Cns examination of left Frontal cortex leasion
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CNS Examination Findings in Left Frontal Cortex Lesion
The left frontal cortex is a large, functionally complex region. Its lesions produce a combination of motor, language, behavioral, cognitive, and autonomic deficits. Below is a systematic examination-based breakdown.
Anatomy of the Left Frontal Lobe (Quick Reference)
The frontal lobe extends from the frontal pole to the central sulcus and is divided into:
- Primary motor cortex (precentral gyrus, area 4)
- Premotor and supplementary motor areas (area 6)
- Frontal eye fields (area 8)
- Broca's area (areas 44/45 - only in the dominant/left hemisphere)
- Prefrontal cortex (dorsolateral and orbitofrontal regions)
- Anterior cingulate (medial aspect)
I. Motor Examination
| Finding | Mechanism |
|---|---|
| Contralateral (right-sided) hemiparesis/hemiplegia | Damage to primary motor cortex (face, arm > leg) |
| UMN pattern - spastic weakness, brisk DTRs, Babinski sign | Corticospinal tract involvement |
| Face and arm > leg weakness | Face/arm homunculus occupies lateral motor cortex; leg is medial |
| Contralateral focal (Jacksonian) motor seizures | Irritative lesion at primary motor cortex |
| Impaired fine motor coordination | Motor planning disruption |
| Motor perseveration | Prefrontal / SMA dysfunction |
| Gegenhalten (paratonia) | Involuntary resistance to passive movement; frontal release sign |
| Motor impersistence | Inability to maintain a motor act (e.g., keep tongue out) |
- Neuroanatomy through Clinical Cases, 3rd Ed. - "Unilateral face and arm weakness is usually caused by a lesion in the contralateral face and arm areas of the motor cortex..."
II. Language Examination (Left Hemisphere - Dominant)
This is the hallmark of a left frontal lesion:
| Finding | Type |
|---|---|
| Broca's (expressive/non-fluent) aphasia | Sparse, effortful, telegraphic speech with preserved comprehension |
| Impaired repetition | Also impaired in Broca's aphasia |
| Word-finding difficulty (anomia) | Especially for verbs |
| Dysarthria | Due to motor cortex involvement |
| Reduced verbal fluency | Bedside FAS (letter fluency) test - severely reduced |
| Impaired writing (dysgraphia) | Motor output of language |
| Global aphasia (acute large lesions) | Evolves toward Broca's over days/weeks |
- Goldman-Cecil Medicine: "expressive aphasia (dominant side)" - Frontal Lobe entry
- Bradley & Daroff's Neurology: Transcortical aphasias also occur with deep frontal white matter involvement
III. Cognitive/Behavioral Examination
These are tested via mental status and neuropsychological components:
| Finding | Description |
|---|---|
| Abulia | Apathy, passivity, markedly delayed responses, soft/brief speech |
| Akinetic mutism (severe medial lesions) | Awake but totally immobile and mute |
| Impaired executive function | Poor planning, reasoning, problem-solving |
| Impaired set-shifting | Fails Wisconsin Card Sorting Test, Trails B |
| Perseveration | Repeating same answer or action; shown on Luria sequencing |
| Confabulation | Filling memory gaps with fabricated content |
| Poor abstract reasoning | Fails proverb interpretation, similarities tests |
| Reduced working memory | Low digit span backward |
| Utilization behavior / environmental dependency | Picks up and uses objects inappropriately |
| Impaired judgment | Fails fire-in-theater or gambling-type tasks |
| Impaired word generation | FAS test: produces < 10 words per letter/minute |
| Left frontal lesions - more associated with depression-like symptoms (vs. right frontal which are more mania-like) |
- Neuroanatomy through Clinical Cases, 3rd Ed., Table 19.10 - full frontal lobe evaluation protocol
IV. Frontal Release Signs (Primitive Reflexes)
These are elicited on physical examination:
| Sign | How to Elicit |
|---|---|
| Grasp reflex | Stroke patient's palm - patient involuntarily grasps |
| Suck reflex | Touch lips - patient makes sucking movements |
| Snout reflex | Tap upper lip - pursing/pouting |
| Root reflex | Stroke corner of mouth - head turns toward stimulus |
| Palmomental reflex | Scratch thenar eminence - ipsilateral chin twitch |
| Glabellar tap (Meyerson's sign) | Tap glabella repeatedly - fails to habituate |
- Rosen's Emergency Medicine: "impaired judgment and insight, as well as the presence of primitive grasp and suck reflexes on physical examination" - with frontal lobe involvement
V. Eye Movement Examination
| Finding | Location | Mechanism |
|---|---|---|
| Ipsilateral conjugate gaze deviation (acute) | Frontal eye fields (area 8) | "Eyes looking away from the hemiplegia" |
| Contralateral forced gaze (ictal) | Epileptiform frontal focus | Eyes/head deviate contralaterally |
| Impaired voluntary saccades contralaterally | Frontal eye field lesion | Slow or absent voluntary gaze to the right |
| Impaired antisaccade task | Dorsolateral prefrontal cortex | Cannot suppress reflexive glance |
| Impaired remembered saccade sequences | Supplementary eye field lesion |
Acute destructive left FEF lesion = right gaze preference (deviation toward lesion) Acute irritative lesion (seizure) = eyes/head deviate to the right (contralateral)
VI. Gait Examination
| Finding | Description |
|---|---|
| Frontal (magnetic) gait | Short shuffling steps, wide-based, difficulty lifting feet, "stuck to floor" |
| Gait apraxia | Cannot sequence normal gait despite intact limb power on testing |
| Associated with incontinence and dementia | Classic frontal lobe triad with hydrocephalus |
VII. Olfactory Examination
| Finding | Cause |
|---|---|
| Anosmia (ipsilateral) | Orbitofrontal tumors (meningioma, olfactory groove) compress olfactory tracts |
| Parosmia | Uncinate gyrus lesion (located at temporal-frontal junction) |
- S. Das Manual on Clinical Surgery: "Parosmia or perversion of sense of smell may be present in a lesion of the uncinate gyrus"
VIII. Bladder/Autonomic
- Urinary incontinence with characteristic unconcern - especially with medial frontal (anterior cingulate and parasagittal) lesions
- Bilateral anterior frontal lesions disturb micturition and defecation (Andrew & Nathan, cited in Adams & Victor)
Summary Table: Left Frontal Lobe vs. Right Frontal Lobe Lesion
| Feature | Left Frontal | Right Frontal |
|---|---|---|
| Language | Broca's aphasia (non-fluent) | Usually no aphasia |
| Motor | Right hemiparesis | Left hemiparesis |
| Gaze (acute) | Deviation to left (toward lesion) | Deviation to right |
| Behavior | Depression-like; abulia | Mania-like; disinhibition |
| Seizure gaze | Eyes deviate to right | Eyes deviate to left |
Bedside Testing Protocol Summary
- Language - fluency, naming, repetition, comprehension (Broca's pattern expected)
- Motor - power, tone (spasticity/gegenhalten), reflexes (UMN), Babinski
- Frontal release signs - grasp, suck, snout, palmomental
- Frontal executive tests - Luria sequencing, go/no-go task, FAS verbal fluency, digit span
- Eye movements - voluntary saccades, antisaccade task
- Gait - observe for magnetic/apraxic gait
- Olfaction - unilateral anosmia
- Behavior - abulia, perseveration, utilization behavior, incontinence
Sources:
- Neuroanatomy through Clinical Cases, 3rd Ed. (Blumenfeld) - Chapter 19 (frontal lobe disorders), Table 19.10
- Goldman-Cecil Medicine - Frontal Lobe Localization summary
- Rosen's Emergency Medicine - Ischemic Stroke section
- Localization in Clinical Neurology, 8e - Frontal lobe saccade pathways
- Adams and Victor's Principles of Neurology, 12th Ed. - Frontal lobe disorders
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