Angular gyrus

Angular gyrus

The Inferior parietal lobule is composed primarily of the Angular gyrus and Supramarginal gyrus

The angular Gyrus is a region of the brain in the Parietal lobe, that lies near the superior edge of the Temporal lobe, and immediately posterior to the Supramarginal gyrus

Located just above the pinna, important on the Dominant hemisphere as part of Wernicke’s area. Note: there is significant individual variability in the location 1).

The Superior temporal sulcus terminates in the Angular gyrus.

It is involved in a number of processes related to Language, number processing and spatial cognition, memory retrieval, attention, and theory of mind. It is Brodmann area 39 of the human brain.

Alexia and agraphia are disorders common to the left inferior Parietal lobe, including the Angular gyrus and Supramarginal gyrus.

Connected to the ipsilateral frontal and caudal lateral prefrontal and inferior frontal regions

Caudate

Parahippocampal gyrus and hippocampus

Precuneus and superior frontal gyrus

Supramarginal gyrus

Via the

Superior longitudinal fasciculus.

Inferior occipitofrontal fasciculus

Inferior longitudinal fasciculus

Occipitofrontal fasciculus

Local arcuate


Burks et al. identified three major types of connections of the Inferior parietal lobule (IPL). (1) Short association fibers connect the Supramarginal gyrus and Angular gyrus, and connect both of these gyri to the Superior parietal lobule 2).

Damage to the angular gyrus manifests as Gerstmann syndrome. Damage may impair one or more of the below functions.

• Dysgraphia/agraphia: deficiency in the ability to write

• Dyscalculia/acalculia: difficulty in learning or comprehending mathematics

• Finger agnosia: inability to distinguish the fingers on the hand

Left-right disorientation


1)

Ojemann G, Ojemann J, Lettich E, Berger M. Cortical Language Localization in Left, Dominant Hemi- sphere. An Electrical Stimulation Mapping Investi- gation in 117 Patients. J Neurosurg. 1989; 71:316– 326
2)

Burks JD, Boettcher LB, Conner AK, Glenn CA, Bonney PA, Baker CM, Briggs RG, Pittman NA, O’Donoghue DL, Wu DH, Sughrue ME. White matter connections of the inferior parietal lobule: A study of surgical anatomy. Brain Behav. 2017 Mar 8;7(4):e00640. doi: 10.1002/brb3.640. eCollection 2017 Apr. PubMed PMID: 28413699; PubMed Central PMCID: PMC5390831.

Sylvian fissure

Sylvian fissure

The lateral sulcus also called Sylvian fissure (SyF) or lateral fissure is one of the most prominent structures of the brain (the fissure separating the temporal lobe from the parietal lobe and frontal lobes).

Sylvian fissure dissection is an essential microneurosurgical skill for neurosurgeons. The safe and accurate opening of the sylvian fissure is desirable for a good prognosis.

The central sulcus joins the Sylvian fissure in only 2 % of cases.

The Sylvian fissure terminates in the supramarginal gyrus (Brodmann area 40).


frankfurtplane.jpg

Approximated by a line connecting the lateral canthus to the point 3/4 of the way posterior along the arc running over convexity from nasion to inion (T-H lines).


The frontotemporal, so-called pterional approach has evolved with the contribution of many neurosurgeons over the past century. It has stood the test of time and has been the most commonly used transcranial approach in neurosurgery. In its current form, drilling the sphenoid wingas far down as the superior orbital fissure with or without the removal of the anterior clinoid process, thinning the orbital roof, and opening the Sylvian fissure and basal cisterns are the hallmarks of this approach.

The bone flap has been removed and the dura mater has been opened as a flap pediculated towards the greater sphenoid wing previously roungered to improve parasellar visualization. Sylvian fissure, Inferior frontal gyrus, Superior temporal gyrus and Middle temporal gyrus are exposed. Three pars of parasylvian inferior frontal gyrus must be distinguished: pars orbitalis (pOr) in relation to the orbital roof; pars triangularis (pT) the widest area of sylvian fissure (good place for start opening of sylvian fissure); pars opercularis (pOp) where Broca’s Area is located.

Compartments

The sylvian fissure extends from the basal to the lateral surface of the brain and presents 2 compartments on each surface,

1 superficial (temporal stem and its ramii) and 1 deep (anterior and lateral operculoinsular compartments). The temporal operculum is in opposition to the frontal and parietal opercula (planum polare versus inferior frontal and precentral gyri, Heschl’s versus postcentral gyri, planum temporale versus supramarginal gyrus). The inferior frontal, precentral, and postcentral gyri cover the anterior, middle, and posterior thirds of the lateral surface of the insula, respectively. The pars triangularis covers the apex of the insula, located immediately distal to the genu of the middle cerebral artery. The clinical application of the anatomic information presented in the article of Wen et al. is in angiography, middle cerebral artery aneurysm surgery, insular resection, frontobasal resection, and amygdalohippocampectomy, and hemispherotomy 1).

Divisions

The SyF is divided into a proximal segment and a distal segment separated by the anterior sylvian point (ASP).

It is the single most identifiable feature of the superolateral face of the brain, and together with the underlying sylvian cistern it constitutes the most frequently used microneurosurgical corridor because of the high proportion of intracranial lesions that are accessible through its opening 2).

The lateral sulcus divides both the frontal lobe and parietal lobe above from the temporal lobe below. It is in both hemispheres of the brain but is longer in the left hemisphere in most people. The lateral sulcus is one of the earliest-developing sulci of the human brain. It first appears around the fourteenth gestational week.

The sylvian fissure or lateral sulcus is the most identifiable feature of the superolateral brain surface and constitutes the main microneurosurgical corridor, given the high frequency of approachable intracranial lesions through this route.

In their original description of the microsurgical anatomy of the subarachnoid cisterns in 1976, Yasargil, et al., 3) emphasized the importance of the SyF, which then became the main microneurosurgical corridor to the base of the brain. In later publications Yasargil, et al., described in detail the microanatomy of this fissure and its underlying cistern 4) 5) 6) and the technique of its opening.

The opening of the fissure at the level of the anterior sylvian point (ASP) shows very soon the insular apex. The limen insula and the middle cerebral artery bifurcation are a little bit deeper and 1-2 cm. anteriorly. The opening of the sylvan fissure posteriorly to the ASP exposes the insula and the opening anteriorly leads to the suprasellar cisterns. The distance between the ASP and the IRP along the SF is 2.3 cm.

Branches

The lateral sulcus has a number of side branches. Two of the most prominent and most regularly found are the ascending (also called vertical) ramus and the horizontal ramus of the lateral fissure, which subdivide the inferior frontal gyrus. The lateral sulcus also contains the transverse temporal gyri, which are part of the primary and below the surface auditory cortex.

Partly due to a phenomenon called Yakovlevian torque, the lateral sulcus is often longer and less curved on the left hemisphere than on the right.

It is also located near Sylvian Point.

The area lying around the Sylvian fissure is often referred to as the perisylvian cortex. The human secondary somatosensory cortex (S2, SII) is a functionally-defined region of cortex in the parietal operculum on the ceiling of the lateral sulcus.

Yasargil divides the SyF into a proximal segment (stem, sphenoidal, anterior ramus) and a distal segment (lateral, posterior ramus) separated by the sylvian point 7) 8). which is located beneath the triangular part of the inferior frontal gyrus (IFG).

The horizontal and the anterior ascending branches of the SyF that delineate the triangular part of the IFG arise at the sylvian point 9).

Variants

Yasargil described four different types of intraoperatively observed anatomical sylvian fissure (SF) variants.

Category I is a straight wide SF, II a straight narrow SF, III a herniated frontal lobe into the SF and IV is a herniated temporal lobe into the SF. 10).

The SF categories used in the present work are based on the Yasargil classification with slight modifications since we categorized the SF on cranial computed tomography (CCT) scans and not anatomically.

Splitting

Insular gliomas represent a unique surgical challenge due to the complex anatomy and nearby vascular elements associated within the Sylvian fissure. For certain tumors, the transsylvian approach provides an effective technique for achieving maximal safe resection.

The goal of the manuscript and video of Safaee et al., are to present and discuss the surgical nuances and appropriate application of splitting the Sylvian fissure. The hope is that this video highlights the safety and efficacy of the transsylvian approach for appropriately selected insular gliomas 11).

Pathology

References

1)

Wen HT, Rhoton AL Jr, de Oliveira E, Castro LH, Figueiredo EG, Teixeira MJ. Microsurgical anatomy of the temporal lobe: part 2–sylvian fissure region and its clinical application. Neurosurgery. 2009 Dec;65(6 Suppl):1-35; discussion 36. doi: 10.1227/01.NEU.0000336314.20759.85. PubMed PMID: 19934983.
2)

Ribas GC, Ribas EC, Rodrigues CJ. The anterior sylvian point and the suprasylvian operculum. Neurosurg Focus. 2005 Jun 15;18(6B):E2. PubMed PMID: 16048297.
3)

Yasargil MG, Kasdaglis K, Jain KK, et al: Anatomical observations of the subarachnoid cisterns of the brain during surgery. J Neurosurg 44:298–302, 1976
4)

Yasargil MG: Microneurosurgery. Stuttgart: Georg Thieme, 1984, Vol I
5)

Yasargil MG: Microneurosurgery. Stuttgart: Georg Thieme, 1994, Vol IV
6) , 8)

Yasargil MG, Krisht AF, Türe U, et al: Microsurgery of insular gliomas: Part I, II, IV. Contemporary Neurosurgery 24:(11):1–8; (13):1–6; (14):1–8, 2002
7)

Türe U, Yasargil DCH, Al-Mefty O, et al: Topographic anatomy of the insular region. J Neurosurg 90:720–733, 1999
9)

Ono M, Kubik S, Abernathey CD: Atlas of Cerebral Sulci. Stuttgart: Thieme, 1990
10)

Yasargil MG. Stuttgart: Thieme Publishers; 1984. Operative anatomy, in Microneurosurgery; pp. 252–90.
11)

Safaee MM, Englot DJ, Han SJ, Lawton MT, Berger MS. The transsylvian approach for resection of insular gliomas: technical nuances of splitting the Sylvian fissure. J Neurooncol. 2016 Nov;130(2):283-287. Review. PubMed PMID: 27294356.

Precentral gyrus

Precentral gyrus

see also Central sulcus region.

The precentral gyrus, forming the posterior border of the frontal lobe, contains the primary motor cortex.

see Brodmann area 4.

The middle frontal gyrus (MFG) often connects to the pre-central gyrus via a thin isthmus 1).

Several methods have been created to aid both neurosurgeons and neuroradiologists in precisely localizing the precentral gyrus. One of them consists of recognizing the intersection between the superior frontal sulcus and the precentral sulcus, being the motor hand area at the same sagittal plane on the precentral gyrus 2) 3).

The intersectional point between the superior frontal sulcus and precentral sulcus (**) is the invagination base of the knob on the precentral gyrus.

Direct cortical stimulation studies and functional magnetic resonance imaging studies have demonstrated that the precentral gyrus lodges the motor primary cortex and the second curvature of the central sulcus, which corresponds to the knob-like form in the precentral gyrus, are specifically associated with contralateral motor hand skills.

Brain surface reformatted imaging improves the diagnostic accuracy of standard anatomical MR imaging for localizing superficial brain lesions in relation to the precentral gyrus. The complementary use of this technique with standard two-dimensional imaging is supported by the fast and simple postprocessing technique and may provide useful information for preoperative surgical planning 4).


Kim et al. reviewed 33 consecutive patients who experienced pharmacologically intractable epilepsy and underwent Precentral gyrus resection (PGR) with intraoperative cortical stimulation and mapping while under awake anesthesia. The etiological diagnoses were brain neoplasm in 26 patients (78.8%), cortical lesion in 4 (12.1%), and no lesion in 3 (9.1%). The mean follow-up period was 62.6 months (range, 12-146 months). All topographical analyses of the resected quadrant area were performed based on postoperative magnetic resonance images.

After PGR, 22 patients (66.7%) experienced neurological worsening, including 5 permanent deficits (15.2%) and 17 transient deficits (51.5%). Permanent deficits included 2 instances of weakness, 1 dysarthria, 1 dysesthesia, and 1 fine-movement disturbance of the hand. While the neurological risk for anterior lower quadrant PGR was 20.0% (1/5), the risk for posterior upper quadrant PGR was 100.0% (10/10). The anterior upper and posterior lower quadrant PGR caused neurological deteriorations in 60.0% (6/10) and 62.5% (5/8) of the patients, respectively. In a multivariate analysis, PGR of the posterior and upper quadrant sections were significant risk factors for post-PGR neurological deteriorations (P = .022 and 0.030, respectively).

The posterior upper quadrant of the precentral gyrus was vulnerable to post-resective neurological impairment 5).

Left precentral gyrus

see Left precentral gyrus


Garcia Santos et al aimed to investigate whether magnetic resonance spectroscopy (MRS) metabolite ratios change in the precentral gyrus of patients with amyotrophic lateral sclerosis (ALS) after spinal cord surgical injection of bone marrow mononuclear cells, as well as their relationship with disability and survival and demonstrates that spinal cord injection of stem cells shows metabolic improvement in the brain that might be related to longer survival and less disability 6).

see Precentral gyrus glioma.

see Precentral gyrus metastases.


Catani et al. identified three intralobar tracts connecting: i) posterior Broca’s area with supplementary motor area (SMA) and pre-supplementary motor area (pre-SMA) (i.e., the frontal aslant tract – FAT); ii) posterior orbitofrontal cortex with anterior polar region (i.e., frontoorbitopolar tract – FOP); iii) posterior precentral cortex with anterior prefrontal cortex (i.e., the frontal superior longitudinal – FSL faciculus system). In addition more complex systems of short U-shaped fibres were identified in the regions of the central, pre-central, perinsular and fronto-marginal sulcus (FMS). The connections between Broca and medial frontal areas (i.e. FAT) and those between the hand-knob motor region and post-central gyrus (PoCG) were found left lateralized in a group of twelve healthy right-handed subjects. The existence of these short frontal connections was confirmed using post-mortem blunt dissections. The functional role of these tracts in motor learning, verbal fluency, prospective behaviour, episodic and working memory is discussed in the study of Catani et al. provides a general model for the local connectivity of the frontal lobes that could be used as an anatomical framework for studies on lateralization and future clinical research in neurological and psychiatric disorders 7).

References

1)

Naidich TP. MR Imaging of Brain Surface Anatomy. Neuroradiology. 1991; 33:S95–S99
2)

Ebeling U, Steinmetz H, Huang YX, Kahn T. Topography and identification of the inferior precentral sulcus in MR imaging. AJR Am J Roentgenol. 1989;153(5):1051-6. doi:10.2214/ajr.153.5.1051
3)

Kido DK, LeMay M, Levinson AW, Benson WE. Computed tomographic localization of the precentral gyrus. Radiology. 1980;135(2):373-7. doi:10.1148/radiology.135.2.7367629
4)

Hattingen E, Good C, Weidauer S, Herminghaus S, Raab P, Marquardt G, Raabe A, Seifert V, Zanella FE. Brain surface reformatted images for fast and easy localization of perirolandic lesions. J Neurosurg. 2005 Feb;102(2):302-10. PubMed PMID: 15739559.
5)

Kim YH, Kim CH, Kim JS, Lee SK, Han JH, Kim CY, Chung CK. Topographical risk factor analysis of new neurological deficits following precentral gyrus resection. Neurosurgery. 2015 Jun;76(6):714-20; discussion 720. doi: 10.1227/NEU.0000000000000712. PubMed PMID: 25734322.
6)

García Santos JM, Inuggi A, Gómez Espuch J, Vázquez C, Iniesta F, Blanquer M, María Moraleda J, Martínez S. Spinal cord infusion of stem cells in amyotrophic lateral sclerosis: Magnetic resonance spectroscopy shows metabolite improvement in the precentral gyrus. Cytotherapy. 2016 Jun;18(6):785-96. doi: 10.1016/j.jcyt.2016.03.296. PubMed PMID: 27173751.
7)

Catani M, Dell’acqua F, Vergani F, Malik F, Hodge H, Roy P, Valabregue R, Thiebaut de Schotten M. Short frontal lobe connections of the human brain. Cortex. 2012 Feb;48(2):273-91. doi: 10.1016/j.cortex.2011.12.001. Epub 2011 Dec 13. PubMed PMID: 22209688.
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