Dr. Yusrah Liaqat

Take detail history of patient and check all baseline testsIn order to perform a head CT, the patient is placed on the CT table in a supine position and the tube rotates around the patient at an angle parallel to the base of the skull.

Region and Planes: Head CT's are usually transaxial and extend from the foramen magnum to vertex. Other planes used are coronal and sagittal.Brain windows are standard. Bone windows and Subdural windows can make a big difference in resolution for these parts of the examination. Slice thickness is between 5 and 10 mm for a routine Head CT.

Plain scans are done without infusion of any medication or agents. IV infusion for contrast enhancement makes some lesions (esp. tumours) much more visible.Several different agents can be used. Omnipaque is used most often. It is given IV. Be sure renal function is OK (via serum creatinine test) before administration and be cautious if there is a tendency to congestive heart failure.

Axis = a line from the bottom of the feet to top of the headTransaxial plane is perpendicular to the axis and shows left and right, anterior and posterior as seen from below. It is the plane used most often for CT scans of the brain..

ATTENUATION COEFFICIENTTtissue contained within each image unit (called a pixel) absorbs a certain proportion of the x-rays that pass through it (e.g., bone absorbs a lot, air almost none). This ability to block x-rays as they pass through a substance is known as attenuation. For a given body tissue, the amount of attenuation is relatively constant and is known as that tissue’s attenuation coeffi cient. In CT, these attenuation coeffi cients are mapped to an arbitrary scale between −1000 hounsfi eld units [HU] (air) and +1000 HU (bone) (Box 69-1). This scale is the Hounsfi eld scale (in honor of Sir Jeffrey Hounsfi eld, who received a Nobel prize for his pioneering work .Acute blood is in the range of 50-100 HU units

Substance HUAir −1000Lung −50Fat −84Water 0CSF 15Blood +30 to +45Muscle +40Soft Tissue +100 to +300

Bone+700(cancellous bone)to +3000 (dense bone)

The HU of common substancesThe Hounsfield scale applies to medical grade CT scans but not to cone beam computed tomography (CBCT) scans.[1]

The HU of common substances

ANATOMYCranial 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.

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A. OrbitB. Sphenoid SinusC. Temporal LobeD. External Auditory CanalE. Mastoid Air CellsF. Cerebellar Hemisphere

A. Frontal LobeB. Frontal Bone (Superior Surface of Orbital Part)C. Dorsum SellaeD. Basilar ArteryE. Temporal LobeF. Mastoid Air CellsG. Cerebellar Hemisphere

A. Frontal LobeB. Sylvian FissureC. Temporal LobeD. Suprasellar CisternE. MidbrainF. Fourth VentricleG. Cerebellar Hemisphere

A. Falx CerebriB. Frontal LobeC. Anterior Horn of Lateral VentricleD. Third VentricleE. Quadrigeminal Plate CisternF. Cerebellum

A. Anterior Horn of the Lateral VentricleB. Caudate NucleusC. Anterior Limb of the Internal CapsuleD. Putamen and Globus PallidusE. Posterior Limb of the Internal CapsuleF. Third VentricleG. Quadrigeminal Plate CisternH. Cerebellar VermisI. Occipital Lobe

A. Genu of the Corpus CallosumB. Anterior Horn of the Lateral VentricleC. Internal CapsuleD. ThalamusE. Pineal GlandF. Choroid PlexusG. Straight Sinus

A. Falx CerebriB. Frontal LobeC. Body of the Lateral VentricleD. Splenium of the Corpus CallosumE. Parietal LobeF. Occipital LobeG. Superior Sagittal Sinus

A. Falx CerebriB. SulcusC. GyrusD. Superior Sagittal Sinus

TRAUMA• 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.

Divided into Linear Depresssed Most clinically significant if the paranasal

sinus or skull base is involved.Fractures must be distinguished from

sutures and venous channels

Linear skull fracture of the right parietal bone (arrows

Due to injury of small arteries or veins on the surface of the brain. The ruptured vessel bleeds into the space between the pia and arachnoid matter. 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.

Deceleration and acceleration or rotational forces that tear bridging veins . The blood collects in the space between the arachnoid matter and the dura matter. The hematoma on CT has the following characteristics:- Crescent shaped- Hyperdense, may contain hypodense foci due to serum, CSF or active bleeding- Does not cross dural reflections

High density, crescent shaped hematoma (arrowheads) overlying the right cerebral hemisphere. Note the shift of the normally midline septum pellucidum due to the mass effect arrow.

The hypodense region (arrow) within the high densityhematoma (arrowheads) may indicate active bleeding

May be difficult to visualize by CT because as the hemorrhage is reabsorbed it becomes isodense to normal gray matter. Suspected when you identify shift of midline structures without an obvious mass. Giving contrast in difficult 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.

Compressed lateral ventricle

Effaced sulci

White matter "buckling“

Thick cortical "mantle

Chronic SDH becomes 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 hematoma (arrowheads). Notice the low attenuation due to reabsorbtion of the hemorrhage over time.

This chronic subdural hematoma (arrowheads) shows 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.

CT Appearance: The hematoma forms a hyperdense biconvex mass and is usually uniformly high density but may contain hypodense foci due to active bleeding.

An epidural hematoma is extradural it can cross the dural reflections unlike a subdural hematoma. However an epidural hematoma usually does not cross suture lines where the dura tightly adheres to the adjacent skull.

Biconvex (lenticellular) epidural hematoma (arrowheads),deep to the parietal skull fracture (arrow).

"shear injury“. Fifty percent of all primary intra-axial injuries are diffuse axonal injuries. 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 axonsill-defined areas of high density or hemorrhage in characteristic locations

ill-defined areas of high density or hemorrhage in characteristic locations

CT Appearance

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 crestsOn 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 common.

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Multiple foci of high density corresponding tohemorrhage (arrows) in an area of low density

(arrowheads) in the left frontal lobe due to cerebral contusion.

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.

STROKESTROKEStroke is a clinical term for sudden, focal neurological deficitStrokes are classified into two major types - hemorrhagic and ischemic. 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 (arrow).

The most common causes: hypertensive hemorrhage. amyloid angiopathy, ruptured vascular malformation, coagulopathy, hemorrhage into a tumor venous infarction drug abuse.

Thalamic hemorrhage (arrow) extending into the left lateral ventricle (arrowheads).

commonly due to vasculopathy involving deep penetrating arteries of the brain. often appears as a high-density hemorrhage in the region of the basal ganglia. Blood may extend into the ventricular system. Intraventricular extension of the hematoma is associated with a poor prognosis

Hypertensive hemorrhage in the basil ganglia.

On imaging, this hemorrhage often has a heterogeneous appearance due to incompletely clotted blood

may 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.

In 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.

High density blood fills the cisterns (arrowheads) .

ADVANTAGES- Is readily available- Is rapid- Allows easy exclusion of hemorrhage- Allows the assessment of parenchymal damage

DISADVANTAGES- Old versus new infarcts is not always clear- No functional information (yet)- Limited evaluation of vertebrobasilar system

A CT is 58% sensitive for infarction within the first 24 hours MRI is 82% sensitive. If the patient is imaged greater than 24 hours after the event, both CT and MR are greater than 90% sensitive.

Ischemic strokes are caused by: thrombosis, embolism of thrombosis hypoperfusion and lacunar infarctions.

1. Dense middle cerebral artery or a dense basilar artery,

High density in the right middle cerebral artery (arrowheads).Compare it with the normal left middle cerebral artery (arrow).

Dense basilar artery (arrow). Compare this to the normal internal carotid artery (arrowhead).

2. Basilar Thrombosis

3. Lentiform Nucleus Obscuration

Hypodensity in the left hemisphere (arrows) involving the caudate nucleus and lentiform nuclei (globus pallidus and putamen).

4. Diffuse Hypodensity and Sulcal Effacement

Hypodensity and sulcal effacement (arrowheads)in the right middle cerebral artery distribution.

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 is performed to look for complications and assess safety of lumbar puncture. Imaging is not usually performed to diagnose meningitis because imaging studies are frequently normal despite the presence of the disease.

Common complications of meningitis:

HydrocephalusVentriculitis / EpendymitisSubdural effusionSubdural empyemaCerebritis / AbscessVasospasm / arterial infarctsVenous thrombosis / venous infarcts

Hydrocephalus

In this post contrast CT scan, note the ring enhancing brain abscess (arrowheads) and enhancement of the ependymal lining of the left lateral ventricle (arrow

Ventriculitis / Ependymitis

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

Glioblastoma Multiforme

ll-defined low density in the right frontal region.

post contrast administration in the same patient reveals patchy enhancement, a portion of which is crossing the corpus callosum (arrow

Meningioma

Most common extra-axial neoplasm of the brain. Middle-aged women are most frequently affected. Twenty percent of meningiomas calcify. On CT, meningiomas are usually isointense to gray matter therefore contrast is administered.

Axial, post contrast CT demonstrating broad based enhancing extra-axial mass.

Cranial CT has assumed a critical role in the practice of emergency medicine for the evaluation of intracranial emergencies, both traumatic and atraumatic. Cranial CT is integral to the practice of emergency medicine and is used on a daily basis to make important, time-critical decisions that directly impact the care of ED patients. An important tenet in the use of cranial CT is that accurate interpretation is required to make good clinical decisions. Cranial CT interpretation is a skill, like ECG interpretation, that can be learned through education, practice, and repetition.

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