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Cortical Localization
David Roman Renner, MD
Department
of Neurology
Reading
Resources:
Lindsay KW, Bone I, Callander R. Clinical
Presentation, Anatomical Conceps and Diagnostic Approach:
Higher Cortical Dysfunction. In:
Neurology and Neurosurgery Illustrated.
Philadelphia, Churchill Livingstone 1998, pp. 105-114.
Rolak LA. Approach to the Patient with Neurologic Disease.
In: Neurology
Secrets. Philadelphia,
Hanley & Belfus, Inc. 1993, pp. 37-44.
What
you are responsible for:
I will write all test questions for this lecture hour, the content of
which is
addressed in this handout and/or the lecture hour.
Your test questions will only be
derived from the section on cortical localization. The
remaining text is included to assist you in localizing lesions in the
neuraxis through a complete neurologic examination.
Syllabus Contents:
Divisions of the Neuroaxis
Content of the Neurologic Examination
Clinical Hallmark of Lesions within the Neuraxis
Typical Neurologic Examination when Lesioning Various Levels of the
Neuraxis
Objectives:
The student should be able to:
1.
state
how hemispheric dominance is defined
2.
lateralize
hemispheric dominance based upon language and handedness
3.
localize
lesions within the hemispheric cortex via clinical exam findings
(You will not be tested on information following the cortical
localization section.)
-
The history and physical accurately localizes most lesions within the neuraxis
-
Divisions of the neuraxis have specialized functions
-
Damage to various divisions produce unique clinical deficits
Localization
is important
Investigation modalities differ widely depending upon the level
affected
Divisions of the Neuraxis:
Cortical Brain
Subcortical
Brain
Brainstem
Cerebellum
Spinal
Cord
Root
Peripheral Nerve
Neuromuscular Junction
Muscle
The neurologic exam allows one to accurately identify which segment of the neuraxis is lesioned. A complete neurologic exam varies between neurologists, but generally consists of testing of:
Higher cortical function
Cranial nerves
Cerebellar
Motor
Sensory
Reflexes
Gait and Station
Higher Cortical Function:
Depends upon hemispheric
dominance
Non-neurologists are able to
state generalizations about hemispheric dominance:
right:
visual/spatial, perception and memory
left:
language and language dependent memory
One should be able to further
localize lesions
Cortical Brain:
Frontal Lobe:
Left
sided lesions:
language
Broca’s
Aphasia
Right
sided lesions:
?judgement?
Bilateral
lesions:
precentral
gyrus: motor homunculous
supplementary
motor cortex: eye and head turn
prefrontal
cortex: personality, initiative
paracentral
lobule: cortical inhibition of
voiding B/B
Parietal
Lobe:
Right
sided lesions:
anosognosia:
left hemineglect
dressing
and constructional apraxia
geographic
agnosia
Left
sided lesions:
Gerstman’s Tetrad (not
triad): L/R confusion, finger
agnosia, acalculia, agraphia without alexia
Bilateral
lesions:
Somatosensory homunculous
abnormal
posture and passive movement
localization
of touch
2-point
discrimination
astereognosis
Temporal:
Right
sided lesions:
hearing
language
Left
sided lesions:
hearing
sounds, rhythm, music
Wernicke’s
Aphasia
Bilateral
lesions:
learning
and memory: mid/inferior gyri
olfaction:
limbic
Auditory
cortex: Heschel’s gyrus
Occipital
Lobe:
Right
sided lesions:
micropsia
macropsia
Left sided lesions:
?
Bilateral
lesions:
visual
hallucinations: elemental and
unformed
prosopagnosia:
familiar faces
cortical
blindness: striate cortices,
normal pupil rx
Anton’s
syndrome: (para)striate, denial
of obvious blindness
Balint’s
syndrome: inability to direct
voluntary gaze with visual
agnosia
Neurologic Examination when Cortical Brain is
Lesioned
Higher Cortical Function:
you may see an aphasia, apraxia, or an agnosia
Cranial Nerves should be
normal, unless there is forced eye deviation
Cerebellar function should be
normal
Motor exam may reveal weakness
of face/arm>leg (or vice versa) with
hypertonia
if corticospinal tracts are hit
Sensory exam may be abnormal
(face/arm>leg, or vice versa)
Reflexes may be abnormal
(hyper-reflexia), and Babinski’s reflex
may
be present if the corticospinal tracts are hit
Subcortical
Brain
Contains deep white radiating
fibers tightly packed together
When lesioned, there is equal
involvement of face/arm/leg. Symptoms
can
include
weakness or sensory abnormalities
Visual abnormalities
occur due to interruption of radiating fibers are contained
within
the subcortical brain
deep
parietal: bilateral homonomous
quad on the floor
deep
temporal (Meyer’s loop): bilateral
homonomous quad in the sky
Neurologic Examination when
Subcortical Brain is Lesioned
Higher cortical function should
be normal
Cranial nerves may reveal a
visual field cut
Cerebellar function is usually
normal
Motor exam may reveal weakness
in face=arm=leg with hypertonia
Sensory exam may reveal sensory
abnormalities in face=arm=leg
Reflexes may be abnormal
(hyper-reflexia) with increased tone, and
Babinski’s
reflex may be present if corticospinal tracts are lesioned
Brainstem
The brainstem is basically a
spinal cord with embedded cranial nerves
Cranial nerve symptoms
with long tract symptoms characterize brainstem
disease
Long
Tract signs: (bilateral and
crossed)
corticospinal
(pyramidal): motor
spinothalamic:
pain/temp to the thalamus
dorsal
columns: prioprioception/vibration
to thal.
(due
to decusation of long tracts, BS lesions do not produce horizontal
motor/sensory
levels as in the cord, but rather vertical levels of
hemiparesis/hemidysesthesias)
Neurologic
Examination when Brainstem is Lesioned
Higher cortical function should
be normal
Cranial nerves may be abnormal
III,
IV, VI: diplopia
V:
decreased facial sensation
VII:
drooping
VIII:
deaf and dizzy
IX,
X, XII: dysarthria and dysphagia
XI:
decreased strength in neck and shoulders
Cerebellar Function should be
normal
Motor exam may reveal
hemi-paresis and hemi-hypertonia
Sensory exam may reveal sensory
abnormalities
Reflexes may be abnormal
(hyper-reflexia) including the jaw jerk
reflex,
with increased tone, and Babinski’s reflex
Cerebellar Function
Some people believe that one
can not test specifically for cerebellar abnormalities
no
single test on examination reliably evaluates the cerebellum
H: hypotonia
A: assynergy of (ant)agonist muscles
N: nystagmus
D: dysmetria, dysarthria
S: stance and gait
T: tremor
Neurologic
Examination when the Cerebellum is Lesioned
Higher cortical function should
be normal
Cranial nerves should be normal
Cerebellar function may reveal
nystagmus, flaccid dysarthria
Motor exam should show
preserved strength, with ipsilateral hypotonia, an ataxic
tremor,
dysmetria
Sensory exam should be normal
Reflexes should be normal
Spinal
Cord
Sensory level
Spasticity/hypertonia almost
always in the legs, sometimes in the arms if the
lesion
is high enough
Weakness
in the legs, extensors > than flexors, distal > proximal
Bowel and bladder
involvement producing incontinence
Neurologic Examination when the Spinal Cord is
Lesioned
Higher cortical function should
be normal
Cranial nerves should be normal
Cerebellar function should be
normal
Motor exam reveals bilateral
leg weakness (extensors worse than flexors) below
the
lesion with increased tone/spasticity
Sensory exam reveals a sensory
level which may be assymetric
Reflexes are increased (hyper-reflexic)
below the level (clonus?)
With
Babinski’s reflex, and the loss of superficial reflexes (Beavor’s sign,
cremasteric,
anal wink, etc)
Root/Radiculopathy
Pain
is the hallmark of a radiculopathy
Sensory abnormalities should
localize to a dermatome
provocative
maneuvres exacerbate the discomfort
Asymmetric weakness in a
myotome
proximal
(C5C6)
distal
(L5S1)
(because
the most common radiculopathy in the cervical region produces
proximal weakness, and the most
common radiculopathy in the lumbosacral region produces distal weakness, one
cannot make the statement that radiculopathies “tend to produce
proximal/distal weakness.”
Neurologic Examination when a Root is Lesioned
Higher cortical function should
be normal
Cranial nerves should be normal
Cerebellar function should be
normal
Motor exam may reveal
assymetric weakness, atrophy, and fasiculations in a
myotome
Sensory exam may reveal
assymetric dysesthesias confined to a dermatome
Reflexes may be decreased
(hypo- to a-reflexia if the root carries a
reflex)
Peripheral Nerve (nonfocal)
Weakness that is distal
predominant, which may start a bit asymmetric, but with
time,
looks symmetric
Sensory
dysesthesias that are distal predominant
Autonomic involvement may occur
Difficulty
focusing eyes
Erectile
dysfunction
Dyshydrosis:
changes in the pattern of sweating
Constipation
Cardiac
arrhythmias
Trophic changes:
smooth shiny skin, vasomotor abnormalities (edema,
temperature
dysregulation, vascular flushing), hair loss, nail changes
Neurologic
Examination with Diffuse Peripheral Nerve Lesioning
Higher cortical function should
be normal
Cranial nerves should be normal
Cerebellar function should be
normal
Motor exam may reveal
distal-predominant weakness, atrophy, and fasiculations
Sensory exam may reveal
distal-predominant sensory loss
Reflexes may reveal distal
hypo- to a-reflexia
Neuromuscular
Junction
Fatiguability
is the hallmark
Weakness:
proximal and symmetric
exacerbated
with use, recovers with rest
often
affects facial muscles (ptosis, dysconjugate gaze, slack jaw)
muscles
have normal bulk and tone
Sensation:
preserved
Neurologic Examination in Disorders of the
Neuromuscular Junction
Higher cortical function should
be normal
Cranial nerves may show
fatiguable ptosis, dysconjugate gaze, slack jaw
Cerebellar function should be
normal
Motor exam may reveal
fatiguable proximal weakness in both UE’s and LE’s
no
atrophy or fasiculations
tone
may be slightly decreased
Sensory exam should be normal
Deep tendon reflexes may be
hypo- to a-reflexic in Lambert Eaton Myasthenic
Syndrome,
or normal in MG
Muscle
Symmetric proximal weakness
of arm and leg muscles
Sensation is normal (though
patients complain of cramping and aching)
Neurologic Examination in Disorders of Muscle
Higher cortical function should
be normal
Cranial nerves may reveal nonfatiguable
ptosis, dysconjugate gaze, slack jaw,
dysphagia,
dysphonia, (dysarthria)
Cerebellar function should be
normal
Motor exam reveals symmetric
proximal weakness in both UE’s and LE’s
atrophy
and fasiculations
Sensory exam should be normal
Reflexes should be preserved
until late in the disease
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Last updated: 10/05/2002 © 2000-2002 John Rose, MD University of Utah School of Medicine