Presentation on theme: "EVERYTHING A MEDICAL STUDENT SHOULD KNOW ABOUT A CT SCAN OF THE HEAD"— Presentation transcript:
1 EVERYTHING A MEDICAL STUDENT SHOULD KNOW ABOUT A CT SCAN OF THE HEAD By Thanh Binh NguyenNeuroradiologistOttawa HospitalLast 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 radiationEffective 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 mSVNatural background 3 /yrCT head 2CT spine 10
7 Canadian Stroke Facts* 40,000-50,000 new stroke’s /year65% of survivors have disability4th leading cause of deathLongest length-of-stay for any diagnosis (37 d)Leading cause of transfer to long term careLeading cause of neuro disability in adultsCost >$2.7 billion/year$27,500 / acute stroke$46,000-$122,000 / patient for chronic care*Canadian Heart and Stroke Foundation
8 Strokedenotes a persistent loss of neurologic function with sudden onsetdiverse etiologies... Ischaemic Cerebrovascular Stroke Venous Congestion / Stroke Hemorrhagic Stroke
17 Watershed (between ACA and MCA) Michaelchuk. Watershed infarct.
18 Ischaemic CV Stroke Thromboembolic most common Hemodynamic Migraine AtheroscleroticDissectionVasospasmHypotensive /asphyxia (watershed)MigraineVasculitisThrombotic: hypercoagulable statesAtheroscleroticCarotidIntracranialCardiac or pulmonary sources, sterile or septicDissection
27 APPROACH TO BRAIN TUMOR Intra-axial(from the brain) versus Extra-axial (from the meninges or skull)Location (supratentorial vs infratentorial)Age of patientImaging characteristicsCould 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 matterSeen with brain tumors, abscessCytotoxic edemaInvolves both white matter and gray matterSeen with infarction
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.OligodendrogliomasYoung, middle-aged adultSolid, 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
47 CEREBRAL INFECTIONEncephalitis: 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 SPREADHematogenous spread: could reach the corticomedullary junction or leptomeninges.Direct extension: ex.sinusitis leading to epidural abscess or subdural empyemasSpread along the nerves (ex.herpes encephalitis along the trigeminal nerve)
49 ABSCESS (could look similar to metastatic lesion on CT) Ring enhancing lesionVasogenic edema