Книги по МРТ КТ на английском языке / Neurosurgery Fundamentals Agarval 1 ed 2019

6.a. The cortical region anterior to the central sulcus corresponds to primary motor cortex. Thus, a lesion in this region may result in UMN findings, one of which is pronator drift. Fasciculations are a LMN finding.

7.c. The clinical vignette describes a case of radial neuropathy, colloquially known as “Saturday night palsy”, due to compression of the radial nerve in the axilla. The radial nerve is responsible for the triceps reflex and arises from the C7 spinal cord root. The biceps­ and brachioradialis reflexes correspond to the C5–C6 spinal cord root.

8.c. The distribution of the sensory deficit­ described in the clinical vignette corresponds to the L5 spinal cord root, which is particularly notable for carrying sensation from the web space between the big toe and the second toe.

9.b. The clinical vignette describes long-standing carpal tunnel syndrome that is confirmed on exam with Tinel’s sign. As compression of the median nerve underlies this syndrome, one would also expect atrophy of the muscles (thenar muscles) supplied by the median nerve over time.

10.d. The clinical vignette describes low back pain that might initially suggest radiculopathy with neurogenic claudication due to degenerative disc disease. However, given an unremarkable neurological examination with a negative straight leg test, it would be prudent to perform FABER/FADIR to evaluate for SI pathology, which can mimic lumbar spinal pathology. Additional tests for SI joint pathology include: compression, thigh thrust, distraction, and Gaenslen.

Suggested Readings

[1]Drislane F, Acosta J, Caplan L, Chang B, Tarulli A. Blueprints neurology. 4th ed. Philadelphia, PA: Lippincott­ Williams & Wilkins; 2013

[2]Gelb DJ. The detailed neurologic examination in adults. 2012. [online] Available from: https://www. uptodate.com/contents/the-detailed-neurologic- examination-in-adults. Accessed June, 2017

[3]Gelb DJ. Introduction to clinical neurology. 5th edition­ . Oxford: Oxford University Press; 2016

[4]Greenberg MS. Handbook of neurosurgery. 8th edition­ . New York, NY: Thieme; 2016

[5]Po-Haong L. The mental status examination in adults. 2014. [online] Available from: https:// www.uptodate.com/contents/the-mental-status-­ examination-in-adults. Accessed June, 2017

[6]Roundy N. Neurosurgery Survival Guide. 2011. [online]­ Available from: http://neurosurgerysurvivalguide.com/. Accessed June, 2017

[7]Strub RL, Black FW. The mental status examination in neurology. 2nd ed. Philadelphia, PA: F.A. Davis; 1985

39

4.1  Introduction

Neurosurgery as a surgical field relies on anatomical knowledge to successfully and safely perform a wide variety of procedures. These might be as simple as a lumbar puncture to the most complex skull base tumor resection. As such, this chapter reviews the most high-yield neuroanatomy topics.

4.2  Bones of the Skull

The human skull is divided into two regions: the face and cranium. The face is composed of 14 bones; while the cranium is composed of 8 bones. Here, we focus on cranial bones ( Table 4.1).

The cranial bones are joined via fibrous joints. Articulations between two adjacent bones are called sutures, and places where two or more sutures meet are named according to their location ( Fig. 4.1).

•Nasion: Suture between the frontal and nasal bones.

•Bregma: Located at the vertex of the skull vault at the point where the sagittal­ suture meets the coronal suture.

•Pterion: Located at the lateral aspect of the skull vault. The point where the greater wing of the sphenoid, the

Table 4.1  Bones of the cranium (8 bones)

frontal, parietal and squamous portion­ of the temporal bone meet.

•Asterion: Located posterolaterally. The point where the parietomastoid, occipitomastoid, and lamboid sutures meet.

•Opisthion: The name given to the posterior border of the foramen magnum at the midline.

•Inion: Also known as external occipital protuberance, correlates with the confluence of the venous sinuses on the internal surface. Routinely used as a surgical landmark.

4.2.1  Cranium

The cranium is an ovoid bony box which functions to protect the encephalon. For anatomical and clinical purposes, the cranium is divided into two segments—superolateral or vault, and inferior or skull base.

Skull Vault

Comprised anteriorly by the vertical segment of the frontal bone; at its middle aspect by the parietal bones superiorly and the squamous portion of the temporal bones inferiorly; and posteriorly by the superior portion of the occipital bone.

Skull Base

The internal surface of the skull base consists of three fossae, each with associated foramina which transmit efferent and ­afferent neurovascular structures ( Fig. 4.2 and Fig. 4.3).

4.2.2  Clinical Applications

Kocher’s point ( Fig. 4.4), Frazier’s point. Please refer to chapter on Operating Room ( Table 6.2).

Sinus Landmarks

A horizontal line across the inion delin­ eates the trajectory of the transverse sinus. A vertical line going from the tip of ­mastoid and passing through the mastoid (digas­ tric) groove delineates the sigmoid sinus. These landmarks are commonly used to plan craniotomies for retrosigmoid approaches ( Fig. 4.5).1

4.3  Cerebrum

4.3.1  Surface Anatomy

The brain is comprised of two hemi­ spheres separated by an interhemispheric fissure (IHF), also known as longitudinal fissure of cerebrum. This fissure runs anteroposteriorly in the midline and it is occupied by an extension of the dura mater, known as the falx cerebri. Both hemispheres are joined together by the interhemispheric commissures: Corpus callosum, fornix, and the anterior com­ missure ( Fig. 4.6).

Each brain hemisphere is divided into five lobules. The divisions are centered around main sulci, which are deep and generally constant across subjects. Each

lobule has its own circumvolutions delineated by secondary and tertiary sulci, the latter demonstrating greatest intersubject variability ( Fig. 4.7).

Frontal Lobe

This is the largest cerebral lobe. When the brain is viewed from a lateral perspective, the frontal lobe is limited posteriorly by the central sulcus and inferiorly by the lateral sulcus (Sylvian fissure).

44

Central Sulcus

Central sulcus separates the frontal and parietal lobes, following an oblique trajectory from superior to inferior, and posterior­ to anterior. It starts at the IHF and ends above the lateral sulcus, leaving a small

communication between the frontal and parietal lobes, called the subcentral gyrus.

Lateral Sulcus (Sylvian Fissure)

Lateral sulcus separates the frontal lobe from the temporal lobe. It is the deepest sulcus in the frontal lobe and covers the insula and branches of the middle cerebral artery (MCA). Two divisions—the anterior/­ horizontal, and the posterior/ascending— divide the inferior frontal gyrus into three segments, resembling the letter M.

The three segments of the inferior frontal gyrus are from anterior to posterior: pars orbitalis, pars triangularis, and pars opercularis (the latter two otherwise known as Broca’s area within the dominant hemisphere).

•Precentral sulcus: Runs parallel to the central sulcus and delineates anteriorly the precentral gyrus or motor

strip (Brodmann area 4, primary motor cortex).

Inferior Surface

The inferior surface of the frontal lobe is limited posteriorly by the medial projection of the Sylvian fissure ( Fig. 4.8). Medially, next to the IHF runs the gyrus rectus (straight gyrus), which is limited laterally by the olfactory sulcus with the olfactory nerve and bulb. This segment lies over the cribriform plate of the ethmoid bone. Lateral to the olfactory sulcus is the orbital segment of the frontal lobe, which is divided into four orbital gyri (anterior, posterior, lateral, and medial) by the orbital sulci which has an H shape.

Secondary Sulci

Secondary sulci divide the lateral surface of the frontal lobe into four gyri.

•Superior frontal sulcus: Divides the superior frontal gyrus (SFG) from the middle frontal gyrus (MFG).

•Inferior frontal sulcus: Divides the MFG from the inferior frontal gyrus (IFG).

Parietal Lobe

The parietal lobe is limited anteriorly by the central sulcus, posteriorly by the parieto-occipital sulcus, inferiorly by the Sylvian fissure, and over the medial ­hemispheric surface by the subparietal sulcus. Two main sulci (i.e., the postcentral and intraparietal) divide this lobule into three main gyri.

Fig. 4.8  The orbital surface of the right frontal lobe. (Reproduced from Yasargil M, Smith R, Young P et al, Microneurosurgery, Volume I, 1st edition,

©1984, Thieme Publishers, New York.)

Postcentral Sulcus

This is the posterior limit of the postcentral gyrus or primary sensory cortex (Brodmann areas 3, 1, and 2). Its anterior limit is the central sulcus.

Intraparietal Sulcus

Originates perpendicular to the postcentral sulcus, dividing the remainder of the lateral surface of this lobule into the superior parietal lobule (SPL) and inferior parietal lobule (IPL). The SPL continues within the medial surface of the hemisphere as the precuneus. The IPL contains the supramarginal gyrus (SMG), also known as Wernicke’s area, and the angular gyrus (AG). Localizing the SMG involves following the Sylvian fissure until its termination within the parietal lobe. The AG can be located by following the superior temporal sulcus instead.

Temporal Lobe

Considered as the most epileptogenic lobule, it is limited superiorly by the Sylvian fissure. Posteriorly, its limit is poorly defined although in some cases, it is possible­ to visualize a temporo-occipi- tal sulcus. Two main sulci divide the lateral surface of temporal lobe into three gyri. The superior temporal sulcus separates the superior temporal gyrus (STG) from the middle temporal gyrus (MTG). The inferior temporal sulcus separates the MTG from the inferior temporal gyrus (ITG). The STG contains the primary auditory area, also known as transverse gyri of Heschl or Brodmann areas 41 and 42.

The inferior surface of the temporal lobe contains two main sulci. The occipitotemporal sulcus, located laterally, divides the ITG and the fusiform gyrus

located laterally on the inferior surface of the temporal lobe. The collateral sulcus, located medially, divides the fusiform gyrus and the parahippocampal gyrus, which continues posteriorly in the occipital­ lobe within the lingual gyrus. ( Fig. 4.9).

Occipital Lobe

Located at the posterior aspect of the hemispheres, the occipital lobe assumes a pyramidal shape, limited dorsally by the parietooccipital sulcus. Ventrally, its boundary with the temporal lobule is not well-defined, as previously mentioned. Its lateral surface has three gyri. The superior gyrus continues anteriorly as the SPL; the middle gyrus continues as the AG, and the inferior occipital gyrus continues as the MTG and ITG. The inferior surface has two gyri, the lateral gyrus is continuous with the fusiform gyrus. The medial gyrus forms the lingual gyrus which continues anteriorly within the temporal lobe.

The medial surface of the occipital lobe is known as the cuneus and is limited by the parieto-occipital sulcus anteriorly and superiorly, and the calcarine sulcus inferiorly. The primary visual area (Brodmann area 17) surrounds the calcarine sulcus.

Medial Surface

The cingulate gyrus is limited superiorly by the cingulate and subparietal sulci, and inferiorly by the sulcus of the corpus callosum. The cingulate sulcus separates the cingulum from the SFG and continues posteriorly and superiorly to form the posterior limit of the paracentral lobule. The paracentral lobule is a continuation of the precentral and postcentral gyri within the medial surface of the hemisphere ( Fig. 4.10).

47

4.3.2  Subcortical Structures Basal Ganglia

The basal ganglia are gray matter nuclei located deep within the cerebral hemispheres ( Fig. 4.11). From medial to lateral these are:

•Thalamus.

•Striatum:

◦Caudate nucleus, divided into head (lateral to the frontal horns of the ventricle and medial to the

anterior limb of the internal capsule), body, and tail.

◦Lentiform nucleus, lateral to the internal capsule, it has a medial segment or globus pallidus (with its internal and external segments), and a lateral segment or putamen.

48

•Claustrum: Thin layer of gray matter separated from the insula by a thin layer of white matter (extreme capsule) and separated from the lentiform nucleus and the striatum by the white matter of the external capsule.

Internal Capsule

Thick layer of white matter running between the caudate nucleus and thalamus medially and the striatum laterally. It has five segments running from anterior to posterior2:

•Anterior limb:

◦Frontopontine fibers.

◦Thalamocortical fibers.

◦Corticothalamic fibers.

◦Caudatoputamenal fibers.