Pocket tutor: Neuroimaging Rory Piper
Note: Page numbers in bold or italic refer to tables or figures respectively.
ABCDE approach, for trauma patient 77, 84
Acoustic neuroma see Vestibular schwannoma
Ageing, features of see Elderly patients
Air, presence of see Pneumocephalus
Anterior circulation, brain 17, 17
Anterior fossa, skull 3, 3
Anteroposterior view 21, 22
Antiplatelet therapy, after ischaemic stoke 103
Aqueduct of Silvius 18, 19
Artefact 72
beam hardening 73, 74
foreign bodies 72, 7374
motion 67, 74
starburst 73, 74
types of 7273
Arterial dissection 115
CT angiography for 115, 116
MRI for 115117, 116
Arterial stenting 115
Arteriovenous malformation 112114
bag of worms 112, 114
CT scan for 112, 113, 114
digital subtraction angiography 112, 114
MRI for 112, 113
multiple flow voids 112, 113
Atlanto-occipital joint 4
Atlas 4
Axial section 22, 23
Axis 5
Basal cisterns 59
Basal ganglia 9
Battle's sign 80
Bitemporal hemianopia 11
Blossoming of contusion 90
Bone window 40, 40
arterial supply to 16, 17, 17
herniation 68, 6869, 69
metastases 137, 148150, 149
venous system of 18, 18
ventricular system of 18, 19
functions of 12
structure of 12, 13
Brain tumour 137140
assessment in 140141
brain metastases 137, 148150
CT for 141
gliomas 142146
image-guided neurosurgery 154156
management of 142
medulloblastoma 152
meningioma 146148
MRI for 141
pituitary adenoma 150151
primary 137
secondary 137
vestibular schwannoma 152154
Broca's area 8, 9
Burst fractures 165166, 167
Carotid artery dissection 115117, 116
Cauda equina 15
Cauda equina syndrome 157159, 173
MRI scan 158
Central nervous system 1 see also Brain; Spinal cord
Central sulcus 8
Cerebellum 12, 13
Cerebral abscess 127132, 129, 141
CT for 128, 130
diffusion-weighted MRI scan 131, 131
MRI for 129, 130131
rim-enhancing effect 129, 130
vasogenic oedema 129, 131
Cerebral aqueduct see Aqueduct of Silvius
Cerebral contusions 8991, 91
burst lobe 90
contrecoup 90, 92
coup 90
CT for 90, 91, 92
haemorrhagic contusions 90, 91
MRI for 90
Cerebral laceration 89
Cerebral oedema 6263
types and features of 64, 65
Cerebritis 127, 130 see also Cerebral abscess
Cerebrospinal fluid 18
CT for 57
MRI for 58, 58, 59
Cerebrospinal fluid cleft sign 146, 147
Cerebrovascular disease 95
arteriovenous malformation 112114
carotid and vertebral artery dissection 115117
dural venous sinus thrombosis 117119
stroke 95112, 96
Cerebrum 8
cerebral cortex 89
hemispheres 8
lobes 8, 8, 9
pituitary gland 11, 11
subcortical structures 911, 10
vascular territories of 17
Cervical spine
CT scans of 4546, 47, 159
plain radiographs of 159
protection 160, 163
Cervical spine fractures 160164
CT scan 163
facet fractures 161, 164
flexion teardrop fracture 161, 163
hangman's fracture 160, 161
Jefferson's fracture 160
MRI for 163
odontoid fracture 160, 162
plain radiography 161163
Circle of Willis 16, 17, 55
Cisterns 7
Contrast-induced nephropathy 32
Computerised tomography (CT) 2425
appearance in 3536
brain 4850, 49
cerebrospinal fluid 57
cervical spine 4546, 47
contrast agent in, use of 25
CT angiography 27, 54
CT perfusion 27
CT venography 27
Hounsfield scale used in 36, 36
image acquisition in 25, 26
meninges 4647, 47, 48
and MRI, comparison of 25
orientation in 3435, 35
safety concerns 3031, 31
skull 40, 4041, 41
spine 4546
vascular system 5253, 54
window, creation of 36, 37
Contrast agents 29, 32, 53
Contrecoup contusions 90, 92 see also Cerebral contusions
Contusions see Cerebral contusions
Coronal section 22, 23
Coronal suture, skull 2, 3
Corpus callosum 9
Cortical atrophy 70, 71
Corticospinal tract 15
Coup contusions 90 see also Cerebral contusions
Craniotomy 85
CT see Computerised tomography (CT)
Cytotoxic oedema 64, 65
Denis’ three-column theory of stability 165, 165
Dexamethasone 138, 174
Diffuse axonal injury 91, 93
CT for 93
MRI for 93
Diffusion tensor imaging 29
Diffusion-weighted imaging 29
Digital subtraction angiography 24, 5556, 56, 57
Disc herniation 168169
Dorsal (posterior) column 15
Dural venous sinuses 7
Dural venous sinus thrombosis 117119, 118
CT for 117
CT venography for 118, 118
MRI for 119
MR venography for 118, 119
Elderly patients 70
cortical atrophy in 70, 71
small vessel disease in 71
ventriculomegaly in 70
Empty delta sign 117
Encephalitis 127
Endovascular coiling 110, 111
Ethmoid air cells 40, 41
Extradural empyema 132
Extradural haematoma 62, 8385, 84
CT scan 76, 84, 84
subdural and, differences between 89
Facet fractures 161, 164
Falx cerebri 7, 46, 47
Fibre tracking see Tractography
Flexion teardrop fracture 161, 163
Foramen magnum 3, 3
Foramen of Munro 18, 19
Frontal lobe 8, 9
Frontal sinus 41, 41
Functional MRI 2930, 155
Gadolinium 29
Glasgow Coma Scale (GCS) score 75, 77, 78
Glioblastoma 144, 145 see also Gli
Gliomas 137138, 139, 140, 142146
high-grade 143, 144146, 145
low-grade 142143, 143, 144
WHO classification of 142, 143
Haematoma 61, 62 see also Intracranial haemorrhage
Haemorrhage 61 see also Intracranial haemorrhage
Hangman's fracture 160, 161
Head injuries 75 see also Traumatic brain injury
Herniation 68, 6869
subfalcine 68, 6869
tonsillar 69, 69
transtentorial 68, 69
Horner's syndrome 115
Hounsfield units (HU) 36
Hydrocephalus 63, 66
communicating 63, 6566
non-communicating 66, 67
normal pressure 6566
Hypothalamus 10, 11
Image-guided neurosurgery 154156
frameless image guidance 154
functional MRI 155
stereotactic surgery 154
tractography 155, 155
Incidental findings, on imaging 71
Infections, of central nervous system 127 see also specific infection
Inflammatory disorders 121
multiple sclerosis 121124
sarcoidosis 124126
Internal capsule 11
Internal carotid artery 56
Intervertebral disc 4
herniation 168169
Intracerebral haemorrhage see Parenchymal brain haemorrhage
Intracranial haemorrhage 61
CT 61
extra-axial 61
intra-axial 61
MRI 62, 63
types of 62
Intracranial pressure, increased 66, 140141
and brain herniation 68, 6869, 69
features of 6667, 67
Intraparenchymal haemorrhage see Parenchymal brain haemorrhage
Intraventricular haemorrhage 62 see also Intracranial haemorrhage
Ischaemia 62
Ischaemic stroke 97103
CT perfusion scan 98, 99
CT scan 98, 99, 100
hyperdense artery sign 98, 99
hypodense area 97
malignant middle cerebral artery infarction 99100, 100101
MRI for 100101, 102
US imaging 103
Jefferson's fracture 160
Lacunar stroke 96
Lambdoid suture, skull 2, 3
Lateral sulcus 89
Lateral view 21, 22
Leptomeningitis 127
Log-rolling technique 159
Lumbar puncture 108
Lumbar sacral spine, MRI scans 52
Lumbar vertebra, MRI scan 53
Magnetic resonance imaging (MRI) 2730
advantages and limitations of 25
appearance in 37
assessment prior to 31
brain 50, 5051, 51
cerebrospinal fluid 58, 58, 59
contrast agents in, use of 29
diffusion tensor imaging 29
diffusion-weighted imaging 29
functional MRI 2930
image acquisition in 2729, 28
meninges 48
MR angiography and venography 29, 53, 55, 55
MRI perfusion 30
MRI spectroscopy 30
orientation in 37
safety concerns 3132
sequences 3738, 38, 39
spinal cord 5152, 52, 53
T1-weighted and T2-weighted MRI signals 39
vascular system 53, 55, 55
ventricular system 58
Malignant middle cerebral artery infarction 99100, 100101, 103
Mastoid air cells 41, 41, 81
Medulloblastoma 152
Meninges 6, 7
arachnoid mater 7
dura mater 67
pia mater 7
Meningiomas 146148
CT scan 147, 147
imaging findings 146147
MRI scan 147, 147, 148
Meningitis 48, 127
Metastatic spinal cord compression 172174, 173
Middle fossa, skull 3, 3
Missile effect 32
MRI see Magnetic resonance imaging (MRI)
MS see Multiple sclerosis (MS)
Multiple sclerosis (MS) 121124
clinically isolated syndrome 123
Dawson's fingers’ 123, 124
McDonald diagnostic criteria for, revised 121
MRI for 122123, 123124, 124
radiologically isolated syndrome 123
Neuroanatomy 1
brainstem 12
cerebellum 12
cerebrum 811
meninges 67, 7
scalp 1
skull 13, 2, 3
spinal cord 1415
spine 4, 45, 5, 6
Neurocranium 1, 2 see also Skull
Neurofibromatosis type 2 152
Neurosarcoidosis 124126
MRI in 125, 125
Nidus 112
Nimodipine 112
Obstructive hydrocephalus 152
Occipital lobe 8, 9
Odontoid fracture 160, 162
Optic chiasm 11, 11
Orientation terminology 20, 2021
anterior 21
contralateral 21
inferior 21
ipsilateral 21
lateral 21
medial 21
posterior 21
superior 21
Osmotic therapy 85
Pachymeningitis 127
Parenchymal brain haemorrhage 62, 103105 see also Intracranial haemorrhage
CT for 104, 105
deep bleeds 104
MRI for 105
primary 104
secondary 104
Parietal lobe 8, 9
Partial anterior circulation stroke 9596, 96
Patient safety 30
contrast agents 32
MRI 3132
radiography and CT 3031, 31
Pepper pot skull 39
Pituitary adenoma 150151
classification of 150
MRI for 150, 151
Pituitary fossa, skull 3, 3
Pituitary gland 3, 11, 11
Plain radiography 2324, 3334
attenuation 3334, 34
cervical spine 42, 4244, 43
orientation in 33
safety concerns 3031, 31
skull 3940
thoracic and lumbar spine 4445, 45, 46
Pneumocephalus 69, 70, 80, 82, 83
Posterior cerebral artery 57
Posterior circulation 17
stroke 96
Posterior communicating artery aneurysm 108
Posterior fossa, skull 3, 3
Radiography, plain see Plain radiography
Sagittal section 22, 23
Sagittal suture, skull 2, 3
SAH see Subarachnoid haemorrhage (SAH)
Sarcoidosis 124126, 125
Scalp 1
SCALP (mnemonic) 1
Sieverts (Sv) 31, 31
Sinuses of skull 4041, 41
Skull 1, 2
base 3, 3
CT for examination 40, 4041, 41
neurocranium 1, 2
pterion 2
radiographs 3940
splanchnocranium 1, 2
sutures of 2, 3
vault 2, 23
venous drainage of 18
Skull fractures 8083, 81, 82
bone window, hypodense lines on 81
comminuted fractures 81, 82
CT scan 81, 81, 82
depressed fractures 81, 82
pneumocephalus 80, 82, 83
Small vessel disease 71
Sphenoid sinus 40, 41
Spinal cord 1415
MRI for 51, 52, 53
Spinal degeneration 167169, 168
Spinal diffusion-weighted imaging 134
Spinal epidural abscess 133135
MRI for 134, 134
Spinal fractures 160
cervical 160164
thoracolumbar 164167
Spinal nerves 15
Spinal tracts 14, 15
Spinal trauma, approach in 159160
Spinal tumours 169170
classification of 170
ependymoma 171172, 172
intradural 169170
meningioma 170171, 171
metastatic spinal cord compression 172174, 173
primary 170
secondary 170
CT scans 4546, 47
plain radiography 4245, 4246
Spinocerebellar tract 15
Spinothalamic tract 15
Splanchnocranium 1, 2 see also Skull
Spondylolisthesis 169
Spondylolysis 169
Spondylosis 169
Stereotactic surgery 154
Stroke 95
haemorrhagic 103112
ischaemic 97103
Oxford (Bamford) classification of 96
parenchymal brain haemorrhage 103105
partial anterior circulation 9596, 96
subarachnoid haemorrhage 103, 105112
transient ischaemic attack 97103
Subarachnoid haemorrhage (SAH) 62, 103, 105112, 106 see also Intracranial haemorrhage
CT angiography for 109, 110
CT for 106, 107109
digital subtraction angiography for 109, 111
modified Fisher grading scale for 109, 109
MRA for 109110
non-traumatic 107, 108
World Federation of Neurosurgical Societies grading scale 107
Subarachnoid space 7
Subcutaneous emphysema 69
Subdural empyema 132, 133
Subdural haematoma 62, 8589, 8688, 89
acute 85, 86, 86
chronic 85, 86, 87
extradural and, differences between 89
isodense 86, 88
subacute 86, 88
Subfalcine herniation 68, 6869
Superior sagittal sinus 18, 18
Tattoo inks 31
Temporal lobe 8, 9
Tentorium cerebelli 7, 46, 48
Terminology, related to radiology 20
orientation 20, 2021
sections 2122, 23
views 21, 22
Thalamus 10, 11
Third cranial nerve palsy 108
Thoracolumbar fractures 164167
burst fractures 165166, 167
imaging findings 166
wedge fractures 165, 166
Thrombolytic therapy 97
Tonsillar herniation 69, 69
and Chiari malformation 69
Total anterior circulation stroke 96
Tractography 29, 155, 155
Transependymal oedema 63, 64, 65
Transient ischaemic attack 97
Trans-sphenoidal hypophysectomy 151
Transtentorial (uncal) herniation 68, 69
Traumatic brain injury 75, 76
assessment in 77
cerebral contusion 8991, 91, 92
CT head scan in 77, 78
differential diagnoses 79
diffuse axonal injury 91, 93
extradural haematoma 8385, 84
GCS score 75, 77, 78
prevention of 75
primary 75
secondary 75
severe 7577, 76
skull fractures 8083, 81, 82
subdural haematoma 8589, 8688, 89
Vascular system 52
CT 5253, 54
digital subtraction angiography 5556, 56, 57
MRI 53, 55, 55
Vasogenic oedema 64, 65
Ventricular system 18, 19, 57, 58
Ventriculitis 127
Ventriculomegaly 63, 66, 70
Vertebrae 4, 4, 5
cervical 45, 5, 6
coccygeal 4, 5
lumbar 4, 5
sacral 4, 5
structure of 4
thoracic 4, 5
Vertebral artery 57
Vertebral dissection 115117
Vestibular schwannoma 152154
cystic component 153, 153
MRI scan 153, 153154
solid component 153, 154
Virchow–Robin spaces 71
Wedge fractures 165, 166
Wernicke's area 8
X-rays see Plain radiography
Chapter Notes

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First principleschapter 1

An understanding of neuroimaging rests on knowledge of the fundamental principles of:
  • neuroanatomy (the structure of the normal brain)
  • neuroimaging terminology (how images are described)
  • neuroimaging modalities (how images are acquired)
  • safety in neuroimaging
1.1 Neuroanatomy
The nervous system is divided into:
  • A central nervous system and
  • A peripheral nervous system
This book focuses on the central nervous system, which comprises the brain and spinal cord.
The scalp
The scalp is the soft tissue covering the skull vault. A mnemonic for the five layers that make up the scalp, from superficial to deep, is SCALP:
  • Skin
  • Connective tissue
  • Aponeurosis (the galea aponeurotica)
  • Loose areolar connective tissue
  • Periosteum (pericranium)
The skull
The skull is divided into:
  • The neurocranium, i.e. the part encasing the brain, and
  • The viscerocranium, i.e. the facial skeleton
The neurocranium
The neurocranium forms the cranial cavity, the space occupied by the brain.2
zoom view
Figure 1.1: Left lateral view of the skull. The neurocranium is shown in blue, and the splanchnocranium in green. The pterion (circled) is the region where the frontal, parietal, temporal and sphenoid bones meet.
zoom view
Figure 1.2: Superior view of the coronal, sagittal and lambdoid sutures.
The skull vault The skull vault (also called the calvaria) comprises the frontal, parietal (left and right), occipital, temporal (left and right), sphenoid and ethmoid bones (Figure 1.1). In the fully developed skull, these bones are strongly held together 3by fibrous joints called sutures, such as the sagittal, coronal and lambdoid sutures on the superior aspect (Figure 1.2).
The skull base
This anatomically complex structure forms the floor of the cranial cavity. It has many foramina, through which the spinal cord, cranial nerves, blood vessels and other structures pass in or out of the cavity. The largest of the foramina is the foramen magnum.
The skull base is divided into the three cranial fossae: anterior, middle and posterior (Figure 1.3). The small hypophyseal fossa, located in the middle fossa, holds the pituitary gland.
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Figure 1.3: Superior view of the anterior, middle and posterior fossae of the skull base.
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Figure 1.4: A typical vertebra and its relationship to the spinal cord and nerve roots.
The spine
The spine protects the spinal cord. It is a column of individual bones called vertebrae; these differ in structure according to their level but have several key features in common, as shown in Figure 1.4 . From superior to inferior, the vertebrae are (Figure 1.5):
  • Seven cervical (C1 to C7)
  • Twelve thoracic (T1 to T12)
  • Five lumbar (L1 to L5)
  • Five sacral (S1 to S5)
  • Four coccygeal (Co1 to Co4; these are fused together)
The vertebral bodies are separated by intervertebral discs. Each disc consists of an inner nucleus pulposus and an outer annulus fibrosis.
The cervical spine has several distinct features (Figure 1.6), including:
  • The first cervical vertebra (C1) is called the atlas; it forms a joint with the occipital condyles (the atlanto-occipital joint)5
zoom view
Figure 1.5: Lateral, ventral and dorsal views of the spine, showing the cervical, thoracic, lumbar, sacral and coccygeal divisions.
  • The second cervical vertebra (C2) is called the axis; its odontoid process forms a pivot joint with the atlas to allow rotation of the head
  • All but the seventh vertebral body of the cervical spine have transverse foramina, which transmit the vertebral arteries6
zoom view
Figure 1.6: Features of the cervical vertebrae.
The meninges
The brain is separated from the skull by three membranous layers called the meninges: the dura, arachnoid and pia mater (Figure 1.7). The meninges extend down the spinal canal to encompass the spinal cord, cauda equina and nerve roots. The dura and arachnoid mater terminates at S2, but an extension of the pia mater, the filum terminale, continues to the coccyx.
Dura mater
The dura mater is the thick, outermost layer of the meninges, and itself has an outer (periosteal) and an inner (meningeal) layer. The outer layer of the dura mater is largely adherent to the skull.7
zoom view
Figure 1.7: The scalp, skull and meninges.
The inner layer deviates deeply at two main locations to form the falx cerebri (within the longitudinal fissure, which separates the right and left cerebral hemispheres) and the tentorium cerebelli (which separates the cerebrum from the cerebellum). The dural venous sinuses are the channels formed between the separation of the two dural layers.
Arachnoid mater
Deep to the dura mater is the arachnoid mater. The arachnoid mater is in contact with the dura mater but separated from the pia mater by the subarachnoid space. Within the subarachnoid space are cerebral arteries, and veins that drain into the dural venous sinuses via bridging veins. Large subarachnoid spaces are termed cisterns.
Pia mater
The pia mater is the innermost meningeal layer. It is in contact with the surface of the brain.8
The cerebrum
The cerebrum is divided into two hemispheres, left and right, separated by the longitudinal (or interhemispheric) fissure. The hemispheres are subdivided into lobes: frontal, temporal, parietal and occipital (Figure 1.8). Each lobe has specific functions (Table 1.1).
Cerebral cortex
The cerebral cortex is the superficial layer of the brain. It has a convoluted structure characterised by gyri and sulci. Two of the most prominent sulci are the central sulcus (or Rolandic fissure), which divides the frontal and parietal lobes, and the lateral sulcus (or Sylvian fissure), which separates the frontal and temporal lobes.
zoom view
Figure 1.8: Lobes of the brain. The postcentral gyrus (somatosensory region) is part of the parietal lobe. The precentral gyrus (primary motor cortex) is part of the frontal lobe.
Table 1.1   Key functions of the cerebrum according to lobe
Voluntary movement (primary motor cortex)
Language* (Broca's area)
Emotion and personality
Intelligence and problem-solving
Language* (Wernicke's area)
Hearing (auditory area)
Sensation (somatosensory cortex)
Spatial orientation †
Processing and integration of sensory information
*Functions of the dominant hemisphere.
†Functions of the non-dominant hemisphere.
The cortex is made up of grey matter, which consists of neuronal cell bodies.
Subcortical structures
White matter is located within the inner part of the cerebrum. It is composed of neuronal axons surrounded by myelin (accounting for the white appearance). Arranged in bundles, these axons form tracts connecting regions of the brain and spinal cord. The corpus callosum is a large white matter tract that connects the two hemispheres of the cerebrum.
Other important subcortical structures include (Figure 1.9):
The basal ganglia This is a group of interconnected subcortical nuclei including the subthalamic nucleus, putamen, caudate nucleus and globus pallidus. They act as a circuit to help fine-tune voluntary movements.10
zoom view
Figure 1.9: Coronal and sagittal sections through the deep structures of the brain.
11The internal capsule This is a pathway for the white matter tracts ascending to or descending from the cerebral cortex.
The thalamus The thalamus relays motor and sensory information to and from the cerebral cortex. It also has a key role in the regulation of consciousness.
The hypothalamus This is located inferior to the thalamus and superior to the pituitary gland. Its functions include mediation of emotional responses and maintenance of homeostasis (e.g. body temperature and blood pressure). The hypothalamus influences the autonomic nervous system and the release of hormones from the pituitary gland.
The pituitary gland
Connected to the hypothalamus by the stalk-like infundibulum, the pituitary gland lies inferior to the optic chiasm (the point at which fibres from the left and right optic nerves cross) (Figure 1.10), and sits within the hypophyseal fossa in the middle cranial fossa. It is divided into an anterior and a posterior lobe. As the so-called ‘master gland’, it controls the secretion of hormones from other endocrine glands.
zoom view
Figure 1.10: Coronal section of the pituitary gland and surrounding anatomy.
The cerebellum
The cerebellum lies in the posterior fossa. It is connected to the brainstem by the superior, middle and inferior cerebellar peduncles.
It has a complex array of folds, called folia, and is divided into the following (Figure 1.11):
  • The left and right hemispheres, divided by the midline vermis
  • The anterior and posterior lobes, divided by the primary fissure
The cerebellum coordinates movement.
The brainstem
The brainstem is divided into three structures (Figure 1.12). From superior to inferior, these are the:
  • Midbrain
  • Pons
  • Medulla
The brainstem is responsible for regulation several vital functions, including:
  • the respiratory and cardiovascular systems
  • the sleep–wake cycle
  • arousal and consciousness
  • bowel and bladder control
  • nausea and vomiting
  • pain
It is also where the nuclei of the cranial nerves (III to XII) are located. Running through the brainstem are white matter tracts made up of the axons of motor and sensory pathways, which enable communication between the brain and the spinal cord.13
zoom view
Figure 1.11: The cerebellum: anterior lobe, posterior lobe, vermis, primary fissure, folia.
zoom view
Figure 1.12: The brainstem.
The spinal cord
The spinal cord is contained within the spinal canal, the space formed by the vertebral foramina of successive vertebrae. It extends from the brainstem via the foramen magnum in the skull base, to the conus medullaris at about the level of L1 (normal range, T12 to L2). From the conus medullaris, the lumbar and sacral nerve roots descend unbound; the extending nerve roots are known collectively as the cauda equina.
zoom view
Figure 1.13: The ascending (sensory) and descending (motor) spinal tracts.
15The spinal cord gives rise to 31 pairs of spinal nerves. The cervical spine has seven vertebrae and the cord has eight cervical spinal nerves:
  • each pair of the C1–C7 nerve roots emerges above the numerically corresponding vertebra, and
  • the pair of C8 nerve roots emerges below the C7 vertebra
All subsequent nerve roots arise below their corresponding vertebrae.
The spinal tracts
The spinal cord contains white matter tracts that transmit information either from the brain to the peripheral nerves or vice versa (Figure 1.13).
Motor information is transmitted via descending pathways, and sensory information via ascending pathways.
The corticospinal tract This is the pathway of neurones descending from the cortex to synapse with the lower motor neurones. They control voluntary muscle action.
The dorsal (posterior) column This pathway of neurones connects sensory nerve endings to the somatosensory region of the cerebral cortex. It is responsible for conscious proprioception and the sensation of vibration and discriminative touch.
The spinothalamic tract This is the neuronal pathway connecting sensory nerve endings to the somatosensory region of the cerebral cortex. It is responsible for the sensation of crude touch, pain and temperature.
The spinocerebellar tract This pathway of neurones connects sensory nerve endings to the cerebellum. It confers unconscious proprioception.16
zoom view
Figure 1.14: The circle of Willis. Key to labels: ① Anterior communicating artery ② Pontine arteries ③ Basilar artery ④ Anterior spinal artery ⑤ Second part (A2) of anterior cerebral artery ⑥ First part (A1) of anterior cerebral artery ⑦ Middle cerebral artery ⑧ Posterior communicating artery ⑨ Posterior cerebral artery ⑩ Superior cerebellar artery ⑪ Labyrinthine artery ⑫ Anterior inferior cerebellar artery ⑬ Vertebral artery ⑭ Posterior inferior cerebellar artery.
zoom view
Figure 1.15: Vascular territories of the cerebrum.
The arterial system
Arterial supply to the brain is divided into the anterior circulation and the posterior circulation. The internal carotid and vertebral arteries meet to form an anastomotic structure named the Circle of Willis (Figure 1.14), which enables some compensation between the two circulations.
Anterior circulation
The anterior circulation is supplied by the internal carotid arteries. It is the primary supply to the anterior and middle cerebral arteries. The anterior cerebral artery supplies the anteromedial side of the brain (Figure 1.15). The middle cerebral artery supplies the lateral side of the brain. The middle cerebral artery gives rise to the lenticulostriate arteries, which supply subcortical structures of the brain (e.g. the basal ganglia).
Posterior circulation
The posterior circulation is supplied by the vertebral arteries. It is the primary supply to the posterior cerebral arteries and the arteries that supply the cerebellum and brainstem. The posterior cerebral arteries supply the base of the cerebrum and the occipital lobes.18
zoom view
Figure 1.16: Venous drainage of the brain and skull.
The venous system
Cortical veins drain into the dural venous sinuses. The largest sinus is the superior sagittal sinus. Where the major sinuses merge (the confluence of sinuses), the venous blood drains into the left and right transverse sinuses and the left and right sigmoid sinuses, and then the left and right internal jugular veins, respectively (Figure 1.16).
The ventricular system
The ventricular system is a collection of four connected compartments filled with cerebrospinal fluid (Figure 1.17). The fluid is produced by the specialised tissue of the choroid plexuses, primarily in the lateral ventricles. It flows from the left and right lateral ventricles, via the interventricular foramina (foramina of Munro), to the third ventricle. It then passes through the cerebral aqueduct (aqueduct of Sylvius) to the fourth ventricle. From the fourth ventricle, the fluid either flows into the subarachnoid space, via the median and lateral apertures (foramina of Magendie and Luschka, respectively), before being absorbed by arachnoid granulations into the bloodstream, or flows down through the spinal subarachnoid space or central canal.19
zoom view
Figure 1.17: Lateral, superior and anterior views of the ventricular system of the brain.
1.2 Radiological terminology
An understanding of the principles of orientation, views and sections is essential to the interpretation of imaging studies. The terms that describe these principles form the language of radiology.
The terms used in radiology generally follow those used in anatomy (Figure 1.18).
zoom view
Figure 1.18: Terms used to describe features of the brain and spinal cord.
  • 21Superior is used to describe a structure that is higher in position, or situated nearer the top of the head, relative to another structure
  • Inferior is used to describe a structure that is lower in position, or situated nearer the soles of the feet, relative to another structure
  • Anterior refers to a structure that is in front of another
  • Posterior refers to a structure that is behind another
  • Medial refers to a structure that is closer to the midline of the body relative to another
  • Lateral refers to a structure that is further away from the midline of the body relative to another
  • Ipsilateral means on the same side of the body relative to another structure
  • Contralateral means on the opposite side of the body relative to another structure
These terms are all used consistently in descriptions of features of the brain and spinal cord. In contrast, the terms rostral, caudal, dorsal and ventral have different meanings when applied to features of these two anatomical sites (Figure 1.18).
Radiographs are produced by transmitting X-rays through the subject. The direction of transmission determines the view obtained (Figure 1.19). An anteroposterior view is produced by transmitting X-rays through the front of the subject towards a detector positioned behind them. A lateral view is produced by transmitting X-rays through the subject from one side (either left or right) towards a detector on the opposite side.
In modern neuroimaging (computerised tomography, CT, and magnetic resonance imaging, MRI), multiplanar techniques are used to visualise the brain and spinal cord in cross-sections, or ‘slices’ (Figure 1.20).22
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Figure 1.19: Principles of radiographic image acquisition.
  • A sagittal section provides an image of the brain or spinal cord in a lateral plane (i.e. from the side), which shows relations between structures in terms of superior versus inferior and anterior versus posterior
  • An axial (or transverse) section provides an image of the brain or spinal cord in a horizontal plane, enabling comparison of anterior versus posterior and medial versus lateral structures
  • A coronal section provides an image of the brain or spinal cord between a front portion and a back portion (similar to an anteroposterior view in radiography); it shows relations between superior versus inferior and medial versus lateral structures23
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Figure 1.20: T1-weighted MRI scan of the head, showing sagittal (a), coronal (b) and axial (c) sections.
1.3 Imaging modalities
A basic understanding of the principles underlying different neuroimaging modalities facilitates interpretation of the images obtained.
Plain radiography
Radiographs are generally easy to acquire (even possible at the bedside), widely available, rapidly acquired, cost effective and have a significantly lower radiation dose than CT. Due to advances in multi-planar neuroimaging, CT and MRI have largely superseded plain radiography in neuroimaging.24
X-rays from a single-source radiation emitter are directed at the body part of interest, positioned in front of an X-ray detector (film or digital). The X-rays are attenuated (absorbed or scattered) to varying degrees by body tissues of different densities. The resulting variation in X-rays reaching the detector is visualised as differences in contrast in the image captured, i.e. the radiograph.
In a radiograph, it is not possible to differentiate the skull from the intracranial contents, because X-rays are highly attenuated by the skull. Therefore, radiography is not used for imaging studies of the brain. However, there are specific indications for skull radiographs in clinical practice, for example to visualise the characteristic lytic lesions of multiple myeloma, for ventriculoperitoneal shunt series, and for skeletal surveys in non-accidental injury in children.
Plain radiographs are routinely used to image the spinal column. Indications include trauma (to investigate for fractures, vertebral alignment and stability), spinal deformities (e.g. scoliosis), degeneration and spinal column tumours. Similarly to skull radiographs, the spinal cord cannot be visualised on spine radiographs due to the high density of the spinal column.
Computerised tomography
The availability and fast image acquisition of CT makes it the imaging modality of choice in neurological emergencies (such as trauma and acute cerebrovascular conditions). The advantages and limitations of CT compared with those of MRI are shown in Table 1.2.
Computerised tomography images the body in cross-section. This is an advantage over plain radiography, in which the interpretation of images is made difficult by the superimposition of body tissues of different densities.25
Table 1.2   Comparison of computerised tomography (CT) and magnetic resonance imaging (MRI)
Rapid acquisition of images (seconds)
Superior detail in images of bone (skull and spine)
No ionising radiation
Superior detail in images of soft tissues
Superior detail in images of brain and spinal cord
Ionising radiation
Slow acquisition (minutes)
Difficult for paediatric patients (anaesthesia often required)
Susceptibility to motion artefact
Magnetic risks and incompatibility issues (e.g. pacemaker)
Beams of X-rays are directed through the patient along multiple linear paths and measured by a series of X-ray detectors (Figure 1.21). Attenuation values for each discrete three-dimensional element of volume (voxel; Figure 1.22) is calculated using data from X-ray paths intersecting at the coordinates of the voxel. Using these values, a three-dimensional density map can be visualised as grey-scale image that we can interpret.
The introduction of contrast agents into the vascular system significantly increases the density of blood vessels, thereby enabling them to be clearly differentiated from surrounding body tissue. Usually the contrast agent is an iodinated compound because their density is clearly visible on CT, they are soluble and do not harm the body. Contrast is used in CT angiography, CT venography and also to identify dysfunction of the blood–brain barrier (e.g. in the case of contrast-enhancing brain tumours).26
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Figure 1.21: CT image acquisition. In plain radiography, a single X-ray beam is transmitted through the patient towards a detector. In CT, the X-ray emitters and detectors rotate around the scanner gantry in order to transmit X-rays in multiple, intersecting paths. Using a method called ‘back-projection’, the attenuation at each voxel is calculated.
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Figure 1.22: A pixel (a picture element) is two-dimensional, i.e. is a square. A voxel (a volume element) is three-dimensional, i.e. is a cube or cuboid.
27CT angiography Contrast is used to improve visualisation of the arterial system. In the context of neuroimaging, it is used to identify vascular abnormalities such as aneurysms.
CT venography Contrast is also used to improve visualisation of the venous system. The venous system can be enhanced selectively by increasing the delay between contrast administration and image acquisition. This technique can be used to investigate for dural venous sinus thrombosis.
CT perfusion This measures cerebral blood flow. It is used to determine the amount of salvageable parenchyma (the penumbra) in patients who have had a stroke, and to identify vasospasm in subarachnoid haemorrhage.
Magnetic resonance imaging
Magnetic resonance imaging (MRI) is a powerful neuroimaging modality. It shows both the structures and pathology of the brain and spinal cord in better detail than CT. However, image acquisition is much longer, the scanner is more claustrophobic and patients can be upset by the loud noises that it makes. Table 1.2 compares the advantages and limitations of MRI and CT.
MRI is based on altering the properties of the abundant hydrogen atoms within the body. This is done by exposing the patient to the strong magnetic field of the large cylindrical magnet that is part of the MRI scanner (Figure 1.23).
Each hydrogen atom contains a single proton nucleus that spins around a central axis. In the magnetic field of the MRI scanner, the central axis of each proton aligns with the direction of the magnetic field. Although aligned, the protons spin out of phase with each other. A radiofrequency pulse is then applied, which causes the central axis of each proton to realign perpendicular to the direction of the magnetic field; consequently, all the protons spin in phase. When the radiofrequency pulse ceases, each proton's central axis realigns with the direction of the magnetic field, and the protons gradually return to spinning out of phase.28
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Figure 1.23: MRI image acquisition.
29Variation in both the alignment of the protons and their phase of spin results in different signals for different tissues. This is represented by differences in the greyscale image generated.
Clinical MRI scanners vary in the strength of their magnetic field (for which the unit is the tesla, T); strengths of 1.5 and 3.0 T are typical. The higher the number of teslas, the higher the signal-to-noise ratio.
Contrast agents are used in MRI to enhance imaging of blood–brain barrier disruption, tumours, inflammation, demyelination and infection. Gadolinium is a commonly used contrast agent used in MRI and works by increasing signal on T1-weighted imaging.
Magnetic resonance angiography and venography These techniques use specific magnetic resonance signals to improve visualisation of the arteries and veins, respectively. Unlike CT angiography and CT venography, they do not necessarily require the use of a contrast agent.
Diffusion-weighted imaging This technique is used to estimate the diffusion of water in tissue. It is used to investigate for cerebral ischaemia, infection, traumatic brain injury and degenerative disease.
Diffusion tensor imaging This is used to study the direction of diffusion within tissues, and can be used to determine the orientation of white matter tracts. In tractography (also called fibre-tracking), data from diffusion tensor imaging are used to generate a three-dimensional map of the white matter tracts. Tractography is increasingly being used for neurosurgical planning and intraoperative guidance.
Functional MRI This is used to measure brain activity. It uses the technique of blood oxygenation level–dependent imaging to show regions of increased blood flow and oxygenation, 30which are assumed to represent regions of increased neuronal activity. As well as being an increasingly useful tool in neuropsychological research, functional MRI is used to prevent iatrogenic injury and subsequent post-surgical neurological deficits in patients undergoing neurosurgery.
MRI spectroscopy This technique is used to measure the chemical composition of tissue. Chemicals measured include N-acetylaspartate, choline, lactate, creatine and glutamate. Spectroscopy is used to investigate and differentiate between brain lesions (e.g. tumours, infarcts and infections).
MRI perfusion This is similar to CT perfusion. It allows the approximate quantification of cerebral blood flow and blood volume. It is particularly useful in the assessment of tumours, for their differentiation from tumour mimics and the identification of aggressive features for targeted biopsy.
1.4 Patient safety
Neuroimaging is not without risk. For each patient, the risks of image acquisition need to be carefully balanced against the clinical usefulness of the images that will be obtained.
Radiography and CT imaging
Both plain radiography and CT use ionising radiation. Radiation causes cellular and genetic damage, and significant exposure increases the risk of developing cancer. Modern equipment minimises the radiation dose but cannot eliminate it. In particular, children are more radiosensitive than adults and the risks versus benefits should be especially carefully considered. The fetus is especially susceptible to irradiation injury. All girls and women of child-bearing age are asked if there is any possibility that they could be pregnant. In pregnancy, clinicians may choose a different imaging modality, deferring non-urgent imaging or carrying out a risk–benefit analysis specific to the patient.31
Table 1.3   Effective doses of ionising radiation in radiography and computerised tomography (CT)
Average recorded effective dose (mSv)
Skull radiograph
Chest radiograph
Cervical spine radiograph
Thoracic spine radiograph
Lumbar spine radiograph
Head CT
Spine CT
Head and neck angiogram
Data from Mettler FA Jr, et al. Radiology 2008; 248:254–263.
The effective dose of radiation to which a patient is exposed is measured in Sieverts (Sv); 1 Sv = 1 J/kg. Example doses are given in Table 1.3, which illustrates the higher dose of CT compared with a radiograph.
MRI safety
The MRI scanner contains a large superconducting magnet, and patients are exposed to its magnetic field. There is no evidence that exposure to high-strength magnetic fields contributes to any pathological processes. However, ferromagnetic objects are made hazardous by their strong attraction to the powerful magnetic field.
32Any external ferromagnetic material that enters the magnetic field is immediately and forcefully propelled towards the bore (centre) of the scanner; this is known as the missile effect. Potential projectiles that could cause injury include oxygen canisters, metal chairs, jewellery, buckles, etc. These must be removed before imaging.
Internal ferromagnetic materials have the potential to be displaced or distorted. Surgical devices, implants (e.g. cochlear implants) and foreign bodies (e.g. metal fragments in the eye). Electronic devices, such as pacemakers, will be damaged. Displacement or dysfunction of these objects will injure or be life-threatening to the patient.
Contrast reactions
All contrast agents have the potential to cause harm. Some may cause contrast-induced nephropathy, therefore the risk and benefits of imaging requiring contrast in patients with renal impairment should be considered carefully. Other risks include immediate or delayed allergic reaction.