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Basic approach to brain CT Dr. Muhammad Bin Zulfiqar

  1. Basic Approach To Brain CT Muhammad Bin Zulfiqar PGR IV SIMS/SHL Alnoor Diagnostic / New Radiology Department
  2. Aims • Introduction • Cross sectional anatomy • Common important pathologies
  3. 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
  4. 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
  5. 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.
  6. CT termonology • Hypodense—Hypointense • Isodense—Isointense • Hyperdense—Hyperintense
  7. Hounsfield units represent logarithmic scale of CT density. Pure water has an HU value of ‘0’. Conventional CT scanners -1024 to 3071—4096 Current 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
  8. CT Windowing • Brain Window— 80 / 35 • Bone Window— 1600 / 600 • Subdural hematoma window— 400 / 35
  9. 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.
  10. ANATOMY 1 Sphenoid sinus 2 Medulla oblongata 3 cerebellum
  11. ANATOMY 4 Fourth ventricle 5 Middle cerebellar peduncle 6 Sigmoid sinus 7 Petrous temporal bone and mastoid air cells 8 Cerebellopontine angle 9 Pons 10 Pituitary fossa
  12. ANATOMY 11 Cerebellar vermis 12 Basilar artery 13 Prepontine cistern 14 Dorsum sellae 15 Temporal horn of lateral ventricle
  13. ANATOMY 16 Ambient cistern 17 Interpeduncular cistern 18 Cerebral peduncle 19 Sylvian fissure
  14. ANATOMY 20 Supra vermian cistern 21 Frontal horn of lateral ventricle 21 Third ventricle
  15. ANATOMY 22 Head of caudate nucleus 23 Insular cortex 24 External capsule 25 Lentiform nucleus 26 Thalamus
  16. ANATOMY 27 Interhemispheric fissure 28 Anterior limb of internal capsule 29 Genu of internal capsule 30 Posterior limb of internal capsule 31 Trigone of lateral ventricle and calcified choroid plexus 32 Occipital horn of lateral ventricle
  17. ANATOMY 33 Body of lateral ventricle 34 Corona radiata
  18. ANATOMY • 35 Centrum semiovale
  19. ANATOMY 36 Pre-central gyrus 37 Central sulcus 38 Post-central gyrus
  20. ANATOMY • 39 ¼ Superior sagittal sinus.
  21. 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.
  22. Skull Fractures 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
  23. Linear skull fracture of the right parietal bone (arrows
  24. 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.
  25. • On CT, subarachnoid hemorrhage appears as focal high density in sulci and fissures or linear hyperdensity in the cerebral sulci.
  26. • Unenhanced scan and a CT angiogram. Extensive subarachnoid haemorrhage secondary to a ruptured MCA aneurysm (arrowheads).
  27. 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
  28. • 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).
  29. • The hypodense region (arrow) within the high density hematoma (arrowheads) may indicate active bleeding
  30. 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
  31. • Compressed lateral ventricle • Effaced sulci • White matter "buckling“ • Thick cortical "mantle
  32. 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.
  33. Crescent shaped chronic subdural collection same density as CSF This chronic subdural hematoma (arrowheads) shows the septations and loculations that often occur over time.
  34. 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.
  35. 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.
  36. • Biconvex (lenticellular) epidural hematoma (arrowheads), deep to the parietal skull fracture (arrow).
  37. 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
  38. Hemorrhage of the posterior limb of the internal capsule (arrow) and hemorrhage of the thalamus (arrowhead). Hemorrhage in the corpus callosum (arrow).
  39. 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. .
  40. 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.
  41. 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.
  42. 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%
  43. Hemorrhage in the cerebellum The most common causes: • hypertensive hemorrhage. • amyloid angiopathy, • ruptured vascular malformation, • coagulopathy, • hemorrhage into a tumor • venous infarction • drug abuse.
  44. 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
  45. Thalamic hemorrhage (arrow) extending into the left lateral ventricle (arrowheads). Hypertensive hemorrhage in the basil ganglia. High density blood fills the cisterns (arrowheads) .
  46. • Coagulopathy related hemorrhage is heterogeneous due to incompletely clotted blood. • AVM bleed may show adjacent calcifications
  47. Ischemic stroke • Dense middle cerebral artery or a dense basilar artery • Basilar Thrombosis • Lentiform Nucleus Obscuration • Diffuse Hypodensity and Sulcal Effacement
  48. 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 (bottom images) middle cerebral artery vascular territories, due to cytotoxic oedema.
  49. 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
  50. 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.
  51. Common complications of meningitis: • Hydrocephalus • Ventriculitis / Ependymitis • Subdural effusion • Subdural empyema • Cerebritis / Abscess • Vasospasm / arterial infarcts • Venous thrombosis / venous infarcts •
  52. Hydrocephalus
  53. 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
  54. 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
  55. 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
  56. 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.
  57. 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.

Editor's Notes

  1. 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.
  2. Can cross the dural reflections at suture sites unlike a subdural hematoma.
  3. Subarachnoid Hemorrhage 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. 
  4. Hemorrhage Due to Arteriovenous Malformationmay 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. Coagulopathy Related Intracerebral Hemorrhage On imaging, this hemorrhage often has a heterogeneous appearance due to incompletely clotted blood