Basics and Anatomy of a brain CT

Dr Gauhar Mahmood Azeem

House Officer, New Radiology Dept. SHL

CT scan machine

CT Head: Extremely important investigation

• CT head is an extremely important investigation used routinely in indoor as well as ER patients.

• A quality physician needs to be able to accurately interpret and act upon certain findings without specialist advise, because these disease processes are time dependant and demand immediate action.

History of the CT

• Sir Godfrey Hounsefield- an electrical engineer-1972

• Nobel Prize for Physiology or Medicine 1979

• Hounsfield units named after him

• Through the years CT’s have come from 1 rotation in 6 minutes to one in under 0.33 seconds

Principle

• 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

• 3D reconstruction is also possible

Slice them up! Usually 5 to 10mm

Basics

• Always describe CT findings as densities, isodense/hypodense/hyperdense

• Higher the density the whiter it is (towards bone)

• Lower the density the darker it is (towards air)

• Brain here is the reference density and thus isodense

Indications for Brain CT

• Acute stroke

• Transient Ischemic Attack

• Acute headache with focal neurological signs

• Acute head injury

• Suspected hydrocephalus

• Mental status change

• Secondary indications when MRI not available including diplopia, CN problems, seizures, syncope etc

Indications for CT brain with IV contrast

• To look for

• Tumours

• Infections (meningial enhancement, abscess)

• Inflammation (MS, granulomatous diseases etc)

Hounsfield again

Hounsfield Units

• Related to the composition and nature of tissue

• Represent the density of the tissue

• Also called CT number

An HFU table

Brain Anatomy as seen by House Officer

Brain anatomy as seen by Professors

Axial Sections of CT brain

• Axial sections are most important in a head CT

• We must have for a complete view posterior fossa and supratentorial(above tentoriumcerebelli) cuts

Axial Sections of CT brain

• Posterior Fossa Cuts

• Above Foramen Magnum, Level of 4th

ventricle, Above 4th ventricle, Tentorial

• Supra Tentorial Cuts

• Third Ventricle Level, Lateral Ventricle Level, Above Ventricular level

Normal Anatomy

A. Orbit B. Sphenoid SinusC. Temporal Lobe D. External Auditory CanalE. Mastoid Air Cells F. Cerebellar Hemisphere

Normal Anatomy

A. Frontal Lobe B. Frontal Bone (Superior Surface of Orbital Part)C. Dorsum Sellae D. Basilar ArteryE. Temporal Lobe F. Mastoid Air CellsG. Cerebellar Hemisphere

Of Cisterns, Sulci and Fissures

• A cistern is any opening in the subarachnoid space of the brain created by a separation of the arachnoid and pia matter. These spaces are filled with cerebrospinal fluid.

• A sulcus is a depression in the cerebral cortex

• A fissure is a large furrow that divides the brain into lobes, and also into the two hemispheres

Normal Anatomy

A. Frontal Lobe B. Sylvian Fissure (divides frontal, parietal from temporal)

C. Temporal Lobe D. Suprasellar CisternE. Midbrain F. Fourth VentricleG. Cerebellar Hemisphere

Normal Anatomy

A. Falx Cerebri B. Frontal LobeC. Anterior Horn of Lateral Ventricle D. Third VentricleE. Quadrigeminal Plate Cistern F. Cerebellum

Normal Anatomy

A. Anterior Horn of the Lateral Ventricle B. Caudate Nucleus (BG)C. Anterior Limb of the Internal Capsule D. Putamen and Globus Pallidus (BG)E. Posterior Limb of the Internal Capsule F. Third VentricleG. Quadrigeminal Plate Cistern H. Cerebellar Vermis

Admit it you’ve percussed your relatives too!

Normal Anatomy

A. Genu of the Corpus Callosum B. Anterior Horn of the Lateral VentricleC. Internal Capsule D. ThalamusE. Pineal Gland F. Choroid PlexusG. Straight Sinus

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

Choroid Plexus and Pineal Gland Calcifications

Calcification of Falx Cerebri

Normal Anatomy

A. Falx Cerebri B. Frontal LobeC. Body of the Lateral Ventricle D. Splenium of the Corpus CallosumE. Parietal Lobe F. Occipital LobeG. Superior Sagittal Sinus

Ventricular system

Normal Anatomy

A. Falx Cerebri B. SulcusC. Gyrus D. Superior Sagittal Sinus

Thank You!