1. EVERYTHING A MEDICAL STUDENT SHOULD KNOW ABOUT A CT SCAN OF THE HEAD
By Thanh Binh Nguyen
Neuroradiologist
Ottawa Hospital
Last updated July 2007

2. What is a CAT scan? CAT scan stands for Computed Assisted Tomography
Cross sectional images are obtained by multiple measurements of the x-rays attenuation from several projections.

3. What are we measuring?
The attenuation coefficient reflects the reduction in the x-ray intensity by the material relative to water.
The Hounsfield Unit is the scale used. (HUwater=0, HUbone >500, HUlung=-500)

4. CT and radiation
Effective dose takes into account which tissue has absorbed what radiation dose (expressed in Sievert)
We can decrease the effective dose in CT by reducing the tube current but image noise will be increased

5. Radiation and risk of cancer
Lifetime risk of developing fatal cancer from radiation exposure in a population is 0.005% per milliSievert(mSv)
Exposure from mSV
Natural background 3 /yr
CT head 2
CT spine 10

6. STROKE

7. Canadian Stroke Facts*
40,000-50,000 new stroke’s /year
65% of survivors have disability
4th leading cause of death
Longest length-of-stay for any diagnosis (37 d)
Leading cause of transfer to long term care
Leading cause of neuro disability in adults
Cost >$2.7 billion/year
$27,500 / acute stroke
$46,000-$122,000 / patient for chronic care
*Canadian Heart and Stroke Foundation

8. Stroke
denotes a persistent loss of neurologic function with sudden onset
diverse etiologies... Ischaemic Cerebrovascular Stroke Venous Congestion / Stroke Hemorrhagic Stroke

9. Anatomy

10. Arterial Territories Anterior Cerebral Middle Cerebral
Posterior Cerebral
Basilar
Superior Cerebellar
Anterior Inferior Cerebellar
Posterior Inferior Cerebellar

11. Supratentorial Territories

12. From Osborne, A: Neuroradiology

13. Left PCA

14. MCA

15. ACA

16. Anterior choroidal infarct

17. Watershed (between ACA and MCA)
Michaelchuk. Watershed infarct.

18. Ischaemic CV Stroke Thromboembolic most common Hemodynamic Migraine
Atherosclerotic
Dissection
Vasospasm
Hypotensive /asphyxia (watershed)
Migraine
Vasculitis
Thrombotic: hypercoagulable states
Atherosclerotic
Carotid
Intracranial
Cardiac or pulmonary sources, sterile or septic
Dissection

19. Hemorrhagic Stroke Primary Intracerebral bleed Subarachnoid hemorrhage
Hypertensive
Amyloid angiopathy
Arteriovenous malformations
Neoplasms
Trauma
Subarachnoid hemorrhage
Aneurysm
AVM’s

20. Hypertensive
Hemorrhage
Classically involves
the deep nucleii

21. Amyloid angiopathy
Godin. Amyloid Angiopathy…

22. Hyperdense vessel
sign

24. Hyperdense vessel
sign & loss of
gray/white
junction...

25. Left insular ribbon sign & effacement of sulci
Roberts L MCA occl ia lysis
Left insular ribbon sign & effacement of sulci

26. NEOPLASM

27. APPROACH TO BRAIN TUMOR
Intra-axial(from the brain) versus Extra-axial (from the meninges or skull)
Location (supratentorial vs infratentorial)
Age of patient
Imaging characteristics
Could you this be something other than neoplasm (infarction, abscess, etc…)? CT with contrast or MRI is often needed.

28. EDEMA Vasogenic edema: Cytotoxic edema
Involves white matter primarily with sparing of gray matter
Seen with brain tumors, abscess
Cytotoxic edema
Involves both white matter and gray matter
Seen with infarction

29. BRAIN TUMORS Extraaxial: meningioma Intraaxial: Primary
Glial tumors: low grade to high grade astrocytoma (glioblastoma multiforme)
Non glial tumor (lymphoma, hemangioblastoma, etc…)
Metastasis (lung, breast, colon, etc…)

30. Unenhanced CT of the head shows a mass in the left frontal lobe with vasogenic edema

31. Ring enhancing lesion (GBM)
Vasogenic edema

32. GLIOMAS Astrocytomas Oligodendrogliomas 85% of cerebral gliomas
Young to middle-aged adults (20-50 years)
Varying degree of malignancy. Highest grade is glioblastoma multiforme which presents as a mass with ill-defined margins, variable enhancement and extensive vasogenic edema.
Oligodendrogliomas
Young, middle-aged adult
Solid, well-defined mass with calcification

33. 70 year old gentleman complaining of dizziness and off balance for one week with associated nausea and vomiting. He also had attack of left facial numbness and left arm numbness for a week. Cerebellar exam showed nystagmus of lateral gaze and left-sided incoordination

34. C+ C-
Left tonsillar herniation

35. C+ C-

36. C+ C-

37. Hyperdense cerebellar mass seen on plain CT scan which enhances homogeneously and causes compression of the 4th ventricle and hydrocephalus C+ C-

38. DIAGNOSIS
BURKITT LYMPHOMA

39. Ct scan of the head with contrast in patient with renal cell carcinoma
Enhancing nodule at corticomedullary junction
Vasogenic edema: involves whiter matter more than gray matter

40. DIAGNOSIS METASTASES Hematogenous seeding to corticomedullary junction
Usually in MCA territory
Usually the degree of edema is out of proportion to the size of the lesion

41. Ct scan of the head without contrast
Hyperdense mass

42. Enhances homgeneously and appears extraaxial

43. Thickening of the adjacent bone (hyperostosis)

44. DIAGNOSIS
MENINGIOMA

45. INFECTION

46. INTRACRANIAL INFECTION
Intraaxial:
Encephalitis
Cerebritis
Abscess
Extraaxial:
Subdural empyema
Epidural abscess
Meningitis

47. CEREBRAL INFECTION
Encephalitis: generalized and difuse infection of the brain. Often of viral origin (ex.herpes simplex)
Cerebritis: localized but poorly demarcated area of parenchymal softening.
Abscess: follows cerebritis. Occurs when a central zone of necrosis becomes encapsulated.

48. MODE OF SPREAD
Hematogenous spread: could reach the corticomedullary junction or leptomeninges.
Direct extension: ex.sinusitis leading to epidural abscess or subdural empyemas
Spread along the nerves (ex.herpes encephalitis along the trigeminal nerve)

49. ABSCESS (could look similar to metastatic lesion on CT)
Ring enhancing lesion
Vasogenic edema

50. SUBDURAL EMPYEMA (C-)

51. SUBDURAL EMPYEMA (C+)

52. TUBERCULOSIS
Basal leptomeningitis (seeding of the subarachnoid space)

53. TUBERCULOSIS
Multiple tuberculomas seen on MRI exam with contrast

54. THE END