Vascular lesions of the parietal cortex and their clinical implications for

vision

Vascular lesions of the parietal cortex and their clinical implications for

vision

Overview

• “Lesion”any localized abnormal structural change in a bodily component

• Interruption of tissue perfusion

• TumourTraumaBlood clots

Stroke

Types of stroke

• Ischaemic – 87%Obstruction of a blood vessel

Thrombus – blood clotEmbolus – fragment of clot stuck in another vessel

• Haemorrhagic – 13%Haematoma – collection of blood outside vessels

Compression of tissueReduced blood flow

Rosamond, W. et al., 2008

Frontal lobe strokemost common

ACT FAST• Facial weakness• Arm and leg weakness• Speech problems• Time to call 999

Unilateral damageContralateral effect

Risk factors of stroke

• Transient Ischaemic Attack (TIA)“Mini Stroke” (<24 hours), 25% patients die within a year

• Most likely candidates for strokeDiabetic women above the age of 55

Smokers twice as likelyHigh cholesterol, alcohol intake and little exercise

• Biggest risk factor?High blood pressure!

Risk factors of stroke

just a 10 mmHg increase in the middle aged individual can increase the risk factor of stroke by 40%! The danger in this is that such a small increase has no physiological signs associated with it and often goes unnoticed.

Gross anatomy of the brain

• Left and right hemispheresDivided by central sulcus, connected by corpus

callosum

• Folds, grooves and cleftsGyri, sulci and fissures

• Four lobes of the brain...

Frontal

Temporal

Occipital

Parietal

Arterial vasculature

• Brain has two main suppliesR+L internal carotid arteriesR+L vertebral arteries

• Both form the circle of Willis on the ventral brain surfacePlays a huge role in reducing the risk of stroke in individuals

Netter, 2002

Vertebral

InternalCarotid

• The circle of Willis reduces the probability of stroke

Anastomosis of 3 arteriesBlood can still flow along an alternate route in case of a blockage

Not a likely preventative measure in the case of embolus formation of lacunar stroke

Arterial vasculature

Netter, 2002

Anterior Cerebral

MiddleCerebral

PosteriorCerebral

Parietal lobe vasculature

• Anterior cerebral arteriesNot associated with areas of visionCan be disregarded for this study

• Middle cerebral arteriesContinuation of internal carotids

• Lacunar strokeOcclusion of one of the brain’s main

penetrating arteries Netter, 2002

Border zone infarction

• Areas where main arteries meet at their distal ends

Blood at low pressureTissue here susceptible to infarction when blood pressure is reduced (Image B)

• Lacunar strokeDepicted in image C

Caplan et. al., 1999

General symptoms of parietal damage

• Parietal lobe functionIntegration of sensory information & spatial sensationDorsal pathway of vision

• ‘Silent’ region of the brainNo obvious visible symptoms as with frontal stroke

• Contralateral neglect

• Bilateral infarcts

General symptoms of parietal damage

• Parietal lobe functionIntegration of sensory information & spatial sensationDorsal pathway of vision

• ‘Silent’ region of the brainNo obvious visible symptoms as with frontal stroke

• Contralateral neglect

• Bilateral infarcts

Contralateral neglect syndrome

Purves et. al., 2008

• Failure to respond to a stimulus on the side contralateral to a lesion

• Apraxia – motor deficitsReaching for objects, writing & drawing

• Only affects the right parietal cortexMediates attention to right and leftSo lesions on the left side are compensated for by right

Right side affected and there is no compensation!

Contralateral neglect syndrome

Purves et. al., 2008

the saccadic eye movements of a “normal” individual. In free viewing of this “interesting scene”, the entire field is scannedIf we introduce a right hemisphere lesion, the right visual field is observed, while the patient ignores the opposite side of the world

Bilateral posterior parietal infarcts

Purves et. al., 2008

• The left and right brains are affectedRight brain compensates for left fieldBUT Left brain cannot sense right fieldSevere right field neglect

• Bálint’s syndrome Lesions at the parieto-occipital borderPsychic paralysis of visual fixationOptic ataxiaSimultagnosia

Simultagnosia

• The patient perceives whole objectsBut can only see a single object at onceRegardless of object size or spatial orientation

• NOT like tunnel visionWhere the visual field constricts

single

Simultagnosia

(Rafal, 2001)The patient was presented with a comb, which he could identify correctly.When a spoon was placed in front of the comb, the patient still only reported the comb to be visibleWhen the spoon was moved. The patient could see the spoon only, and not the comb

When both the spoon and comb were moved, the patient only reported to see “what looks like a blackboard with some writing on it”

When the examiner turned round, he saw a blackboard behind him

Simultagnosia

Robertson and Grabowecky, unpublished observations (Rafal, 2001)

SSSSSS

SSSSSS

SSS

SSS

SSSSSS

SSSSSS

SSS

SSS

S S

S S S S

S SS SS S

S SS S

ALIPYB

GHCFXT

IUC

WRW

SJHNSU

VQZUCU

ELX

QJZ

B R

Q P F S

M NG YS F

S BG VTHE ALPHABETTWICE!

In a more recent study, the question that needed clarifying was what exactly an “object” was to the patient.

An image was constructed of several small letter Ss that were arranged to make an overall H shape

This image was presented to a subject, who reported to only seeing the local SOn repeated testing over several months, he only reported seeing the global H shape twice!When the H shape was constructed from many different lettersThe subject reported to seeing “the alphabet”

RehabilitationTreatment

• Remedial approachRe-train the damaged CNS with general daily activities

• Functional approachUse a person’s strengths and abilities to compensate

• Multicontext approachTargeted strategies within varied environments

References

• BUPA (2007) The British United Provident Association Limited, England, accessed 1 March 2009, <http://www.bupa.co.uk/about/asp/history/index.asp>

• Caplan, L.R., Hurst, J.W., Chimowitz, M.J. (1999) Clinical Neurocardiology, Informa Health Care, 14

• Al-Khawaja, I., (2001) Neurovisual rehabilitation in Balint's syndrome, J Neurol Neurosurg Psychiatry, 70, 416

• Moore, K.L., Dalley, A.F. (2006) Clinically Oriented Anatomy, 5th Edition, Lippincott Williams & Wilkins, 921-932

• Mensah, G.A. (2008). Epidemiology of stroke and high blood pressure in Africa. Heart, 94, 697-705.

• Netter, F.H. (2002) Interactive Atlas of Human Anatomy, CD-ROM, 3rd Edition, Saunders

• Purves, D., Augustine, G.J., Fitzpatrick, D. et al. (2008), Neuroscience, 4th Edition, Sinauer Associates Inc, 668-671

• Rafal, R. (2001), Handbook of Neuropsychology, 2nd Edition, Elsevier Science, Vol. 4, 121-139

• Rosamond, W., Flegal, K., Furie, K., Go, A., Greenlund, K., Haase, N., Hailpern, S.M., Ho, M., Howard, V., Kissela, B., et al. (2008). Heart disease and stroke statistics--2008 update: a report from the American Heart Association Statistics Committee and Stroke Statistics Subcommittee. Circulation 117, e25-146.