Clinical Skills Exam: Lesion Localization

Cerebellar lesions

Cause symptoms on the same side (ipsilateral).

Cerebral lesions

Cause symptoms on the opposite side (contralateral).

Brain lesion

Leads to weakness on the opposite side of the body.

Spinal cord lesion

Causes weakness on the same side of the body.

Lesion above corticospinal tract decussation

Results in contralateral weakness.

Lesion below corticospinal tract decussation

Results in ipsilateral weakness.

Upper motor neurons

Located in the brain or spinal cord before the anterior horn.

Lower motor neurons

Located from the anterior horn to the muscle.

Signs of an upper motor neuron lesion

Spasticity, hyperreflexia, +Babinski, minimal atrophy.

Signs of a lower motor neuron lesion

Flaccidity, hyporeflexia/areflexia, fasciculations, muscle wasting.

Positive Babinski sign

Indicates an upper motor neuron lesion.

Hyperreflexia

Caused by an upper motor neuron lesion.

Hyporeflexia

Caused by a lower motor neuron lesion.

Fasciculations

Associated with a lower motor neuron lesion.

Lesion in the spinothalamic tract

Causes opposite side loss of pain and temperature below the lesion.

Lesion in the posterior column

Causes same side loss of vibration and proprioception below the lesion.

Spinothalamic tract crossing

Crosses 1-2 levels after spinal entry.

Posterior column crossing

Crosses in the medulla.

Lesion of posterior column in the medulla

Affects the ipsilateral side below the lesion.

Lesion of spinothalamic tract in spinal cord

Affects the contralateral side below the lesion.

Cerebellar lesion symptoms

Ataxia, unsteady gait, nystagmus, dysarthria, decreased muscle tone.

Basal ganglia lesion symptoms

Rigidity, bradykinesia, involuntary movements, posture/gait disturbances.

Thalamic lesion effects

Contralateral sensory loss.

Hypothalamic lesion effects

Dysautonomia, endocrine changes.

Reticular activating system (RAS) lesion

Leads to impaired consciousness or coma.

CN I lesion

Results in loss of smell (anosmia).

CN II lesion

Results in visual field defects, papilledema from increased ICP.

CN III lesion

Results in ptosis, diplopia, impaired EOMs, pupillary dilation.

CN IV lesion

Results in difficulty looking down/inward (vertical diplopia).

CN VI lesion

Results in inability to abduct eye, horizontal diplopia.

CN V lesion

Results in jaw weakness/deviation, facial sensory loss.

Peripheral CN VII lesion

Causes entire face weakness (Bell's palsy).

Central CN VII lesion

Lower face weakness only (forehead spared)

CN VIII lesion

Hearing loss and vertigo

CN IX/X lesion

Palate fails to rise, uvula deviates to normal side, dysphonia

CN XI lesion

Shoulder droop, weakness in shrugging

CN XII lesion

Tongue deviates toward the weak side

Clonus

Indicates upper motor neuron lesion

4+ reflex grade

Hyperactive reflex with clonus → UMN lesion

0 or 1+ reflex grade

Hyporeflexia or areflexia → LMN lesion

Lesion in corticospinal tract above medulla

Causes contralateral weakness

Lesion in corticospinal tract below medulla

Causes ipsilateral weakness

Pronator drift

Indicates corticospinal tract lesion

Babinski test positive

Indicates corticospinal (UMN) lesion

Brudzinski sign positive

Indicates meningeal irritation (possible meningitis)

Kernig sign positive

Indicates meningeal irritation (pain/resistance on leg extension)

Fixed, dilated pupils

Indicate compression of CN III from temporal lobe herniation

Decorticate rigidity

Indicates lesion in cerebral hemispheres (flexor response)

Decerebrate rigidity

Indicates lesion in diencephalon, midbrain, or pons (extensor response)

Lesion in diencephalon/midbrain

Causes decerebrate rigidity

Lesion in cerebral hemispheres

Causes decorticate rigidity

Positive Romberg with eyes open and closed

Indicates cerebellar ataxia

Positive finger-to-nose dysmetria

Suggests cerebellar lesion

Intention tremor

Indicates cerebellar lesion

Impaired rapid alternating movements (RAMs)

Indicate cerebellar lesion (dysdiadochokinesis)

Unsteady gait with falling to one side

Suggests cerebellar lesion on that side

Lesion in thalamus

Leads to contralateral sensory loss

Lesion in brainstem cranial nerve nuclei

Causes ipsilateral cranial nerve deficits with contralateral body weakness

Lesion in spinal cord anterior horn

Affects lower motor neurons → flaccid paralysis

Lesion in internal capsule

Results in contralateral motor and sensory deficits

Lesion in basal ganglia

Results in movement tone abnormalities such as rigidity and bradykinesia

Metabolic coma pupil finding

Equal and reactive pupils

Structural coma pupil finding

Unequal or fixed pupils

Fixed and dilated pupil

Suggests compression of CN III due to herniation

Stroke affecting motor cortex

Causes contralateral weakness or paralysis

Stroke affecting sensory cortex

Causes contralateral sensory loss

Stroke affecting brainstem

Causes cranial nerve abnormalities with crossed findings (ipsilateral CN + contralateral body)