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

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Presentation on theme: "EVERYTHING A MEDICAL STUDENT SHOULD KNOW ABOUT A CT SCAN OF THE HEAD By Thanh Binh Nguyen Neuroradiologist Ottawa Hospital Last updated July 2007."— Presentation transcript:

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. (HU water =0, HU bone >500, HU lung =-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 frommSV 1. Natural background3 /yr 2. CT head2 3. CT spine10


7 *Canadian Heart and Stroke Foundation Canadian Stroke Facts* 40,000-50,000 new stroke’s /year 65% of survivors have disability 4 th 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

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)

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


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 Left tonsillar herniation C- C+

35 C- C+

36 C- C+

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


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

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)



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



52 Basal leptomeningitis (seeding of the subarachnoid space) TUBERCULOSIS

53 Multiple tuberculomas seen on MRI exam with contrast


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