CT Scan Head basics

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 apparatus2) X ray tube-akin to that in a X ray machine.3) Detectors 4) Patient couch5) Viewing console

X-RAY TUBE

1.X-ray tube & collimator2.Detector assembly3.Tube controller4.High freq. generator5.Onboard computer6.Stationary computer

INTERNAL STRUCTURE OF GANTRY

1)xray tube-akin to that in a x ray machine.2)detectors 3)gantry- which houses xray apparatus4)patient couch5)viewing console

PRINCIPLE1. 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 data4. X ray beam moves around the patient in a circular path5. 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

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Image Formation

Image

Attenuation

Rec

epto

r

Dec

oder

X R

ays

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 cl

assical 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 HYPODENSEFat ---70 HYPODENSEPure water 0 ISODENSECSF +8 ISODENSEWhite matter +30 HYPERDENSEGray matter +45 HYPERDENSEBlood +70 HYPERDENSEBone/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

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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

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BRAIN ANATOMY

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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 CANALE= 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 LOBED=SUPRASELLAR CISTERN E=MIDBRAIN F=FOURTH VENTRICLE G= CEREBELLAR HEMISPHERE

NORMAL ANATOMY……..

A=FALX CEREBRI B=FRONTAL LOBE C=ANTERIOR HORN LAT VENTRICLED=THIRD VENTRICLE E=QUADRIGEMINAL PLATE CISTERN F=CEREBELLUM

NORMAL ANATOMY……..

A=ANTERIOR HORN LAT VENTRICLE B=CAUDATE NUCLEUS C=ANT LIMB INT CAPSULED=GLOBUS PALLIDUS AND PUTAMEN E=POST LIMB INT CAPSULE F=THIRD VENTRICLEG=QUADRIGEMINAL PLATE CISTERN H=CEREBELLAR VERMIS I=OCCIPITAL LOBE

NORMAL ANATOMY……..

A=GENU OF CORPUS CALLOSUM B=ANT HORN OF LATERAL VENTRICLE C=INT CAPSULED=THALAMUS E=PINEAL GLAND F=CHOROID PLEXUS G=STARAIGHT SINUS

NORMAL ANATOMY…….

A=FALX CEREBRI B=FRONTAL LOBE C=BODY OF LATERAL VENTRICLED=SPLENIUM OF CORPUS CALLOSUM E=PARIETAL LOBE F=OCCIPITAL LOBEG=SUPERIOR SAGITTAL SINUS

NORMAL ANATOMY……..

A=FALX CEREBRI B=SULCUS C=GYRUS D=SUPERIOR SAGGITAL SINUS

1. Frontal bone2. Superior frontal gyrus3. Coronal suture4. Precentral sulcus5. Falx cerebri6. Precentral gyrus7. Parietal bone8. Paracentral lobule9. Central sulcus10. Postcentral gyrus11. Superior parietal lobule12. Precuneus13. Sagittal suture14. Superior saggital sinus

Frontal bone

Falx cerebri

Central sulcus

Parietal bone

Superior saggital sinus

1. Frontal bone2. Superior saggital sinus3. Superior frontal gyrus4. Coronal suture5. Falx cerebri6. Middle frontal gyrus7. Longitudinal cerebral fissure8. Precentral sulcus9. Precentral gyrus10. Central sulcus11. Cerebral white matter (centrum

semiovale)12. Postcentral gyrus13. Paracentral lobule14. Supramarginal gyrus15. Parietal bone16. Inferior parietal lobule17. Precuneus18. Parieto-occipital sulcus19. Occipital bone

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CORPUS CALLOSUM

CORONA RADIATA

2 Frontal sinus5 Falx cerebri6 Caudate nucleus (head)9 Corpus callosum (genu)11 Lateral ventricle 12 Third ventricle13 Central sulcus14 Precentral gyrus15 Fornix16 Postcentral gyrus17 Interventricular foramen(foramen of Monro)18 Lateral sulcus19 Claustrum20 insular Cistern 22 Insula23 Thalamus25 Pineal gland31 Vermis of cerebellum 32 Lateral ventricle (trigone with choroid plexus) 33 Straight sinus 34 Middle temporal gyrus37 Superior sagittal sinus 38 Occipital gyri

2 Frontal sinus3 Falx cerebri7 Corpus callosum (genu)13 External capsule14 Putamen15 Septum verum(precommissural septum)16 Cistern of lateral cerebral fossa(insular cistern)17 Hypothalamus19 Third ventricle20 Claustrum21 Superior temporal gyrus22 Extreme capsule27 Hippocampus28 Thalamus30 Pineal gland (calcified)31 Tentorium cerebelli32 Quadrigeminal plate 33 Vermis of cerebellum34 Quadrigeminaland ambient cisterns35 Straight sinus37 Superior sagittal sinus38 Lateral ventricle (trigone)

1 Frontal sinus2 Frontal bone3 Falx cerebri4 Orbital gyri5 Straight gyrus6 Anterior cerebral artery7 Anterior communicating artery8 Internal carotid artery9 Superior temporal gyrus10Mi ddle temporal gyrus11 Middle cerebral artery12 Posterior communicatingartery13 Optic chiasm14 Amygdaloid body15 Pituitary stalk16 Lateral ventricle (temporalhorn)17 Dorsum sellae18 Hippocampus19 Pentagon of basal cisterns20Infe rior temporal gyrus21 Posterior cerebral artery22 Parahippocampal gyrus23 Tentorium cerebelli24 Basilar artery and basal sulcus25 Pons26 Sigmoid sinus27 Cerebellar peduncle (middle)28 Fourth ventricle29 Dentate nucleus30V ermis of cerebellum (superiorpart)31 Temporal bone32 Confluence of the sinuses33 Cerebellar hemisphere34 Transverse sinus35 Occipital bone

1 Frontal bone2 Frontal sinus3 Straight gyrus4 Temporal muscle5 Orbital gyri6 Roof of orbit7 Superior temporal gyrus8 Optic nerve9 Internal carotid artery10Pi tuitary gland11 Middle temporal gyrus12 Dorsum sellae13 Parahippocampal gyrus14 Basilar artery15 Lateral ventricle (temporalhorn)16 Inferior temporal gyrus17 Trigeminal nerve (V)18 Trochlear nerve19 Pontine cistern20Mas toid antrum21 Tentorium cerebelli22 Fourth ventricle23 Pons24 Temporal bone25 Cerebellar peduncle26 Vermis of cerebellum27 Sigmoid sinus28 Cerebellar hemisphere29 Dentate nucleus30Occip ital sinus31 Occipital bone32 Semispinalis capitis muscle

1 Nasal bone2 Eyeball3 Medial rectus muscle4 Nasal septum5 Ethmoidal cells6 Zygomatic bone7 Pterygopalatine fossa8 Inferior rectus muscle9 Occipital bone (basilar part)10T emporal muscle11 Foramen ovale withmandibular nerve12 Sphenoidal sinus13 Temporal bone (apex of thepetrous pyramid)14 Zygomatic arch15 Internal carotid artery16 Masseter muscle17 Jugular vein (bulb)18 Lateral pterygoid muscle(superior head)19 External auditory meatus20Auditor y tube21 Medulla oblongata22 Head of mandible23 Mastoid process24 Foramen lacerum25 Sigmoid sinus26 Vertebral arteries27 Petro-occipital fissure28 Flocculus29 Cerebellar tonsil30Dig astric muscle31 Splenius capitis muscle32 Cerebellar hemisphere (caudal lobe)33 Rectus capitis posterior minor muscle34 Cisterna magna (posterior cerebellomedullarycistern)35 Rectus capitis posterior major muscle36 Occipital bone37 Semispinalis capitis muscle38 Trapezius muscle

Cerebellar hemisphere

medulla

Cisterna magna

eye ball

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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

63ICH

InfarctsAnterior cerebral artery infarct

Middle cerebral artery infarct

Posterior cerebral artery infarct

Hyper dense MCA sign

Internal cerebral artery infarctACA+MCA

hemorrhage

Intra parenchymal hemorrhage in putamen Sub arachnoid hemorrhage

hyperdensities in sylvian fissure,basal cysterns

Neuro infections• Bacterial meningitis

– Radiological signs• Meningeal enhancement• Cerebral edema

• Complications– Abscess stages

• Sub dural abscess,• Epidural abscess

Bacterial meningitisIndicatations 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 sulciNormal 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

TuberculomaNeurocysticerosisCNS crptococcosisMetastasisAbscess (also cerebritis)Glioblastoma, Granuloma Infarct (esp. Basal ganglia)Contusion (rare) AIDS (Toxoplasmosis, etc.)Lymphoma (common in AIDS ) NeurosarcoidosisDemyelination (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 noncoalisingThese findings are not pathognomic,above signs can be seen viceversa

neurocysticercosis

TUBERCULOMAs

central dot sign Stary sky

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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

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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