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How To Read A Head CT Scan

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Beginner level information regarding head CT Scan, What it is, principle, basic slices, indication etc.

Publié dans : Santé & Médecine
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How To Read A Head CT Scan

  1. 1. How To Read A Head CT Scan Ahsan Aziz Assistant Registrar, NIMH
  2. 2. Scheme Of The Topic • Basic Principles of CT scan • Normal Neuroanatomy as seen on head CT scan • How to describe a CT head • Some abnormal tomography
  3. 3. BASIC PRINCIPLES OF CT SCAN
  4. 4. History • Sir Godfrey Hounsfield- introduced CT scan in 1972 • Won Nobel prize in 1979
  5. 5. 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
  6. 6. 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
  7. 7. PRINCIPLES OF CT………
  8. 8. 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.
  9. 9. TECHNIQUE….. Slice thickness may vary, but in general, it is between 5 and 10 mm for a routine Head CT
  10. 10. CT Planes
  11. 11. Axial Plane Coronal Plane Sagittal Plane
  12. 12. BASICS…. • X-RAYS ARE ABSORBED TO DIFFERENT DEGREES BY DIFFERENT TISSUES (rays pass freely through air but not through bone) • 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 ( Bone is the best example) • Anything darker (lower density) than brain= hypodense (CSF and air are classical examples)
  13. 13. HOUNSFIELD UNITS • CT scanners record the attenuation (brightness) of each pixel in Hounsfield Units (HU) • Related to composition & nature of tissue • Represent the density of tissue • Also called as CT NUMBER • Marks between -1000 to +1000 • More negative more black, more positive more white
  14. 14. Hounsfield Units of different tissues Air --- 1000 (Darkest Black) Fat ---70 Pure water 0 CSF +8 White matter +30 Gray matter +45 Blood +70 Bone/calcification +1000 (White)
  15. 15. Densities on CT scan…….
  16. 16. NORMAL NEUROANATOMY AS SEEN ON HEAD CT SCANS
  17. 17. AXIAL SECTIONS OF CT HEAD POSTERIOR FOSSA CUTS -Above the foramen magnum level -Level of fourth ventricle -Above the fourth ventricle level -Tentorial SUPRATENTORIAL CUTS -Third ventricular level -Lateral ventricular level -Above the corpus callosum
  18. 18. Lateral View of Brain
  19. 19. NORMAL ANATOMY……. A= ORBIT , B= SPHENOID SINUS , C= TEMPORAL LOBE, D=EXTERNAL AUDITORY CANAL E= MASTOID AIR CELLS F= CEREBELLAR HEMISPHERES
  20. 20. 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
  21. 21. NORMAL ANATOMY……. A=FRONTAL LOBE B= SYLVIAN FISSURE C=TEMPORAL LOBE D=SUPRASELLAR CISTERN E=MIDBRAIN F=FOURTH VENTRICLE G= CEREBELLAR HEMISPHERE
  22. 22. NORMAL ANATOMY…….. A=FALX CEREBRI B=FRONTAL LOBE C=ANTERIOR HORN LAT VENTRICLE D=THIRD VENTRICLE E=QUADRIGEMINAL PLATE CISTERN F=CEREBELLUM
  23. 23. 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
  24. 24. 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
  25. 25. 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
  26. 26. NORMAL ANATOMY…….. A=FALX CEREBRI B=SULCUS C=GYRUS D=SUPERIOR SAGGITAL SINUS
  27. 27. Normal neuroanatomical Shapes to Identify distortions
  28. 28. Orbits and Ethmoid air cells
  29. 29. Base of skull, Midline bony prominence, Prepontine cistern, Pretrous bone, Frontal sinus
  30. 30. Star shape ~ Circle of Willis, Fourth ventricle, Temporal horn ~ slit
  31. 31. Midbrain and interpeduncular Cistern (Heart shaped)
  32. 32. Third ventricle (Smiley face)
  33. 33. Third ventricle, basal ganglia
  34. 34. Body of lateral ventricle (Twin banana)
  35. 35. Reading a CT Head Outside to Inside steps
  36. 36. 1. Skin and Soft Tissue Examine Normal Contour of skin • Hematoma • Foreign body • Surgical conditions • Skin and soft tissue pathology
  37. 37. 2. Bone Examine • Bony contour (fracture, bone tumor) • Sutures • Mastoid air cells
  38. 38. 3. Sinuses Evaluate • Superior sagittal sinus • Frontal sinus • Ethmoid sinus • Sphenoid sinus • Maxillary sinus
  39. 39. 3. Sinuses ….. • Look for • Sinusitis • Mucosal thickening • Blood in sinus (Traumatic) • Mucous retention cyst and polyp
  40. 40. 3. Sinuses …..
  41. 41. 4. Sulci Identify • Sulci • Sylvian fissure • Central sulcus • Post central sulcus • Precentral sulcus Sulci will be deeper with age Blood in sulcus is important
  42. 42. 4. Sulci…..
  43. 43. 5. Brain parenchyma Identify lobes Frontal, Parietal, Temporal, Occipital Identify structures Midbrain, Pons, Medulla, cerebellum Identify deep structures Corpus callosum, Caudate nucleus, Lentiform nucleus, Thalamus, Internal capsule
  44. 44. 5. Brain parenchyma…. Look for • Symmetry between both sides • Gray and white matter differentiation • Change in density
  45. 45. Midbrain and Lentiform Nucleus
  46. 46. 5. Brain Parenchyma
  47. 47. 5. Brain Parenchyma…. Epidural hemorrhage Lens Shaped
  48. 48. 5. Brain Parenchyma…. Subdural hemorrhage Crescent shape
  49. 49. 5. Brain Parenchyma…. Subarachnoid hemorrhage
  50. 50. 5. Brain Parenchyma…. Intraparenchymal hemorrhage
  51. 51. 6. Cisterns Identify cisterns Supraseller, Ambient, Prepontine, Cisterna magna Cisterns can be filled with blood in subarachnoid hemorrhage
  52. 52. Supraseller and Basal Cisterns
  53. 53. 7. Ventricles Identify ventricles Evaluate for any change in • Size • Shape • Symmetry • Density • Mass effect
  54. 54. 7. Ventricles Lateral Ventricles Third ventricle
  55. 55. 7. Ventricles…. Cerebral Aqueduct Fourth Ventricle
  56. 56. 7. Ventricles …. Hydrocephalus
  57. 57. 7. Ventricles… Mass effect
  58. 58. 8. Midline shift Identify midline structures • Falx Cerebri and Fornix • Pineal Gland • Great vein of Galen
  59. 59. 8. Midline shift…. Falx cerebri Fornix
  60. 60. 8. Midline shift… Pineal Gland (Calcified) Great vein of Galen
  61. 61. 8. Midline shift… 1. Select a slide where both lateral ventricles are prominent. 2. Draw a line joining falx cerebri anteriorly and posteriorly. 3. The septum between ventricles should not deviate more than 5mm from midline.
  62. 62. 8. Midline shift… Prominent ventricles Draw a midline
  63. 63. 8. Midline Shifts….. Right sided abscess causing left sided midline shift
  64. 64. Recap 1. Skin and Soft tissue 2. Bony contour 3. Sinuses 4. Sulci 5. Brain parenchyma 6. Cisterns 7. Ventricles 8. Midline shift
  65. 65. Other concerns (Calcification)
  66. 66. Indication of Head CT scan..(Absolute) • GCS less than 10 any time following head injury • Skull fracture • Blood or CSF coming out of nose, ear, or panda eye following injury • Sudden severe headache • Headache with vomiting (Exclude migraine and tension type headache) • Focal neurological sign (paralysis, cranial nerve palsy etc.) • First Seizure after 20 years of age or not responding to anti- epileptic drugs • First episode of psychosis
  67. 67. CT or MRI scan? Depends on suspected pathology CT is better in  Bone pathology  Acute hemorrhagic conditions MRI is better in  Posterior fossa pathology (Brainstem and cerebellum)  White matter disease  Better gray and white matter differentiation  Orbital or aural cavity pathology
  68. 68. Prefer CT scan in … • Acute trauma or bony fracture • Calcified lesions • Suspected acute intracerebral hemorrhage • Suspected subarachnoid hemorrhage
  69. 69. Prefer MRI scan in… • Arteriovenous malformations • Epilepsy and adult onset seizures • Hemangiomas • Hydrocephalus • Infection / Inflammation • Infratentorial tumors • Lacunar infarcts • Lyme disease
  70. 70. Prefer MRI in… • Meningioma • Multiple sclerosis • Orbit and optical nerve disease • Pituitary dysfunction • Posterior fossa abnormality • Space occupying lesion • Stroke (use Diffusion weighted MRI)
  71. 71. Prefer MRI in… • Syringomyelia • Vascular abnormalities • White matter disease
  72. 72. Further reading for those who are interested • Window level and width (to fix density of image) • Contrast CT scan
  73. 73. Reference • Osborn Diagnostic Imaging (Brain), 1st edition • Radiology in Medical Practice by Prof. A. B. M. Abdullah • Head and Neck Imaging, 4th edition • Fundamentals of Diagnostic Radiology, 4th edition

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