Ct scan brain lecture by rashimul haque rimon

HOW TO INTERPRET CT SCAN OF THE
BRAIN
Dr. Rashimul Haque (Rimon)
Associate professor
Department of Neuro-Medicine
Uttara Adhunik Medical College

MUST FOR EVERY PHYSICIAN
• CT SCAN is a very useful tool for the care of
the patient especially in the emergency
department.
• Every physician should have a basic
knowledge of ct scan

What is CT scan
• CT scan or CAT scan means A computed
tomography (CT) scan.
• It uses X-rays to make detailed pictures of
structures inside of the body.

History
• Sir Godfrey hounsfield-
1972
• Nobel prize in 1979

Parts of CT scan machine
• Gantry
• X-ray tube
• Detector
• Patient couch
• Viewing
console

Principle of CT scan
• X rays are passed through the patient in a
circular path.
• The absorption data is used in a computer to
reconstruct high definition images.
• The images are seen on a computer output
device or films and be interpreted

Types of head CT’s
• Non-contrast
• Contrast
– IV contrast is given to better evaluate:
• Vascular structures
• Tumors
• Sites of infection
– Relative contraindications:
• Allergy, renal failure

Preparation
• Don’t need to restrict the intake of any food or
fluids before the scan.
• However, if contrast is needed, you may be asked
not to eat or drink anything for 4-6 hours before
the test.
• Sensitivity Test for the contrast
• Inform Consent form is sign after explanation
given  must be signed before the test started.

Plane
 Transaxial plane
 used most often for head CT’s
 Coronal plane
 good for evaluation of pituitary/sella
and sinuses
 Saggital plane
 rarely used (more common in MRI)
 Plane refers to how the picture slices are orientated

Axial Sections of CT brain
• Axial sections are most important in a head CT

Plane examples
Axial plane Coronal plane Saggital plane

Window
• In head CT, 2 windows are commonly used
BRAIN window BONE window

Slice them up!
Usually 5 to 10mm

Normal image of CT scan (axial plane)

Normal CT scan (sagital & coronal plane)

Quality of CT Brain
• The Quality of the CT scanner,
• The skills of the radiographer, and
• The cooperation of the patient.
• There are common artifacts that should be
taken in to consideration when viewing CT
brain images.

TECHNIQUE…..
Slice thickness may
vary, but in general, it is
between 5 and 10 mm
for a routine Head CT

Lobar anatomy ( infratentorial )

Lobar anatomy ( basal ganglia level)

Lobar anatomy (supra ventricular level)

HOUNSFIELD UNITS
• Represent the density of tissue
• Also called as CT NUMBER
• Related to composition & nature of tissue

air --- 1000
fat ---70
Pure water 0
Csf +8
White matter +30
Gray matter +45
blood +70
Bone/calcification +1000

• Hounsfield Units
•
• Radiodensity on CT is measured in Hounsfield Units (HU).
• HU range from -1000 to +1000.
• By definition water (CSF) = 0.
• Air is -1000 because it is the least dense structure.
• Bone is the most dense and measures +1000.
• Fat is less dense than water and therefore measures -100.
• Brain parenchyma is more dense than water and ranges from +20 to +40.
• White matter is less dense than gray matter due to the fat within the
myelin within the white matter.
• Acute blood is bright on CT and measures + 55 to +75 HU.
• Calcification is more dense than blood and will measure in the low 100's.

BASICS….
• X-RAYS ARE ABSORBED TO DIFFERENT DEGREES BY
DIFFERENT TISSUES
• Always describe CT findings as densities-
• isodense/hypodense/hyperdense.
• Higher the density (hyperdense) = whiter is the appearance
• Lower the density( hypodense) = darker the appearance
• Anything of the density as brain= isodense
• Brain parencgyma is the reference density

Density
What Is Bright on CT?
(hyperdense)
• Blood
• Bone
• Calcium
• Contrast
• Metal
• Air
• Csf/water
• Infarct
• Cerebral edema
What is Dark on CT
(Hypodense)

Hypodense lesion CT scan
• Infarction
• Edema
• Cyst

Distribution of blood vessel in brain

Distribution of blood vessel in brain ..cont…

Distribution of major cerebral arteries

•Cystic changes in the brain

Hyperdense lesion in the brain
• Calcification
• Hemorrhage

Choroid plexus and pineal body
calcification

Hemorrhage timeline
• If you see a bleed in CT, try to assess if its new or old:
• ACUTE bleed (< 3 days)
– Hyperdense (80-100 HU) relative to brain
• SUBACUTE bleed (3-14 days)
– Hyperdense, isodense, or hypodense relative to brain
• CHRONIC bleed (>2 weeks)
– Hypodense (<40 HU) relative to brain

Sub dural hematoma (sub acute)

Subdural hematoma ( different stage )

• ICSOL ( INTRACRANIAL SPACE
OCCUPYING LESION )

Multiple ring enhancing shadow

Causes of multiple ring enhancing
shadow
• primary and secondary brain tumor
• Tuberculosis
• Brain abscess
• Cysticercosis
• Demyelinating disorder
• Toxoplasma
• Fugal infection

Normal Pressure hydrocephalus
(NPH)

Hydrocephalus
• Expansion of the ventricular system on the
basis of an increase in the volume of CSF
• May be due to:
– Overproduction of CSF (rare)
– Underabsorption of the outflow of CSF
– Obstruction of the outflow of CSF from the
ventricles

Types of Hydrocephalus
• Obstructive
– Communicating (extraventricular)
– Non-communicating (intraventricular)
• Non-obstructive
– Over production of CSF (rare)
• Normal pressure Hydrocephalus
– a buildup of cerebrospinal fluid puts pressure on
the brain. (due to aging)

• Non-Communicating Hydrocephalus: Axial CT scans. Note the massive enlargement of the lateral
and third ventricles. This pattern is one of non-communicating (obstructive) hydrocephalus, which
occurs from impaired drainage through the cerebral aqueduct which connects the third and fourth
ventricles. This picture differs from communicating hydrocephalus wherein all the ventricles are
enlarged. Note that the cortical ribbon is extremely thin near the skull, from the constant pressure
of the underlying obstructive hydrocephalus. Before the bony sutures of the skull have fused in a
child, hydrocephalus may present as progressive and abnormal enlargement of the head
(macrocephaly). In this case, the cause of the hydrocephalus was likely the intraventricular
hemorrhage associated with premature birth, with subsequent scarring and gliosis of the cerebral
aqueduct.Hydrocephalus is recognized as enlarged ventricles out of proportion to the amount of
cerebral atrophy. Non-communicating (obstructive) hydrocephalus occurs when the ventricular
system is not in continuity with the subarachnoid space. Most often, the site of the blockage in
non-communicating hydrocephalus is at the cerebral aqueduct, but rarely can occur at the foramen
of Monro, the third ventricle, or the outlet of the fourth ventricle. Acute non-compensated, non-
communicating (obstructive) hydrocephalus is a neurosurgical emergency as the non-compensated
hydrocephalus results in a progressive increase in intracranial pressure, which if left unchecked will
result in herniation and brain death. It is potentially treatable by shunting.

• Intracranial tuberculoma can occur with or without tuberculous
meningitis. Numerous small tuberculomas are common in patients
with miliary pulmonary tuberculosis. A non-caseating tuberculoma
usually appears hyperintense on T2-weighted and slightly
hypointense on T1-weighted images. A caseating tuberculoma
appears iso- to hypointense on both T1-weighted and T2-weighted
images, with an iso- to hyperintense rim on T2-weighted images.
Tuberculomas on contrast administration appear as nodular or ring-
like enhancing lesions. [9] The diameter of these enhancing lesions
usually ranges from 1 mm to 5 cm. Tuberculomas frequently show
varied types of enhancement, including irregular shapes, ring-like
shapes, open rings and lobular patterns. Target-like lesions are
common. Pre-contrast, the magnetization transfer MRI helps in
assessing the disease load in patients with CNS tuberculosis

• Anterior cerebral artery
• The anterior cerebral artery (ACA) branches off
the internal carotid artery and supplies the
anterior medial portions of the frontal and
parietal lobes.
• Classic signs of an ACA stroke are contralateral leg
weakness and sensory loss. Keep in mind that
behavioral abnormalities and incontinence also
may occur.

Effects of a complete MCA stroke
• The hallmarks of an MCA stroke are the focus of most
public-awareness messages and prehospital stroke
assessment tools—facial asymmetry, arm weakness, and
speech deficits. Complete MCA strokes typically cause:
• hemiplegia (paralysis) of the contralateral side, affecting
the lower part of the face, arm, and hand while largely
sparing the leg
• contralateral (opposite-side) sensory loss in the same areas
• contralateral homonymous hemianopia—visual-field
deficits affecting the same half of the visual field in both
eyes.

Posterior cerebral artery
• The posterior cerebral artery (PCA) arises from
the top of the basilar artery and feeds the
medial occipital lobe and inferior and medial
temporal lobes. Vision is the primary function
of the occipital lobe, so a stroke affecting PCA
distribution commonly causes visual deficits—
specifically contralateral homonymous
hemianopia.

Cerebellar strokes
• Cerebellar strokes commonly impair balance
and coordination. Assess for ataxia
(incoordination) by having the patient extend
the index finger and then alternately touch
your finger and his or her nose. Do this on
both sides.

Brain stem strokes
• Although rare, brain stem strokes can be devastating.
Signs and symptoms differ with the specific stroke
location, but may include hemiparesis or quadriplegia,
sensory loss affecting either the hemibody (half of the
body) or all four limbs, double vision, dysconjugate
gaze, slurred speech, impaired swallowing, decreased
level of consciousness, and abnormal respirations.
Patients with brain stem strokes are likely to be
critically ill and may require emergency intubation and
mechanical ventilation.

Artifacts
• Beam
hardening
• Bone
• Foreign body
• Motion

SIGNS & SYMPTOMS (cont’d)
BASILAR ARTERY
• Coma
• “Locked-In” Syndrome
• Cranial Nerve Palsies
• Apnea
• Visual Symptoms
• Drop Attacks
• Dysphagia
• Dysarthria
• Vertigo
• “Crossed” weakness and sensory
loss affecting the ipsilateral face
and contralateral body.

• . As per this study the HU for acute infarct is
>19.13 HU, Sub-acute infarct 9.55 – 19.13 HU
and chronic infarct is < 9.55 HU helps to grade
the cerebral infarct which make the diagnosis
easier & quicker and it’s useful to the patient
those who are not co-operated with MRI.
• PDF file:

Basal ganglia level
Going up there is cut in the third ventricle
Frontal horn , occipital horn of lateral ventricle
and third ventricle.
Caudate nucleus, lentiform nucleus, thalamus,
Internal capsule

Normal Calcifications in the brain
• Pineal Gland
– seen in 2/3 of the adult population and increases with age
– calcification over 1cm in diameter or under 9 years of age may be suggestive
of a neoplasm
• Hebenula
– it has a central role in the regulation of the limbic system and is often calcified
with a curvilinear pattern a few millimeters anterior to the pineal body in 15%
of the adult population
• Choroid Plexus
– a very common finding, usually in the atrial portions of the lateral ventricles
– calcification in the third or fourth ventricle or in patients less than 9 years of
age is uncommon

Normal Calcifications in the brain
• Basal Ganglia Calcification
– are usually idiopathic incidental findings that have an incidence of ~1% (range
0.3-1.5%) and increases with age
– usually demonstrate a faint punctuate or a coarse conglomerated symmetrical
calcification pattern
• Falx, Dura Matter, Tentorium Cerebelli
– occur in ~10% of the elderly population
– dural and tentorial calcifications are usually seen in a laminar pattern and can
occur anywhere within the cranium
• Superior Saggital Sinus
– common age-related degeneration sites and usually have laminar or mildly
nodular patterns

• Tuberculomas tend to be larger than 20 mm in
diameter, have an irregular outline, cause
more mass effect and have a progressive focal
neurologic deficit, whereas cysts tend to be
<20 mm in diameter, have a smooth regular
outline and seldom cause progressive focal
neurologic deficits

• In general, abscesses are characterized by a thin, uniform ring, which is
thinner on the medial border, and with a smoother outer margin; satellite
lesions are often present. A thick, irregular, ring-like enhancement
suggests a necrotic brain tumor. Some low-grade brain tumors are "fluid-
secreting" and may form heterogeneously enhancing lesions. These low-
grade brain tumors may present with an incomplete ring sign and may
reveal the classic "cyst-with-nodule" morphology. [3] Multiple enhancing
lesions can be seen in patients with multifocal glioma. However, the
presence of more than three distinct lesions is unusual for a patient with
primary brain tumor. The radiological differential considerations for a
cystic tumor with an enhancing mural nodule include pilocytic
astrocytoma, hemangioblastoma, pleomorphic xanthoastryocytoma,
meningioma and ganglioglioma. These benign brain tumors rarely present
as multiple enhancing lesions. Demyelinating lesions, including both
classic multiple sclerosis and tumefactive demyelination, may present with
an open ring or incomplete ring sign, and are often misdiagnosed as brain
neoplasms.

Ct scan brain lecture by rashimul haque rimon

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