EVERYTHING A MEDICAL STUDENT SHOULD KNOW ABOUT A CT SCAN OF THE HEAD

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. 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 Stroke Facts* *Canadian Heart and Stroke Foundation

8. Stroke • denotes a persistent loss of neurologic function with sudden onset • diverse etiologies... Ischaemic Cerebrovascular StrokeVenous Congestion / StrokeHemorrhagic Stroke

9. Anatomy

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

11. SupratentorialTerritories

12. From Osborne, A: Neuroradiology

13. Left PCA

14. MCA

15. ACA

16. Anterior choroidal infarct

17. Watershed (between ACA and MCA)

18. Ischaemic CV Stroke • Thromboembolic most common • Hemodynamic • Atherosclerotic • Dissection • Vasospasm • Hypotensive /asphyxia (watershed) • Migraine • Vasculitis • Thrombotic: hypercoagulable states

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

20. Hypertensive Hemorrhage Classically involves the deep nucleii

21. Amyloid angiopathy

22. Hyperdense vessel sign

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

25. 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: • 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 • 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 Enhancingnodule 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-)