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

Apical Ligament

The apical ligament is a short ligament, attaching the vertex of the dens to the anterior edge of the foramen magnum.

Tectorial Membrane

This membrane lies posteriorly to the alar and apical ligaments. It is divided into a medial segment and two lateral segments.

The medial segment runs from the anterior edge of the foramen magnum to the body of C2 where it continues to the posterior longitudinal ligament of the spine.

The lateral segments (left and right), connect C2 with the occipital condyles.

Atlanto-Occipital Membrane

This membrane is composed of two segments:

•Anterior segment: Connects the anterior arch of C1 with the anterior edge of the foramen magnum. Considered to be an extension of the anterior longitudinal ligament of the spine.

•Posterior segment: Connects the posterior arch of C1 to the posterior edge of the foramen magnum. The posterior atlantooccipital membrane is traversed by the vertebral arteries after they exit the transverse foramen to enter the cranium via the foramen magnum. It is also the equivalent of the ligamentum flavum for the remaining segments of the spine.

Posterior Longitudinal

Like its anterior counterpart, this ligament runs over the posterior surface of the ­vertebral bodies from the internal aspect of the basilar segment of the occipital bone to the coccyx.

Supraspinous Ligament

This is a thick fibrous band attached to the vertex of the spinous processes throughout the entire length of the spine. At the cervical segment, this ligament turns into the ligamentum nuchae.

Interspinous Ligament

Differing from the previously described ligaments, the interspinous ligament has a segmental distribution, joining the space between spinous processes. It attaches superiorly at the inferior border of the overlying spinous process and inferiorly at the underlying spinous process. Posteriorly it attaches to the supraspinous ligament, whereas anteriorly it attaches to the ligamentum flavum.

Ligamentum Flavum

This ligament has two segments (left and right). Each are thick, short, strong, and elastic. They attach superiorly at the anterior segment of the lamina and inferiorly over the superior border of the underlying lamina.

4.7.3  Common Ligaments Anterior Longitudinal

This ligament runs anteriorly to the vertebral bodies of the spine from the basilar portion of the occipital bone, to the anterior segment of the second vertebra of the sacrum. ( Fig. 4.29)

4.8  Vascular Anatomy

4.8.1  Arterial Anatomy

The vascular supply of the intracranial CNS components is from branches and anastomoses of the carotid and vertebral arteries ( Fig. 4.30).

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Common Carotid Artery

The common carotid arteries (CCAs) differ in their origin. On the right side, the brachiocephalic trunk bifurcates into the right CCA and the right subclavian artery; on the left, it arises directly from the aortic arch.

Generally, both CCAs bifurcate into the external carotid artery (ECA) and internal carotid artery (ICA) 1 cm superior to the thyroid cartilage corresponding to the level of the 4th cervical vertebra (C4).4

External Carotid Artery

Collateral branches: These follow an ascending order of bifurcation ( Fig. 4.31):

• Superior thyroid artery.

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•Lingual artery.

•Ascending pharyngeal artery.

•Facial artery.

•Occipital artery.

•Posterior auricular artery.

•Parotid arteries.

Terminal branches: The ECA bifurcates into two terminal branches approximately 4 cm superior to the mandibular angle. These two terminal branches are:

1.Superficial temporal artery.

2.Maxillary artery: This artery gives off approximately 14 different branches (variable). Relevant are:

◦◦ Middle meningeal artery: Enters the skull via the foramen spinosum. Its trajectory along the internal surface of the squamous portion of the temporal bone makes it highly

­susceptible to bleeding after pterional trauma, which may result in epidural hematoma.

◦◦ Accessory meningeal artery: This artery is inconstant, entering the skull via the foramen ovale.

◦◦ Anterior and posterior deep temporal arteries supply the anterior and posterior portions of the temporal muscle.

Internal Carotid Artery

From the carotid bifurcation, the ICA travels directly into the cranial cavity via the carotid foramen before ending at the level of the optic nerve3( Fig. 4.32). For anatomical purposes, the ICA has been divided into seven segments:

•C1 or cervical segment: From the carotid bifurcation to the carotid foramen at the skull base, no branches originate from this segment.

•C2 or petrous segment: From the carotid foramen to the posterior edge of the foramen lacerum. The segment of the petrous bone where the ICA runs is known as the carotid canal. In this segment, it gives off the caroticotympanic artery.

Fig. 4.30  Coronal view of the arteries from the aortic arch, which supply the brain. (Reproduced from Meyers

S, Differential Diagnosis in Neuroimaging: Brain and Meninges, 1st edition, ©2016, Thieme Publishers, New York.)

•C3 or lacerum segment: Small segment where the ICA passes over the foramen lacerum.

•C4 or cavernous segment: From the foramen lacerum to the anterior clinoid process. Multiple branches originate from this segment:

◦Meningohypophyseal trunk: A surgically important branch giving off three arteries:

–Tentorial artery or Bernasconi and Cassinari artery.

–Dorsal meningeal artery.

–Inferior hypophyseal artery.

◦Inferolateral trunk.

◦Medial trunk or McConnell’s artery, goes to the capsule of the pituitary gland.

•C5 or clinoid segment: Between the proximal and distal dural rings.

•C6, ophthalmic segment: From the distal dural ring to the posterior communicating artery (P-Comm). Two important branches from this segment:

◦Ophthalmic artery.

◦Superior hypophyseal artery.

•C7 or communicating segment: From the P-Comm artery to the bifurcation of the ICA into anterior and middle

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cerebral artery. The branches of this segment are:

◦P-Comm.

◦Anterior choroidal artery (ACh).

Anterior Cerebral Artery

The anterior cerebral artery (ACA) arises from the ICA lateral to the optic chiasm, it supplies the medial surface of the cerebral hemisphere except for the medial occipital lobes ( Fig. 4.33). Grossly, the ACA can be divided into precommunicating and postcommunicating segments based upon their proximal and distal location to anterior communicating artery (ACoA). Another classification dividing the ACA into five segments follows5:

•A1 or precommunicating segment:

From the ICA bifurcation to the ACoA.

•A2: From the ACoA to the junction of the rostrum and genu of the corpus callosum. The recurrent artery of Heubner may arise either from A1, A2, or at the A1/A2 junction. The A2 segment commonly gives off the infraorbital artery and the frontopolar artery.6

•A3: This artery travels around the genu of the corpus callosum and continues to the A4 segment after turning sharply, posterior to the genu. The branches of the A3 segment are highly variable and include the callosomarginal artery which may give off three further arteries including anterior internal frontal artery, middle internal frontal

artery, and the posterior internal frontal artery.6 In some cases, these three arteries may arise directly from the

A3 segment. Additionally, the pericallosal artery may arise from the A3 segment or it could be a direct continuation of the ACA.

Fig. 4.32 Microsurgical anatomy of the internal carotid artery and ophthalmic artery. (a) Superior and

(b) leftlateralviewofthe internal carotid artery showing its segmental anatomy:

C1, cervical segment; C2, petrous segment; C3, lacerum segment; C4, cavernous segment; C5, clinoidal segment; C6, ophthalmic segment; and C7, communicating segment. Dolenc's loops of cavernous ICA are also shown: anterior loop, medial loop, lateral loop, and posterior loop. AChA, anterior choroidal artery; ACP, anterior clinoid process; OphA, ophthalmic artery; PCoA, posterior communicating artery; SHA, superior hypophyseal artery; Tent, tentorium. (Reproduced from

Lawton M, Seven Aneurysms:

Tenets and Techniques for

Clipping, 1st edition, ©2011,

Thieme Publishers, New York.)

•A4 and A5: Segments run over the body of the corpus callosum. These segments are themselves separated from each other by a vertical line running posterior to the coronal suture. The A4 segment gives off the paracentral lobular artery, whereas the A5

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segment gives off the superior internal parietal artery and the inferior internal parietal artery.6

Middle Cerebral Artery

The middle cerebral artery (MCA) arises from the ICA ( Fig. 4.34). Its branches terminate at the lateral surface of the cerebral hemispheres. For anatomical purposes, the MCA its divided into four segments7:

•M1 or sphenoidal, horizontal segment: From the origin of the MCA to the bifurcation of the MCA into a superior and inferior trunk. The lateral lenticulostriate arteries arise from this segment.

•M2 or insular segment: Runs in the depth of the Sylvian fissure from its bifurcation.

•M3 or opercular segment: From the depth of the Sylvian fissure on its posterior segment to the surface of the Sylvian fissure.

•M4 or cortical segment: Starts at the surface of the Sylvian fissure posteriorly and gives multiple branches which

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Fig. 4.33  Schematic representation of the relevant anatomy of the distal anterior cerebral artery and its surrounding structures. The most common sites for traumatic aneurysms are denoted (*). a., artery. (Reproduced from

Spetzler R, Kalani M, Nakaji P, Neurovascular Surgery,

2nd edition, ©2015, Thieme Publishers, New York.)

travel to the cortical surfaces of the hemispheres.

Vertebral Artery

The vertebral artery (VA) arises directly from the subclavian artery on each side from where it runs superiorly to enter the transverse foramen of C6 on its way to the posterior cranial cavity. The VA is divided into four segments:

•V1 or prevertebral: Goes from its origin at the subclavian artery to C6.

•V2 or vertebral segment: Runs within the transverse foramen from C6 to C2.

•V3 or extradural segment: From C2 to the foramen magnum.

•V4 or intradural: From its entry to the dura of the foramen magnum until its junction at the contralateral VA forming the basilar artery (BA).

Collateral Branches

•Anterior meningeal artery.

•Posterior meningeal artery.

•Posterior spinal artery.

•Anterior spinal artery, formed from two branches (left and right) originating from each of the VAs prior to their continuation as the single BA. This artery runs in the surface of the anterior median fissure.

•Posterior inferior cerebellar artery (PICA), supplies the posterolateral medulla, the 4th ventricle, and the posteroinferior cerebellar hemispheres.

Basilar Artery

The BA originates from the unison of the two VAs over the anterior brainstem surface ( Fig. 4.34). It runs over the anterior surface of the pons giving off numerous

CNIIItravelsoneithersideoftheSCAand posterior cerebral arteries.

collateral branches. It terminates at the level of the interpeduncular cistern, where it contributes to the posterior cerebral arteries. The branches of the BA are:

•Anterior inferior cerebellar artery.

•Labyrinthine artery.

•Pontine arteries.

•Superior cerebellar artery (SCA).

Posterior Cerebellar Artery

The posterior cerebellar artery (PCA) arises from the bifurcation of the BA at the ­interpeduncular cistern ( Fig. 4.34). It terminates at the medial surface of the occipital lobe. It is divided into four segments7:

•P1 or precommunicating segment: From the bifurcation of the BA to the junction of the P-Comm. This segment gives off multiple perforators to the thalamus, hypothalamus, subthalamus, and the anterolateral segment of the midbrain.

•P2 or ambient segment: From the junction of the P-Comm to the posterior edge of the midbrain. Some of the PCA branches at this segment are the lateral posterior choroidal artery and thalamogeniculate arteries.

•P3 or quadrigeminal segment: From the posterior edge of the midbrain to the anterior limit of the calcarine fissure. The branches of this segment supply the posteroinferior temporal lobe (posterior temporal artery), occipital lobe (parieto-occipital artery and calcarine artery) and the posterior segment of the corpus callosum (posterior pericallosal artery).

Circle of Willis

The ICA and vertebrobasilar arterial system are connected through a polygon located between the interpeduncular

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fossa, mammillary bodies, infundibulum and optic chiasm ( Fig. 4.35). This arterial polygon (which is complete in approximately 20% of the population)2 is formed by the anastomoses of the tip of the BA, PCA (P1), and P-Comm posterolaterally, and the ICA, ACA (A1), and ACoA anterolaterally. The circle of Willis gives off multiple penetrating arteries to anatomical structures within its vicinity.

4.8.2  Venous Anatomy

Dural Sinuses

•Superior sagittal sinus (SSS): From the foramen cecum at the cribriform laminae of the ethmoid bone to the internal occipital protuberance, where the confluence of the sinuses is lo-

cated ( Fig. 4.36) . Trauma to the vertex of the skull may cause rupture of the SSS, resulting in vertex epidural hematoma.8

•Inferior sagittal sinus (ISS): Runs within the inferior edge of the falx cerebri and is formed by smaller cortical veins from medial hemispheric surfaces.

•Straight sinus: Formed by the Vein of Galen (deep vein of the brain) and the ISS. Also ends at the sinusoidal confluence.

•Transverse sinuses: One per side, originating from the confluence of the sinuses. Runs laterally and continues drains into the sigmoid sinus. Receives drainage from the vein of Labbé.

•Sigmoid sinus: Continuation of the transverse sinus and the point at which transverse sinuses meet. Receives an anastomosis from the superior petrosal vein which drains the cavernous sinus. The sigmoid sinus ends at the jugular foramen, where it receives an anastomosis from the inferior petrosal sinus. It continues as the internal jugular vein following its exit from the jugular foramen.

Cerebral Veins

Superficial Veins

The superficial veins of the brain form multiple anastomoses which terminate within two main veins:

•Vein of Trolard: Located superiorly, drains from the sylvian fissure to the SSS.

•Vein of Labbé: Located inferiorly, drains from the sylvian fissure to the transverse sinus.

Deep Veins

•Internal cerebral vein: Receives the thalamostriate vein (caudate and thalamus) at the foramen of Monro, and the septal vein (septum pellucidum, anterior corpus callosum and head of the caudate).2

•Basal vein of Rosenthal: This vein drains the base of the brain (anterior and medial temporal lobe) from the anterior perforated substance to join the internal cerebral vein and form the vein of Galen.

•Vein of Galen or Great cerebral vein:

Formed by the internal cerebral veins and the veins of Rosenthal. The vein of Galen then joins the ISS to form the straight sinus.

4.9  Top Hits

4.9.1  Questions

1.The middle meningeal artery enters the skull through:

a) Foramen lacerum b) Foramen ovale c) Foramen rotundum d) Foramen spinosum

2.What are the branches of the meningohypophyseal trunk?

a)  Anteriorchoroidalartery—posteriorcho- roidalartery—dorsalmeningealartery

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Pearls

•Knowing surface anatomy is key to perform bedside procedures such as lumbar punctures/drains and external ventricular drains.

•Understand the different anatomical­ segments for the main arteries supplying the brain: ICA, MCA, ACA, PCA, and vertebral artery.

•Recognize the main venous structures such as dural sinuses as well as Trolard and Labbé veins.

•A firm command of the various dermatomes and myotomes is essential to ensure a proper neurological exam for patients with spinal cord injury.

b)  Anterior choroidal artery—tentorial artery—anterior meningeal artery c)  Tentorialartery—anteriormeningeal artery—inferior hypophyseal artery d)  Tentorial artery—dorsal meningeal artery—inferior hypophyseal artery e)  Tentorial artery—dorsal meningeal artery—superior hypophyseal artery

3.Which of the following options better describes the trajectory of the corticospinal tract:

a)  Primary motor cortex—internal capsule—corona radiata—cerebel- lar peduncle—anterior pons—pyra- mids—spinal cord

b)  Primary motor cortex—corona ra- diata—cerebral peduncle—anterior pons—pyramids—posterior column of the spinal cord

c)  Primary motor cortex—corona ra- diata—cerebellar peduncle—anterior pons—pyramids—anterior and lateral columns of the spinal cord

d)  Primary motor cortex—corona ra- diata—cerebral peduncle—anterior pons—pyramids—anterior and lateral columns of the spinal cord