• Computed tomography (CT) scan machines uses X-rays, a
powerful form of electromagnetic energy.
• Sir Godfrey hounsfield-1972
• Nobel prize in 1979 with cormack
• six generation of scanners
• Latest 728 multidetector ct
G.N.HOUNSFIELD ALLAN M. CORMACK
• Internal structure of an object can be
reconstructed from multiple projections of the
• Uses x rays applied in sequence of slices
across the organ
• Images reconstructed from x-ray absorption
• Xray beam moves around the patient in a
Beam of light projected in two direction's,
detecting two different shadows
Region and Planes
• transaxial and extend from the foramen magnum to vertex.
• Slice thickness is between 5 and 10 mm for a routine Head CT.
Hounsfield units represent logarithmic scale of CT density.
Pure water has an HU value of ‘0’.
Conventional CT scanners -1024 to 3071—4096
Current CT scans measure from – 1204 to + 3407.
DESCRIPTION Approx. HU DENSITY
Calcium > 1000 Hyperdense
Acute blood 60-80 Hyperdense
Grey matter 38 (32-42) Hyperdense
White matter 30 (22-32) Hyperdense
CSF 0-10 ISODENSE
Fat -30 to - 100 Hypodense
Air - 1000 Hypodense
• Cranial cross-sectional anatomy is very important to know prior to
analyzing a head CT.
• Once the normal structures are identified, abnormalities can be
detected and a diagnosis may be possible.
• Symmetry is an important concept in anatomy and is almost always
present in a normal head CT unless the patient is incorrectly
positioned with the head cocked at an angle.
• Approximately 45% of injuries result from transportation accidents,
26% from falls, and 17% from assaults. Other causes, such as sports
injuries, comprise the remainder of cases.
• Two-thirds of the patients are less than 30 years of age, and
• Men are twice as likely as are women to be injured.
The bone windows must be examined carefully.
Most clinically significant if the paranasal sinus or
skull base is involved.
Fractures must be distinguished from sutures and
• The ruptured vessel bleeds into the space between the pia and
• When traumatic, subarachnoid hemorrhage occurs most commonly
over the cerebral convexities or adjacent to otherwise injured brain
(adjacent to a cerebral contusion)
• In the absence of significant trauma, the most common cause of
subarachnoid hemorrhage is the rupture of a cerebral aneurysm.
• On CT, subarachnoid hemorrhage appears as focal high density in sulci
and fissures or linear hyperdensity in the cerebral sulci.
• Unenhanced scan and a CT angiogram. Extensive subarachnoid
haemorrhage secondary to a ruptured MCA aneurysm (arrowheads).
Acute Subdural Hematoma
• The blood collects in the space between the arachnoid matter and
the dura matter.
• Characteristics of hematoma :
• Crescent shaped
• Hyperdense, may contain hypodense foci due to serum, CSF or active
• Does not cross dural reflections at suture sites
• High density, crescent / semilunar / concavo-convex shaped
hematoma (arrowheads) overlying the right cerebral hemisphere.
shift of the normally midline septum pellucidum due to the mass
effect also seen (arrow).
• The hypodense region (arrow)
within the high density
hematoma (arrowheads) may
indicate active bleeding
Subacute Subdural Hematoma
• May be difficult to visualize as becomes isodense to normal gray
• Suspicion raise when shift of midline structures without an obvious
• Contrast study can help in difficult
Chronic Subdural Hematoma
• Low density as the hemorrhage is further reabsorbed.
• Usually uniformly low density but may be loculated.
• Rebleeding often occurs and causes mixed density and fluid levels.
Crescent shaped chronic subdural
collection same density as CSF
This chronic subdural hematoma
the septations and loculations that
often occur over time.
• An epidural hematoma is usually associated with a skull fracture.
• Often occurs when an impact fractures the calvarium. The fractured
bone lacerates a dural artery or a venous sinus. The blood from the
ruptured vessel collects between the skull and dura.
• Hyperdense biconvex
• Usually uniformly high density but may contain hypodense foci due to
• Usually does not cross suture lines where the dura tightly adheres to
the adjacent skull.
Diffuse Axonal Injury
• "shear injury“.
• Fifty percent of all primary intra-axial injuries are diffuse axonal
• Acceleration, deceleration and rotational forces cause portions of the
brain with different densities to move relative to each other resulting
in the deformation and tearing of axons
• ill-defined areas of high density or hemorrhage in characteristic
Hemorrhage of the posterior limb of the
internal capsule (arrow) and hemorrhage
of the thalamus (arrowhead).
Hemorrhage in the corpus callosum (arrow).
• most common primary intra-axial injury.
• Often occurs when the brain impacts an
osseous ridge or a dural fold. The foci of
punctate hemorrhage or edema are located
along gyral crests
• On CT cerebral contusion appears as an ill-
defined hypodense area mixed with foci of
hemorrhage. After 24-48 hrs, hemorrhagic
transformation or coalescence of petechial
hemorrhages into a rounded hematoma is
• Traumatic intraventricular hemorrhage is
associated with diffuse axonal injury, deep gray
matter injury, and brainstem contusion. An
isolated intraventricular hemorrhage may be
due to rupture of subependymal veins.
• Stroke is a clinical term for sudden, focal neurological deficit
• Hemorrhagic strokes account for 16% of all strokes.
• An ischemic stroke is caused by blockage of blood flow in a major
cerebral blood vessel, usually due to a blood clot.
• Hemorrhagic strokes account for 16% of all strokes.
• Intracerebral hemorrhage is the most common, accounting for 10%
of all strokes.
• Subarachnoid hemorrhage, due to rupture of a cerebral aneurysm,
accounts for 6%
Hemorrhage in the cerebellum
The most common causes:
• hypertensive hemorrhage.
• amyloid angiopathy,
• ruptured vascular malformation,
• hemorrhage into a tumor
• venous infarction
• drug abuse.
• Often appears as a high-density hemorrhage in the region of
• Basal ganglia
• Pons / midbrain
• Blood may extend into the ventricular system. Intraventricular
extension of the hematoma is associated with a poor prognosis
• Coagulopathy related hemorrhage is heterogeneous due to
incompletely clotted blood.
• AVM bleed may show adjacent calcifications
• Dense middle cerebral artery or a dense
• Basilar Thrombosis
• Lentiform Nucleus Obscuration
• Diffuse Hypodensity and Sulcal Effacement
Hypodensity in the left
hemisphere (arrows) involving
nucleus and lentiform nuclei
(globus pallidus and putamen).
Loss of insular ribbon sign, subtle
hypodensity and effacement of sulci
Large areas of hypodensity within the
left (top images) and right (bottom
images) middle cerebral artery vascular
territories, due to cytotoxic
CT of Subacute Infarction
• The CT of a subactue infarction has the
following findings in 1 -3 days:
- Increasing mass effect
- Wedge shaped low density
- Hemorrhagic transformation
• Imaging in suspected meningitis patients has no role except
• to look for complications
• assess safety of lumbar puncture
• Imaging is not usually performed to diagnose meningitis because
imaging studies are frequently normal despite the presence of the
Ventriculitis / Ependymitis
• In this post contrast CT scan, note the
brain abscess (arrowheads) and
enhancement of the
ependymal lining of the left lateral
• Intracranial tumors generally present with a focal neurological deficit,
seizure, or headache.
• They may present as well defined circumscribed masses on contrast
studies or as irregular masses with necrosis and haemorrhage
ll-defined low density in the right frontal
post contrast administration in the same
patient reveals patchy
enhancement, a portion of which is crossing
the corpus callosum (arrow
Axial, post contrast CT
demonstrating broad based
enhancing extra-axial mass.
• Most common extra-axial
neoplasm of the brain.
• Middle-aged women are most
• Twenty percent of meningiomas
• On CT, meningiomas are usually
isointense to gray matter
therefore contrast is administered.
Take Home Message
• Cranial CT has assumed a Pivotal role in the practice of emergency
medicine for the evaluation of intracranial emergencies, both
traumatic and atraumatic.
• Cranial CT interpretation is a skill, like ECG interpretation, that can be
learned through education, practice, and repetition.
cases helps because the interface between the hematoma and the adjacent brain usually becomes more obvious due to enhancement of the dura and adjacent vascular structures.
Can cross the dural reflections at suture sites unlike a subdural hematoma.
Subarachnoid HemorrhageIn the absence of trauma, the most common cause of subarachnoid hemorrhage is a ruptured cerebral aneurysm.
Cerebral aneurysms tend to occur at branch points of intracranial vessels and thus are frequently located around the Circle of Willis.
Hemorrhage Due to Arteriovenous Malformationmay or may not be visible on a CT scan.
Some contain dysplastic areas of calcification and may be visible as serpentine enhancing structures after contrast administration.
Coagulopathy Related Intracerebral HemorrhageOn imaging, this hemorrhage often has a heterogeneous appearance due to incompletely clotted blood