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CT Scan Head basics

The document outlines the basics of CT scans of the head, including principles, neuroanatomy, and relevant pathologies. It details the components of CT scanners, the construction of images from x-ray data, and how various tissues appear on scans in terms of density. Additionally, it discusses the indications for CT scans in diagnosing neurological conditions, including trauma, infections, and tumors.

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CT Scan Head basics Dr Ravi M Soni DM SR III
Contents: • BASIC PRINCIPLES OF CT SCAN • NORMAL NEUROANATOMY AS SEEN ON HEAD CT SCANS • ILLUSTRATIONS • BRIEF DESCRIPTION OF RELEVANT PATHOLOGIES
BASIC PRINCIPLES OF CT SCAN
HISTORY • Sir Godfrey hounsfield-1972 • Nobel prize in 1979 • Original scanners took approximately 6 minutes to perform a rotation (one slice) and 20 minutes to reconstruct. Despite many technological advances since then, the principles remain the same.
PARTS 1 ) Gantry- which houses X ray apparatus 2 ) X ray tube-akin to that in a X ray machine. 3 ) Detectors 4 ) Patient couch 5 ) Viewing console
X-RAY TUBE 1.X-ray tube & collimator 2.Detector assembly 3.Tube controller 4.High freq. generator 5.Onboard computer 6.Stationary computer INTERNAL STRUCTURE OF GANTRY 1)xray tube-akin to that in a x ray machine. 2)detectors 3)gantry- which houses xray apparatus 4)patient couch 5)viewing console
PRINCIPLE 1. Internal structure of an object can be reconstructed from multiple projections of the object. 2. Uses X rays applied in sequence of slices across the organ 3. Images reconstructed from X ray absorption data 4. X ray beam moves around the patient in a circular path 5. CT scan provides a 3D display of the intracranial anatomy built up from a vertical series of transverse axial tomograms. 6. Each tomogram represents a horizontal slice through the patient’s head. Beam of light projected in two direction's, detecting two different shadows
TECHNIQUE…..  Slice thickness may vary, but in general, it is between 5 and 10 mm for a routine Head CT
9 Image Formation Image Attenuation Receptor Decoder XRays
BASICS…. • X-RAYS ARE ABSORBED TO DIFFERENT DEGREES BY DIFFERENT TISSUES • Always describe CT findings as densities- isodense/hypodense/hyperdense. • Higher the density = whiter is the appearance • Lower the density = darker the appearance • Brain is the reference density • Anything of the density as brain= isodense* • Higher density than brain= hyperdense ( skull is the best example) • Anything darker (lower density) than brain= hypodense( CSF and air are classical examples)
HOUNSFIELD UNITS • Hounsfield Unit (HU)- mean attenuation of x-rays by different tissues. • Related to composition & nature of tissue • Represent the density of tissue • Also called as CT NUMBER
DESCRIPTION OF TISSUE APPROX. HU DENSITY Air --- 1000 HYPODENSE Fat ---70 HYPODENSE Pure water 0 ISODENSE CSF +8 ISODENSE White matter +30 HYPERDENSE Gray matter +45 HYPERDENSE Blood +70 HYPERDENSE Bone/calcification +1000 HYPERDENSE
Densities on ct scan……. WHITE MATTER GREY MATTER
Physiologic calcifications • Chorid plexus-rare before 10yrs • Basal ganglia-rare before 40ys • Pineal gland-common after 30 yr rare before 10yr • Falx • Dentate nuclei
16 INDICATIONS • To diagnose neuro infections and their complications • Stroke to distinguish infarct from hemorrhage • CT angio before thrombolysis • CT venogram for cerebral venous thrombosis(cvt) • Acute changes in mental status • Focal neurologic findings • Trauma • Suspected SAH • CNS tumors
NORMAL NEUROANATOMY AS SEEN ON HEAD CT SCANS
18 BRAIN ANATOMY
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21 Compartments Supratentorial: -Cerebrum -Lateral and third vent. Infratentorial -Brain stem -Cerebellum -Fourth ventricle
AXIAL SECTIONS OF CT HEAD POSTERIOR FOSSA CUTS -ABOVE THE FORAMEN MAGNUM LEVEL -LEVEL OF THE FOURTH VENTRICLE -ABOVE THE FOURTH VENTRICULAR LEVEL -TENTORIAL SUPRATENTORIAL CUTS -THIRD VENTRICULAR LEVEL -LATERAL VENTRICULAR LEVEL -ABOVE THE VENTRICULAR LEVEL
Lateral View of Brain
NORMAL ANATOMY……. A= ORBIT , B= SPHENOID SINUS , C= TEMPORAL LOBE, D=EXTERNAL AUDITORY CANAL E= MASTOID AIR CELLS F= CEREBELLAR HEMISPHERES
NORMAL ANATOMY……. A=Frontal Lobe, B= Frontal Bone (Superior Surface of Orbital Part), C= Dorsum Sellae, D=Basilar Artery E= Temporal Lobe F= Mastoid Air Cells G=Cerebellar Hemisphere
NORMAL ANATOMY……. A=FRONTAL LOBE B= SYLVIAN FISSURE C=TEMPORAL LOBE D=SUPRASELLAR CISTERN E=MIDBRAIN F=FOURTH VENTRICLE G= CEREBELLAR HEMISPHERE
NORMAL ANATOMY…….. A=FALX CEREBRI B=FRONTAL LOBE C=ANTERIOR HORN LAT VENTRICLE D=THIRD VENTRICLE E=QUADRIGEMINAL PLATE CISTERN F=CEREBELLUM
NORMAL ANATOMY…….. A=ANTERIOR HORN LAT VENTRICLE B=CAUDATE NUCLEUS C=ANT LIMB INT CAPSULE D=GLOBUS PALLIDUS AND PUTAMEN E=POST LIMB INT CAPSULE F=THIRD VENTRICLE G=QUADRIGEMINAL PLATE CISTERN H=CEREBELLAR VERMIS I=OCCIPITAL LOBE
NORMAL ANATOMY…….. A=GENU OF CORPUS CALLOSUM B=ANT HORN OF LATERAL VENTRICLE C=INT CAPSULE D=THALAMUS E=PINEAL GLAND F=CHOROID PLEXUS G=STARAIGHT SINUS
NORMAL ANATOMY……. A=FALX CEREBRI B=FRONTAL LOBE C=BODY OF LATERAL VENTRICLE D=SPLENIUM OF CORPUS CALLOSUM E=PARIETAL LOBE F=OCCIPITAL LOBE G=SUPERIOR SAGITTAL SINUS
NORMAL ANATOMY…….. A=FALX CEREBRI B=SULCUS C=GYRUS D=SUPERIOR SAGGITAL SINUS
1. Frontal bone 2. Superior frontal gyrus 3. Coronal suture 4. Precentral sulcus 5. Falx cerebri 6. Precentral gyrus 7. Parietal bone 8. Paracentral lobule 9. Central sulcus 10 . Postcentral gyrus 11 . Superior parietal lobule 12 . Precuneus 13 . Sagittal suture 14 . Superior saggital sinus
Frontal bone Falx cerebri Central sulcus Parietal bone Superior saggital sinus
1. Frontal bone 2. Superior saggital sinus 3. Superior frontal gyrus 4. Coronal suture 5. Falx cerebri 6. Middle frontal gyrus 7. Longitudinal cerebral fissure 8. Precentral sulcus 9. Precentral gyrus 10 . Central sulcus 11 . Cerebral white matter (centrum semiovale) 12 . Postcentral gyrus 13 . Paracentral lobule 14 . Supramarginal gyrus 15 . Parietal bone 16 . Inferior parietal lobule 17 . Precuneus 18 . Parieto-occipital sulcus 19 . Occipital bone
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CORPUS CALLOSUM CORONA RADIATA
2 Frontal sinus 5 Falx cerebri 6 Caudate nucleus (head) 9 Corpus callosum (genu) 11 Lateral ventricle 12 Third ventricle 13 Central sulcus 14 Precentral gyrus 15 Fornix 16 Postcentral gyrus 17 Interventricular foramen (foramen of Monro) 18 Lateral sulcus 19 Claustrum 20 insular Cistern 22 Insula 23 Thalamus 25 Pineal gland 31 Vermis of cerebellum 32 Lateral ventricle (trigone with choroid plexus) 33 Straight sinus 34 Middle temporal gyrus 37 Superior sagittal sinus 38 Occipital gyri
2 Frontal sinus 3 Falx cerebri 7 Corpus callosum (genu) 13 External capsule 14 Putamen 15 Septum verum (precommissural septum) 16 Cistern of lateral cerebral fossa (insular cistern) 17 Hypothalamus 19 Third ventricle 20 Claustrum 21 Superior temporal gyrus 22 Extreme capsule 27 Hippocampus 28 Thalamus 30 Pineal gland (calcified) 31 Tentorium cerebelli 32 Quadrigeminal plate 33 Vermis of cerebellum 34 Quadrigeminal and ambient cisterns 35 Straight sinus 37 Superior sagittal sinus 38 Lateral ventricle (trigone)
1 Frontal sinus 2 Frontal bone 3 Falx cerebri 4 Orbital gyri 5 Straight gyrus 6 Anterior cerebral artery 7 Anterior communicating artery 8 Internal carotid artery 9 Superior temporal gyrus 10Mi ddle temporal gyrus 11 Middle cerebral artery 12 Posterior communicating artery 13 Optic chiasm 14 Amygdaloid body 15 Pituitary stalk 16 Lateral ventricle (temporal horn) 17 Dorsum sellae 18 Hippocampus 19 Pentagon of basal cisterns 20Infe rior temporal gyrus 21 Posterior cerebral artery 22 Parahippocampal gyrus 23 Tentorium cerebelli 24 Basilar artery and basal sulcus 25 Pons 26 Sigmoid sinus 27 Cerebellar peduncle (middle) 28 Fourth ventricle 29 Dentate nucleus 30V ermis of cerebellum (superior part) 31 Temporal bone 32 Confluence of the sinuses 33 Cerebellar hemisphere 34 Transverse sinus 35 Occipital bone
1 Frontal bone 2 Frontal sinus 3 Straight gyrus 4 Temporal muscle 5 Orbital gyri 6 Roof of orbit 7 Superior temporal gyrus 8 Optic nerve 9 Internal carotid artery 10Pi tuitary gland 11 Middle temporal gyrus 12 Dorsum sellae 13 Parahippocampal gyrus 14 Basilar artery 15 Lateral ventricle (temporal horn) 16 Inferior temporal gyrus 17 Trigeminal nerve (V) 18 Trochlear nerve 19 Pontine cistern 20Mas toid antrum 21 Tentorium cerebelli 22 Fourth ventricle 23 Pons 24 Temporal bone 25 Cerebellar peduncle 26 Vermis of cerebellum 27 Sigmoid sinus 28 Cerebellar hemisphere 29 Dentate nucleus 30Occip ital sinus 31 Occipital bone 32 Semispinalis capitis muscle
1 Nasal bone 2 Eyeball 3 Medial rectus muscle 4 Nasal septum 5 Ethmoidal cells 6 Zygomatic bone 7 Pterygopalatine fossa 8 Inferior rectus muscle 9 Occipital bone (basilar part) 10T emporal muscle 11 Foramen ovale with mandibular nerve 12 Sphenoidal sinus 13 Temporal bone (apex of the petrous pyramid) 14 Zygomatic arch 15 Internal carotid artery 16 Masseter muscle 17 Jugular vein (bulb) 18 Lateral pterygoid muscle (superior head) 19 External auditory meatus 20Auditor y tube 21 Medulla oblongata 22 Head of mandible 23 Mastoid process 24 Foramen lacerum 25 Sigmoid sinus 26 Vertebral arteries 27 Petro-occipital fissure 28 Flocculus 29 Cerebellar tonsil 30Dig astric muscle 31 Splenius capitis muscle 32 Cerebellar hemisphere (caudal lobe) 33 Rectus capitis posterior minor muscle 34 Cisterna magna (posterior cerebellomedullary cistern) 35 Rectus capitis posterior major muscle 36 Occipital bone 37 Semispinalis capitis muscle 38 Trapezius muscle
Cerebellar hemisphere medulla Cisterna magna eye ball
53 Pathology • Trauma: -EDH -SDH -SAH -ICH -IVH -Contusion: salt and pepper • Tumours • Infection:-Abscess, Granulomas • Vascular :-Haemorrhagic and ischemic • Congenital:- Hydrocephalous, encephalocoel • Degenerative:- Atrophy and NPH
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Extradural hematoma Convex shape Subdural hematoma Cresent shape Skull fracture
62SDH & ICH
63 ICH
Infarcts Anterior cerebral artery infarct Middle cerebral artery infarct Posterior cerebral artery infarct Hyper dense MCA sign Internal cerebral artery infarct ACA+MCA
hemorrhage Intra parenchymal hemorrhage in putamen Sub arachnoid hemorrhage hyperdensities in sylvian fissure,basal cystern
Neuro infections • Bacterial meningitis – Radiological signs • Meningeal enhancement • Cerebral edema • Complications – Abscess stages • Sub dural abscess, • Epidural abscess
Bacterial meningitis Indicatations for ct Head before lumbar puncture- to look for obstructive hydrocephalus-to prevent herniation to conform meningeal involvement—by meningeal enhancement
Meningitis complications suggested by seizures, altered sensorium, focal deficits Encephalitis- cerebral edema is seen others cerebral abscess epidural/sub dural empyema arteritis leading to infarct hydrocephalus seen well effaced Gyri and sulci Normal parenchyma cerebral edema
hydrocephalus
• Sub dural effusion
• cerebral abscess stages Early cerebritis early capsule, thin rim Late capsular, thick rim Multi loculated Late cerebritis
d/d for multiple ring enhancing lesions Tuberculoma Neurocysticerosis CNS crptococcosis Metastasis Abscess (also cerebritis) Glioblastoma, Granuloma Infarct (esp. Basal ganglia) Contusion (rare) AIDS (Toxoplasmosis, etc.) Lymphoma (common in AIDS ) Neurosarcoidosis Demyelination (active) Resolving hematoma, Radiation change (necrosis)
TUBERCULOMA
• Non contrast ct normal or may show complications • On contrast basal enhancing exudates,meningeal anhancement, tubeculomas with ring enhancement,ependimitis Basal exudate enhancement Tuberculomas with perilesional edema Coalising tuberculomas
NEUROCYSTICERCOSIS
• Stages vesicular stage- live stage only hypo dense lesion with out perilesional edema/ring enhancement colloidal stage- perilesional edema with ring enhancement granular stage- scolex gets calcified resulting in central hyper density nodular stage- entire lesion gets calcified nodular stage- vesicular stage- colloidal stage- granular stage- nodular stage-
• Tuberculous granuloma neurocysticercosis >20 mm size <20mm large perilesional edema usually small area irregular margine regular margin Coalising lesions noncoalising These findings are not pathognomic,above signs can be seen viceversa neurocysticercosis TUBERCULOMAs central dot sign Stary sky
78 CT scan of the brain showing early signs of a left middle cerebral artery ischaemic CVE. In this picture only loss of definition of the gyri are seen clearly (look at cortical surface under red arrow and compare to other side) Acute Infarct
79 MCA infarction: on CT an area of hypoattenuation appearing within six hours is highly specific for irreversible ischemic brain damage Acute Infarct
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King George's Medical University UP, Lucknow INDIA