BOF 3) 55 year old female presented with altered consciousness and dysplasia, conjugate eye deviation to right side and flaccid paralysis of lower limbs. Other examinations were normal. The lesion could be in? 1) L-cerebellar infarction 2) R-internal capsule 3) R-frontal lobe 4) R-temporal lobe 5) R-parietal lobe
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Now I have enough to give a thorough, well-sourced answer. Let me reason through this carefully.
Answer: 3) Right Frontal Lobe
Breaking Down the Clinical Findings
| Finding | Localizing Value |
|---|---|
| Conjugate eye deviation to the RIGHT | Lesion in the right frontal eye field (FEF) - "eyes look toward the stroke" |
| Flaccid paralysis of lower limbs | Upper motor neuron lesion affecting the leg area (parasagittal/medial cortex) |
| Dysphasia | Left hemisphere language area involvement (but wait - see below) |
| Altered consciousness | Large hemispheric lesion |
| Other examinations normal | No brainstem signs, no cerebellar signs |
The Key Rule - "Look Toward the Stroke"
As confirmed by Goldman-Cecil Medicine:
"Horizontally and conjugately deviated eyes owing to a hemispheric lesion follow the rules of 'look toward a stroke, look away from a seizure' because of ablation or stimulation of the frontal lobe gaze center."
- Goldman-Cecil Medicine, Cranial Nerve Examination section
The frontal eye field (FEF) in the posterior frontal lobe (Brodmann area 8) normally drives conjugate gaze to the opposite side. When it is destroyed by a stroke, the intact contralateral FEF is unopposed and drives the eyes toward the side of the lesion. Therefore:
- Conjugate deviation to the right = right FEF is damaged = right frontal lobe lesion
Why the Lower Limbs Are Affected
The homunculus in the frontal lobe has a somatotopic organization:
- The leg area is represented in the medial/parasagittal portion of the primary motor cortex (supplementary motor area and paracentral lobule)
- A large right frontal lobe lesion (e.g., from anterior cerebral artery territory infarction or a large MCA territory lesion) can preferentially affect the lower limb representation
Eliminating the Other Options
Option 2 - R Internal Capsule:
- Would cause conjugate deviation to the right? Possibly (subcortical near FEF fibers), but the internal capsule lesion classically causes contralateral hemiplegia of face + arm + leg equally (capsular hemiplegia), not selective lower limb weakness. Also, isolated IC lesions typically do NOT cause dysphasia (language areas are cortical).
Option 1 - L Cerebellar Infarction:
- Would cause ipsilateral cerebellar signs (ataxia, dysmetria, nystagmus), NOT conjugate eye deviation toward the right or dysphasia. This is eliminated.
Options 4 & 5 - R Temporal / R Parietal lobe:
- Temporal lobe: May cause visual field defects (Wernicke's aphasia in dominant hemisphere) but not the classic conjugate deviation + lower limb pattern.
- Parietal lobe: Causes sensory deficits, neglect, but not primarily the motor + gaze pattern described.
Note on "Dysplasia" vs. "Dysphasia"
The question likely means dysphasia (speech impairment). This is a tricky point:
- Dysphasia typically localizes to the left (dominant) hemisphere
- However, in a right frontal lobe lesion, dysphasia is not expected unless the patient is left-handed or has crossed dominance
- This may represent transcortical motor aphasia from SMA involvement, or the question intends to test the eye deviation + motor pattern regardless of the aphasia detail
- Some BOF/MCQ questions use "dysphasia" loosely to mean any speech difficulty
The combination of right conjugate eye deviation + lower limb paralysis is the definitive localizing clue here, and both point to the right frontal lobe.
Final Answer: 3) Right Frontal Lobe
The right frontal lobe (likely a large infarct in the right ACA-MCA territory) explains:
- Eyes deviate right (toward the lesion) - frontal eye field destruction
- Flaccid lower limb paralysis - medial motor cortex / parasagittal involvement
- Altered consciousness - large hemispheric lesion with mass effect
- Speech disturbance - supplementary motor area or if patient has right hemisphere language dominance
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