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

HEAD

By Thanh Binh NguyenNeuroradiologistOttawa 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. (HUwater=0, HUbone >500, HUlung=-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 from mSV1. Natural background 3 /yr2. CT head 23. CT spine 10

STROKE

*Canadian Heart and Stroke Foundation

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

Stroke

denotes a persistent loss of neurologic function with sudden onset

diverse etiologies...

Ischaemic Cerebrovascular StrokeVenous Congestion / StrokeHemorrhagic Stroke

Anatomy

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

Cerebellar Posterior Inferior

Cerebellar

Supratentorial Territories

From Osborne, A: Neuroradiology

Left PCA

MCA

ACA

Anterior choroidal infarct

Watershed (between ACA and MCA)

Ischaemic CV Stroke

Thromboembolic most common Hemodynamic

Atherosclerotic Dissection Vasospasm Hypotensive /asphyxia (watershed)

Migraine Vasculitis Thrombotic: hypercoagulable states

Hemorrhagic Stroke

Primary Intracerebral bleed Hypertensive Amyloid angiopathy Arteriovenous malformations Neoplasms Trauma

Subarachnoid hemorrhage Aneurysm AVM’s Trauma

HypertensiveHemorrhage

Classically involvesthe deep nucleii

Amyloid angiopathy

Hyperdense vessel sign

Hyperdense vessel sign & loss of gray/whitejunction...

Left insular ribbon sign & effacement of sulci

NEOPLASM

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+

C- C+

C- C+

Hyperdense cerebellar mass seen on plain CT scan which enhances homogeneously and causes compression of the 4th 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

Enhances homgeneously and appears extraaxial

Thickening of the adjacent bone (hyperostosis)

DIAGNOSIS

MENINGIOMA

INFECTION

INTRACRANIAL INFECTION

Intraaxial: Encephalitis Cerebritis Abscess

Extraaxial: Subdural empyema Epidural abscess Meningitis

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

TUBERCULOSIS

Multiple tuberculomas seen on MRI exam with contrast

THE END