CT scan Head Basics with normal anatomy and interpretation. I have included some important relevant pathologies also.

1. CT Scan Head basics
Dr Ravi M Soni
DM SR III

2. Contents:
•
BASIC PRINCIPLES OF CT SCAN
•
NORMAL NEUROANATOMY AS SEEN ON HEAD CT SCANS
•
ILLUSTRATIONS
•
BRIEF DESCRIPTION OF RELEVANT PATHOLOGIES

3. BASIC PRINCIPLES OF CT SCAN

4. 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.

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. 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

7. 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

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

9. 9
Image Formation
Image
Attenuation
Receptor
Decoder
XRays

11. 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)

12. 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

13. 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

14. Densities on ct scan…….
WHITE MATTER
GREY MATTER

15. 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. 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

17. NORMAL NEUROANATOMY AS SEEN ON HEAD CT
SCANS

18. 18
BRAIN ANATOMY

19. 19

20. 20

21. 21
Compartments
Supratentorial:
-Cerebrum
-Lateral and third vent.
Infratentorial
-Brain stem
-Cerebellum
-Fourth ventricle

22. 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

23. Lateral View of Brain

24. NORMAL ANATOMY…….
A= ORBIT , B= SPHENOID SINUS , C= TEMPORAL LOBE, D=EXTERNAL AUDITORY CANAL
E= MASTOID AIR CELLS F= CEREBELLAR HEMISPHERES

25. 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

26. NORMAL ANATOMY…….
A=FRONTAL LOBE B= SYLVIAN FISSURE C=TEMPORAL LOBE
D=SUPRASELLAR CISTERN E=MIDBRAIN F=FOURTH VENTRICLE
G= CEREBELLAR HEMISPHERE

27. NORMAL ANATOMY……..
A=FALX CEREBRI B=FRONTAL LOBE C=ANTERIOR HORN LAT VENTRICLE
D=THIRD VENTRICLE E=QUADRIGEMINAL PLATE CISTERN F=CEREBELLUM

28. 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

29. 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

30. 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

31. NORMAL ANATOMY……..
A=FALX CEREBRI B=SULCUS C=GYRUS D=SUPERIOR SAGGITAL SINUS

36. 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

37. Frontal
bone
Falx cerebri
Central
sulcus
Parietal bone
Superior
saggital
sinus

39. 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

40. 40

41. CORPUS CALLOSUM
CORONA RADIATA

43. 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

45. 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)

47. 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

49. 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

51. 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

52. Cerebellar
hemisphere
medulla
Cisterna
magna
eye ball

53. 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

54. 54

55. 55

56. 56

57. 57

58. 58

59. 59

60. 60

61. Extradural hematoma
Convex shape
Subdural hematoma
Cresent shape
Skull fracture

62. 62SDH & ICH

63. 63
ICH

64. Infarcts
Anterior cerebral artery infarct
Middle cerebral artery infarct
Posterior cerebral artery infarct
Hyper dense MCA sign
Internal cerebral artery infarct
ACA+MCA

65. hemorrhage
Intra parenchymal hemorrhage
in putamen Sub arachnoid hemorrhage
hyperdensities in sylvian fissure,basal cystern

66. Neuro infections
•
Bacterial meningitis
–
Radiological signs
•
Meningeal enhancement
•
Cerebral edema
•
Complications
–
Abscess stages
•
Sub dural abscess,
•
Epidural abscess

67. Bacterial meningitis
Indicatations for ct Head
before lumbar puncture-
to look for obstructive hydrocephalus-to prevent herniation
to conform meningeal involvement—by meningeal
enhancement

68. 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

69. hydrocephalus

70. •
Sub dural effusion

71. •
cerebral abscess
stages
Early cerebritis
early capsule, thin rim
Late capsular, thick rim
Multi loculated
Late cerebritis

72. 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)

73. TUBERCULOMA

74. •
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

75. NEUROCYSTICERCOSIS

76. •
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-

77. •
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. 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. 79
MCA infarction: on CT an area
of hypoattenuation appearing
within six hours is highly specific
for irreversible ischemic brain
damage
Acute Infarct

80. 80

81. 81

82. 82

83. 83

84. King George's Medical University UP, Lucknow
INDIA