The document discusses the localization of central and peripheral nervous system pathology, detailing the functions and common lesions associated with various brain regions and spinal cord areas. It highlights how lesions affect motor and sensory functions, leading to specific clinical manifestations such as weakness, sensory deficits, and cognitive disorders. Additionally, it explores imaging modalities like CT and MRI for diagnosing these conditions, emphasizing their advantages and limitations.

1. Localisation of CNS Pathology
Dr GW Ngwende
MBChB (UZ), MMed(Medicine), FCP(ECSA), PGD Clin
Neuro(UCL), FEBN, FRCP(Lond)

2. 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.

3. 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.

4. Frontal lobe
 FUNCTIONS: cognition,
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)
non-fluent aphasia,
hemiparesis, partial
seizures.

5. 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.

6. 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.

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

8. 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.

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

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

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

12. 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.

13. 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).

14. 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.

15. Thoracic spinal cord
 FUNCTION: Motor and sensory functions of the arms and
legs, bladder function.
 COMMON LESIONS: usually tumours metastases 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 is spared).

16. 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.

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

18. Spinal cord localization

19. Spinal cord syndromes

20. 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.

21. 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.

22. 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, paraesthesias,
weakness, flaccidity, loss of reflexes, and loss of vibratory
and position sense in the nerve distribution.

23. 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.

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

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

26. 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.

27. 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)

28. 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)

29. 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.

30. 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.

31. 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.