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:
EVERYTHING A MEDICAL STUDENT SHOULD KNOW ABOUT A CT SCAN OF THE HEAD By Thanh Binh Nguyen Neuroradiologist Ottawa Hospital Last updated July 2007
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.
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)
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
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
*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
Stroke denotes a persistent loss of neurologic function with sudden onset diverse etiologies... Ischaemic Cerebrovascular Stroke Venous Congestion / Stroke Hemorrhagic Stroke
Hypertensive Hemorrhage Classically involves the deep nucleii
Hyperdense vessel sign
Hyperdense vessel sign & loss of gray/white junction...
Left insular ribbon sign & effacement of sulci
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.
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
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…)
Unenhanced CT of the head shows a mass in the left frontal lobe with vasogenic edema
Ring enhancing lesion (GBM) Vasogenic edema
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
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
Left tonsillar herniation C- C+
Hyperdense cerebellar mass seen on plain CT scan which enhances homogeneously and causes compression of the 4 th ventricle and hydrocephalus C- C+
DIAGNOSIS BURKITT LYMPHOMA
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
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
Ct scan of the head without contrast Hyperdense mass
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.
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)
Ring enhancing lesion Vasogenic edema ABSCESS (could look similar to metastatic lesion on CT)
SUBDURAL EMPYEMA (C-)
SUBDURAL EMPYEMA (C+)
Basal leptomeningitis (seeding of the subarachnoid space) TUBERCULOSIS
Multiple tuberculomas seen on MRI exam with contrast