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BASICS OF CT HEAD By Dr. Vinay Sharma MD Consultant Radiologist Sharma Diagnostic Centre Pathankot

Wilhelm Conrad Röntgen discovers x-rays in 1895 William David Coolidge invents the hot cathode x-ray tube in 1913  Hounsfield scale used measure of radiodensity  used in evaluating CT scans.  Nobel Prize  (1979) Hounsfield units (symbol HU) Air at −1000 HU water at 0 HU Cortical Bone at +1000 HU ( 1919 – 2004) Sir Godfrey Newbold Hounsfield

1972 2004 Used for head examinations – 64 slice scanner Water bath required 80 x 80 matrix 4 minutes per revolution 1 image per revolution 8 levels of grey Overnight image reconstruction 2004 – 64 slice scanner 1024 x 1024 matrix 0.33s per revolution 64 images per revolution 0.4mm slice thickness 20 images reconstructed/second

CT Scan Basics

CT - SCAN Has assumed a critical role in the daily practice of Emergency Medicine for evaluating intracranial emergencies. (e.g. Trauma, Stroke, SAH, ICH). Most practitioners have limited experience with interpretation. In many situations, the Emergency Physician must initially interpret and act on the CT without specialist assistance.

CT Scan Basics:- A CT image is a computer-generated picture based on multiple x-ray exposures taken around the periphery of the subject. X-rays are passed through the subject, and a scanning device measures the transmitted radiation. The denser the object, the more the beam is attenuated, and hence fewer x-rays make it to the sensor.

Hounsfield units Densities on CT Scan

Focuses the spectrum of gray-scale used on a particular image. CT Scan Basics: Windowing Focuses the spectrum of gray-scale used on a particular image.

What Is Bright on CT? Air CSF/H20 What Is Dark on CT? Blood Contrast Bone Calcium Metal What Is Bright on CT? Air CSF/H20 What Is Dark on CT?

Advantages to CT Disadvantages to CT Costs less than MRI Better access Shows up acute bleed A good quick screen Good visualization of bony structures and calcified lesions Resolution Beam-hardening artifact Limited views of the posterior fossa and poor visualization of white-matter disease

CT Artifacts

CT Protocolling CT head protocols Variables With or Without contrast CT Brain CT Brain with posterior fossa images CT Angiogram/Venogram CT Perfusion CT of Sinuses CT of Orbit CT of Temporal bones CT of Mastoid bones CT of Skull CT of Face Variables Plain or contrast enhanced Slice positioning Slice thickness Slice orientation Slice spacing and overlap Timing of imaging and contrast administration Reconstruction algorhithm Radiation dosimetry Patient Information Is the patient pregnant? Radiation safety Can the patient cooperate for the exam?

Normal CT

Normal CT Older person

Normal Enhanced CT

HOW TO READ CT-SCAN 1)…Normal Radiological Anatomy 2)… How to look at the images? (a) Where to look? Systematic approach (b) what look for: (i) abnormal opacity (ii) abnormal radiolucency (iii) distortion or displacement of a normal structure 3)…How to interpret the abnormality? (a) Recognizing the abnormality, (b) Describing it in generic terms, (c) Giving a specific diagnosis

How to build up a normal mental image ? Normal Radiological Anatomy Normal radiological image of certain age and sex is a “Mental Image” that must be developed How to build up a normal mental image ? By developing a “Systematic Approach” to examine the radiological image Advantages Minimizes the chance of missing an abnormality Makes complex images easier to read with practice Builds up a mental databank of what is normal

Normal VS, Abnormal It is not possible to call an image abnormal if the normal appearance is not known!!

CT SCAN WITHOUT CONTRAST

The documentary evidence of name and age Technical factors

On non-contrast head CT: In order to recognize the abnormal, you first need to know the appearance of the normal. On non-contrast head CT: Bone is white Calcium is white; Acute hemorrhage is usually white Brain parenchyma is light grey; White matter is darker than grey matter CSF is very dark grey; Sulci, cisterns and ventricles Air is black; Nasal cavity, sinuses, mastoid air cells White Light Grey Charcoal Grey Black

Bone is white CSF is very dark grey Air is black; Brain parenchyma is light grey; White matter is darker than grey matter

(Normal anatomical structures) Areas of interest (Normal anatomical structures) I. Check Brain Parenchyma Check grey/white differentiation Gyri Look for blood Surgeons need to know . . . (size of hematoma, extent of midline shift, herniation) II. Check CSF spaces: Ventricles, Cisterns and Sulci CSF spaces (ventricles and cisterns) size, symmetry, midline shift herniation Subfalcine – cingulate gyrus crosses falx Transtentorial – temporal lobe into tentorial notch Cerebellar – cerebellum into foramen magnum

(Normal anatomical structures) Areas of interest (Normal anatomical structures) III. Check face and skull bones on bone windows Do not confuse sutures with fracture especially in pediatric patients IV. Check “air spaces” Sinuses Nasal airway Ear Canals and Mastoid air cells

Learn and Know Different Parts of Brain

Correlate Different Parts of Brain at Particular Slice of CT Scan

Correlate Different Parts of Brain at Particular Slice of CT Scan

Correlate Different Parts of Brain at Particular Slice of CT Scan

What to look for? (In CT Head) Brain tissue (window) Bone detail (window)

Brain tissue (window) Brain tissue Without Contrast Frontal lobe Midbrain Cerebellum RIGHT LEFT Brain tissue Without Contrast Brain tissue With Contrast

Brain tissue Without Contrast Brain tissue With Contrast Nonenhanced CT scan shows a hyperdense mass resulted in midline shift to the right aspect in the left frontal lobe Contrast enhanced CT shows a homogeneous enhancing mass located in the left frontal lobe.

What to look for :- (i) abnormal opacity (ii) abnormal radiolucency (iii) distortion or displacement of a normal structure Normal Distortion or displacement of a normal structure abnormal radiolucency Frontal lobe Midbrain Cerebellum RIGHT LEFT abnormal opacity

What to look for…….. Film findings: Rt. frontoparietal subdural hematoma (6 mm) Midline marker Rt. temperoparietal epidural hematoma (1.8 cm) 6 mm leftward shift of lateral ventricles Right lateral ventricle Left lateral ventricle Effacement of R sulci BIDMC

Epidural Subdural Hematoma Parenchymal Hemorrhage Subarachnoid Hemorrhage

A subarachnoid hemorrhage occurs with 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. The most common cause of subarachnoid hemorrhage is trauma. In the absence of significant trauma, the most common cause of subarachnoid hemorrhage is the rupture of a cerebral aneurysm. When traumatic, subarachnoid hemorrhage occurs most commonly over the cerebral convexities or adjacent to otherwise injured brain (i.e. adjacent to a cerebral contusion). If there is a large amount of subarachnoid hemorrhage, particularly in the basilar cisterns, the physician should consider whether a ruptured aneurysm led to the subsequent trauma. Cerebral angiography may be needed for further evaluation. On CT, subarachnoid hemorrhage appears as focal high density in sulci and fissures or linear hyperdensity in the cerebral sulci. Again, the most common location of posttraumatic subarachnoid hemorrhage is over the cerebral convexity. This may be the only indication of cerebral injury. High density blood (arrowheads) fills the sulci over the  right cerebral convexity in this subarachnoid hemorrhage.

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 density hematoma (arrowheads) may indicate active bleeding. Deceleration and acceleration or rotational forces that tear bridging veins can cause an acute subdural hematoma. 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

Sub - acute subdural hematoma (arrowheads). Subacute SDH may be difficult to visualize by CT because as the hemorrhage is reabsorbed it becomes isodense to normal gray matter. A subacute SDH should be suspected when you identify shift of midline structures without an obvious mass. Giving contrast may help in difficult cases because the interface between the hematoma and the adjacent brain usually becomes more obvious due to enhancement of the dura and adjacent vascular structures. Some of the notable characteristics of subacute SDH are: - Compressed lateral ventricle - Effaced sulci - White matter "buckling" - Thick cortical "mantle" Note ….The compression of gray and white matter in the left hemisphere due to the mass effect.

Crescent shaped chronic subdural hematoma (arrowheads) 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.

Biconvex (lenticellular) epidural hematoma (arrowheads), deep to the parietal skull fracture (arrow). An epidural hematoma is usually associated with a skull fracture. It 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. On CT, the hematoma forms a hyperdense biconvex mass. It is usually uniformly high density but may contain hypodense foci due to active bleeding. Since 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.

Hemorrhage in the corpus callosum (arrow). Hemorrhage of the posterior limb of the internal capsule (arrow) and hemorrhage of the thalamus (arrowhead). Hemorrhage in the corpus callosum (arrow). Diffuse axonal injury is often referred to as "shear injury". It is the most common cause of significant morbidity in CNS trauma. 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. Immediate loss of consciousness is typical of these injuries. The CT of a patient with diffuse axonal injury may be normal despite the patient's presentation with a profound neurological deficit. With CT, diffuse axonal injury may appear as ill-defined areas of high density or hemorrhage in characteristic locations. The injury occurs in a sequential pattern of locations based on the severity of the trauma. The following list of diffuse axonal injury locations is ordered with the most likely location listed first followed by successively less likely locations: - Subcortical white matter  - Posterior limb internal capsule - Corpus callosum - Dorsolateral midbrain

Multiple foci of high density corresponding to hemorrhage (arrows) in an area of low density (arrowheads) in the left frontal lobe due to cerebral contusion. Intraventricular hemorrhage (arrow) found in a trauma patient. Note the subarachnoid hemorrhage in the sulci in the subarachnoid space (arrowheads). Cerebral contusions are the most common primary intra-axial injury. They often occur when the brain impacts an osseous ridge or a dural fold. The foci of punctate hemorrhage or edema are located along gyral crests. The following are common locations: - Temporal lobe - anterior tip, inferior surface, sylvian region - Frontal lobe - anterior pole, inferior surface - Dorsolateral midbrain - Inferior cerebellum On CT, cerebral contusion appears as an ill-defined hypodense area mixed with foci of hemorrhage. Adjacent subarachnoid hemorrhage is common. After 24-48 hours, hemorrhagic transformation or coalescence of petechial hemorrhages into a rounded hematoma is common.

Abscess

Intracranial Air 58

Mass Effect 59

Hydrocephalus

cerebral atrophy is parenchymal volume loss

BONE WINDOW Normal Linear fracture Linear fracture Depressed fracture SELLA TURCICA CORONAL SUTURE GROOVE FOR MCA EXT.AUD MEATUS ORBITAL GROOVE Depressed fracture Normal BONE WINDOW Linear fracture Linear fracture

CONCLUSION If no blood is seen, all cisterns are present and open, the brain is symmetric with normal gray-white differentiation, the ventricles are symmetric without dilation, and there is no fracture, then there is no emergent diagnosis from the CT scan.

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