Patient understands speech, cannot write (agraphia), has anomia, and cannot distinguish left versus right – which brain lobe is lesioned?

Parietal Lobe Lesion

The lesion is in the parietal lobe (Answer A), specifically the left inferior parietal lobule, which produces a constellation of deficits including agraphia (inability to write), anomia (word-finding difficulty), and left-right disorientation while preserving auditory comprehension—classic features of Gerstmann syndrome or angular gyrus syndrome.

Clinical Reasoning

Preserved Comprehension Rules Out Temporal Lobe

• The patient understands what is being told to him, which indicates intact auditory comprehension 1
• Temporal lobe lesions (particularly Wernicke's area in the posterior superior temporal gyrus) produce impaired comprehension, which this patient does not have 2
• Damage to the mid-to-posterior middle temporal gyrus specifically impairs multiword comprehension, which is preserved in this patient 2

Agraphia + Anomia + Left-Right Disorientation Localizes to Parietal Lobe

• Agraphia (inability to write) occurs with parietal lobe lesions, particularly involving the angular gyrus and supramarginal gyrus 3
• Anomia (word-finding difficulty) with preserved comprehension suggests a disconnection between semantic knowledge and word retrieval, which involves parietal-temporal junction areas 4
• Left-right disorientation is a classic localizing sign for left inferior parietal lobule damage, specifically the angular gyrus region 3
• The combination of these three deficits points to the temporal-parietal junction and inferior parietal lobule 1

Why Not Frontal Lobe

• Frontal lobe lesions (Broca's area) produce non-fluent, effortful speech with preserved comprehension, but the primary deficit is in speech production, not writing or left-right orientation 5, 6
• Broca's aphasia involves impaired repetition due to arcuate fasciculus damage, which is not the primary presentation here 5

Why Not Occipital Lobe

• Occipital lobe lesions produce visual deficits (alexia without agraphia, visual field defects), not the language and spatial orientation deficits described 3
• This patient has agraphia (cannot write), not pure alexia, ruling out occipital pathology 3

Common Pitfall

The key distinguishing feature is preserved auditory comprehension—if comprehension were impaired, you would consider temporal lobe (Wernicke's area). The triad of agraphia, anomia, and left-right disorientation with intact comprehension is pathognomonic for left inferior parietal lobule lesions 1, 3.