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Radiological Anatomy of the Brain: A Concise Guide
- 1. R A D I O L O G I C A L A N ATO M Y O F B R A I N Dr. JITENDRA K PATIL Prof. Department of Radio-diagnosis, DY Patil medical college, hospital & research institute Kolhapur
- 2. D E V E L O P M E N T • 4 stages : 1. Dorsal induction (primary and secondary neurulation) 2. Ventral induction (patterning of the forebrain) 3. Neuronal proliferation and migration 4. Myelination
- 4. N E U R U L AT I O N third week of development- the notochord appears in the mesoderm Formation of neural plate. Formation of neural tube (precusor to the brain and spinal cord). Formation of neural crest
- 5. C L I N I C A L R E L E VA N C E : N E U R A L T U B E D E F E C T S
- 6. L AT E R D E V E L O P M E N T • 5th week- swellings appear in the cranial end • 3 primitive (primary) vesicles • 5 secondary vesicles
- 8. D E V E L O P M E N T O F V E N T R I C L E S • Each of the subdivisions encloses a part of the original cavity of the neural tube • form the ventricular system of adult brain. • Telencephalic vesicle cavity- Lateral Ventricle • Diencephalon cavity with central part of telencephalon- Third ventricle • Intraventricular foramen of Monro- communication between lateral ventricles and the third ventricle • Mesencephalon cavity- Aqueduct of Sylvius (communication between third ventricle and fourth ventricle)
- 10. F O R M AT I O N A N D C I R C U L AT I O N O F C S F • CSF formed in the ventricles- mainly in lateral ventricle by choroid plexuses Formation in ventricles- mainly lateral ventricle by choroid plexus Third ventricle Fourth Ventricle Subarachnoid space around brain and spinal cord interventricular foramen of Monro. cerebral aqueduct. • median foramen of Magendie • two lateral foramina of Luschka
- 12. A N AT O M Y- M E N I N G E S • thin layers of tissue between the brain and the inner table of the skull • 3 layers: • Dura mater • Arachnoid mater • Pia mater • Subarachnoid space
- 14. T E N TO R I U M C E R E B E L L I 4/27/2023 Sample Footer Text 14 Clinical Note: In the context of subarachnoid haemorrhage or subdural haematoma the tent may become more dense due to layering of blood
- 15. FA L X C E R E B R I 4/27/2023 Sample Footer Text 15 Clinical Note: Pathological processes may cause 'mass effect' with deviation of the falx towards one side Clinical Note: Meningiomas are benign intracranial tumours which may arise from any part of the meninges, including the falx or tentorium
- 16. C S F S PA C E S • brain is surrounded by cerebrospinal fluid (CSF) within the sulci, fissures and basal cisterns and found centrally within the ventricles. • 'CSF spaces', also known as the 'extra-axial spaces’. • lower density than the grey or white matter of the brain • assessment of brain volume
- 17. S U L C I A N D G Y R I • Gyrus -a fold of the brain surface • Sulcus - furrow between the gyri which contains CSF 4/27/2023 Sample Footer Text 17
- 22. F I S S U R E S • The fissures are large CSF-filled clefts which separate structures of the brain • The interhemispheric fissure separates the cerebral hemispheres • The Sylvian fissures separate the frontal and temporal lobes 4/27/2023 Sample Footer Text 22
- 23. L AT E R A L V E N T R I C L E S
- 25. T H I R D V E N T R I C L E
- 26. F O U R T H V E N T R I C L E
- 27. C E R E B R A L H E M I S P H E R E S
- 28. Brain lobes - CT brain (superior slice) Brain lobes - CT brain (inferior slice)
- 29. F R O N TA L L O B E • Anterior to central sulcus • Precentral gyrus - primary motor cortex • Lateral surface of precentral gyrus - head and face • Medial surface supplies lower limb • Upper limb - the largest area of cortical representation • Premotor cortex lies anterior to precentral gyrus • Three further frontal lobe gyri: • superior, • middle, • inferior, separated by the superior and inferior frontal sulci. • The dominant hemisphere of the frontal lobe also contains Broca’s area (involved with motor aspects of speech). It is situated in the pars opercularis,. 4/27/2023 Sample Footer Text 29
- 31. N E U R O L O G I C A L D E F I C I T S O F F R O N TA L L O B E • Unilateral dominant side: • Broca aphasia • Destruction of frontal eye field: impaired gaze to contralateral side • Hemiparesis/ hemiplegia • Problems with repetition: lesions affecting arcuate fasciulus • Unilateral non-dominant side • Hemiparesis/ hemiplegia • Bilateral lesions • Intellectual impairment • Personality change • Disinhibition • Apathy • Abulia (loss of drive) • Urinary incontinence • Foster Kennedy syndrome- anosmia, ipsilateral optic atrophy, and contralateral papilledema 4/27/2023 Sample Footer Text 31
- 32. PA R I E TA L L O B E • In parietal lobe there are : • postcentral gyrus, • a superior parietal lobule • and an inferior parietal lobule • postcentral gyrus -primary somesthetic area • Inferolateral surface - face, lips and tongue • Superolateral surface - upper limb • Medial aspect -lower limb. • superior parietal lobule - behavioral interaction of an individual with the surrounding space • The inferior parietal lobule - integration of diverse sensory information for speech and perception. 4/27/2023 Sample Footer Text 32
- 33. Lateral surface- Angular gyrus and supramarginal gyrus Medial surface- Precuneus
- 34. • unilateral lesions involving the dominant hemisphere: • Gerstmann syndrome: right-left disorientation, finger agnosia, agraphia (without alexia), acalculia. • contralateral hemianopia • sensory loss • contralateral neglect (less common than non-dominant) • bilateral astereognosis: inability to identify an object by touch alone • unilateral lesions involving the non-dominant hemisphere • contralateral sensory loss • contralateral neglect • contralateral hemianopia • topographic memory loss • anosognosia: impaired self-awareness • dressing apraxia 4/27/2023 Sample Footer Text 34 N E U R O L O G I C A L D E F I C I T S O F PA R I E TA L L O B E
- 35. T E M P O R A L L O B E • Superior gyrus • middle, and inferior temporal gyri are separated by the two transverse sulci • The superior temporal gyrus contains two important functional structures • the transverse temporal gyri of Heschl, (the primary auditory area), • Wernicke’s area caudal to the transverse gyri of Heschl, which is involved in the comprehension of spoken language • inferior temporal gyrus is involved with perception of visual form and color • Medial temporal lobe contains limbic structures (parahippocampal gyrus, uncus). 4/27/2023 Sample Footer Text 35
- 36. • deficits arising from unilateral lesions involving the dominant hemisphere: • alexia: acquired dyslexia (inability to read) • agraphia: inability to write • acalculia: inability to calculate • Wernicke's dysphasia: receptive dysphasia • nominal dysphasia: inability to name objects (lesions involving the posterior-superior temporal lobe) • contralateral homonymous superior quadrantanopia: 'pie in the sky' visual field defect (due to disruption of Meyer's loop which dips into the temporal lobe) • deficits arising from unilateral lesions involving the non-dominant hemisphere: • contralateral homonymous superior quadrantanopia • prosopagnosia: failure to recognize faces • irritative lesions involving either lobe can give rise to the following: • formed visual hallucinations • focal seizures • memory disturbances (e.g. déjà vu and other memory disturbances) 4/27/2023 Sample Footer Text 36 N E U R O L O G I C A L D E F I C I T S O F T E M P O R A L L O B E
- 37. O C C I P I TA L L O B E • medial surface (from superior to inferior) • parieto-occipital sulcus • cuneus • calcarine sulcus • site of the primary visual cortex • lingual gyrus • collateral sulcus • posterior segment, extending from temporal lobe • fusiform gyrus • Functional areas- • primary visual cortex (Brodmann area 17) • secondary visual (association) cortex (Brodmann areas 18 and 19)
- 39. • deficits arising from unilateral lesions involving the dominant hemisphere: • hemianopia: retrochiasmal lesion (lesions involving the optic tract, thalamic lateral geniculate nucleus, occipital lobe) • color dysnomia: interruption of fibers streaming from the occipital cortex to the Wernicke's area • Anton syndrome: those who suffer cortical blindness but affirm quite adamantly that they are able to see • irritative lesions involving either lobe can give rise to the following: • visual hallucinations (e.g. seeing flashes of light) 4/27/2023 Sample Footer Text 39 N E U R O L O G I C A L D E F I C I T S O F O C C I P I TA L L O B E
- 40. Lobes v 'regions' • CT does not clearly show the anatomical borders of the lobes of the brain. For this reason radiologists often refer to 'regions', such as the 'parietal region' or 'temporal region', rather than lobes. • If more than one adjacent region needs to be described then conjoined terms can be used such as 'temporo-parietal region' or 'parieto-occipital region'
- 41. G R E Y M AT T E R A N D W H I T E M AT T E R
- 42. G R E Y M AT T E R S T R U C T U R E S • Cortex • Insula • Basal ganglia • Thalamus
- 43. C O R T I C A L G R E Y M AT T E R
- 44. I N S U L A
- 45. B A S A L G A N G L I A
- 46. W H I T E M AT T E R S T R U C T U R E S • internal capsules • corona radiata • corpus callosum
- 47. I N T E R N A L C A P S U L E
- 48. C O R P U S C A L L O S U M
- 50. P O S T E R I O R F O S S A
- 52. VA S C U L A R T E R R I T O R I E S
- 57. • ]
Editor's Notes
- At the end of week two, a structure called the primitive streak appears as a groove in the epiblast layer of the bilaminar disk. Cells within the epiblast migrate downward through the primitive streak, giving rise to three layers from the initial two. These three germinal layers form the trilaminar embryonic disk: Endoderm – innermost layer Mesoderm – middle layer Ectoderm – outermost layer The nervous system is derived from the ectoderm, which is the outermost layer of the embryonic disc
- Notochord secretes growth factors which stimulate the differentiation of the overlying ectoderm into neuroectoderm- forming thickened structure known as neural plate lateral edges of the neural plate then rise to form neural folds. The neural folds move towards each other and meet in the midline, fusing to form the neural tube. The formation of neural tube is known as neurulation, and is achieved by the end of the fourth week of development. During fusion of the neural folds, some cells within the folds migrate to form neural crest. They give rise to melanocytes, craniofacial cartilage and bone, smooth muscle, peripheral and enteric neurons and glia
- Dura -tough outermost layer, closely applied to the inner table of the skull Arachnoid- thin layer closely applied to the dura mater Subarachnoid space- space between the arachnoid mater and the pia mater which contains delicate trabeculated connective tissue and CSF Pia mater- very thin layer applied to the surface of the brain
- The tentorium cerebelli - an infolding of the dura mater - forms a tent-like sheet which separates the cerebrum (brain) from the cerebellum
- The falx is an infolding of the meninges which lies in the midline and separates the left and right cerebral hemispheres
- The brain surface is formed by folds of the cerebral cortex known as gyri. Between these gyri there are furrows, known as sulci, which contain CSF.
- • Th e precentral gyrus contains an area at its superiorlateral part, which resembles an upside-down omega Uncus
- Th e central sulcus is a useful landmark but can present some difficulty on CT and MR images. To help determine the position of the central sulcus. • On axial scans, follow the superior frontal sulcus from anterior to posterior until it meets and forms an angle with the precentral sulcus – the central sulcus is the next one behind (Fig. 1.45k ). • On lateral sagittal images note the Y-shaped sulcus of the pars triangularis at the anterior end of the Sylvian fi ssure. Th e next major fi ssure posterior to the Y is the precentral sulcus (Fig. 1.58d ). • On medial sagittal images follow the cingulate sulcus as it ascends superiorly and posteriorly towards the vertex as the pars marginalis (Fig. 1.58a ), which on axial images looks like a bracket (Fig. 1.45k ). Th e central sulcus indents the medial part of the paracentral lobule at the vertex on the medial surface of the cerebrum just in front of the pars marginalis. • Th e precentral gyrus is usually larger than the postcentral gyrus (and the cortex is slightly thicker)
- . They can be divided into five parts: the anterior (frontal) horn, the ventricular body, the collateral (atrium) trigone, the inferior (temporal) horn, and the posterior (occipital) horn.
- There is a small lateral recess on each side of the fourth ventricle that contains choroid plexus that protrudes through the foramina of Luschka into the subarachnoid space. A small median aperture in the caudal part of the ventricle is known as the foramen of Magendie. Via the two lateral foramina of Luschka and the single medial foramen of Magendie, CSF flows into the ventricular system into the subarachnoid space around the brain and spinal cord
- pars opercularis, which lies in the posterior aspect of the inferior frontal gyrus. A V-shaped area of cortex immediately anterior to it is a useful and constant cortical landmark, called the pars triangularis
- angular gyrus is found on the lateral surface of the cerebrum at the posterior termination of the Sylvian fi ssure (Fig. 1.45f ). Th e supramarginal gyrus lies in front of the angular gyrus
- White matter has a high content of myelinated axons. Grey matter contains relatively few axons and a higher number of cell bodies. As myelin is a fatty substance it is of relatively low density compared to the cellular grey matter. White matter, therefore, appears blacker than grey matter.
- Structures visible on CT
- White matter of the brain lies deep to the cortical grey matter. The internal capsules are white matter tracts which connect with the corona radiata and white matter of the cerebral hemispheres superiorly, and with the brain stem inferiorly. The corpus callosum is a white matter tract located in the midline. It arches over the lateral ventricles and connects white matter of the left and right cerebral hemispheres.