PARIETAL LOBE
DR ARUN S
Introduction No independent existence as anatomical / physiological unit Operates in conjunction with brain as a whole Strategically situated b/w other lobes Greater variety of clinical manifestations
than rest of the hemisphere Dysfunction likely to be overlooked
unless special techniques used
History
In 1874 Bartholow recorded odd sensation from legs on stimulating post central gyrus through skull wounds
Cushing in 1909 --- Electrical stimulation in conscious human beings under LA –– mainly tactile hallucinations
Critchley (1953) – monograph on “ The Parietal Lobes” Djerine – alexia , agraphia -- angular
gyrus lesion Liepmann--- ideomotor & ideational
apraxia in (L) sided lesion
Neuroanatomy
Occupies middle third of cerebral hemispheres
Situated b/w frontal ,temporal ,occipital lobes with anatomical & functional continuity
Boundaries
Anterior –Central sulcus & its imaginary continuation over inner paracentral lobule medially
Posterior- parieto occipital sulcus on mesial aspect & its continuation (imaginary) to join pre occipital notch inferolaterally
Lower- Sylvian fissure & its imaginary extension backwards
Lateral surface
2 well defined sulci
Post central sulcus –parellel to Fissure of Rolando
Inter parietal sulcus- runs AP from post central sulcus to occipital lobe
Lateral surface
Gyri Post central gyrus- primary sensory
area(3,1,2) Superior parietal lobule(5,7) Inferior parietal lobule ( Ecker’s
lobule ) Supramarginal gyrus (area 40)
arches over Sylvian fissure Angular gyrus (area 39 ) - arches
over the superior temporal sulcus
Mesial surface
Paracentral lobule- mesial part of post central gyrus
Precuneus- behind post central gyrus
Subjacent part of cingulate gyrus- below sub parietal sulcus
Vascular supply
Lateral - MCA
Artery of Rolandic fissureArtery of inter parietal fissure Artery of post parietal fissure Inter opercular parietal arteryArtery to angular gyrus
Mesial - ACA mainly & PCA to a slight extent
Venous drainage
Superficial middle cerebral vein –lies in lateral fissure
Vein of Trolard (superior anastomotic vein) - connects sup middle cerebral vein to SSS
Vein of Labbe’ ( inferior anastomotic vein ) - connects sup middle cerebral
vein to Transverse sinus
Post central gyrus
Granular cortex Receives most of its afferents from VPL
nucleus of thalamus Projects to somatosensory association
cortex (area 5) Some parts (except hand & foot )
connected to opposite somatosensory cortex via corpus callosum
Representation of C/L side of body
Postcentral gyrus
Superior part represent the LL Middle part -- the trunk & UL and Lower part --the face Amount of cortex devoted to any
particular body area – proportional to sensory acuity
Tips of fingers & lips larger area of representation
Posterior parietal region Superior & inferior Parietal lobule
Connections Post central gyrus
Superior parietal area
Area 5b- occupies large portion of Sup parietal lobule
Extends over medial surface to include pre cuneus
No large pyramidal cells in layer V Granular layer – great depth &
density
Inferior parietal area
Supra marginal & angular gyrus No pyramidal cells Granular cortex well developed Close proximity to occipital & temporal
lobe
Parietal lobe functions
Difficult to describe due to bewildering range of symptoms
Simple functional division Anterior region- post central
gyrus / sensory strip Posterior region – lies behind post
central gyrus & is composed of tertiary cortex
Functions of anterior region Somato sensory perception Tactile perception Body sense Visual object recognition
Functions of posterior region
Language Reception of spoken language
Reading Spatial orientation & attention
Route following L- R discrimination
CalculationIntentional movementPraxis Constructional ability
DrawingShort term auditory memory
Optic radiation passes to Occipital Lobe via deep region . Lesion --- VF defects
Angular & supramarginal gyri of dominant hemisphere – imp in language & related functions
APRAXIA
Definition Difficulty in performing skilled motor
acts which can not be explained by an elementary sensory or motor deficit or language comprehension disorder
Apraxia
Limb apraxia – Limb kinetic / melokinetic Ideomotor Ideational
Disassociation Conduction Conceptual Constructional & dressing –often
associated with neglect & visual perceptual disorders
Scattered , fragmented
Loss of spatial relations
Faulty orientation
Energetic drawing
Addition of lines to make drawing correct
Coherent , simplified
Preservation of spatial relations
Correct orientation
Slow & laborious
Gross lack of details
Tests
Pressure sensitivity Two point discrimination Point localisation Position sense Tactual object recognition
Two point discrimination
Use a compass / calibrated 2 point esthesiometer 1mm tip of tongue 2-4 mm finger tips 4-6 mm dorsum of fingers 8-12 mm on palm 20-30 mm on dorsum of palm
AmorphosynthesisInability to synthesize separate tactile
sensations into perception of form Lack of recognition of C/L body & of
space
Astereognosis Loss of ability to recognize object by
touch Unable to name objects, describe or
demonstrate their use Primary sensations intact
Asomatognosia
Agnosia relates to patient’s own body
TypesAnosognosia
Autotopagnosia
Anosognosia
Ignorance of existence of disease More with (R ) PL lesions U/L neglect may co exist
Deny weakness /sensory loss of affected limb
Extreme cases- disowns limb
Autotopagnosia
Impairment in localization / naming of parts of own body
Patient unable to point to body parts named by examiner / move them
May not be able to identify them on examiner’s body / on diagram
Finger agnosia
Inability to recognize , name & point to individualized fingers on self & others – usually middle 3 fingers
Form of autotopagnosia B/L lesion Central feature of Gerstmann
syndrome
Language dysfunction
Dominant PL lesion Defect in reception of spoken
language & reading Conduction aphasia
Agraphia
Spontaneous writing & writing on command more affected than copy righting
Irregular & tremulous script, misspelling , semantic & syntactial errors
Site – inferior parietal lobule
Apractic agraphia- agraphia despite normal sensory, motor & visual feed back, word & letter knowledge
Lesion- Dom sup parietal lobule Visuo spatial agraphia- neglect of (U)
side of paper in writing Lesion -- (R) temp- parietal
junction
Effects of unilateral disease of the parietal lobe, right or left
A. Corticosensory syndrome and sensory extinction
B. Mild hemiparesis (variable), unilateral muscular atrophyin children, hypotonia, poverty of movement, hemiataxia
C. Homonymous hemianopia or inferior quadrantanopia(incongruent or congruent) or visual inattention
D. Abolition of optokinetic nystagmus with target movingtoward side of the lesion
E. Neglect of the opposite side of external space
Effects of unilateral disease of the dominant (left) parietallobe
A. Disorders of language (especially alexia)B. Gerstmann syndrome (dysgraphia, dyscalculia, finger agnosia, right-left confusion)C. Tactile agnosia (bimanual astereognosis)D. Bilateral ideomotor and ideational apraxia
Effects of unilateral disease of the nondominant (right) parietal lobe
A. Visuospatial disorders
B. Topographic memory loss
C. Anosognosia, dressing and constructional apraxias
D. Confusion
E. Tendency to keep the eyes closed, resist lid opening,and blepharospasm
Effects of bilateral disease of the parietal lobes
A. Visual spatial imperception, spatial disorientation, andcomplete or partial Balint syndrome