Basic Approach To Brain CT

Muhammad Bin ZulfiqarPGR IV SIMS/SHL

Alnoor Diagnostic / New Radiology Department

Aims• Introduction• Cross sectional anatomy• Common important pathologies

HISTORY• 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

PRINCIPLE• Internal structure of an object can be

reconstructed from multiple projections of the object.

• Uses x rays applied in sequence of slices across the organ

• Images reconstructed from x-ray absorption data

• Xray beam moves around the patient in a circular path

Beam of light projected in two direction's, detecting two different shadows

Region and Planes• transaxial and extend from the foramen magnum to vertex. • Coronal • Sagittal

• Slice thickness is between 5 and 10 mm for a routine Head CT.

CT termonology• Hypodense—Hypointense• Isodense—Isointense• Hyperdense—Hyperintense

Hounsfield units represent logarithmic scale of CT density.Pure water has an HU value of ‘0’.Conventional CT scanners -1024 to 3071—4096Current 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

CT Windowing• Brain Window— 80 / 35• Bone Window— 1600 / 600 • Subdural hematoma window— 400 / 35

ANATOMY• 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.

ANATOMY1 Sphenoid sinus2 Medulla oblongata3 cerebellum

ANATOMY4 Fourth ventricle5 Middle cerebellar peduncle6 Sigmoid sinus7 Petrous temporal bone and mastoid air cells8 Cerebellopontine angle9 Pons10 Pituitary fossa

ANATOMY11 Cerebellar vermis12 Basilar artery13 Prepontine cistern14 Dorsum sellae15 Temporal horn of lateral ventricle

ANATOMY16 Ambient cistern17 Interpeduncular cistern18 Cerebral peduncle19 Sylvian fissure

ANATOMY20 Supra vermian cistern21 Frontal horn of lateral ventricle21 Third ventricle

ANATOMY22 Head of caudate nucleus23 Insular cortex24 External capsule25 Lentiform nucleus26 Thalamus

ANATOMY27 Interhemispheric fissure28 Anterior limb of internal capsule29 Genu of internal capsule30 Posterior limb of internal capsule31 Trigone of lateral ventricle and calcified choroid plexus32 Occipital horn of lateral ventricle

ANATOMY33 Body of lateral ventricle34 Corona radiata

ANATOMY• 35 Centrum semiovale

ANATOMY36 Pre-central gyrus37 Central sulcus38 Post-central gyrus

ANATOMY• 39 ¼ 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.

Skull FracturesThe 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

Subarachnoid Hemorrhage• 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.

• 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

bleeding• 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 densityhematoma (arrowheads) may indicate active bleeding

Subacute Subdural Hematoma• May be difficult to visualize as becomes isodense to normal gray

matter. • Suspicion raise when shift of midline structures without an obvious

mass.• Contrast study can help in difficult

• Compressed lateral ventricle• Effaced sulci• White matter "buckling“• Thick cortical "mantle

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 (arrowheads) shows the septations and loculations that often occur over time.

Epidural Hematoma• 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

• Hyperdense biconvex • Usually uniformly high density but may contain hypodense foci due to

active bleeding. • Extradural• 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).

Diffuse Axonal Injury• "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 axons

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

Hemorrhage of the posterior limb of the internal capsule (arrow) and hemorrhage of the thalamus (arrowhead).

Hemorrhage in the corpus callosum (arrow).

Cerebral Contusion

• 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 common.

.

Intraventricular Hemorrhage• 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• Stroke is a clinical term for sudden, focal neurological deficit• Hemorrhagic• 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 Stroke• 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,• coagulopathy,• hemorrhage into a tumor• venous infarction • drug abuse.

Hypertensive Hemorrhage• Often appears as a high-density hemorrhage in the region of

• Basal ganglia• Thalamus• Pons / midbrain• cerebellum

• Blood may extend into the ventricular system. Intraventricular extension of the hematoma is associated with a poor prognosis

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

Hypertensive hemorrhage in the basil ganglia.

High density blood fills the cisterns (arrowheads) .

• Coagulopathy related hemorrhage is heterogeneous due to incompletely clotted blood.

• AVM bleed may show adjacent calcifications

Ischemic stroke• Dense middle cerebral artery or a dense

basilar artery• Basilar Thrombosis• Lentiform Nucleus Obscuration• Diffuse Hypodensity and Sulcal Effacement

Hypodensity in the left hemisphere (arrows) involving the caudate 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 (bottomimages) middle cerebral artery vascular territories, due to cytotoxicoedema.

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

Infections—Meningitis• 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 disease.

Common complications of meningitis:• Hydrocephalus• Ventriculitis / Ependymitis• Subdural effusion• Subdural empyema• Cerebritis / Abscess• Vasospasm / arterial infarcts• Venous thrombosis / venous infarcts

Hydrocephalus

Ventriculitis / Ependymitis

• 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

Intracranial Tumors• 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 region.

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

Glioblastoma Multiforme

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

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.

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.

THANK YOU