Cortical Stroke Syndromes: Localize the Dysfunction
Localize cortical dysfunction using motor maps, measured language, attention, and visual fields before testing arterial territories and lesion extent.
A weak hand, a missed word, and an unseen half of space are observations, not artery names. First ask which tissue could lose those functions while preserving the functions you actually tested. Then use arterial territories as a working model, not a substitute for the examination.
Orient: dysfunction before the vessel
Localization asks where; diagnosis and mechanism ask what happened and why. Cerebral motor commands mostly cross before reaching their target limbs, and ascending body sensory pathways have crossed before reaching the cerebrum. A left cerebral lesion therefore usually causes right-sided limb weakness or sensory loss. A cerebral face-and-body pattern is typically contralateral together. This differs from a brainstem pattern combining an ipsilateral cranial-nerve deficit with contralateral body dysfunction. “Crossed” cerebral control does not mean crossed face-body signs. [1][2]
Test alertness, hearing, vision, language comprehension, and ability to cooperate before interpreting a failed task. Establish what changed and when. A patient with old left-sided inattention and new right-sided weakness may have more than one lesion. A normal task is useful only if the patient could perform it reliably; failure to follow a spoken command does not automatically mean weakness.
Write a tissue hypothesis such as “left lateral sensorimotor cortex with language-network involvement.” Compare it with a compact deep lesion, peripheral nerve disease, or brainstem injury. Aphasia, neglect, and cortical sensory deficits increase suspicion for cerebral networks, but subcortical disconnection and altered cortical perfusion can produce similar signs. Their absence does not exclude a small cortical infarct.
Abrupt focal weakness, language change, or visual loss requires urgent stroke evaluation. Ischemia, hemorrhage, seizure-related dysfunction, and other disorders can overlap clinically. Localization alone neither proves ischemia nor determines reperfusion eligibility. Do not wait to finish this lesson or every examination maneuver before seeking emergency care. [9]
Predict: right arm and right face sensory loss points to which cerebral side?
The left cerebrum. That side inference alone does not distinguish cortex, thalamus, and their connecting pathways.
Motor map: medial leg, lateral face and hand
The precentral gyrus contains primary motor cortex; the postcentral gyrus contains primary somatosensory cortex. Their body maps curve onto the medial hemisphere in the paracentral lobule. The leg and foot lie mainly medially. The hand, arm, and face lie laterally, with the face inferior to the hand. A motor homunculus is a schematic of this unequal cortical representation, not a literal little person or an exact boundary between vessels. [1][2]
Right leg-predominant weakness with relatively preserved face and hand suggests left medial motor tissue. Extension posteriorly into adjacent medial sensory cortex can add right leg sensory dysfunction. Left hand weakness accompanied by impaired left-hand touch recognition suggests right lateral sensorimotor tissue rather than an isolated radial nerve injury. Small cortical lesions can affect a hand selectively; they need not disable the whole arm.
The corona radiata gathers descending fibers into the internal capsule. Corticospinal fibers serve the limbs; corticobulbar fibers serve cranial motor systems. A compact deep lesion can weaken face, arm, and leg together without aphasia or neglect. Weakness need not be equal, and sensory fibers can also be involved. Forehead sparing suggests a supranuclear facial pattern but does not distinguish motor cortex from capsule. Neither hypertension nor “pure motor” proves a particular perforator mechanism.
Recognition is not basic sensation
Stereognosis means recognizing a familiar object by touch; graphesthesia means recognizing a figure traced on skin. First establish adequate touch, position sense, attention, and hand exploration. Use familiar objects and demonstrate the task. If basic sensation is absent, failed object recognition cannot independently establish a cortical association deficit. Aphasia can prevent naming a correctly recognized key. Matching shapes or demonstrating an object's use helps separate recognition from naming. With those prerequisites intact, unilateral failure supports contralateral parietal sensory-network dysfunction. [6]
Predict: a lesion causing left-hand tactile recognition failure extends into the neighboring motor hand area. Which hand becomes weak?
The left hand. Both networks are in the right hemisphere; crossing does not change as the lesion crosses the central sulcus.
Language and attention: test the network
Handedness is not proof of language dominance. Language is usually left-dominant, but the side must be stated when a case depends on it. “Dominant” here means language-dominant, not globally superior. Spatial attention uses both hemispheres, with an important right-hemisphere contribution; severe persistent left neglect is especially associated with right frontoparietal network injury. Language dominance does not simply reverse every other specialization. [3][4]
Aphasia is impaired language. Dysarthria is impaired articulation: words may be slurred while grammar, naming, comprehension, reading, and writing remain intact. Speech apraxia concerns planning speech movements and may coexist with aphasia. Listen to spontaneous sentences, test naming, ask commands without gestures, and test repetition of words and unfamiliar sentences. Check hearing and allow a response with an unaffected limb. Copying a signature is not a sufficient writing assessment; request an original sentence or writing to dictation.
Expressive or Broca-type pattern: reduced, effortful, often agrammatic output; relatively better comprehension; impaired repetition. Complex grammar comprehension can still fail. The syndrome involves a dominant frontal language network, not invariably one small cortical spot.
Receptive or Wernicke-type pattern: fluent but error-filled speech, impaired comprehension, and impaired repetition. Fluent speech is not evidence of intact language.
Conduction pattern: relatively fluent output and relatively preserved comprehension, but disproportionately impaired repetition, often with sound substitutions and attempted corrections. Dorsal temporoparietal connections, including arcuate pathways, matter; this is not proof of an isolated arcuate fasciculus lesion.
Global pattern: severe impairment of output, comprehension, and repetition, suggesting extensive dysfunction across language networks. The bedside pattern does not measure final infarct size.
Preserved sentence repetition changes the interpretation: poor comprehension with fluent output suggests a transcortical sensory pattern rather than classic Wernicke aphasia. Reduced initiation with preserved repetition may occur with medial frontal or adjacent network injury. Independent face-hand weakness supports additional lateral motor involvement; leg-predominant weakness instead raises medial motor involvement. [3]
Hemispatial neglect is reduced attention to contralesional space, objects, or the body. Test cancellation, drawing, and personal attention, not just visual fields. In extinction, a patient detects either stimulus alone but misses the contralesional one during simultaneous bilateral stimulation. This can occur with touch as well as vision. Compare single and double stimulation at the same locations. A true hemianopia can coexist with neglect: repeated failure to see single targets throughout a half-field must not be relabeled extinction. [4][6]
Predict: a patient detects either hand touch alone but reports only the right during simultaneous touch. What did the double stimulation reveal?
Left tactile extinction, an attentional competition effect. It does not establish that left primary sensation is absent.
Visual fields: follow a half of the world
Examine each eye separately while the patient fixes on a central target. Homonymous hemianopia is loss of the same side of visual space in both eyes. Right visual space projects through the left optic tract, lateral geniculate nucleus, optic radiations, and occipital visual cortex. A right homonymous defect therefore localizes to the left postchiasmal pathway, not to a blind right eye. A monocular defect usually points anterior to the chiasm, to retina or optic nerve; temporal field loss in both eyes suggests the crossing fibers at the chiasm. [5]
Optic radiations spread through several lobes. Temporal fibers, including Meyer's loop, carry the contralateral upper visual quadrant. Parietal fibers carry the contralateral lower quadrant. A field cut alone is not a precise lobe locator because occipital lesions can also produce quadrant defects. Combine it with independently measured language, sensory recognition, or attention findings. Large lesions can interrupt multiple bundles and produce a complete hemianopia.
Macular sparing means preserved central vision within an otherwise affected half-field. It can accompany occipital infarction when central-field cortex remains supplied, including through variable collateral flow. It is neither obligatory in PCA infarction nor sufficient to prove a PCA occlusion. Absence of sparing does not identify a tumor. Likewise, isolated homonymous hemianopia does not prove occipital injury: an optic tract, geniculate, or radiation lesion remains possible. Field testing and imaging provide complementary information. [5][7]
Seeing, recognizing, and reading are different
After confirming adequate acuity and fields, compare recognition by sight with recognition by touch or voice. Visual object-recognition failure despite tactile recognition suggests higher visual processing rather than loss of object knowledge. Face-recognition failure with preserved recognition by voice is called prosopagnosia and implicates occipitotemporal networks. Difficulty attending to several objects at once is simultanagnosia; it is not equivalent to a missing half-field. [4][5]
In the classic left-dominant reading-disconnection model, left occipital injury removes right-field input and splenial injury blocks transfer of surviving right-hemisphere visual information to left language networks. Alexia without agraphia means impaired reading with genuinely preserved writing, not merely successful copying. Bilateral visual cortical injury can cause cortical blindness with preserved pupillary light responses, because retinal input to pretectal brainstem circuits branches away before visual cortex. Denial of established blindness is an Anton-type presentation, not proof of a particular embolic source. [3][5][7]
Predict: a right parietal lesion extends into nearby optic radiations. Which quadrant is particularly at risk?
The left lower visual quadrant in both eyes. A real lesion's extent may produce a larger or less tidy defect.
Territories: a useful model with variable edges
Now place the tissue hypothesis on a vascular map. The anterior cerebral artery (ACA) usually supplies medial frontal-parietal tissue, including much of the leg map. Medial frontal involvement can reduce initiative, called abulia, and impair continence or gait initiation. These findings are not required in every ACA lesion. The middle cerebral artery (MCA) usually supplies much of the lateral hemisphere: face-hand sensorimotor tissue and major language or attention networks. Deep MCA branches also supply subcortical structures. [1][2]
The posterior cerebral artery (PCA) commonly supplies occipital and inferomedial temporal tissue, with deep branches supplying structures such as the thalamus. It is not exclusively a visual artery. Medial temporal injury can impair new memory formation: compare immediate registration with delayed retention while checking attention and language. Thalamic injury can produce contralateral sensory loss and later central pain. A territory involving deep motor pathways can include weakness. [7]
The internal carotid system supplies ACA and MCA, while the vertebral arteries join the basilar system. Communicating arteries and pial collateral channels link circulations, but their capacity varies. A proximal occlusion puts tissue at risk; collateral flow and reperfusion influence what actually infarcts. Superficial territory borders overlap and vary between people. Do not name a distal branch from a motor distribution alone, or infer a cardiac source merely because atrial fibrillation is present.
Watershed or border-zone regions lie between major arterial supply systems. They include cortical ACA-MCA and MCA-PCA borders and internal white-matter borders. Low systemic pressure or a severe upstream stenosis can compromise flow. Bilateral proximal arm weakness after hypotension can fit anterior border-zone injury, but is not specific to it and does not require hip weakness. Watershed lesions need not be bilateral.
Embolic fragments can also reach distal border regions; low flow can impair their clearance. A 50-patient study found both perfusion abnormalities and microembolic signals, sometimes together. Thus border-zone location alone cannot choose low flow versus embolism. Interpret perfusion, vessel imaging, embolic-source evidence, and timing together; a normal later perfusion study does not exclude earlier low flow. [8]
Predict: border-zone infarcts coexist with reduced perfusion and detected embolic signals. Must one mechanism be discarded?
No. Flow limitation and embolization can coexist and interact; the distribution does not establish a single exclusive cause.
Synthesis: test the proposed extent
Build the smallest anatomical explanation that accounts for all reliable findings, then try to disprove it. Dominant posterior language dysfunction plus a superior homonymous quadrant defect supports temporal-network and radiation involvement. The same language pattern with marked face-hand weakness requires motor-system involvement as well. Neither combination names an exact arterial branch.
Dominant parietal dysfunction can impair writing, calculation, finger identification, and left-right discrimination, a cluster often called Gerstmann syndrome. Confirm comprehension and motor ability before interpreting those tasks. If new hand weakness accompanies those deficits, an isolated angular-region lesion is insufficient: consider extension toward lateral motor tissue, deeper fibers, or an additional lesion. [3][4]
A destructive frontal eye-field lesion may bias gaze toward its hemisphere, because that field normally helps direct gaze away. Preserved reflex eye movements despite impaired voluntary gaze support a supranuclear problem, rather than failure of the final brainstem gaze machinery. Seizures can produce a different gaze pattern. [10] A unilateral cranial-nerve palsy with opposite body weakness instead demands a brainstem comparison. Classic locked-in syndrome usually reflects bilateral ventral pontine injury, not a cortical language deficit; awareness may be demonstrated through preserved vertical gaze or blinking. [11] See the brainstem stroke companion.
Time course constrains diagnosis separately from location. Gradually progressive language dysfunction suggests a different process from abrupt aphasia; a mass or inflammatory lesion can occupy the same tissue as an infarct. Seizures and migraine phenomena can mimic stroke, and functional symptoms require positive clinical evidence rather than a normal scan alone. Imaging tests lesion location, extent, age, hemorrhage, and vascular status. If the report and examination disagree, recheck both and consider coexisting lesions, rather than changing laterality to fit a memorized syndrome.
Predict: a tiny old right occipital infarct is reported in a patient with new aphasia and right-hand weakness. Does that report explain the new syndrome?
No. In a patient with left language dominance, the new findings implicate left language and motor networks. An old lesion is not automatically the cause of new deficits.
Practice: commit to tissue, then test the inference
For each original clinical example, identify the decisive impaired and preserved functions before comparing choices. Distinguish the anatomical conclusion from what still requires imaging or etiologic investigation.
Case 1
Show answer and explanations for case 1
A. Impaired position sense in the right foot (Best answer)
Right leg-predominant weakness places the lesion in left medial motor cortex. Posterior extension into medial somatosensory cortex threatens right foot sensation, including position sense.
B. Impaired position sense in the left foot (Why this does not fit)
A right medial motor lesion would affect the left leg, unlike the starting examination. Posterior sensory extension does not reverse laterality; left foot loss would require right-sided sensory tissue involvement.
C. Impaired touch localization in the right hand (Why this does not fit)
The affected right leg maps medially in the left hemisphere, not to the lateral hand area. A medial posterior extension threatens leg sensation; right hand touch localization would require more lateral sensory involvement.
D. Impaired touch localization in the left hand (Why this does not fit)
The initial deficit implicates left medial motor cortex, not right lateral cortex. Left hand sensory loss would require opposite-hemisphere lateral sensory involvement, not the described contiguous extension.
Takeaway: Crossing determines side; the medial body map and direction of extension determine the new deficit.
The recognition deficit is in the left hand despite intact primary sensation, implicating right parietal sensory networks. Adjacent right motor hand cortex controls the left hand; right hand weakness would require left motor tissue.
B. Left foot weakness (Why this does not fit)
The controlled deficit points to right lateral parietal hand-processing tissue. The foot motor area lies medially rather than immediately anterior at the same lateral level.
C. Left hand weakness (Best answer)
Impaired left-hand recognition with intact primary sensation and nonverbal matching supports right parietal sensory-network dysfunction. Anterior extension at the hand level reaches right precentral tissue and predicts left hand weakness.
D. Right foot weakness (Why this does not fit)
The left-hand deficit places the sensory-network problem on the right. Right foot weakness would require left medial motor involvement, differing in both side and body-map location.
Takeaway: Test basic sensation and naming confounds before using tactile recognition to localize; then use the neighboring motor map.
A. Left posterior temporal cortex extending into temporal optic radiations (Why this does not fit)
The effortful agrammatic pattern fits dominant frontal language dysfunction better than a posterior receptive pattern. Temporal radiation involvement predicts visual loss, not the observed face-hand weakness.
B. Left frontal language cortex extending into lateral precentral cortex (Best answer)
Effortful agrammatic speech with impaired repetition and relatively preserved simple comprehension supports a dominant frontal language pattern. Right face-hand weakness with preserved leg strength requires lateral left motor involvement, matching this extension.
C. Left frontal language cortex extending only onto the medial leg motor surface (Why this does not fit)
The frontal language component fits the measured speech and comprehension pattern. An extension confined to medial leg motor tissue predicts leg weakness rather than the face-hand pattern.
D. Left lateral precentral cortex with language networks spared (Why this does not fit)
Lateral motor injury can impair articulation, but does not by itself explain agrammatic language and impaired repetition. It fits face-hand weakness, yet leaves the independent language deficit unexplained.
Takeaway: Aphasia and motor topography are separate constraints on lesion extent.
A. Left posterior language network with parietal optic radiations (Why this does not fit)
The impaired comprehension and repetition fit dominant posterior language dysfunction. Parietal radiation involvement preferentially threatens the lower-right quadrant, not the measured upper-right quadrant.
B. Left occipital cortex with the language network spared (Why this does not fit)
Left occipital injury can produce a right visual-field deficit. It does not explain impaired auditory comprehension and repetition when visual cues are removed.
C. Right temporal language cortex with temporal optic radiations (Why this does not fit)
A temporal receptive language pattern is present, but established language dominance places it on the left. Right temporal radiation injury predicts an upper-left rather than upper-right field defect.
D. Left posterior temporal language network with temporal optic radiations (Best answer)
Fluent erroneous output with poor comprehension and repetition supports left posterior language-network dysfunction. Left temporal optic radiation involvement explains the additional upper-right homonymous quadrant defect.
Takeaway: The language tasks and the quadrant independently constrain the tissue; neither names a distal arterial division.
A. Left dorsal temporoparietal language network and parietal optic radiations (Best answer)
Disproportionate repetition failure with relatively preserved fluency and comprehension supports a conduction-type dorsal language-network deficit. Left parietal optic radiation involvement accounts for the independent lower-right field defect.
B. Left dorsal temporoparietal language network and temporal optic radiations (Why this does not fit)
The dorsal language-network component fits the repetition-comprehension dissociation. Temporal radiation injury would preferentially affect the upper-right quadrant rather than the lower-right quadrant.
C. Left occipital visual cortex with dorsal language connections intact (Why this does not fit)
Occipital injury can explain a quadrant defect. Intact dorsal language connections do not account for the disproportionate repetition deficit; the visual finding alone is insufficient.
D. Right parietal attention network and parietal optic radiations (Why this does not fit)
Right parietal injury can affect attention, but does not fit the specified left-dominant conduction-type language pattern. Right parietal radiation injury would cause lower-left rather than lower-right visual loss.
Takeaway: Conduction is a network pattern, not proof of a single arcuate lesion; a quadrant defect supplies an independent extent clue.
A. A small left frontal language cortical lesion (Why this does not fit)
Preserved written naming, grammar, and comprehension argue against a primary aphasic syndrome. A small language lesion does not explain substantial weakness of face, arm, and leg together.
B. An isolated peripheral facial nerve lesion (Why this does not fit)
A peripheral facial lesion can distort speech without aphasia. It cannot explain accompanying right arm and leg weakness; the motor distribution requires a central pathway explanation.
C. A compact left deep motor pathway lesion involving corticobulbar and corticospinal fibers (Best answer)
The preserved language tasks indicate dysarthria rather than demonstrated aphasia. A left deep motor pathway lesion can affect contralateral face, arm, and leg together without cortical network signs.
D. A small left lateral motor hand-face cortical lesion (Why this does not fit)
A motor cortical lesion could cause dysarthria while preserving language. A small lateral hand-face lesion would not adequately explain the substantial leg weakness, making compact deep motor involvement the better fit.
Takeaway: Dysarthria is not aphasia; extensive body-map weakness without network deficits favors, but does not prove, deep motor involvement.
A. Missing left-hand touch only during bilateral stimulation (Why this does not fit)
Detection of either hand alone with failure during competition already demonstrates left tactile extinction. Repeating that baseline result does not establish new optic radiation injury.
B. Missing single targets in the lower-left quadrant of both eyes (Best answer)
The baseline examination shows left attentional extinction with intact single-target fields. Right parietal radiation injury adds a lower-left homonymous quadrant defect even without a competing target.
C. Missing single targets in the upper-left quadrant of both eyes (Why this does not fit)
The baseline deficit reflects attention rather than established primary field loss. An upper-left defect would fit right temporal rather than the specified parietal radiation extension.
D. Missing single targets in the lower-right quadrant of both eyes (Why this does not fit)
The initial left neglect pattern is consistent with right parietal dysfunction. A lower-right defect points to left parietal visual pathways, not extension of this right lesion.
Takeaway: Use single-target testing to distinguish a new visual-pathway deficit from extinction.
A. A right visual pathway deficit without an attention deficit (Why this does not fit)
Single-target left homonymous loss supports right postchiasmal visual pathway dysfunction. That alone does not explain left tactile extinction despite preserved unilateral touch detection.
B. A right attention deficit without a visual pathway deficit (Why this does not fit)
Left tactile extinction supports an attention-network deficit. Persistent loss of single visual targets across a homonymous half-field supplies separate evidence of visual pathway dysfunction.
C. A left optic nerve deficit with a right attention deficit (Why this does not fit)
The tactile finding is consistent with right attention-network dysfunction. An optic nerve lesion affects one eye, not the same half of visual space in both eyes.
D. Right postchiasmal visual pathway dysfunction with right-sided attention-network dysfunction (Best answer)
The same left hemifield missing in both eyes localizes visual loss to a right postchiasmal pathway. Left tactile extinction independently supports right-sided attention-network dysfunction; both can coexist.
Takeaway: Neglect does not erase a demonstrable hemianopia, and hemianopia does not explain tactile extinction.
A. Right occipital visual cortex alone (Why this does not fit)
Left-hand recognition failure with preserved primary sensation implicates a right parietal sensory network. Occipital cortex can explain the field defect but not this independent tactile-recognition deficit.
B. Right parietal sensory association tissue and adjacent parietal optic radiations (Best answer)
The controlled left-hand recognition failure supports right parietal sensory-network involvement. Right parietal radiations carry lower-left visual information, fitting the separate field defect.
C. Right temporal visual association tissue and temporal optic radiations (Why this does not fit)
Temporal visual association dysfunction concerns recognition through vision rather than this tactile task. Temporal radiation injury preferentially threatens the upper-left, not lower-left, quadrant.
D. Left parietal sensory association tissue and adjacent parietal optic radiations (Why this does not fit)
Left parietal sensory-network injury would preferentially affect right-hand recognition. Left parietal radiation injury would affect the lower-right rather than lower-left field.
Takeaway: Nonverbal tactile testing and formal fields constrain different components of a posterior lesion.
A. Left lateral motor cortex (Why this does not fit)
The seeing left field still delivers visual information to right occipital cortex. A motor lesion does not explain why that information fails to reach preserved language systems, and would threaten writing execution.
B. Right optic nerve (Why this does not fit)
The seeing left visual field is represented in the right cerebral visual pathway, not exclusively in one optic nerve. Right optic nerve injury would create monocular loss rather than selectively interrupt transfer to left language networks.
C. The splenium of the corpus callosum (Best answer)
The intact right occipital system still processes the seeing left field. Splenial injury can disconnect that surviving visual information from left language networks, causing alexia despite genuinely preserved writing.
D. Left occipital cortex alone (Why this does not fit)
Left occipital injury explains the lost right field but leaves right occipital input from the left field available. Without the additional disconnection, it does not adequately explain inability to read words in the seeing field with preserved language.
Takeaway: Prove writing with new language, then ask why surviving visual input cannot reach it.
A. Detection of the left visual hemifield (Why this does not fit)
Intact fields and detection of facial features argue against a primary left hemifield defect. Recognition by voice does not restore a missing field; the selective difficulty concerns identity from faces.
B. General knowledge of familiar people (Why this does not fit)
The patient can visually detect faces and still recognizes ordinary objects. Immediate recognition by voice demonstrates preserved person knowledge, opposing a general loss of identity knowledge.
C. Spoken-language comprehension (Why this does not fit)
The visual examination identifies a face-specific recognition problem rather than a language task failure. Recognition through familiar voices gives no evidence of a primary auditory language-comprehension deficit.
D. Visual recognition of familiar facial identities (Best answer)
Preserved fields, feature detection, and object recognition separate higher face processing from basic vision. Recognition by voice shows that person knowledge survives; access through faces is selectively impaired.
Takeaway: Prosopagnosia is a recognition deficit, not blindness or proof that all knowledge of people is lost.
A. Extensive left language-network dysfunction with left deep motor-pathway involvement (Best answer)
Severe impairment of output, comprehension, and repetition supports a global language pattern in the dominant left network. A compact left deep motor component can account for substantial right face-arm-leg weakness in addition to the language dysfunction.
B. Extensive left language-network dysfunction with all motor pathways spared (Why this does not fit)
The extensive dominant language-network component fits the global language pattern. Sparing all motor pathways cannot account for objective right face-arm-leg weakness.
C. An isolated left internal-capsule motor lesion with language networks functioning normally (Why this does not fit)
A deep left motor lesion can explain contralateral face-arm-leg weakness and articulation difficulty. Normally functioning language networks do not explain the severe comprehension and repetition deficits.
D. Extensive right language-network dysfunction with right deep motor-pathway involvement (Why this does not fit)
Established left dominance conflicts with assigning the global language deficit to a right language network. Right deep motor injury would also predict left rather than right face-arm-leg weakness.
Takeaway: A global language pattern and a compact motor pattern constrain different components; they do not measure final infarct volume.
A. Embolization without a flow-limiting contribution (Why this does not fit)
Hypotension, reduced perfusion, and severe upstream disease provide evidence for compromised flow. Microembolic signals support embolization, but do not negate the independent perfusion evidence.
B. Flow failure without an embolic contribution (Why this does not fit)
Reduced perfusion after hypotension supports flow failure. Detected cerebral microembolic signals add evidence for embolization, so excluding that contribution discards data.
C. Flow limitation and embolization acting together (Best answer)
Hypotension and measured low perfusion beyond severe disease support a flow-limiting contribution. Microembolic signals independently support embolization; impaired washout can allow these mechanisms to interact.
D. Local hemorrhagic injury producing both abnormalities (Why this does not fit)
The described imaging establishes border-zone infarction with reduced perfusion, not a hemorrhage. Microembolic signals support circulating embolic material rather than a local hemorrhage as the unifying explanation.
Takeaway: Do not force a single mechanism when flow and embolic evidence coexist.
A. Ongoing hemodynamic failure as the demonstrated mechanism (Why this does not fit)
Stable pressure and normal contemporaneous perfusion do not demonstrate ongoing flow failure. The positive microembolic study instead supplies direct evidence of embolization.
B. Embolization, without demonstrated ongoing flow limitation (Best answer)
The observed pressure and perfusion data do not establish current flow limitation; they cannot exclude an earlier transient episode. Detected microembolic signals directly support embolization, making this the appropriately bounded interpretation.
C. Both ongoing flow limitation and embolization as demonstrated mechanisms (Why this does not fit)
The perfusion assessment does not demonstrate ongoing flow limitation. Embolization has direct support, but adding a proven hemodynamic contribution exceeds the available evidence.
D. Neither embolization nor flow limitation has objective support (Why this does not fit)
Current flow limitation is not shown, and distribution alone would not establish it. The positive microembolic monitoring is objective evidence that prevents dismissing embolization.
Takeaway: A cortical border-zone pattern is not a mechanism label; distinguish demonstrated current flow failure from unmeasured prior events.
A. A right parietal recognition deficit is established (Why this does not fit)
Right-hand primary sensation is inadequate, so the tactile task cannot independently establish a higher recognition deficit. Preserved recognition by other routes does not reverse laterality or identify a right parietal lesion.
B. A left parietal recognition deficit is established (Why this does not fit)
Contralateral left parietal dysfunction is possible, but impaired primary sensation confounds the task. Preserved recognition through vision and the other hand argues against lost object knowledge, not for a proven left association lesion.
C. The object is unfamiliar to the patient (Why this does not fit)
Primary sensation is poor in the failed hand and can account for inadequate information reaching recognition systems. Recognition visually and with the other hand directly contradicts unfamiliarity.
D. The task cannot independently establish a cortical recognition deficit (Best answer)
Adequate primary sensation is required to interpret object recognition; that prerequisite is absent. Other-route recognition shows that object knowledge is available but does not locate the cause of the right-hand sensory deficit.
Takeaway: A prerequisite failure limits inference; it does not prove the absence or presence of cortical injury.
A. Left parietal sensory-network dysfunction beyond the language naming deficit (Best answer)
Correct use with either hand shows recognition can survive the inability to name, so naming failure alone is not astereognosis. Right-only failure on nonverbal shape matching despite adequate primary sensation supports additional left parietal sensory-network dysfunction.
B. Bilateral parietal recognition failure inferred from inability to name the key (Why this does not fit)
Correct use demonstrates recognition in both hands despite absent spoken names. The nonverbal task is asymmetric, opposing a bilateral recognition deficit inferred simply from naming.
C. Right parietal sensory-network dysfunction beyond the language naming deficit (Why this does not fit)
The naming limitation does not explain away the need for nonverbal testing. Right-hand nonverbal failure points contralaterally to left rather than right parietal sensory networks.
D. A naming deficit alone accounts for every failed task (Why this does not fit)
The key-naming failures can be explained by aphasia because use remains correct. The picture-matching response requires no spoken naming, so its right-only failure needs an additional sensory-network explanation.
Takeaway: Separate language output from recognition before adding a cortical sensory localization.
A. Left posterior language tissue with left lateral motor cortex (Why this does not fit)
The receptive language pattern must be interpreted using the established right-sided dominance, not the usual left-sided default. Left motor injury would also produce right rather than the observed left face-hand weakness.
B. Right posterior language tissue with right medial leg motor cortex (Why this does not fit)
Right posterior language involvement fits the measured comprehension and repetition failure. Medial leg motor involvement does not explain left face-hand weakness with preserved leg strength.
C. Right posterior language tissue with right lateral motor involvement (Best answer)
Established right dominance places this receptive language-network dysfunction on the right. Left face-hand weakness independently requires right lateral motor-system involvement; the combined extent fits.
D. Right lateral motor cortex with posterior language networks spared (Why this does not fit)
Right lateral motor involvement fits the left face-hand weakness. Motor dysfunction alone cannot explain fluent meaningless language with poor comprehension and repetition.
Takeaway: Use documented dominance rather than handedness; independently account for motor laterality and extent.
A. Posteriorly into left medial primary sensory cortex (Why this does not fit)
The new deficit is reduced spontaneous initiation rather than newly measured primary sensation loss. Sensory extension would not best explain abulia with preserved repetition and unchanged requested movement strength.
B. Into left lateral motor hand cortex (Why this does not fit)
Requested strength has not worsened and the new problem is initiation across behaviors. Lateral hand motor extension would add hand weakness rather than this generalized reduction of spontaneous activity.
C. Into left posterior temporal language cortex (Why this does not fit)
Sentence repetition remains accurate and there is no new demonstrated receptive language deficit. Posterior temporal language injury is a poorer explanation than medial frontal initiation-network involvement.
D. Into adjacent medial frontal initiation networks (Best answer)
The stable strength under command separates the new inactivity from greater paralysis. Medial frontal initiation-network involvement explains reduced spontaneous speech and movement with retained repetition.
Takeaway: Abulia is reduced initiation, not automatically aphasia or additional weakness.
A. Reduced primary sensation in the right face and body (Best answer)
The compact right-sided motor deficit places the matching deep lesion in the left hemisphere. Left ascending thalamocortical sensory fibers carry right-sided sensory information, so their involvement adds right face-body sensory loss.
B. Reduced primary sensation in the left face and body (Why this does not fit)
The original right-sided weakness implicates a left rather than right deep motor lesion. Left sensory loss would require right ascending sensory-pathway involvement, not this contiguous expansion.
C. Greater right-sided weakness without any new sensory deficit (Why this does not fit)
The initial deficit is explained by left descending motor-pathway injury. Expansion specifically into ascending sensory fibers adds sensory dysfunction; more weakness alone describes further motor injury instead.
D. Loss of spoken-language comprehension without a primary sensory deficit (Why this does not fit)
The compact motor pattern with preserved language does not establish a language-network lesion. The specified extension reaches sensory fibers, not a receptive language network, so comprehension loss is not the predicted added deficit.
Takeaway: Deep motor lesions can become sensorimotor when neighboring ascending fibers are involved; sensory loss does not mandate cortex.
A. It shifts the localization to the right optic nerve (Why this does not fit)
The same right half-field is lost in both eyes and MRI locates the lesion in left occipital cortex. Absent central sparing does not convert a homonymous defect into a monocular optic-nerve deficit.
B. It remains compatible with the demonstrated occipital infarct (Best answer)
The homonymous pattern and MRI support left occipital injury. Central-field cortex can be infarcted rather than spared; absence of macular sparing does not refute occipital ischemia.
C. It establishes a tumor instead of the demonstrated infarct (Why this does not fit)
MRI demonstrates an acute occipital infarct matching the field loss. Macular sparing is not a stroke-versus-tumor rule, so its absence cannot establish a tumor.
D. It establishes a separate temporal-radiation lesion (Why this does not fit)
Left temporal radiation injury can affect the right upper quadrant, but the imaging already identifies an occipital lesion. Lack of macular sparing does not independently establish an additional radiation lesion.
Takeaway: Macular sparing is a variable feature, not a required diagnostic sign.
A. Left occipital visual cortex without medial temporal involvement (Why this does not fit)
Occipital injury can account for a visual-field defect. It does not adequately explain the independent new retention deficit despite intact registration and attention.
B. Left medial temporal tissue with parietal optic radiations (Why this does not fit)
Medial temporal dysfunction can account for impaired new memory formation. Parietal radiation involvement preferentially affects the lower-right rather than upper-right quadrant.
C. Right medial temporal tissue with right temporal optic radiations (Why this does not fit)
Medial temporal dysfunction is compatible with new memory difficulty, though the verbal task alone does not prove side. Right temporal radiation involvement predicts an upper-left rather than upper-right field defect.
D. Left medial temporal tissue with temporal optic radiations (Best answer)
Poor delayed retention despite adequate registration and attention supports medial temporal memory-network dysfunction. The upper-right homonymous defect independently places associated temporal radiation involvement on the left.
Takeaway: Do not infer hemisphere from a memory complaint alone; combine controlled memory testing with an independent field map.
A. Left lateral motor tissue or its face-hand output fibers (Best answer)
Preserved comprehension and initial pointing ability reduce language and motor confounds in the initial dominant parietal task failures. New right face-hand weakness with a spared foot requires additional left lateral motor-system involvement beyond the initial association network.
B. Left medial leg motor tissue (Why this does not fit)
The initial controlled task failures fit a dominant parietal network. Medial leg motor extension would predict right leg or foot weakness, not the observed face-hand pattern.
C. Right lateral face-hand motor tissue (Why this does not fit)
The initial controlled association tasks implicate the dominant left parietal network. Right motor injury would cause left face-hand weakness, opposite to the later change.
D. The same isolated left parietal association tissue with motor pathways spared (Why this does not fit)
The initial deficits can be explained by parietal association dysfunction after controlling comprehension and movement. New objective weakness cannot be accounted for by an association-only hypothesis that spares all motor pathways.
Takeaway: Control task prerequisites; then use a genuinely new motor sign to expand the lesion hypothesis.
A. Left frontal eye-field and left lateral motor cortex (Why this does not fit)
Preserved reflex movements favor supranuclear rather than final common gaze-pathway failure. A destructive left frontal lesion would more typically bias gaze left and weaken the right side, opposite to the examination.
B. Right pontine horizontal gaze machinery with descending motor pathways (Why this does not fit)
Damage to horizontal gaze machinery is less compatible with full reflex horizontal movements. The left weakness indicates right motor-pathway involvement, but does not rescue the mismatch in gaze physiology.
C. Right frontal eye-field network with right lateral motor involvement (Best answer)
Full reflex movements despite impaired voluntary left gaze support a supranuclear gaze problem. A destructive right frontal eye-field lesion can bias gaze right, while neighboring right motor involvement explains left face-arm weakness.
D. Right frontal eye-field network with motor pathways spared (Why this does not fit)
The gaze pattern fits a right frontal supranuclear disturbance. Sparing motor pathways leaves the independently measured left face-arm weakness unexplained.
Takeaway: Gaze direction is interpreted with reflex testing, seizure context, and the motor examination, not alone.
A. Expansion confined to the old right occipital lesion (Why this does not fit)
The old right occipital lesion explains the persistent left homonymous defect. An expansion confined there does not explain new left-dominant language dysfunction and right hand weakness.
B. The old right occipital lesion plus new left frontal language and motor involvement (Best answer)
The unchanged left field defect remains explained by the documented old right occipital injury. New agrammatic language with right hand weakness requires additional left language and motor-system involvement.
C. A single new left frontal lesion explaining both old and new findings (Why this does not fit)
A left frontal lesion can explain the new language and right hand findings. It cannot replace the established right occipital explanation for the persistent left homonymous field defect.
D. The old right occipital lesion plus new right frontal motor involvement (Why this does not fit)
The old lesion explains the stable left field defect. New right frontal involvement would favor left weakness and does not match the specified left-dominant aphasic syndrome.
Takeaway: Do not assign every abnormality to the latest scan finding; separate established deficits from new ones.
A. Left lower facial weakness (Why this does not fit)
A right-hand cortical sensory deficit supports left parietal involvement accompanying the focal weakness. Inferior spread within left motor cortex affects the right lower face, not the left.
B. Right foot weakness (Why this does not fit)
Controlled right-hand recognition failure supports left cortical involvement rather than a radial lesion alone. The foot representation is medial, not inferior along the lateral hand-to-face progression.
C. Left foot weakness (Why this does not fit)
The right-sided hand findings implicate left sensorimotor networks. Left foot weakness would require right medial motor tissue, not the described contiguous left lateral spread.
D. Right lower facial weakness (Best answer)
Right-hand nonverbal sensory-recognition failure with primary sensation intact supports a left cortical network lesion rather than isolated radial neuropathy. The face area lies inferior to the hand on lateral motor cortex, so spread there predicts right lower facial weakness.
Takeaway: A cortical hand lesion can imitate a peripheral palsy; controlled sensory testing and the map predict the next deficit.
