The document provides information on neurologic localization including: 1. It describes lesions of the central nervous system (CNS) like the brain and spinal cord can result in cognitive disorders, spasticity, and sensory alterations while peripheral nervous system (PNS) lesions result in weakness and loss of reflexes. 2. Common sites of lesions in the brain are described like the frontal lobe where strokes, tumors, and trauma can cause cognitive disorders, gaze deviations, and hemiparesis. 3. Imaging modalities for the nervous system are discussed including CT scans, MRI, MRA and their strengths and weaknesses in evaluating different neurologic conditions.

1. Neurologic localization
Prof. Saad M. Alrajeh, M.D., FAAN,
MANA

5. Central nervous system
 The CNS (upper motor neuron) includes the brain
and spinal cord. Upper motor neuron lesions
result in cognitive disorders, spasticity,
hyperreflexia, sensory alterations, and pathologic
reflexes.
 Cerebral hemispheres
 White matter tracts
 Cerebellum
 Basal ganglia
 Cranial nerves I and II
 Spinal cord
 In general, cerebral lesions involving grey matter
(cortex) are associated with defects in higher
cortical function (e.g.. dementia, aphasia) and
seizures, whereas those involving white matter
(subcortex) are associated with paresis and
hemisensory defects.

6. Peripheral nervous system
 The PNS includes lower motor neurons and the
nervous outside the CNS. Lower motor neuron
lesions result in weakness, flaccidity, sensory
alterations, and loss of deep tendon reflexes but
absence of pathologic reflexes
 Cranial nerves III and XII
 Spinal nerves and nerves roots
 Cauda equina
 Lower motor neurons including anterior horn
cells, nerve roots, peripheral nerves,
neuromuscular junctions, and skeletal muscles
 plexuses

7. Frontal lobe
 FUNCTIONS:
cognation, personality,
speech, reasoning
ability.
 COMMON LESIONS:
Strokes, tumours, and
trauma
 LESION RESULT IN:
cognitive disorder (e.g.
dementia), gaze
deviation to side of
lesions, aboulia
(slowness of response)
nonfluent aphasia,
hemiparesis, partial
seizers.

8. Temporal lobe
 FUNCTIONS: Memory and
emotions.
 COMMON LESIONS:
Tumours and trauma.
 LESIONS RESULT IN:
Memory impairment,
homonymous hemianopia,
aphasia (if dominant
hemisphere), complex
partial seizures.

9. Parietal lobe
 FUNCTIONS: Sensation,
praxis (ability to carry out
desired acts).
 COMMON LESIONS:
Strokes, tumours, and
trauma.
 LESIONS RESULT IN:
Hemiparesis, hemisensory
deficits, apraxia (difficulty
performing previously
learned tasks), partial
seizures.

10. Occipital lobe
 FUNCTION: Vision.
 COMMON LESIONS:
Strokes, tumours, and
trauma.
 LESIONS RESULT IN:
Homonymous
hemianopasia or
blindness

11. Common localizin signs in focal
epilepsy

12. Thalamus
 FUNCTIONS:
Integration of sensory
functions.
 COMMON LESIONS:
Strokes, haemorrhage
 LESIONS RESULT IN:
Altered sensation and
pain on opposite side,
gaze deviation usually
to side of lesion.

13. Internal Capsule
 FUNCTIONS:
Pathway for motor
and sensory
systems.
 COMMON
LESIONS: Strokes,
haemorrhage.
 LESIONS RESULT
IN: Contralateral
hemiparesis and
hemisensory
deficits.

14. Cerebellum
 FUNCTION:
Balance and
coordination.
 COMMON
LESIONS: Strokes,
haemorrhage.
 LESIONS RESULT
IN: Ataxia,
dysmetria,
incoordination.

15. Midbrain
 FUNCTIONS: Integration
of vertical eye movement,
sensory and motor
function.
 COMMON LESIONS:
Stroke.
 LESION RESULT IN:
Papillary dilatation,
paralysis, oculomotor
weakness frequently
accompanied by
contralateral hemiparesis,
tremor, or ataxia; paresis
of upgaze.

16. Pons
 FUNCTION: Vital function
(e.g.., breathing,
consciousness, cardiac
function), motor and
sensory functions, lateral
eye movement.
 COMMON LESIONS:
Stroke, Multiple sclerosis.
 LESIONS RESULT IN:
Hemi- or quadriplegia,
pinpoint pupils, horizontal
gaze palsy, internuclear
opthalmoplegia, coma or
“locked-in” state; upbeat
nyastagmus is common.

17. Medulla
 FUNCTION: Swallowing,
cardiac function, balance,
lingual movements, motor
and sensory function.
 COMMON LESIONS: Strokes,
syrnix.
 LESIONS RESULT IN: Lateral
medullary or Wallenberg's
syndrome (crossed sensory
syndrome- numbness on one
side of the face and the
opposite side of the body,
hoarseness, dysphagia,
Horner's syndrome, and
ipsilateral ataxia); medial
medullary syndrome
(ipsilateral tongue deviation
and contralateral
hemiparesis).

18. Cervical spinal cord
 FUNCTIONS: sensory and
motor function of the
arms and legs.
 COMMON LESIONS:
usually spondylosis
(cervical degenerative
joint disease), MS,
trauma.
 LESIONS RESULT IN:
Quadra- or paraparesis,
spasticity in arms and
legs with Babinski’s sign,
sensory level in cervical
area, urinary retention,
loss of position sense.

19. Thoracic spinal cord
 FUNCTION: Motor and sensory functions of
the arms and legs, bladder function.
 COMMON LESIONS: usually tumours
metastatic to bone or intradural tumours
(e.g. meningioma, neurofibromas); strokes
and herniated disks are rare.
 LESIONS RESULT IN: spastic paraparesis or
paraplegia with bilateral Babinski’s sign;
sensory level in thoracic area; urinary
retention; loss of position sense in feet
(unless anterior spinal artery syndrome, in
which posterior column function spared).

20. Conus medullaris
 FUNCTION: bladder and bowel
function.
 COMMON LESIONS: usually
tumours in region of L1.
 LESIONS RESULT IN: Saddle
anaesthesia, bladder and bowel
dysfunction, pain in legs may occur
late in course.

21. Cauda equina
 FUNCTIONS: Sensory and motor
function in legs, bladder and bowel
function.
 COMMON LESIONS: Usually
herniated lumbar disks or
maningeal cancer.
 LESIONS RESULT IN: Scattered
pain and weakness in legs, loss of
knee and/or ankle reflexes, bladder
and bowel dysfunction.

22. Spinal cord localization

23. Spinal cord syndromes

24. Anterior horn cells
 FUNCTIONS: Motor function to
individual muscles.
 COMMON LESIONS: Usually motor
neuron disease (e.g.., ALS)
 LESIONS RESULT IN: Weakness,
flaccidity, fasciculation, and atrophy
in the distribution of the motor unit,
loss of reflexes.

25. Nerve root
 FUNCTIONS: Sensory and motor
function to individual muscles.
 COMMON LESIONS: Disk herniation.
 LESIONS RESULT IN: Usually
causes pain and parasthesias in the
dermatomal distribution and
weakness in myotomal distribution.

26. Peripheral nerve
 FUNCTIONS: Sensory and motor
function to individual muscles.
 COMMON LESIONS: Usually
peripheral neuropathies, solitary
nerve or plexus lesions,
mononeuritis multiplex.
 LESIONS RESULT IN: Numbness,
paresthesias, weakness, flaccidity,
loss of reflexes, and loss of
vibratory and position sense in the
nerve distribution.

27. Neuromuscular junction
 FUNCTION: Motor function to
individual muscles.
 COMMON LESIONS: Usually
myasthenia gravis.
 LESIONS RESULT IN: Variable
weakness with fatigability; absence
of sensory findings and normal
reflexes.

28. Muscle disease
 FUNCTION: Movement of joints and
strength.
 COMMON LESIONS: Usually
muscular dystrophies or
polymyositis.
 LESIONS RESULT IN: Proximal
muscle weakness with intact
reflexes and absence of sensory
symptoms or findings.

29. Neuroimaging
 Common neuroimaging modalities
include:
 X-ray
 CT scanning
 MRI

30. Computerized tomography (CT) scans
 Excellent initial investigations for cerebral lesions,
particularly because it is quick and universally
available.
 Excellent use in trauma, intracerebral haemorrhage,
and shift in midline structures.
 Contrast enhancement is necessary for evaluation of
stroke and neoplasm.

31. Computerized tomography (CT) scans
 Weakness of CT scanning: fails to show infarcts
for up to 24h, unable to detect early stage
subdural haematoma, lack of anatomic detail,
fails to identify multiple sclerosis plaques, and
detection of neoplasms require contrast
enhancement.
 If used with mylography, CT scanning may be
helpful in spine disease or ruptured disks.
 May be a necessary test in patients who cannot
undergo MRI scanning (e.g., claustrophobia,
pacemaker, metallic stent, aneurysmal clips)

32. Magnetic Resonance imaging (MRI)
 Gives excellent anatomic detail and shows virtually all
structural diseases.
 Diffusion weighting image (DWI) is extremely valuable
to identify early stroke signs.
 Apparent diffusion coefficient (ADC) maps may show
restricted diffusion (e.g., stroke).
 Perfusion imaging is helpful in demonstrating area at
risk in stroke (ischemic penumbra)

33. Magnetic Resonance imaging (MRI)
 Gradient echo is helpful for hemorrhage, both
old and new.
 T2 weighting shows edema and white-matter
lesions well.
 FLAIR sequences are useful for evaluation of
multiple sclerosis.
 Contrast enhancement with gadolinium will
show neoplasms and enhance meninges.
 A superb non-invasive test for spinal cord
disease or herniated disks in cervical or lumbar
region.

34. Imaging of the cerebral circulation
 Magnetic resonance angiography (MRA) is initial imaging of
choice; 2-D time of flight shows extracranial circulation (vertebrals
and carotid bifurcations); 3-D time of flight demonstrates intracranial
circulation; contrast enhanced studies will show aortic arch and aortic
braches.
 CT angiography (CTA) with reconstructed views will demonstrates
cervical and intracranial circulation well; better than MRA for detecting
cerebral aneurysms.
 Magnetic resonance venogram (MRV) may be performed to
evaluate suspected venous sinus occlusion.
 Carotid duplex US is non-invasive method of identifying carotid
stenosis; widely used but accuracy is very technician-dependant; less
useful in posterior circulation.
 A combination of MRI,CTA, and carotid Doppler usually accurately
determines the degree of carotid stenosis; otherwise, catheter
angiogram may be necessary.

35. Imaging of the cerebral circulation
 Transcranial Doppler may be helpful in identifying intracranial
stenosis or occlusion; also used to identify cerebral emboli as
there is an audible signal that can be imaged as well; however,
highly technician dependant.
 Catheter angiography is still considered the “gold standard” for
identifying arterial stenosis and aneurysms; carries a risk 1% risk
of stroke as complication; generally necessary only to determine
the degree of extracranial carotid artery stenosis in preparation
for endratrectomy or stenting; however, accuracy of MRA, CTA,
and Doppler US is usually sufficient such that catheter angiogram
is needed only when uncertainty remains; may be necessary to
identify arteriovenous malformations.