Handbook of Neurosurgery Part I: Anatomy and Physiology PDF

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| 24.07.19 - 07:11 www.ebook2book.ir | 24.07.19 - 07:11 Part I 1 Gross Anatomy, Cranial and Spine 64 Anatomy and Physiology 2 Vascular Anatomy 82 3 Neurophysiology and Regional Brain Syndromes 98 I www.ebook2book.ir | 24.07.19 - 07:11 64 Anatomy and Physiology 1 1 Gross Anatomy, Cranial and Spine 1.1 Cortical surface anatomy 1.1.1 Lateral cortical surface ▶ Fig. 1.1. For abbreviations, see ▶ Table 1.1 and ▶ Table 1.2. The middle frontal gyrus (MFG) is usu- ally more sinuous than the IFG or SFG, and it often connects to the pre-central gyrus via a thin isth- mus.1 The central sulcus joins the Sylvian fissure in only 2% of cases (i.e., in 98% of cases there is a “subcentral” gyrus). The intraparietal sulcus (ips) separates the superior and inferior parietal lobules. The IPL is composed primarily of the AG and SMG. The Sylvian fissure terminates in the SMG (Brodmann’s area 40). The superior temporal sulcus terminates in the AG. 1.1.2 Brodmann’s areas ▶ Fig. 1.1 also identifies the clinically significant areas of Brodmann’s (Br.) map of the cytoarchitec- tonic fields of the human brain. Functional significance of these areas is as follows: 1. Br. areas 3, 1, 2: primary somatosensory cortex 2. Br. areas 41 & 42: primary auditory areas (transverse gyri of Heschl) 3. Br. area 4: precentral gyrus, primary motor cortex (AKA “motor strip”). Large concentration of giant pyramidal cells of Betz 4. Br. area 6: premotor area or supplemental motor area. Immediately anterior to motor strip, it plays a role in contralateral motor programming 5. Br. area 44: (dominant hemisphere) Broca’s area (classically “motor speech area” see speech & language (p. 98)) 6. Br. area 17: primary visual cortex 7. Wernicke’s area: (dominant hemisphere) most of Br. area 40 and a portion of Br. area 39 (may also include ≈ posterior third of STG). Significant in speech & language (p. 98) 8. the striped portion of Br. area 8 in ▶ Fig. 1.1 (frontal eye field) initiates voluntary eye movements to the opposite direction CENTRAL SULCUS (Rolandic fissure) Br. 3 Br. 4 Br. 1 Br. 6 Br. 2 Br. 8 Br. 40 cs Br. 44 pr Br. 39 SP ips L c s po CG Pre SMG CG ios IPL f st G po SF Po AG FG s to M POp IFG PT st s sfs los POr STG ifs its OG MTG pocn LATERAL SULCUS ITG Br. 42 Br. 17 (Sylvian fissure) Br. 41 Anterior Posterior Fig. 1.1 Left lateral cerebral cortical surface anatomy. Br. = Brodmann’s area (shaded). See ▶ Table 1.1 and ▶ Table 1.2 for abbreviations (lowercase = sulci, UPPERCASE = gyri). www.ebook2book.ir | 24.07.19 - 07:11 Gross Anatomy, Cranial and Spine 65 Table 1.1 Cerebral sulci (abbreviations) Abbreviation Sulcus 1 cins cingulate sulcus cs central sulcus ips-ios intraparietal-intraoccipital sulcus los lateral occipital sulcus pM pars marginalis pocn pre-occipital notch pocs post-central sulcus pof parieto-occipital fissure pos parieto-occipital sulcus prcs pre-central sulcus sfs, ifs superior, inferior frontal sulcus sps superior parietal sulcus sts, its superior, inferior temporal sulcus tos trans occipital sulcus Table 1.2 Cerebral gyri and lobules (abbreviations) Abbreviation Gyrus / lobule AG angular gyrus CinG cingulate gyrus Cu cuneus LG lingual gyrus MFG, SFG middle & superior frontal gyrus OG orbital gyrus PCu precuneous PreCG, PostCG pre- and post-central gyrus PL paracentral lobule (upper SFG and PreCG and PostCG) IFG inferior frontal gyrus POp pars opercularis PT pars triangularis POr pars orbitalis STG, MTG, ITG superior, middle & inferior temporal gyrus SPL, IPL superior & inferior parietal lobule SMG supramarginal gyrus 1.1.3 Medial surface Pars marginalis ▶ Fig. 1.2. The cingulate sulcus terminates posteriorly in the pars marginalis (pM) (plural: partes marginales). On axial imaging, the pMs are visible on 95% of CTs and 91% of MRIs,2 they are usually the most prominent of the paired grooves straddling the midline, and they extend a greater distance into the hemispheres.2 On axial CT or MRI, the pM is posterior to the widest biparietal diameter.2 The pMs curve posteriorly in lower slices and anteriorly in higher slices (here, the paired pMs form the “pars bracket”—a characteristic “handlebar” configuration straddling the midline). AC-PC line The “AC-PC line” connects the anterior commissure (AC) and the posterior commissure (PC) on a mid- line sagittal image. The AC is the horizontally positioned white matter tract that crosses in front of the fornix. The PC is the white-matter band at the level of the pineal that crosses at the posterior third www.ebook2book.ir | 24.07.19 - 07:11 66 Anatomy and Physiology 1 prcs CENTRAL SULCUS SFG P PL pM sps cins cins PCu CinG pus callosum cor pos pc ac Cu LG AC-PC pons Fig. 1.2 Medial aspect of the right hemisphere. Abbreviations: see ▶ Table 1.1 for sulci and ▶ Table 1.2 for gyri; AC-PC = AC-PC line (see text). ventricle. The AC-PC line is used in functional neurosurgery and is also used as the baseline for axial MRI scans (and for recent CT scanners). In the more entrenched Talairach definition,3 it passes through the superior edge of the AC and the inferior edge of the PC (as illustrated in ▶ Fig. 1.2). Alternative Schaltenbrand definition4: a line passing through the midpoint of the AC & PC, allowing both AC & PC to be imaged on a single thin axial MRI slice. These definitions differ by 5.81° ± 1.07°.5 The orbitomeatal line (p.243) (used in older CT scanners) is ≈ 9° steeper than the Talairach AC-PC line.5 1.1.4 Somatotopic organization of primary sensory and motor cortex The primary motor cortex (AKA “motor strip”) and primary (somato)sensory cortex are organized somatotopically so that specific regions of the brain map correspond to specific areas of the body as shown in ▶ Fig. 1.3. The regions are often drawn with a caricature of a human figure (the homunculus—Latin for “little man”) along with the labels shown here. Some key points: the representation of the arm and face are draped over the convexity of the brain, while the foot and leg areas are located along the upper aspect of the medial surface. Areas with fine motor or sensory function (e.g. fingers, tongue) have a larger area of representation. 1.2 Central sulcus on axial imaging See ▶ Fig. 1.4. Identification of the central sulcus is important to localize the motor strip (contained in the PreCG). The central sulcus (CS) is visible on 93% of CTs and 100% of MRIs.2 It curves posteriorly as it approaches the interhemispheric fissure (IHF), and often terminates in the paracentral lobule, just anterior to the pars marginalis (pM) within the pars bracket (see above)2 (i.e., the CS often does not reach the midline). Pointers: parieto-occipital sulcus (pos) (or fissure): more prominent over the medial surface, and on axial imaging is longer, more complex, and more posterior than the pars marginalis6 post-central sulcus (pocs): usually bifurcates and forms an arc or parenthesis (“lazy-Y”) cupping the pM. The anterior limb does not enter the pM-bracket and the posterior limb curves behind the pM to enter the IHF www.ebook2book.ir | 24.07.19 - 07:11 Gross Anatomy, Cranial and Spine 67 1 should shouldrm trunk trunk neck head hip for wris d elbo hip elborm leg a ee arm er ea t er kn wri w w foot ha ers ha rs fin st fin th n nd g th ge um um b toes ankle ne b ey e ck no bro toes se genitals w eye fac face upper e lip Primary motor cortex Primary sensory cortex lips lips (pre-central gyrus) (post-central gyrus) jaw lower lip tongue teeth, gums swallowing tongue intra- abdominal central sulcus Fig. 1.3 Somatotopic organization of primary sensory and motor cortex. The labels are placed along a cross section of the brain taken through the motor and the sensory cortex indicated on the drawing of the brain shown below the slices. Fig. 1.4 Retouched axial FLAIR MRI with labels for gyri/sulci shown in the left hemisphere, and an unlabeled mirror image shown as the right hemisphere for reference. The in- verted blue Ω (omega) illustrates the hand “knob” (see text). See ▶ Table 1.1 and ▶ Table 1.2 for abbreviations. p prcs SFG PreCG “motor strip” cs Ω PostCG PL PM PM hand “knob” pocs www.ebook2book.ir | 24.07.19 - 07:11 68 Anatomy and Physiology Hand “knob”: The alpha motor neurons for hand function are located in the superior aspect of the pre- 1 central gyrus7 which appears as a knob-like protrusion (shaped like an inverted greek letter omega Ω) projecting posterolaterally into the central sulcus on axial imaging8 (▶ Fig. 1.4). On sagittal imaging it has a posteriorly projecting hook-like appearance and is even with the posterior limit of the Sylvian fissure.8 1.3 Surface anatomy of the cranium 1.3.1 Craniometric points See ▶ Fig. 1.5. Pterion: region where the following bones are approximated: frontal, parietal, temporal and sphenoid (greater wing). Estimated location: 2 finger-breadths above the zygomatic arch, and a thumb’s breadth behind the frontal process of the zygomatic bone (blue circle in ▶ Fig. 1.5). Asterion: junction of lambdoid, occipitomastoid and parietomastoid sutures. Usually lies within a few millimeters of the posterior-inferior edge of the junction of the transverse and sigmoid sinuses (not always reliable9—may overlie either sinus). Vertex: the topmost point of the skull. Lambda: junction of the lambdoid and sagittal sutures. Stephanion: junction of coronal suture and superior temporal line. vertex bregma PARIE TAL stephanion AL O NT pterion FR cs stl ophyron lambda sq glabella sp nasion sz TEMPORAL fn GWS fz ls rhinion ss pm nm L sm TA PI CI ZYG tz ID OC NASAL zm TO AS om M inion prosthion MA XILL A asterion inferior opisthion alveolar point LE IB M AND gonion gnathion or menton Fig. 1.5 Craniometric points & cranial sutures. Named bones appear in all upper case letters. The blue circle is the pterion. Abbreviations: GWS = greater wing of sphenoid bone; stl = superior temporal line; ZYG = zygomatic. For basion, see ▶ Fig. 12.1. Sutures: cs = coronal, fn = frontonasal, fz = frontozygomatic, ls = lambdoid, nm = nasomaxillary, om = occipitomas- toid, pm = parietomastoid, sm = squamomastoid, sp = sphenoparietal, sq = squamosal, ss = sphenosquamous, sz = sphenozygomatic, tz = temporozygomatic, zm = zygomaticomaxillary. www.ebook2book.ir | 24.07.19 - 07:11 Gross Anatomy, Cranial and Spine 69 Glabella: the most forward projecting point of the forehead at the level of the supraorbital ridge in the midline. 1 Opisthion: the posterior margin of the foramen magnum in the midline. Bregma: the junction of the coronal and sagittal sutures. Sagittal suture: midline suture from coronal suture to lambdoid suture. Although often assumed to overlie the superior sagittal sinus (SSS), the SSS lies to the right of the sagittal suture in the major- ity of specimens10 (but never by > 11 mm). The most anterior mastoid point lies just in front of the sigmoid sinus.11 1.3.2 Relation of skull markings to cerebral anatomy Taylor-Haughton lines Taylor-Haughton (T-H) lines can be constructed on an angiogram, CT/MRI scout film, or skull X-ray. They can be constructed on the patient in the O.R. based on visible external landmarks.12 T-H lines are shown as dashed lines in ▶ Fig. 1.6. 1. Frankfurt plane, AKA baseline: line from inferior margin of orbit through the upper margin of the external auditory meatus (EAM) (as distinguished from Reid’s base line: from inferior orbital margin through the center of the EAM)13 (p 313) 2 cm 1/2 N-I 3/4 N-I s cu ul l s tra cen re su ©2001 Mark S fis Greenberg, M.D. n N ia lv Sy I EAM Frankfurt plane posterior ear line condylar line Fig. 1.6 Taylor-Haughton lines and other localizing methods. N = nasion. I = inion. www.ebook2book.ir | 24.07.19 - 07:11 70 Anatomy and Physiology 2. the distance from the nasion to the inion is measured across the top of the calvaria and is divided 1 into quarters (can be done simply with a piece of tape which is then folded in half twice) 3. posterior ear line: perpendicular to the baseline through the mastoid process 4. condylar line: perpendicular to the baseline through the mandibular condyle 5. T-H lines (p. 69) can then be used to approximate the Sylvian fissure (see below) and the motor cortex Motor cortex Numerous methods utilize external landmarks to locate the motor strip (pre-central gyrus) or the central sulcus (Rolandic fissure) which separates motor strip anteriorly from primary sensory cortex posteriorly. These are just approximations since individual variability causes the motor strip to lie anywhere from 4 to 5.4 cm behind the coronal suture.14 The central sulcus cannot even be reliably identified visually at surgery.15 1. method 1: the superior aspect of the motor cortex is almost straight up from the EAM near the midline 2. method 216: the central sulcus is approximated by connecting: a) the point 2 cm posterior to the midposition of the arc extending from nasion to inion (illus- trated in ▶ Fig. 1.6), to b) the point 5 cm straight up from the EAM 3. method 3: using T-H lines, the central sulcus is approximated by connecting: a) the point where the “posterior ear line” intersects the circumference of the skull (▶ Fig. 1.6; usually about 1 cm behind the vertex, and 3–4 cm behind the coronal suture), to b) the point where the “condylar line” intersects the line representing the Sylvian fissure 4. method 4: a line drawn 45° to Reid’s base line starting at the pterion points in the direction of the motor strip17 (p 584–5) Sylvian fissure AKA lateral fissure On the skin surface: 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). On the skull (once it is exposed in surgery): the anterior portion of the Sylvian fissure follows the squamosal suture (▶ Fig. 1.7)18 and then deviates superiorly to terminate at Chater’s point, which is located 6 cm above the EAM on a line perpendicular to the orbitomeatal line; it is also ≈ 1.5 cm above the squamosal suture along the same perpendicular line. A 4 cm craniotomy centered at Chater’s point provides access to potential recipient vessels in the angular gyrus for EC/IC bypass surgery.19,20 Angular gyrus Located just above the pinna, important on the dominant hemisphere as part of Wernicke’s area (p. 98). Note: there is significant individual variability in the location.21 1.3.3 Relationship of ventricles to skull ▶ Fig. 1.8 shows the relationship of non-hydrocephalic ventricles to the skull in the lateral view. Some dimensions of interest are shown in ▶ Table 1.3.22 In the non-hydrocephalic adult, the lateral ventricles lie 4–5 cm below the outer skull surface. The center of the body of the lateral ventricle sits in the midpupillary line, and the frontal horn is inter- sected by a line passing perpendicular to the calvaria along this line.23 The anterior horns extend 1–2 cm anterior to the coronal suture. Average length of third ventricle ≈ 2.8 cm. The midpoint of Twining’s line ( in ▶ Fig. 1.8) should lie within the 4th ventricle. 1.4 Surface landmarks of spine levels Estimates of cervical levels for anterior cervical spine surgery may be made using the landmarks shown in ▶ Table 1.4. Intraoperative C-spine X-rays are essential to verify these estimates. The scapular spine is located at about T2–3. The inferior scapular pole is ≈ T6 posteriorly. Intercristal line: a line drawn between the highest point of the iliac crests across the back will cross the midline either at the interspace between the L4 and L5 spinous processes, or at the L4 spi- nous process itself. www.ebook2book.ir | 24.07.19 - 07:11 Gross Anatomy, Cranial and Spine 71 1 Sylvian fissure Chater’s point 1.5 cm sq 6 cm OM line EAM Fig. 1.7 Relationship of the Sylvian fissure to the squamosal suture and Chater’s point. Abbreviations: EAM = external auditory meatus; sq = squamosal suture; OM line = orbitomeatal line (a line used in CT scanning that connects the lateral canthus to the midpoint of the EAM). The dashed black line is perpendicular to the OM line. The red circle indicates Chater’s point. The Sylvian fissure is highlighted by the broken yellow line and is situated under the anterior squamosal suture. 1.5 Cranial foramina and their contents 1.5.1 Summary See ▶ Table 1.5. 1.5.2 Porus acusticus AKA internal auditory canal (▶ Fig. 1.9). The filaments of the acoustic portion of VIII penetrate tiny openings of the lamina cribrosa of the cochlear area.25 Transverse crest: separates superior vestibular area and facial canal (above) from the inferior ves- tibular area and cochlear area (see below).25 Vertical crest (AKA Bill’s bar—named after Dr. William House): separates the meatus to the facial canal anteriorly (containing VII and nervus intermedius) from the vestibular area posteriorly (con- taining the superior division of vestibular nerve). Bill’s bar is deeper in the IAC than the transverse crest. The “5 nerves” of the IAC: 1. facial nerve (VII) (mnemonic: “7-up” as VII is in superior portion) 2. nervus intermedius: the somatic sensory branch of the facial nerve primarily innervating mecha- noreceptors of the hair follicles on the inner surface of the pinna and deep mechanoreceptors of nasal and buccal cavities and chemoreceptors in the taste buds on the anterior 2/3 of the tongue 3. acoustic portion of the VIII nerve (mnemonic: “Coke down” for cochlear portion) 4. superior branch of vestibular nerve: passes through the superior vestibular area to terminate in the utricle and in the ampullæ of the superior and lateral semicircular canals (mnemonic superior = LSU (Lateral & Superior semicircular canals and the Utricule)) 5. inferior branch of vestibular nerve: passes through inferior vestibular area to terminate in the saccule www.ebook2book.ir | 24.07.19 - 07:11 72 Anatomy and Physiology 1 cs B D1 FM F A O V3 Aq T Twining D2 D3 V4 D4 opisthion baseline sigmoid sinus sella turcica Fig. 1.8 Relationship of ventricles to skull landmarks. Abbreviations: (F = frontal horn, B = body, A = atrium, O = occipital horn, T = temporal horn) of lateral ventricle. FM = foramen of Monro. Aq = Sylvian aqueduct. V3 = third ventricle. V4 = fourth ventricle. cs = coronal suture. Di- mensions D1–4 see ▶ Table 1.3. Table 1.3 Dimensions from ▶ Fig. 1.8 Dimension Description Lower limit Average Upper (▶ Fig. 1.8) (mm) (mm) limit (mm) D1 length of frontal horn anterior to FM 25 D2 distance from clivus to floor of 4th ventricle at level 33.3 36.1 40.0 of fastigiuma D3 length of 4th ventricle at level of fastigiuma 10.0 14.6 19.0 D4 distance from fastigiuma to opisthion 30.0 32.6 40.0 afastigium: the apex of the 4th ventricle within the cerebellum www.ebook2book.ir | 24.07.19 - 07:11 Gross Anatomy, Cranial and Spine 73 Table 1.4 Cervical levels24 Level Landmark 1 C1–2 angle of mandible C3–4 1 cm above thyroid cartilage (≈ hyoid bone) C4–5 level of thyroid cartilage C5–6 crico-thyroid membrane C6 carotid tubercle C6–7 cricoid cartilage Table 1.5 Cranial foramina and their contentsa Foramen Contents nasal slits anterior ethmoidal nn., a. & v. superior orbital fissure Cr. Nn. III, IV, VI, all 3 branches of V1 (ophthalmic division divides into nasociliary, frontal, and lacrimal nerves); superior ophthalmic vv.; recurrent meningeal br. from lacrimal a.; orbital branch of middle meningeal a.; sympathetic filaments from ICA plexus inferior orbital fissure Cr. N. V-2 (maxillary div.), zygomatic n.; filaments from pterygopalatine branch of maxillary n.; infraorbital a. & v.; v. between inferior ophthalmic v. & pterygoid venous plexus foramen lacerum usually nothing (ICA traverses the upper portion but doesn’t enter, 30% have vidian a.) carotid canal internal carotid a., ascending sympathetic nerves incisive foramen descending septal a.; nasopalatine nn. greater palatine foramen greater palatine n., a., & v. lesser palatine foramen lesser palatine nn. internal acoustic meatus Cr. N. VII (facial); Cr. N. VIII (stato-acoustic)—see text & ▶ Fig. 1.9 hypoglossal canal Cr. N. XII (hypoglossal); a meningeal branch of the ascending pharyngeal a. foramen magnum spinal cord (medulla oblongata); Cr. N. XI (spinal accessory nn.) entering the skull; vertebral aa.; anterior & posterior spinal arteries foramen cecum occasional small vein cribriform plate olfactory nn. optic canal Cr. N. II (optic); ophthalmic a. foramen rotundum Cr. N. V2 (maxillary div.), a. of foramen rotundum foramen ovale Cr. N. V3 (mandibular div.) + portio minor (motor for Cr. N. V) foramen spinosum middle meningeal a. & v. jugular foramen internal jugular v. (beginning); Cr. Nn. IX, X, XI stylomastoid foramen Cr. N. VII (facial); stylomastoid a. condyloid foramen v. from transverse sinus mastoid foramen v. to mastoid sinus; branch of occipital a. to dura mater aAbbreviations: a. = artery, aa. = arteries, v. = vein, vv. = veins, n. = nerve, nn. = nerves, br. = branch, Cr. N. = cranial nerve, fmn. = foramen, div. = division 1.6 Internal capsule 1.6.1 Architectural anatomy For a schematic diagram, see ▶ Fig. 1.10; ▶ Table 1.6 delineates the thalamic subradiations. Most IC lesions are caused by vascular accidents (thrombosis or hemorrhage). 1.6.2 Vascular supply of the internal capsule (IC) 1. anterior choroidal: ⇒ all of retrolenticular part (includes optic radiation) and ventral part of pos- terior limb of IC www.ebook2book.ir | 24.07.19 - 07:11 74 Anatomy and Physiology 1 facial canal (Cr. N. VII with NI*) Fig. 1.9 Right internal auditory canal (porus acusticus) & nerves. Abbreviations: Cr. N. = cranial nerve; vertical crest (“Bill’s bar”) NI = nervus intermedius. superior vestibular area (superior (to utricle & superior & vestibular lateral semicircular canals) nerve) transverse crest (crista falciformis) inferior vestibular area (to saccule) (inferior vestibular foramen singulare (to nerve) posterior semicircular canal) cochlear area (acoustic portion of Cr. N. VIII) lateral ventricle head of caudate }INTERNAL - genu CAPSULE frontopontine tract INTERNAL CAPSULE - anterior limb corticobulbar tract } } (A) anterior thalamic radiation face } shoulder (B) arm hand superior thalamic trunk radiation hip } foot (C) putamen posterior thalamic globus pallidus radiation } corticorubral tract (D) corticospinal tract auditory radiation INTERNAL CAPSULE - posterior limb } optic radiation thalamus lateral geniculate body ascending thalamocortical fibers medial geniculate body descending corticofugal fibers third ventricle Fig. 1.10 Internal capsule schematic diagram (left side shows tracts, right side shows radiations). 2. lateral striate branches (AKA capsular branches) of middle cerebral artery: ⇒ most of anterior AND posterior limbs of IC 3. genu usually receives some direct branches of the internal carotid artery 1.7 Cerebellopontine angle anatomy For normal anatomy of right cerebellopontine angle, see ▶ Fig. 1.11. 1.8 Occipitoatlantoaxial-complex anatomy ▶ Ligaments of the occipitoatlantoaxial complex. Stability of the occipitoatlantal joint is primarily due to ligaments, with little contribution from bony articulations and joint capsules (see ▶ Fig. 1.12, ▶ Fig. 1.13, ▶ Fig. 1.14): www.ebook2book.ir | 24.07.19 - 07:11 Gross Anatomy, Cranial and Spine 75 Table 1.6 Four thalamic “subradiations” (AKA thalamic peduncles), labeled A-D in ▶ Fig. 1.10 Radiation Connection Comments 1 anterior medial & anterior ↔ frontal lobe (A) thalamic nucleus superior rolandic areas ↔ ventral thalamic nuclei general sensory fibers from (B) body & head to terminate in postcentral gyrus (areas 3,1,2) posterior occipital & posterior ↔ caudal thalamus (C) parietal inferior transverse temporal ↔ MGB (small) includes auditory (D) gyrus of Heschl radiation retractor Fig. 1.11 Normal anatomy of right on cerebellar cerebellopontine angle viewed from hemisphere V behind (as in a suboccipital approach).25 Meckel's foramen of cave Luschka pons flocculus choroid plexus VII IAC VIII IX foramen of jugular Magendie foramen X cerebellar XI tonsil XII PICA olive medulla 1. ligaments that connect the atlas to the occiput: a) anterior atlantooccipital membrane: cephalad extension of the anterior longitudinal ligament. Extends from anterior margin of foramen magnum (FM) to anterior arch of C1 b) posterior atlantooccipital membrane: connects the posterior margin of the FM to posterior arch of C1 c) the ascending band of the cruciate ligament 2. ligaments that connect the axis (viz. the odontoid) to the occiput: a) tectorial membrane: some authors distinguish 2 components superficial component: cephalad continuation of the posterior longitudinal ligament. A strong band connecting the dorsal surface of the dens to the ventral surface of the FM above, and dorsal surface of C2 & C3 bodies below accessory (deep) portion: located laterally, connects C2 to occipital condyles b) alar (“check”) ligaments26 occipito-alar portion: connects side of the dens to occipital condyle atlanto-alar portion: connects side of the dens to the lateral mass of C1 c) apical odontoid ligament: connects tip of dens to the FM. Little mechanical strength 3. ligaments that connect the axis to the atlas: a) transverse atlantal ligament (TAL) or (usually) just transverse ligament: the horizontal com- ponent of the cruciate ligament. Attaches at the medial tubercles of C1. Traps the dens against the anterior atlas via a strap-like mechanism (▶ Fig. 1.14). Provides the majority of the strength (“the strongest ligament of the spine”27) b) atlanto-alar portion of the alar ligaments (see above) c) descending band of the cruciate ligament www.ebook2book.ir | 24.07.19 - 07:11 76 Anatomy and Physiology 1 apical odontoid ligament cruciate ligament, ascending band anterior atlantooccipital membrane posterior C1 atlantooccipital transverse anterior membrane ligament longitudinal ligament ligamentum flavum cruciate ligament, descending band C2 spinal tectorial cord membrane posterior C3 longitudinal ligament Fig. 1.12 Dorsal view of the cruciate and alar ligaments. Viewed with tectorial membrane removed. (Modified with permission from “In Vitro Cervical Spine Biomechanical Testing” BNI Quarterly, Vol. 9, No. 4, 1993.) ascending clivus band right alar ligament accessory (deep) portion of tectorial C1 membrane transverse CRUCIATE band LIGAMENT descending C2 band Fig. 1.13 Sagittal view of the ligaments of the craniovertebral junction. (Modified with permission from “In Vitro Cervical Spine Biomechanical Testing” BNI Quarterly, Vol. 9, No. 4, 1993.) www.ebook2book.ir | 24.07.19 - 07:11 Gross Anatomy, Cranial and Spine 77 anterior anterior 1 tubercle arch right alar odontoid ligament process (C2) transverse (atlantal) ligament (TAL) ss ma teral transverse la process foramen medial transversarium tubercles tectorial superior membrane articular facet posterior arch posterior tubercle Fig. 1.14 C1 viewed from above, showing the transverse and alar ligaments, and the critially important transverse atlantal ligament (TAL) AKA transverse ligament. (Modified with permission from “In Vitro Cervical Spine Biomechanical Testing” BNI Quarterly, Vol. 9, No. 4, 1993.) The most important structures in maintaining atlantooccipital stability are the tectorial membrane and the alar ligaments. Without these, the remaining cruciate ligament and apical dentate ligament are insufficient. 1.9 Spinal cord anatomy 1.9.1 Dentate Ligament The dentate ligament separates dorsal from ventral nerve roots in the spinal nerves. The spinal accessory nerve (Cr. N. XI) is dorsal to the dentate ligament. 1.9.2 Spinal cord tracts Anatomy ▶ Fig. 1.15 depicts a cross-section of a typical spinal cord segment, combining some elements from different levels (e.g. the intermediolateral gray nucleus is only present from T1 to ≈ L1 or L2 where there are sympathetic (thoracolumbar outflow) nuclei). It is schematically divided into ascending and descending halves; however, in actuality, ascending and descending paths coexist on both sides. ▶ Fig. 1.15 also depicts some of the laminae according to the scheme of Rexed. Lamina II is equiv- alent to the substantia gelatinosa. Laminae III and IV are the nucleus proprius. Lamina VI is located in the base of the posterior horn. Sensation Pain and temperature: body Receptors: free nerve endings (probable). 1st order neuron: small, finely myelinated afferents; soma in dorsal root ganglion (no synapse). Enter cord at dorsolateral tract (zone of Lissauer). Synapse: substantia gelatinosa (Rexed II). www.ebook2book.ir | 24.07.19 - 07:11 78 Anatomy and Physiology 1 S = sacral T = thoracic MOTOR bi-directional SENSORY (descending paths C = cervical (ascending paths) paths) { { { 7 8 9 10 intermediolateral 6 S TC I gray nucleus (sympathetic) III II IV V 11 5 STC VI 12 VII X VIII IX IX CTS dentate ligament 4 13 3 14 2 15 cm 1 2.5-4 anterior spinal anterior motor artery nerve root Fig. 1.15 Schematic cross-section of cervical spinal cord. See ▶ Table 1.7, ▶ Table 1.8 and ▶ Table 1.9 for path names. Table 1.7 Descending (motor) tracts (↓) in ▶ Fig. 1.15 Number Path Function Side of (▶ Fig. 1.15) body 1 anterior corticospinal tract skilled movementa opposite 2 medial longitudinal fasciculus ? same 3 vestibulospinal tract facilitates extensor muscle tone same 4 medullary (ventrolateral) reticulospinal tract automatic respirations? same 5 rubrospinal tract flexor muscle tone same 6 lateral corticospinal (pyramidal) tract skilled movement same aThe terminal fibers of this uncrossed tract usually cross in the anterior white commissure to synapse on alpha motor neurons or on internuncial neurons. A minority of the fibers do remain ipsilateral. Also, the anterior corticospinal tract is easily identified only in the cervical and upper thoracic regions. www.ebook2book.ir | 24.07.19 - 07:11 Gross Anatomy, Cranial and Spine 79 Table 1.8 Bi-directional tracts in ▶ Fig. 1.15 Number (▶ Fig. 1.15) Path Function 1 7 dorsolateral fasciculus (of Lissauer) ? 8 fasciculus proprius short spinospinal connections Table 1.9 Ascending (sensory) tracts (↑) in ▶ Fig. 1.15 Number Path Function Side of body (▶ Fig. 1.15) 9 fasciculus gracilis joint position, fine touch, same 10 fasciculus cuneatus vibration 11 posterior spinocerebellar tract stretch receptors same 12 lateral spinothalamic tract pain & temperature opposite 13 anterior spinocerebellar tract whole limb position opposite 14 spinotectal tract unknown, ? nociceptive opposite 15 anterior spinothalamic tract light touch opposite 2nd order neuron: axons cross obliquely in the anterior white commissure ascending ≈ 1–3 segments while crossing to enter the lateral spinothalamic tract. Synapse: VPL thalamus. 3rd order neurons pass through IC to postcentral gyrus (Brodmann’s areas 3, 1, 2). Fine touch, deep pressure and proprioception: body Fine touch AKA discriminative touch. Receptors: Meissner’s & pacinian corpuscles, Merkel’s discs, free nerve endings. 1st order neuron: heavily myelinated afferents; soma in dorsal root ganglion (no synapse). Short branches synapse in nucleus proprius (Rexed III & IV) of posterior gray; long fibers enter the ipsilat- eral posterior columns without synapsing (below T6: fasciculus gracilis; above T6: fasciculus cuneatus). Synapse: nucleus gracilis/cuneatus (respectively), just above pyramidal decussation. 2nd order neuron axons form internal arcuate fibers, decussate in lower medulla as medial lemniscus. Synapse: VPL thalamus. 3rd order neurons pass through IC primarily to postcentral gyrus. Light (crude) touch: body Receptors: as fine touch (see above), also peritrichial arborizations. 1st order neuron: large, heavily myelinated afferents (Type II); soma in dorsal root ganglion (no synapse). Some ascend uncrossed in posterior columns (with fine touch); most synapse in Rexed VI & VII. 2nd order neuron: axons cross in anterior white commissure (a few don’t cross); enter anterior spinothalamic tract. Synapse: VPL thalamus. 3rd order neurons pass through IC primarily to postcentral gyrus. 1.9.3 Dermatomes and sensory nerves Dermatomes are areas of the body where sensation is subserved by a single nerve root. Peripheral nerves generally receive contributions from more than one dermatome. Lesions in peripheral nerves and lesions in nerve roots may sometimes be distinguished in part by the pattern of sensory loss. A classic example is splitting of the ring finger in median nerve or ulnar nerve lesions, which does not occur in C8 nerve root injuries. ▶ Fig. 1.16 shows anterior and posterior view, each schematically separated into sensory derma- tomes (segmental) and peripheral sensory nerve distribution. www.ebook2book.ir | 24.07.19 - 07:11 80 Anatomy and Physiology 1 ANTERIOR POSTERIOR { V1 trigeminal V2 C2 nerve V3 superior clavicular occipitals C2 C3 C3 INTERCOSTALS posterior C4 C4 T2 T3 lateral C5 T4 medial T4 C5 axillary T6 T6 T2 RADIAL T8 T2 T8 post. cutaneous T10 T1 dorsal cutan. T12 0 T1 T1 musculocutan. T1 C6 C6 2 medial cutan. S5 L1 clunials S4 radial S3 C8 C8 L2 ilio- median L3 L4 inguinal L3 ulnar S1 C7 lateral cutan. FEMORAL posterior C7 nerve of thigh anterior cutaneous L4 cutaneous saphenous L5 L5 SCIATIC L4 COMMON PERONEAL lat. cutan. sup. peroneal deep peroneal TIBIAL sural S1 S1 plantars { lateral medial DERMATOMES CUTANEOUS DERMATOMES (anterior) NERVES (posterior) Fig. 1.16 Dermatomal and sensory nerve distribution. (Redrawn from “Introduction to Basic Neurology,” by Harry D. Patton, John W. Sundsten, Wayne E. Crill and Phillip D. Swanson, © 1976, pp 173, W. B. Saunders Co., Philadelphia, PA, with permission.) References Naidich TP. MR Imaging of Brain Surface Anatomy. in axial computed tomography sections. Int J Neuroradiology. 1991; 33:S95–S99 Neuroradiol. 1998; 4:105–111 Naidich TP, Brightbill TC. The pars marginalis, I: A Penfield W, Boldrey E. Somatic motor and sensory "bracket" sign for the central sulcus in axial plane representation in the cerebral cortex of man as CT and MRI. Int J Neuroradiol. 1996; 2:3–19 studied by electrical stimulation. Brain. 1937; 60: Talairach J, Tournoux P, Talairach J, et al. Practical 389–443 examples for the use of the atlas in neuroradiogic Yousry TA, Schmid UD, Alkadhi H, et al. Localization examinations. In: Co-planar stereotactic atlas of the of the motor hand area to a knob on the precentral human brain. New Tork: Thieme Medical Publishers, gyrus. A new landmark. Brain. 1997; 120 (Pt 1): Inc.; 1988:19–36 141–157 Schaltenbrand G, Bailey P. Introduction to Day JD, Tschabitscher M. Anatomic position of the Stereotaxis with an Atlas of Human Brain. Stuttgart asterion. Neurosurgery. 1998; 42:198–199 1959 Tubbs RS, Salter G, Elton S, et al. Sagittal suture as Weiss KL, Pan H, Storrs J, et al. Clinical brain MR an external landmark for the superior sagittal sinus. imaging prescriptions in Talairach space: technolo- J Neurosurg. 2001; 94:985–987 gist- and computer-driven methods. AJNR Am J Barnett SL, D'Ambrosio AL, Agazzi S, et al. Petroclival Neuroradiol. 2003; 24:922–929 and Upper Clival Meningiomas III: Combined Valente M, Naidich TP, Abrams KJ, et al. Differentiating Anterior and Posterior Approach. In: Meningiomas. the pars marginalis from the parieto-occipital sulcus London: Springer-Verlag; 2009:425–432 www.ebook2book.ir | 24.07.19 - 07:11 Gross Anatomy, Cranial and Spine 81 Willis WD, Grossman RG. The Brain and Its Ojemann G, Ojemann J, Lettich E, et al. Cortical Environment. In: Medical Neurobiology. 3rd ed. St. Language Localization in Left, Dominant Hemisphere. Louis: C V Mosby; 1981:192–193 An Electrical Stimulation Mapping Investigation in 117 1 Warwick R, Williams PL. Gray's Anatomy. Philadelphia Patients. J Neurosurg. 1989; 71:316–326 1973 Lusted LB, Keats TE. Atlas of Roentgenographic Kido DK, LeMay M, Levinson AW, et al. Computed Measurement. 3rd ed. Chicago: Year Book Medical tomographic localization of the precentral gyrus. Publishers; 1972 Radiology. 1980; 135:373–377 Ghajar JBG. A Guide for Ventricular Catheter Martin N, Grafton S, Viñuela F, et al. Imaging Placement: Technical Note. J Neurosurg. 1985; 63: Techniques for Cortical Functional Localization. Clin 985–986 Neurosurg. 1990; 38:132–165 Watkins RG. Anterior Cervical Approaches to the Anderson JE. Grant's Atlas of Anatomy. Baltimore: Spine. In: Surgical Approaches to the Spine. New Williams and Wilkins; 1978; 7 York: Springer-Verlag; 1983:1–6 Wilkins RH, Rengachary SS. Neurosurgery. New Rhoton AL,Jr. The cerebellopontine angle and poste- York 1985 rior fossa cranial nerves by the retrosigmoid Rahmah NN, Murata T, Yako T, et al. Correlation approach. Neurosurgery. 2000; 47:S93–129 between squamous suture and sylvian fissure: Dvorak J, Panjabi MM. Functional Anatomy of the OSIRIX DICOM viewer study. PLoS One. 2011; 6. Alar Ligaments. Spine. 1987; 12:183–189 DOI: 10.1371/journal.pone.0018199 Dickman CA, Crawford NR, Brantley AGU, et al. In Chater N, Spetzler R, Tonnemacher K, et al. Micro- vitro cervical spine biomechanical testing. BNI vascular bypass surgery. Part 1: anatomical studies. Quarterly. 1993; 9:17–26 J Neurosurg. 1976; 44:712–714 Spetzler R, Chater N. Microvascular bypass surgery. Part 2: physiological studies. J Neurosurg. 1976; 45: 508–513 www.ebook2book.ir | 24.07.19 - 07:11 82 Anatomy and Physiology 2 Vascular Anatomy 2 2.1 Cerebral vascular territories ▶ Fig. 2.1 depicts approximate vascular distributions of the major cerebral arteries. There is consid- erable variability of the major arteries1 as well as the central distribution. The lenticulostriates may originate from different segments of the middle or anterior cerebral artery. Recurrent artery of Heubner (RAH) (AKA medial striate artery) origin: junction of the ACA and a-comm in 62.3%, proxi- mal A2 in 23.3%, A1 in 14.3%.2 2.2 Cerebral arterial anatomy 2.2.1 General information The symbol “⇒” is used to denote a region supplied by the indicated artery. See Angiography (cere- bral) (p. 251) for angiographic diagrams of the following anatomy. 2.2.2 Circle of Willis See ▶ Fig. 2.2. A balanced configuration of the Circle of Willis is present in only 18% of the popula- tion. Hypoplasia of 1 or both p-comms occurs in 22–32%, absent or hypoplastic A1 segments occur in 25%. Key point: the anterior cerebral arteries pass over the superior surface of the optic chiasm. 2.2.3 Anatomical segments of intracranial cerebral arteries 1. carotid artery: see below for segments 2. anterior cerebral3: a) A1 (precommunicating): ACA from origin to ACoA b) A2 (postcommunicating): ACA from ACoA to branch-point of callosomarginal CORONAL VIEW AXIAL VIEW anterior cerebral artery middle cerebral artery RAH MCA AChA internal carotid anterior choroidal artery PCommA basilar artery posterior cerebral artery Fig. 2.1 Vascular territories of the cerebral hemispheres. RAH = recurrent artery of Heubner. www.ebook2book.ir | 24.07.19 - 07:11 Vascular Anatomy 83 optic n. (Cr. N. II) central retinal a. ACAs 2 a-comm a. (hidden) ophthalmic a. pituitary ICA superior hypophyseal a. MCA p-comm a. medial & lateral lenticulostriate aa. P2 P1 anterior choroidal a. PCA oculomotor n. choroid plexus (Cr. N. III) SCA { pons pontine aa. AICA basilar a. vertebral a. PICA anterior spinal a. Fig. 2.2 Circle of Willis viewed anterior and inferior to the brain. c) A3 (precallosal): from branch-point of callosomarginal curving around the genu of the corpus callosum to superior surface of corpus callosum 3 cm posterior to the genu d) A4: (supracallosal) e) A5: terminal branch (postcallosal) 3. middle cerebral4: a) M1: MCA from origin to bifurcation (horizontal segment on AP angiogram). A classical bifur- cation into relatively symmetrical superior and inferior trunks is seen in 50%, no bifurcation occurs in 2%, 25% have a very proximal branch (middle trunk) arising from the superior (15%) or the inferior (10%) trunk creating a “pseudo-trifurcation”, a pseudo-tetrafurcation occurs in 5% lateral fronto-orbital and prefrontal branches arise from M1 or superior M2 trunk www.ebook2book.ir | 24.07.19 - 07:11 84 Anatomy and Physiology precentral, central, anterior and posterior parietal arteries arise from a superior (60%), mid- dle (25%), or inferior (15%) trunk the superior M2 trunk does not give any branches to the temporal lobe b) M2: MCA trunks from bifurcation to emergence from Sylvian fissure 2 c) M3–4: distal branches d) M5: terminal branch 4. posterior cerebral (PCA) (several nomenclature schemes exist3,5): a) P1: PCA from the origin to posterior communicating artery (AKA mesencephalic, precommu- nicating, circular, peduncular, basilar…). The long and short circumflex and thalamoperforat- ing arteries arise from P1 b) P2: PCA from origin of p-comm to the origin of inferior temporal arteries (AKA ambient, post- communicating, perimesencephalic), P2 traverses the ambient cistern, hippocampal, anterior temporal, peduncular perforating, and medial posterior choroidal arteries arise from P2 c) P3: PCA from the origin of the inferior temporal branches to the origin of the terminal branches (AKA quadrigeminal segment). P3 traverses the quadrigeminal cistern d) P4: segment after the origin of the parieto-occipital and calcarine arteries, includes the corti- cal branches of the PCA 2.2.4 Anterior circulation Anatomic variants Bovine circulation: the common carotids arise from a common trunk off the aorta. External carotid 1. superior thyroid a.: 1st anterior branch 2. ascending pharyngeal a. a) neuromeningeal trunk of the ascending pharyngeal a.: supplies IX, X & XI (important when embolizing glomus tumors, 20% of lower cranial nerve palsy if this branch is occluded) b) pharyngeal branch: usually the primary feeder for jugular foramen tumors (essentially the only cause of hypertrophy of the ascending pharyngeal a.) 3. lingual a. 4. facial a.: branches anastamose with ophthalmic a.; important in collateral flow with ICA occlu- sion (p. 1331) 5. occipital a. ⇒ posterior scalp 6. posterior auricular 7. superficial temporal a) frontal branch b) parietal branch 8. (internal) maxillary a.—initially within parotid gland a) middle meningeal a. anterior branch posterior branch b) accessory meningeal c) inferior alveolar d) infra-orbital e) others: distal branches of which may anastomose with branches of ophthalmic artery in the orbit Internal carotid artery (ICA) Lies posterior & medial to the external carotid (ECA). Segments of the ICA and its branches See ▶ Fig. 2.3 for angiographic appearance, and ▶ Fig. 2.46 for anatomic illustration. 1. C1 (cervical): begins in the neck at the carotid bifurcation where the common carotid artery divides into internal and external carotid arteries. Encircled with postganglionic sympathetic nerves (PGSN), the ICA travels in the carotid sheath with the IJV and vagal nerve. C1 ends where the ICA enters the carotid canal of the petrous bone. No branches 2. C2 (petrous): still surrounded by PGSNs. Ends at the posterior edge of the foramen lacerum (f- Lac) (inferomedial to the edge of the Gasserian ganglion in Meckel’s cave). Three subdivisions: www.ebook2book.ir | 24.07.19 - 07:26 Vascular Anatomy 85 2 Fig. 2.3 Internal carotid arteriogram (AP view). ACom: anterior communicating artery CM: callosomarginal artery FP: frontopolar artery LS: lenticulostriate arteries OF: orbitofrontal artery PCal: pericallosal artery PCom: posterior communicating artery RH: recurrent artery of Heubner (Reprinted courtesy of Eastman Kodak Company) a) vertical segment: ICA ascends then bends as the… b) posterior loop: anterior to the cochlea, bends antero-medially becoming the… c) horizontal segment: deep and medial to the greater and lesser superficial petrosal nerves, anterior to the tympanic membrane (TM) 3. C3 (lacerum): the ICA passes over (but not through) the foramen lacerum (f-Lac) forming the lat- eral loop. Ascends in the canalicular portion of the f-Lac to the juxtasellar position, piercing the dura as it passes the petrolingual ligament to become the cavernous segment. Branches (usually not visible angiographically): a) caroticotympanic (inconsistent) ⇒ tympanic cavity b) pterygoid (vidian) branch: passes through the f-Lac, present in only 30%, may continue as the artery of the pterygoid canal 4. C4 (cavernous): covered by a vascular membrane lining the sinus, still surrounded by PGSNs. Passes anteriorly then supero-medially, bends posteriorly (medial loop of ICA), travels horizon- tally, and bends anteriorly (part of anterior loop of ICA) to the anterior clinoid process. Ends at the proximal dural ring (incompletely encircles ICA). Many branches, main ones include: a) meningohypophyseal trunk (MHT) (largest & most proximal). 2 causes of a prominent MHT: (1) tumor (usually petroclival meningioma—see below), (2) dural AVM (p. 1316). Branches: a. of tentorium (AKA artery of Bernasconi & Cassinari): the blood supply of petroclival meningiomas dorsal meningeal a. (AKA dorsal clival a.) www.ebook2book.ir | 05.08.19 - 19:41 86 Anatomy and Physiology ACA MCA Fig. 2.4 Segments of the internal caro