An Introduction to Imaging the Brain. Dr Amy Davis

Transcription

1 An Introduction to Imaging the Brain Dr Amy Davis

2 Common reasons for imaging: Clinical scenarios: - Trauma (NICE guidelines) - Stroke - Tumours - Seizure - Neurological degeneration memory, motor dysfunction, movement disorders - Psychiatric (to exclude underlying organic cause) Symptoms/ presentation: - Loss of consciousness - Seizure - Headache - Focal neurological deficit - Psychiatric hallucination, personality change - Slow neurological development in infants - Cranial nerve palsies

3 Plain film - rarely done now; Modes of Imaging: CT Uses computer processed X-rays to produce tomographic images, or slices of specific areas of the body. Typically used to look for infarction, haemorrhage, tumours, calcification, oedema, hydrocephalus and bone trauma. CT uses ionising radiation and should be used with some caution.

4 Question 1 -What is the typical radiation dose of a CT brain? mSv mSv mSv mSv

5 Question 1 -What is the typical radiation dose of a CT brain? mSv = CXR 2.1.4mSv = CT head mSv = Transatlantic flight 4.6.6mSv = CT chest

6 Modes of imaging: MRI Non-ionising Advantages: good soft tissue definition, better anatomical detail, more sequences = more information which can help distinguish between different diseases Limitations: long scan times mins, Artefact - very sensitive to movement Some ferromagnetic metals and implants cannot be imaged, i.e. cardiac pacemakers, metal valves and metal foreign bodies.

7 MR sequences how to tell what they are: Different planes can be obtained axial, coronal and sagittal. T1 Grey matter is darker than white matter, CSF is black. (T1 post contrast The blood vessels will be bright if they contain contrast, the mucosa of the paranasal sinuses will be high signal). T2 White matter is darker than grey matter, CSF is bright.

8 MR sequences how to tell what they are: FLAIR White matter is darker than grey matter but CSF or fluid is dark. This is because the signal from fluid is suppressed, for example to look at high signal changes next to the ventricles in MS.

9 MR sequences how to tell what they are: Diffusion Weighted Imaging (DWI) - This measures the diffusion of water molecules. Restricted diffusion can be seen in certain conditions for example infarcts. Restricted diffusion is seen as high signal on DWI and as low values on a corresponding apparent diffusion coefficient (ADC) map. Depending on the signal characteristics this can help to age infarcts. Other conditions with restricted diffusion include abscesses and hypercellular tumours.

10 Modes of imaging -Digital Subtraction Angiography DSA is a type of fluoroscopy used in interventional radiology to clearly visualise blood vessels.

11 Clinical scenarios - ICH 54 year old alcoholic found unconscious, GCS 14/15 = SDH 18 year old moped vs car RTA. Obvious head injury, likely skull fracture = EDH 32 year old sudden onset headache, like being hit with a bat 10/10 pain = SAH

12 Imaging modalities in intracranial haemorrhage CT Quick, accessible, more useful than MRI in detecting hyperacute blood Hyperacute blood on CT is brighter than normal brain parenchyma MRI more specific than CT in determining age of haemorrhage and is more sensitive in detecting blood after hours

13 Aims of imaging in acute ICH Detect presence of haemorrhage Localise and differentiate site of haemorrhage Acute vs chronic Detect any underlying cause Identify complications relating to haemorrhage: Mass effect- midline shift Hydrocephalus Associated traumatic injury eg skull fracture

14 Intra-axial haemorrhage Extravasated blood in brain Parenchyma Causes: - Traumatic contusion - Tumour/ mass- lobar - Haemorrhagic transformation of infarct - Hypertensive bleed- typically basal ganglia/ pons/ thalamus -Cerebral venous thrombosis Amyloid angiopathy- peripheral

15 Extra-axial haemorrhage by compartment Extradural (Middle meningeal artery) Lens shape/ biconvex Strips dura away from skull Usually traumatic Commonly associated with skull fracture Blood is limited by sutures Subdural haematoma 'Crescent' shape Crosses sutures Tracks along dural reflections - Blood limited by interhemispheric fissure and tentorium More common in older patients Torn bridging cortical veins

16 Question 2 - Where is the blood? 1. Intra-axial 2. Extra-axial

17 Question 2 - Where is the blood? 1. Intra-axial 2. Extra-axial

18 Question 3 What is the diagnosis? 1. Subarachnoid haemorrhage 2. Subdural haematoma 3. Intra-axial haematoma 4. Extradural haematoma 5. Cerebral contusion

19 Question 3 What is the diagnosis? 1. Subarachnoid haemorrhage 2. Subdural haematoma 3. Intra-axial haematoma 4. Extradural haematoma 5. Cerebral contusion

20 SDH vs EDH

21 Subarachnoid haemorrhage Hyperdense (acute) blood follows the contours of the sulci, fissures, basal cisterns and ventricles May be complicated by hydrocephalus Traumatic or nontraumatic spontaneous No cause identified in 10-15%, Sensitivity of CT for subarachnoid blood decreases with time. Correlation with LP may be necessary.

22 Aneurysm investigations: If atraumatic, cause for SAH requires further investigation: CT Angiogram may demonstrate an aneurysm If negative, may need catheter angiogram (more invasive)

23 STROKE IMAGING Stroke = abrupt interruption in the blood flow to the brain causing sudden loss of neurological function 3rd leading cause of death in UK (after heart disease and cancer) and 2 nd leading cause of morbidity. It is the leading cause of acquired disability Age > 55 years M:F 2:1 Heterogenous group of cerebrovascular disorders

24 Stroke imaging Aetiology: Ischaemic (80%) Large-vessel atherosclerosis Cardiogenic emboli Small-vessel occlusion (lacunar infarct) Dissection (young adults 15% of strokes) Haemorrhagic (20%) Hypertension Amyloid angiopathy Vascular malformation e.g. AVM Bleeding diathesis / anticoagulation Venous infarction

25 Acute stroke imaging objectives: Confirm it is a stroke and exclude alternative diagnosis e.g. mass Haemorrhagic vs ischaemic Determine whether suitable for thrombolysis: Extent of infarct Differentiate between irreversibly affected tissue and tissue at risk (penumbra) that may be salvaged. Post-thrombolysis complications? Vascular imaging to look at vessel patency- carotid, vertebral and basilar arteries

26 Non-contrast CT MRI T2, FLAIR, DWI CTA / MRA (Perfusion CT / MR) What imaging to do?

27 Stroke imaging Non contrast CT Standard imaging done in acute setting Readily available Quick and inexpensive Gold standard for detecting acute hemorrhage Early signs on CT Loss of gray/white matter differentiation Hypodense parenchyma due to oedema Hyperdense artery- due to acute thrombus Mass effect: ventricular or sulcal effacement Early signs present in up to 92% of cases (Tomura N et al. Radiology 1988;168: )

28 Evolution of CT changes following a stroke Hyperacute <12 hours May be normal or subtle changes, hyperdense artery, loss of definition of lentiform nucleus and insular ribbon sign Acute hours Hypodensity, loss of G-W matter differentiation, local mass effect Subacute 1-3 days 4-7 days Wedge shape area of low density, increasing mass effect. +/- haemorrhagic transformation Gyral enhancement, mass effect, oedema 1-8 weeks Resolving mass effect, contrast enhancement, transient calcification Chronic Months-years Resolving mass effect, contrast enhancement, transient calcification

29 MRI in stroke imaging: More sensitive and specific for acute infarct than CT But MRI less widely available and more time consuming, therefore only performed in select patients in the acute setting More common to confirm diagnosis if negative CT

30 MRI stroke sequences Diffusion weighted imaging (DWI) is sensitive in detecting small, early infarcts Conventional T1 and T2 changes may lag up to 6hrs post infarct Decreased/ restricted diffusion occurs within minutes of arterial occlusion. Infarcted tissue then progresses through a sequence of DWI/ADC changes: Acute (0-7 days) DWI / ADC Subacute (1-3 weeks) DWI / ADC / Chronic (>3 weeks) DWI /ADC

31 CT / MR Angiogram/DSA Images are obtained following intravenous contrast, acquisition timed so that neck and cerebral arteries are maximally opacified. Acute thrombus can be seen as a filling defect. Stenoses due to plaque to can be defined and if significant, guide further endovascular or surgical intervention.

32 Vascular territories: Anterior and middle cerebral arteries, the posterior cerebral and the basilar arteries. The clinical syndrome can indicate which vascular territory is likely to be affected MCA is most commonly infarcted territory- probably because it is the largest territory and due to the direction of flow from ICA to MCA which favours the passage of emboli.

33 Question 4 What is the diagnosis?

34 Question 4 What is the diagnosis? 1. Right MCA territory infarct 2. Right infarct with haemorrhagic transformation 3. Right infarct with SAH 4. Right ACA, MCA and PCA territory infarct 5. SAH with right sided cerebral oedema

35 Right MCA infarct and hyperdense MCA sign

36 CNS Tumours Classification: The location of the tumour helps to narrow the differential diagnosis. Brain tumours can be intra or extra-axial.

37 How to tell if a lesion is intra-axial or extra-axial: The most important features are at the interface between the lesion and the brain. Intra-axial Grey matter is expanded, there is no CSF cleft, the dura and pial vessels are peripheral to the mass and there is either no change or CSF spaces are reduced. Extra-axial Grey matter is buckled, there is a CSF cleft, the dura and pial vessels are on the inner surface of the mass and the CSF spaces are expanded.

38 Common extra-axial masses Meningioma: Occur anywhere meninges exist Most common non-glial tumour Middle/late decades Female 2:1 Male Multiple in approx 8% Bone changes- Hyperostosis or osteolysis Sinus enlargement- pneumosinus/blistering Calcification Thick, enhancing dura- tail

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40 Common intra-axial masses Glioma ~ 30% of all brain and CNS tumours and 80% of all malignant brain tumours. Can be low or high grade (high grade are more likely to demonstrate contrast enhancement). Small tumours can be missed on CT. Features include; heterogenous, poorly marginated mass with peritumoral oedema; central necrosis; internal haemorrhage and rarely calcification. Contrast enhancement can be variable, but is typically described as ring enhancing.

41 Glioblastoma

42 Glioblastoma

43 Common intra-axial masses Lymphoma More common in immunocompromised patients. CT typically shows focal, nodular areas of high attenuation with ill-defined margins and little surrounding oedema and marked, diffuse contrast enhancement. In immunocompromised patients the lesions can be low attenuation due to central necrosis with ring enhancement. MRI will show iso to low signal intensity on T1 and iso to high signal intensity on T2 with diffuse contrast enhancement, unless immunocompromised where they are more likely to have ring enhancement.

44 Lymphoma

45 Question 5 - What is the diagnosis?

46 Question 5 - What is the diagnosis? 1. Metastases 2. Lymphoma 3. Multiple meningiomas 4. Lymphoma and Meningioma

47 Question 5 - What is the diagnosis? 1. Metastases 2. Lymphoma 3. Multiple meningiomas 4. Lymphoma and Meningioma

48 Question 6 - What is the diagnosis?

49 Question 6 - What is the diagnosis? 1. Glioblastoma multiforme 2. Lymphoma 3. Metastases

50 Question 6 - What is the diagnosis? 1. Glioblastoma multiforme 2. Lymphoma 3. Metastases

51 Metastases Commonly from Lung, colon, breast, renal and melanoma. Usually older patients with known tumours, but can be present at diagnosis Single or multiple Varied imaging appearance (nodule, ring enhancing, central necrosis, oedema, hyperdense/haemorrhagic)

52 Thank you