“HOW TO READ A HEAD CT SCAN”

4 MARCH, 2013

MUST FOR EVERY PHYSICIAN

• CT HEAD is an extremely useful diagnostic tool used routinely in the care of A&E patients.

• The treating physician needs to be able to accurately interpret and act upon certain CT findings without specialist (e.g., radiologist) assistance, because many disease processes are time dependent and require immediate action.

• It has been shown that even a brief educational intervention can significantly improve the physician’s ability to interpret cranial CT scans.

SCHEME OF THE LECTURE

• BASIC PRINCIPLES OF CT SCAN

• NORMAL NEUROANATOMY AS SEEN ON HEAD CT SCANS

• ILLUSTRATIONS

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

PRINCIPLE

• Uses X rays applied in sequence of slices across the organ

• Images reconstructed from X ray absorption data

• X ray beam moves around the patient in a circular path

PRINCIPLES OF CT………

PRINCIPLE…..

• CT scan provides a 3D display of the intracranial anatomy built up from a vertical series of transverse axial tomograms.

• Each tomogram represents a horizontal slice through the patient’s head.

TECHNIQUE…..

Slice thickness may vary, but in general, it is between 5 and 10 mm for a routine Head CT

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

• Related to composition & nature of tissue• Represent the density of tissue• Also called as CT NUMBER

air --- 1000fat ---70Pure water 0Csf +8White matter +30Gray matter +45blood +70Bone/calcification +1000

Densities on ct scan…….

NORMAL NEUROANATOMY AS SEEN ON HEAD CT SCANS

AXIAL SECTIONS OF CT HEAD

POSTERIOR FOSSA CUTS-ABOVE THE FORAMEN MAGNUM LEVEL-LEVEL OF THE FOURTH VENTRICLE-ABOVE THE FOURTH VENTRICULAR LEVEL-TENTORIALSUPRATENTORIAL 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

WHENEVER THE BRAIN SWELLS , THE GYRI BECOME LARGER AND THE SULCI SHRINK

BASICS….

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

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

Physiological calcifications

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

THANKS

1. Frontal bone2. Superior frontal gyrus3. Falx cerebri4. Middle frontal gyrus5. Cingulate sulcus6. Coronal suture7. Pericallosal artery8. Precentral gyrus9. Corona radiata10. Central sulcus11. Corpus callosum12. Postcentral gyrus13. Lateral ventricle(choroid plexus)14. Postcentral sulcus15. Parietal bone16. Supramarginal gyrus17. Precuneus18. Angular gyrus19. Parieto-occipital sulcus20. Occipital gyri21. Cuneus22. Occipital bone23. Superior saggital sinus