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The angular gyrus is a hub where number sense, writing, spatial orientation and finger representation all overlap in the brain's map of the body and space. Damage there produces four odd-looking deficits that all trace back to one crossroads region breaking down.

• Gerstmann's syndrome arises from a lesion of the dominant (typically left) angular gyrus, at the parieto-temporo-occipital junction.
• The angular gyrus integrates visual, spatial, language and number-processing information, so its disruption produces a cluster of seemingly unrelated deficits.
• The four core features are finger agnosiaThe inability to recognise familiar objects, sounds, or faces despite normal senses.Read more →, acalculia, agraphia and left-right disorientation.
• Complete tetrads are uncommon; partial presentations (two or three features) are frequently seen clinically.
• Common causes include ischaemic stroke, tumour, or other focal dominant parietal pathology.

• A 68-year-old man cannot name his individual fingers when touched, cannot perform simple subtraction, writes illegibly with letter omissions, and confuses left and right.
• A patient with a suspected left angular gyrus lesion cannot identify which finger has been touched with eyes closed despite normal sensation.
• A 70-year-old woman with a dominant parietal lobeThe part of the brain near the crown of the head, involved in touch sensation and spatial awareness.Read more → infarct cannot perform simple mental arithmetic despite intact language comprehension.
• Questions naming the dominant angular gyrus as the classic lesion site for this tetrad.

• Gerstmann's syndrome vs Balint's syndrome — Gerstmann is a unilateral dominant angular gyrus lesion causing finger agnosiaThe inability to recognise familiar objects, sounds, or faces despite normal senses.Read more →/acalculia/agraphia/left-right disorientation, whereas Balint's is bilateral parieto-occipital damage causing simultanagnosiaThe inability to perceive more than one object in a scene at the same time, despite normal vision.Read more →, optic ataxiaLoss of full control of body movements, causing an unsteady, uncoordinated gait or actions.Read more → and ocular apraxia.
• Finger agnosiaThe inability to recognise familiar objects, sounds, or faces despite normal senses.Read more → vs astereognosis — finger agnosia is specific to identifying one's own fingers, whereas astereognosis is a broader failure to identify objects by touch.
• Acalculia vs developmental dyscalculia — acalculia is acquired after focal brain injury, whereas dyscalculia is a lifelong developmental learning difficulty.
• Dominant vs non-dominant parietal lesions — dominant lesions produce the Gerstmann tetrad, whereas non-dominant lesions more typically cause neglect and constructional apraxia.

• Expecting all four Gerstmann features to always be present together — partial presentations are common and still point to the same localisation.
• Confusing finger agnosiaThe inability to recognise familiar objects, sounds, or faces despite normal senses.Read more → with a primary sensory deficit — basic touch sensation is intact; the deficit is in naming/identifying the fingers.
• Mislabelling acalculia as aphasia when language comprehension is otherwise preserved.
• Assuming any parietal stroke gives Gerstmann's syndrome — the syndrome specifically localises to the dominant angular gyrus, not the parietal lobeThe part of the brain near the crown of the head, involved in touch sensation and spatial awareness.Read more → generally.

• Localise the clue to the relevant anatomical level, cell type, pathway or molecular process.
• Map that structure or process to its normal function.
• Predict the deficit or clinical sign produced when it is disrupted.
• Reject options that belong to a neighbouring structure, pathway or level of explanation.