Blood supply to the brain is carried by four large arteries:
two internal carotid arteries supply the anterior brain seg- ments and two vertebral arteries carry blood to the posterior segments of the brain, including the occipital lobes, parts of the temporal lobe, splenium of the corpus callosum, caudal parts of the thalamus, caudal parts of the internal capsule, cerebellum, and the brainstem (Nieuwenhuys et al. 1991). At the base of the brain these four arteries form an arterial ring, the arterial circle of Willis that interconnects the two supply territories (Fig. 1.17). The anterior, middle and posterior cerebral arteries are divided into four segments: segment A1, for the anterior cerebral artery, is located anterior to the ante- rior communicating artery, A2 lies posteriorly; segment M1, for the middle cerebral artery, forms the horizontal segment, and M2 is located on the insula. Segment P1, for the poste- rior cerebral artery, is situated between the bifurcation of the basilar artery and the posterior communicating artery, and P2 between the posterior communicating artery and the anterior temporal artery; located posteriorly are segments P3 and P4, which supply the lateral and medial occipital lobes.
The spatial relationship of the cranial nerve roots to the arteries is shown in Fig. 1.17, including the vulnerable
‘transition zone’, the transition from the peripheral myelin of Schwann cells to the central myelin of oligodendro- cytes. It becomes apparent that the vascular loops of the superior cerebellar artery can be a threat to the roots of the trigeminal nerve, vascular loops of the anterior inferior cerebellar artery (= AICA) can affect the facial, vestibulo- cochlear and abducens nerves, and loops of the posterior inferior cerebellar artery (= PICA) can represent a threat to the glossopharyngeal and vagus nerves.
While the surface of the vascular network is characterized by considerable variability, the internal organization of the branches in the brainstem is relatively constant and similar at all levels. Three different vascular territories can be differentiated:
A ventral vascular territory
•
A lateral vascular territory and
•
A dorsal vascular territory (Fig.
• 1.18)
The spinal cord veins represent an extension of the brain- stem veins, which form a vascular net around the brainstem, consisting of interconnected longitudinal veins and hori- zontally branches, in addition to branches connecting them with the basal cerebral vessels.
1.6.1 Mesencephalon
The mesencephalon is enveloped on both sides by several arterial arches that give rise to the radially arranged inner vessels. The short arterial arches emerge from the arcuate branches of the posterior cerebral artery, while the longer arterial arches emerge from the posterior cerebral, the quad- rigeminal, superior cerebellar, and posterior choroidal arteries.
The ventral vascular territory comprises the nuclei of the oculomotor and trochlear nerves, the medial longitudi- nal fasciculus, the Edinger-Westphal nucleus, and para- median regions of the ventral tegmental area up to the mesencephalic aqueduct, as well as the red nucleus and medial parts of the substantia nigra and the cerebral peduncle. This territory is supplied by a number of para- median branches, the interpeduncular perforating arteries (from the P1 segment of the posterior cerebral artery), the posterior communicating artery, as well as the short and long circumferential arteries. Some of the paramedian vessels emerge from the anterior choroidal artery branch of the internal carotid artery.
The lateral vascular territory comprises lateral parts of the tegmentum (cerebral peduncle and medial lemniscus), the substantia nigra, as well as the medial and lateral geniculate body. It is supplied by the radial vessels from the long and short circumferential arteries.
1.6 Brain Stem Vascularization 33
Basilar artery P1
posterior cerebral artery
Posterior communicating artery
Posterior choroidal arteries P2
posterior cerebellar artery Superior cerebellar artery
Quadrigeminal artery Posterior cerebral artery
Superior cerebellar artery
Posterior cerebral artery Posterior choroidal artery Interpeduncular perforating arteries (PI) Superior cerebellar artery
N. III
Pontine branches
Lateral branches
Medial branches Pontine branches
Lateral branches
Medial branches Basilar artery
a
b
Vertebral artery Anterior spinal artery
Posterior spinal artery
Posterior inferior cerebellar artery (PICA)
Vertebral artery Anterior spinal artery
c
Posterior inferior cerebellar artery (PICA) Fig. 1.18 The arterial blood
supply to the brainstem in cross-sections. Three cross- sections are shown at the level of the mesencephalon (a), the pons (b), and the medulla (c); the arteries are shown on the right and their supply territories are indicated on the left. P1 and P2 represent sections of the posterior cerebral artery
34 1 Neuroanatomy of the Brainstem
The dorsal vascular territory, the tectum or the superior colliculus, receives blood from the quadrigeminal artery (usually a branch from the P1 segment of the posterior cerebral artery) and – more caudal at the level of N. IV and the inferior colliculus – from the superior cerebellar artery (Fig. 1.18a).
1.6.2 Pons
Blood supply to the pons is carried via three groups of arteries arising from the basilar artery. The ventral group of arteries arises from the medial branches, the lateral group from the lateral branches, and the dorsal group from pontine branches.
The paramedian branches can extend to the floor of the ven- tricle where they supply the medial tegmentum, the pontine nuclei, including the corticospinal fibers passing through this structure, and the roots of the abducens nerve emerging from the brainstem. The short circumferential branches are found only in the lateral part of the pontine base, while the long cir- cumferential branches supply the entire pontine tegmentum, including the facial nucleus, vestibulocochlear and trigeminal nerves, as well as a segment of the middle cerebellar peduncle.
An additional blood supply is carried by the branches of the anterior inferior cerebellar artery (AICA) to the caudal pons, and by branches of the superior cerebellar artery to the rostral pons (Fig. 1.18b).
1.6.3 Medulla Oblongata
The medulla oblongata is supplied via two to three branches of the vertebral artery: the anterior spinal artery, posterior inferior cerebellar artery (PICA), and the spinal artery (a branch of the PICA) (Fig. 1.18c). Similar to the pons and the mesencephalon, a lateral and a dorsal vascular group can be differentiated.
The medial medulla is supplied by branches of the ante- rior spinal artery which ascends in the midline, (frequently to the left or right side), to the floor of the fourth ventricle. They supply the hypoglossal nerve and the nucleus of the hypo- glossal nerve, the nucleus of the dorsal vagus nerve, the cor- ticospinal tract, the medial lemniscus, the medial longitudinal fasciculus, and the medial accessory olivary nucleus. An occlusion occurring in the ventral vascular group leads to the medial medullary syndrome (Déjerine).
Branches of the lateral vascular group can emerge from PICA or from the vertebral artery and enter the medulla oblongata lateral to the inferior olive. They supply parts of the tegmentum, including the solitary tract nucleus, dorsal motor vagal nucleus, spinal trigeminal nucleus and ambiguus nucleus, a part of the vestibular and dorsal column nuclei
with the ascending spinothalamic tract (anterolateral path- ways for pain), spinal trigeminal tract, the central descending sympathetic pathway, and a part of the inferior cerebellar peduncle. Obstructions in this lateral vascular group result in lateral medullary syndromes (Wallenberg syndrome inclu- sive of Horner syndrome).
The branches of the dorsal vascular group emerge at the level of the obex from the PICA and the ascending branch of the posterior spinal artery. They supply the dorsal column nuclei as well as the spinal trigeminal tract and nucleus.
Lesions of these vessels are rare. In a more rostral location blood supply to the entire dorsal medulla is carried exclu- sively via the PICA; branches of the AICA are involved in blood supply at the rostral border with the pons only.
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P.P. Urban and L.R. Caplan (eds.), Brainstem Disorders,
DOI: 10.1007/978-3-642-04203-4_2, © Springer-Verlag Berlin Heidelberg 2011
37
Diagnostic Imaging, Interventional Treatment of Brainstem Lesions and Electrophysiologic Diagnostics
2
Contents
2.1 Neuroradiology. . . 38 2.1.1 Conventional Native Diagnostics. . . 38 2.1.2 Computed Tomography . . . 39 2.1.2.1 Principles and Techniques . . . 39 2.1.2.2 CT in Investigations of the Brainstem . . . 39 2.1.2.3 Risks. . . 40 2.1.3 Magnetic Resonance Imaging . . . 40 2.1.3.1 Principles and Techniques . . . 40 2.1.3.2 MRI Investigations of the Brainstem . . . 42 2.1.3.3 Specialized Methods . . . 45 2.1.3.4 Risks. . . 46 2.1.4 Angiography and Endovascular Interventions. . . 47 2.1.4.1 Diagnostic Angiography . . . 47 2.1.4.2 Endovascular Interventions . . . 49 Recanalization . . . 49 Embolization . . . 51
2.2 Ultrasound Diagnostics . . . 54 2.2.1 Vascular Ultrasound. . . 54 2.2.1.1 Anatomic Principles. . . 54 2.2.1.2 Principles and Techniques . . . 54 Continuous Wave (cw) Doppler. . . 54 Pulsed Doppler Sonography
(Pulsed Wave Doppler, pw Doppler) . . . 55 Color Duplex Sonography . . . 55 2.2.1.3 Ultrasound Signal Enhancers. . . 55 2.2.1.4 Reference Values . . . 56 2.2.1.5 Stenosis Criteria. . . 56 2.2.1.6 Clinical Application. . . 57 Brainstem Infarction/TIA . . . 57 Basilar Artery Thrombosis. . . 58
Subclavian Steal Syndrome or Subclavian Steal
Phenomenon. . . 58 Rotational Vertebral Artery Occlusion . . . 58 2.2.2 B-Mode Sonography of the Brainstem . . . 59 2.2.2.1 Principles and Techniques . . . 59 2.2.2.2 Clinical Application. . . 60 Early Diagnosis of Idiopathic Parkinson’s Disease . . . . 60 Differential Diagnosis of Parkinson Syndromes . . . 61 Diagnosis of Affective Disturbances . . . 61 2.3 Electrophysiologic Diagnostics . . . 61 2.3.1 Blink Reflex . . . 61 2.3.1.1 Anatomic and Physiologic Principles . . . 61 2.3.1.2 Clinical Application. . . 62 2.3.1.3 Interpretation of Findings . . . 63 2.3.2 Masseter Reflex . . . 65 2.3.2.1 Anatomic Principles. . . 65 2.3.2.2 Clinical Application and Normal Values . . . 66
2.3.2.3 Interpretation of Findings . . . 68 2.3.2.4 Conclusion . . . 69 2.3.3 Early Acoustic Evoked Potentials . . . 70 2.3.3.1 Anatomic and Physiologic Principles . . . 70 2.3.3.2 Application. . . 70 Stimulation. . . 70 Recording. . . 71 2.3.3.3 Physiologic Variability of EAEP and
Abnormal Findings . . . 71 2.3.3.4 Evaluation . . . 71 Central Lesions . . . 72 Multiple Sclerosis . . . 72 Brainstem Ischemia/Bleeding . . . 74 Brain Death . . . 74 2.3.4 Vestibulocollic Reflex . . . 75 2.3.4.1 Anatomic and Physiologic Principles . . . 75 2.3.4.2 Application. . . 75 2.3.4.3 Evaluation and Reference Values. . . 75 2.3.4.4 Interpretation . . . 76 2.3.5 Exteroceptive Suppression of Masticatory
Muscle Activity . . . 76 2.3.5.1 Anatomic and Physiologic Principles . . . 76 Afferences of Exteroceptive Suppression . . . 76 Interconnection of ES1 . . . 77 Interconnection of ES2 . . . 78 2.3.5.2 Clinical Application. . . 78 Stimulation. . . 78 Recording. . . 78 2.3.5.3 Evaluation . . . 78 2.3.5.4 Reference Values/Normal Variants and Pathologic
ES Criteria . . . 78 2.3.5.5 Interpretation of Findings . . . 79 2.3.6 Somatosensory Evoked Potentials . . . 81 2.3.6.1 Anatomic and Physiologic Principles . . . 81 2.3.6.2 Application. . . 81 Stimulation. . . 81 Recording. . . 82 2.3.6.3 Evaluation . . . 82 The Generator Question and the Interconnection
of SEPs. . . 82 Far-Field Potentials . . . 82 2.3.6.4 Interpretation of Findings . . . 83 2.3.6.5 Brainstem Lesions . . . 83 Brain Death . . . 84 2.3.7 Transcranial Magnetic Stimulation . . . 84 2.3.7.1 Anatomic and Physiologic Principles . . . 84 2.3.7.2 Application. . . 85 Corticofacial Projections . . . 85 Corticolingual Projections . . . 85 2.3.7.3 Evaluation . . . 85 TMS of Corticofacial Projections . . . 85 TMS of Corticolingual Projections . . . 86
38 2 Diagnostic Imaging, Interventional Treatment of Brainstem Lesions and Electrophysiologic Diagnostics