Common brain lesions

Understanding brain lesions is critical in neurology and medicine, as specific lesions in various brain regions can lead to distinct clinical presentations. The table below summarizes some of the most common brain lesions, detailing their location, effects, and associated examples.

Brain Lesion Locations and Effects

Region	Clinical Consequences	Eyes look toward the brain lesion (away from the hemiplegic side)
Frontal Lobe	Disinhibition, deficits in concentration, orientation, judgment; reemergence of primitive reflexes
Frontal Eye Fields	Eyes look toward the brain lesion (away from hemiplegic side)	Seen in destructive lesions (e.g., MCA stroke)
Paramedian Pontine Reticular Formation	Eyes look away from the brain lesion (toward the hemiplegic side)
Medial Longitudinal Fasciculus	Internuclear ophthalmoplegia: impaired adduction of ipsilateral eye, nystagmus of contralateral eye with abduction	Commonly seen in multiple sclerosis
Dominant Parietal Cortex	Agraphia, acalculia, finger agnosia, left-right disorientation	Gerstmann syndrome
Nondominant Parietal Cortex	Agnosia of the contralateral side of the world	Hemispatial neglect syndrome
Hippocampus (Bilateral)	Anterograde amnesia (inability to form new memories)
Basal Ganglia	Resting tremor, chorea, athetosis	Parkinson’s disease, Huntington’s disease, Wilson’s disease
Subthalamic Nucleus	Contralateral hemiballismus
Mammillary Bodies (Bilateral)	Wernicke-Korsakoff syndrome: confusion, ataxia, nystagmus, ophthalmoplegia, amnesia, confabulation, personality changes	Often related to thiamine deficiency (e.g., chronic alcohol use)
Amygdala (Bilateral)	Klüver-Bucy syndrome: disinhibited behavior, including hyperphagia, hypersexuality, hyperorality	Often associated with HSV-1 encephalitis
Dorsal Midbrain	Parinaud syndrome: vertical gaze palsy, pupillary light-near dissociation, lid retraction, convergence-retraction nystagmus	Causes include stroke, hydrocephalus, pinealoma
Reticular Activating System (Midbrain)	Reduced arousal and wakefulness	May result in coma
Cerebellar Hemisphere	Intention tremor, limb ataxia, loss of balance; ipsilateral deficits; fall toward lesion	Lateral cerebellar lesions affect limbs (lateral localization)
Cerebellar Vermis	Truncal ataxia (wide-based gait), nystagmus	Degeneration often associated with chronic alcohol use
Red Nucleus (Midbrain)	Decorticate (flexor) posturing: lesion above red nucleus; Decerebrate (extensor) posturing: lesion at/below red nucleus	Decerebrate posturing generally indicates a worse prognosis

Brain Lesion Locations and Effects

Key Points to Remember

Location-Specific Symptoms: Each brain lesion location produces specific clinical manifestations that can aid diagnosis.
Primitive Reflexes: Frontal lobe lesions may cause reemergence of primitive reflexes, which can indicate cortical damage.
Eye Movement Signs: Frontal eye field and paramedian pontine reticular formation lesions cause characteristic eye deviations, aiding in lesion localization.
Functional Hemisphere Differences: Dominant and nondominant parietal cortices have distinct roles, with the dominant side linked to language and calculation skills, while the nondominant side relates to spatial awareness.
Associated Syndromes: Several brain regions are associated with distinct syndromes (e.g., Klüver-Bucy syndrome with amygdala lesions, Wernicke-Korsakoff syndrome with mammillary body damage).
Posturing as a Prognostic Indicator: Decorticate and decerebrate posturing signify varying levels of brain injury severity, with decerebrate posturing suggesting a more severe prognosis.

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Common brain lesions

Brain Lesion Locations and Effects

Key Points to Remember

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