standardize outcome assessment 1).


Using an administrative database and chart review, Ramayya et al., identified 101 first-time external ventricular drain placements performed at the bedside. They collected data regarding demographics, medical comorbidities, complications, and catheter tip location. They performed univariate and multivariate statistical analysis using MATLAB. They corrected for multiple comparisons using the false discovery rate (FDR) procedure.

Multivariate regression analyses revealed that revision procedures were more likely to occur after drain blockage (odds ratio [OR] 17.9) and hemorrhage (OR 10.3, FDR-corrected P values < 0.01, 0.05, respectively). Drain blockage was less frequent after placement in an “optimal location” (ipsilateral ventricle or near foramen of Monroe; OR 0.09, P = 0.009, FDR-corrected P < 0.03) but was more likely to occur after placement in third ventricle (post-hoc P values < 0.015). Primary diagnoses included subarachnoid hemorrhage (n = 30, 29.7%), intraparenchymal hemorrhage with intraventricular extravasation (n = 24, 23.7%), tumor (n = 20, 19.8%), and trauma (n = 17, 16.8%). Most common complications included drain blockage (n = 12, 11.8%) and hemorrhage (n = 8, 7.9%). In total, 16 patients underwent at least 1 revision procedure (15.8%).

Bedside external ventricular drain placement is associated with a 15% rate of revision, that typically occurred after drain blockage and postprocedure hemorrhage. Optimal placement within the ipsilateral frontal horn or foramen of Monroe was associated with a reduced rate of drain blockage 2).

References

1)

Miller KJ, Halpern CH, Sedrak MF, Duncan JA, Grant GA. A novel mesial temporal stereotactic coordinate system. J Neurosurg. 2018 Jan 1:1-9. doi: 10.3171/2017.7.JNS162267. [Epub ahead of print] PubMed PMID: 29372873.
2)

Ramayya AG, Glauser G, Mcshane B, Branche M, Sinha S, Kvint S, Buch V, Abdullah KG, Kung D, Chen HI, Malhotra NR, Ozturk A. Factors Predicting Ventriculostomy Revision at a Large Academic Medical Center. World Neurosurg. 2018 Nov 29. pii: S1878-8750(18)32755-4. doi: 10.1016/j.wneu.2018.11.196. [Epub ahead of print] PubMed PMID: 30503293.

Carotid artery stenosis

Carotid artery stenosis is a narrowing or constriction of the inner surface (lumen) of the carotid artery, usually caused by atherosclerosis.

Carotid artery stenosis (CS) is a major cause of ischemic stroke.

Classification

Asymptomatic carotid artery stenosis.

Symptomatic carotid artery stenosis

Clinical features

The mechanisms underlying acute cerebrovascular syndrome in patients with carotid artery stenosis remain unclear.

Carotid artery stenosis can present with no symptoms or with symptoms such as transient ischemic attacks (TIAs) or strokes, contributing to up to 10%-20% of strokes or transient ischemic attacks.

Cortical infarction occurs as a result of vulnerable plaque. Reduced cerebral perfusión induces border-zone infarction. Both factors are implicated in mixed-pattern infarction. Developments in noninvasive diagnostic modalities allow us to explore the mechanisms behind acute cerebrovascular syndrome in carotid artery stenosis and to determine the ideal therapies 1).

Diagnosis

Currently, MRI is the gold standard in carotid plaque imaging, with its high resolution and high sensitivity for identifying intraplaque hemorrhage (IPH), ulceration, lipid-rich necrotic core (LRNC), and inflammation. However, MRI is limited due to time constraints.

CT also allows for high-resolution imaging and can accurately detect ulceration and calcification, but cannot reliably differentiate LRNC from IPH.

PET/CT is an effective technique to identify active inflammation within the plaque, but it does not allow for assessment of anatomy, ulceration, IPH, or LRNC.

Ultrasonography, with the aid of contrast enhancement, is a cost-effective technique to assess plaque morphology and characteristics, but it is limited in sensitivity and specificity for detecting LRNC, plaque hemorrhage, and ulceration compared with MRI.

US can detect congenital variants, dissection, stenosis, and vasculopathy. In addition, correlation of US findings with both magnetic resonance imaging and computed tomography more comprehensively demonstrates the complementary nature of these imaging modalities 2).

Also summarized is how these advanced imaging techniques are being used in clinical practice to risk stratify patients with low- and high-grade carotid artery stenosis. For example, identification of IPH on MRI in patients with low-grade carotid artery stenosis is a risk factor for failure of medical therapy, and studies have shown that such patients may fair better with carotid endarterectomy (CEA). MR plaque imaging has also been found to be useful in identifying revascularization candidates who would be better candidates for CEA than carotid artery stenting (CAS), as high intraplaque signal on time of flight imaging is associated with vulnerable plaque and increased rates of adverse events in patients undergoing CAS but not CEA 3).

Treatment

Case series

Sixty-seven consecutive procedures were performed for internal carotid artery stenosis with CAS at the Ise Red Cross Hospital between November 2015 and February 2018. Procedures for emergency CAS for stroke in evolution or crescendo transient ischemic attack were excluded (n = 12). The embolic debris from remaining procedures (n = 55) was stained with hematoxylineosin and the red blood cells, white blood cells, and fibrinwere quantified by color-based segmentation. Cholesterol crystals and calcification were examined histopathologically. Diffusion-weighted imaging (DWI) was performed 1-3 days after CAS, and the images were used to classify procedures according to the presence of new lesions.

Of the 55 CAS procedures, new DWI lesions were identified after 32. One patient had symptomatic cerebral embolism. Higher proportions of patients with cholesterol crystals in embolic debris (17 vs. 78%, p < 0.001) and higher proportion of white blood cells (mean 2.3 [0-9.9] vs. 4.2% [0-29.9%], p < 0.01) were observed in the embolic debris of procedures with and without new DWI lesions.

Cholesterol crystals were common in the embolic debris from patients with postoperative ischemic lesions after CAS. These results suggest that inflammatory destabilization of the intraplaque lipid component is related to postprocedural DWI lesions 4).

References

1)

Kashiwazaki D, Akioka N, Kuwayama N, Noguchi K, Tanaka K, Kuroda S. Pathophysiology of acute cerebrovascular syndrome in patients with carotid artery stenosis: a magnetic resonance imaging/single-photon emission computed tomography study. Neurosurgery. 2015 Apr;76(4):427-34. doi: 10.1227/NEU.0000000000000655. PubMed PMID: 25621983.
2)

Deurdulian C, Emmanuel N, Tchelepi H, Grant EG, Malhi H. Beyond the Bifurcation: There Is More to Cerebrovascular Ultrasound Than Internal Carotid Artery Stenosis! Ultrasound Q. 2015 Nov 19. [Epub ahead of print] PubMed PMID: 26588099.
3)

Brinjikji W, Huston J 3rd, Rabinstein AA, Kim GM, Lerman A, Lanzino G. Contemporary carotid imaging: from degree of stenosis to plaque vulnerability. J Neurosurg. 2016 Jan;124(1):27-42. doi: 10.3171/2015.1.JNS142452. Epub 2015 Jul 31. PubMed PMID: 26230478.
4)

Maekawa K, Shibata M, Nakajima H, Kitano Y, Seguchi M, Kobayashi K, Sano T, Yabana T, Miya F. Cholesterol Crystals in Embolic Debris are Associated with Postoperative Cerebral Embolism after Carotid Artery Stenting. Cerebrovasc Dis. 2019 Jan 2;46(5-6):242-248. doi: 10.1159/000495795. [Epub ahead of print] PubMed PMID: 30602147.
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