1. CT HEAD, STROKE, HEAD AND NECK, SOFT TISSUE NECK

CT Head Anatomy and Head CT Assessment/Search Patterns

Terminology

  • Intracranial: Within the skull
  • Intracerebral: Within the brain parenchyma
  • Intra-axial: Within the brain parenchyma
  • Extra-axial: Outside brain parenchyma (skull, meninges, CSF, cisterns, ventricles, choroid plexus, pineal and pituitary gland)
  • Intraventricular: Within ventricular system (extra-axial)
  • Haemorrhage/Haematoma: Loss of blood from damaged blood vessel
  • Coup brain injury: Brain injured at point of trauma
  • Contrecoup brain injury: Brain injured opposite side of trauma
  • Coup-contrecoup brain injury: Combination

Skull Bones and Sutures

  • Identify skull bones and sutures and their CT appearances on schematic image.

Brain Lobes and Fossae

  • Identify brain lobes and know the fossae they are positioned in on a CT image.

Meninges

  • Meninges: Thin layers of tissue between brain and inner table of skull.
    • Act with CSF to protect the CNS from mechanical damage.
  • Dura Mater
    • Dural venous sinuses located between the two layers of dura matter
    • 4 dural reflections: falx cerebri, tentorium cerebelli, falx cerebelli, diaphragma sellae
  • Arachnoid Mater
    • Connective tissue, avascular, no innervation
    • Underneath is sub-arachnoid space (SAS) – contains CSF which acts to cushion brain and spinal cord
  • Pia mater
    • Adheres to brain surface
    • Located underneath SAS

CSF Spaces

  • Brain surrounded by CSF
  • CSF appears hypodense
  • CSF spaces:
    • Within sulci
      • Gyri – folds of cerebral cortex
      • Between gyri are furrows = sulci
    • In fissures (deep sulci)
    • In subarachnoid cisterns
    • Centrally within ventricles
  • CSF is of lower density than grey or white matter of the brain, therefore appears darker on CT images.

Grey vs. White Matter

  • Grey matter
    • Consist of neuronal cell bodies and minimal axon
    • Appears brighter on CT
  • White matter
    • Consists of myelin – fatty substance (lower density)
    • Appears darker on CT

CT Head Image Evaluation

  1. Midline shift/mass effect
    • Mass will cause compression effect of hemisphere
    • Under pressure midline structures will shift away from side of pressure
    • Can affect contralateral side
  2. Sulci/gyri
    • Are they of normal side?
    • If asymmetry, are they wider (more CSF) or narrower (effaced)?
    • Global or focal changes?
    • Normal hypodense CSF?
  3. Ventricles
    • Asymmetry or bilateral changes?
    • Dilation (so more CSF seen)? At what level?
    • Are ventricle(s) effaced?
    • Contain normal hypodense CSF?
  4. Grey white matter differentiation (GWMd)
    • Loss of GWMd =
      • due to cytotoxic cerebral oedema,
      • involves both grey and white matter
      • early stages of cerebral ischaemia, hypoxia (global = brain death)
    • Increase of GWMd =
      • Due to vasogenic cerebral oedema (extracellular fluid passes into cells resulting in cells swelling dt disruption of BBB)
      • Trauma, tumours, abscesses, late stages of cerebral iscahaemia
  5. Focal areas of altered density
    • Hypodense regions (air, fat, etc.) – are these normal densities for that anatomy or is it due to pathology?
    • Hyperdense regions (normal bone, IV contrast vs acute bleeds, calcification, tumours
    • In instances of haemorrhages appearance compared to brain parenchyma will alter depending on age of haemorhgae
    • Hyperdense to isodense to hypodense
  6. Bone and soft tissues
    • Cortical bone has highest density on CT scan, viewed on separate bony windows with appropriate algoriths
    • Fractures or tumours with bony involvement
    • Trauma = increase in subcutaneous tissues
    • Assess for inflammatory soft tissue swelling
  7. Other factors relating to pathology
    • Is it well defined area with margins (well circumscribed), is it ill defined, is it infiltrative
    • Size
    • What is the density of the area – hypo, hyper, iso, mixed (heterogenous)
    • Is it a singular are, are there multiple or is it global
    • How does it react with regards to IV contrast
      • Does it enhance
      • Does it all enhance
      • Only peripheral enhancement
    • Where is it located in the brain – rt side, frontal, occipital, parietal, posterior fossa, etc.

CT Head Protocol and Pathologies

Clinical Indications for CT Head Scan (6 possible)
  1. Head trauma – evaluate fractures, hemorrhages or brain injuries
  2. Stroke symptoms – distinguish between ischemic and hemorrhagic strokes
  3. Severe headache – rule out aneurysms, subarachnoid hemorrhage, or other pathologies
  4. Altered mental status – identify casues such as infection, bleeding, or mass effect
  5. Seizures – especially new-onset seizures to identify structural abnormalities
  6. Follow up on known pathology – monitoring known conditions like tumours or post-surgical changes
CT Head Scanning Protocol
  • Patient positioning
    • Supine, head secured
    • Align head to orbitomeatal line
  • Image reconstruction
    • Axial slices – thins
      • Typically at 5mm intervals
    • Reconstructions
      • Coronal and sagittal reformats
  • Window used
    • Brain (soft tissue): WW80, WL40
    • Bone: W300, L400
    • Subdural: WW200, WL80
  • IV contrast usage:
    • Used for visualising vascular structures and lesions
    • Typical indications: tumors, infections, vascular abnormalities
    • Non-contrast scans preferred initially to detect hemorrhage
Blood-Brain Barrier (BBB) and IV Contrast
  • BBB restricts certain substances from entering the brain
  • IV contrast agents cross the BBB in disrupted areas (e.g. tumours, abcesses)
  • Normal brain parenchyma does not enhance with IV contrast
Normal Contrast Enhanced Structures on a CT Head Image
  • Vessels: Circle of Willis, dural sinuses
  • Choroid plexus: typically enhances due to lack of BBB
  • Meninges: may show enhancement
  • Pituitary gland: enhances due to its vascularity
  • Tumours/lesions: enhance if BBB is disrupted
Intracranial Hemorrhages
  • Epidural Hemorrhage (EDH)
    • Location: Between dura mater and skull
    • Causes: trauma with skull fracture, infection/abscess, coagulopathy (blood overclotting/underclotting), hemorrhagic tumours, vascular malformations
    • Presentation: lucid interval followed by rapid deterioration
  • Subdural hemorrhage (SDH)
    • Location: Between dura mater and arachnoid mater
    • Causes: head injury with no associated skull #, tearing of bridging veins
    • E.g. seizures, elderly, alcohol, clotting disorders, anti coagulants, shaken baby
    • Presentation: gradual onset of symptoms, headache, confusion
      • Acute – greater damage, poorer prognosis
      • Subacute
      • Chronic
  • Subarachnoid hemorrhage (SAH)
    • Location: in subarachnoid space
    • Causes: ruptured aneurysm, trauma
    • Presentation: sudden severe “thunderclap” headache
  • Intracerebral hemorrhage (ICH)
    • Location: Within brain parenchyma
    • Causes: hypertension, trauma, anticoagulant therapy
    • Presentation: focal neurological deficits, headache, altered conciousness
  • Intraventricular hemorrhage (IVH)
    • Location: within the ventricular system
      • Primary – within ventricles itself
      • Secondary – extension of IPH or sah
    • Causes: extension of ICH, trauma
    • Presentation: similar to ICH, may lead to hydrocephalus
CT Image Identification of Intracranial Hemorrhage Types
  • EDH:
    • Lens-shapes biconvex hyperdensity
    • Well defined margins
    • Tend to be confinded by lateral sutures, tend to not cross suture lines
    • SWIRL SIGN = active bleeding
      • Hyperdense blood has clotted and has high haemoglobin component, whilst active hyperacute bleed appears hypodense (or isoechoic) to normal brain parenchyma as it has not yet clotted
  • SDH:
    • Crescent-shaped hyperdensity
    • Follows shape of inner skull
    • +/- midline shift
    • Can extend into interhemispheric fissure + falx (not confined by sutures)
    • May extend over tentorium cerebelli
    • HEMATOCRIT EFFECT = layering effect on CT
      • Fresh blood is denser than old blood
      • Because patient lying on back, heavier blood goes down
  • SAH:
    • Hyper density in basal cisterns, sulci – areas we would normally see hypodense normal CSF
    • Requires further imaging (CTA COW/carotids + CT perfusion study)
  • ICH:
    • Localised hyperdensity within brain tissue
    • SPOT SIGN = ongoing bleed within haematoma itself
      • CTA reveals where contrast is coming from (where bleed is – hyperdense against chronic blood)
  • IVH:
    • Hyperdensity within ventricles
Haemorrhagic vs. Ischaemic Stroke
  • Haemorrhagic stroke – rupture of blood vessels = hyperdense
  • Ischemic stroke – lack of blood supply = hypodense
    • Thrombotic event – obstruction due to dysfunction within vessel itself
    • Embolic event – obstruction due to debris from elsewhere in body
Ischaemic Stroke Changes on Non-Contrast CT Head
  • Non contrast CT scan to exclude intracranial haemorrhage è DEDICATED HEAD STROKE PROTOCOL:
    • CTA COW/Carotids
    • CT perfusion scan
  • POTENTIAL CHANGES SEEN IN ISCHEMIC STROKE ON NCCT
    • Early signs
      • Hyperdense artery sign (acute clot)
      • Loss of GWMd
      • Sulcal effacement
      • Insular ribbon sign
    • Later signs
      • Hypodensity in affected vascular territory
      • Mass effect due to edema
      • Haemorrhagic transformation (if present)
Brain Tumours
  • Primary: benign and malignant, or glial (brain parenchyma/intra axial) and non-glial (structures in brain e.g. nerves, blood vessels, glands/extra axial)
  • Secondary: malignant metastases
  • PRIMARY
    • Meningiomas – benign, from meninges
    • Gliomas – malignant, from glia (within brain parenchyma)
      • Astrocytoma
        • Low grade (in children)
        • High grade (in adults)
      • Medulloblastoma – in cerebellum, usually in children
      • Glioblastoma – worst prognosis
  • SECONDARY
    • Brain metastases
      • Secondary tumours that have spread from cancers elsewhere in body –
      • Lung, breast, melanoma, kidney, and colon
      • Appearance on CT:
        • Often multiple lesions, typically at the grey-white matter junction, with surrounding edema and possible enhancement after contrast administration
Brain Abscesses
  • Presentation: fever and chills
  • Occurance: Bacterial infection leading to pus accumulation within brain parenchyma, following head trauma, surgery or via hematogenous spread from distant infections
  • Appearance on CT:
    • Pre contrast –
      • Low density area with poorly defined borders
      • Central areas of necrosis is hypodense
      • +/- fairly visible surrounding capsule
    • Post contrast –
      • Ring enhancement - Well defined ring-enhancing lesion with a central area of hypodensity (necrosis) and surrounding edema)
Ventriculomegaly vs. Hydrocephalus
  • Both mean enlargement of ventricles, hydrocephalus = + increase in intracranial pressure
  • Ventriculomegaly = enlarged ventricles, without necessarily increased intracranial pressure
    • Causes – can be congenital or due to loss of brain tissue (e.g., atrophy
  • Hydrocephalus = enlarged ventricles due to accumulation of CSF with increased intracranial pressure
    • Causes – obstruction of CSF flow, impaired absorption, or overproduction of CSF (too much CSF)
Categories and Causes of Hydrocephalus
  • Congenital hydrocephalus – from birth defects
  • Acquired hydrocephalus – from tumours, infection, bleeding within brain (SAH, IPH) blocking movement or absorption of CSF
  • Normal pressure hydrocephalus
    • Older people
    • Increased size of ventricles, but not accompanied by cerebral atrophy (as comes with age)
Identifying Hydrocephalus on CT
  • Signs: enlarged ventricles, thinning of cortical mantle, and periventricular edema
  • Look for: dilated lateral and third ventricles in non-communicating hydrocephalus or all ventricles in communicating hydrocephalus
Normal Calcifications on CT Head
  • Common locations: pineal gland, choroid plexus, falx cerebri, basal ganglia, and the tentorium cerebelli
  • Appearance: typically hyperdense (bright) spots on non-contrast CT images, usually small and symmetrical

Stroke Imaging, Head & Neck Vessels, Soft Tissue Neck

Arterial Supply of Head and Neck

  • Blood supply mostly through carotid and vertebral arteries
  • Bilaterally:
    • Common carotid arteries, divide into:
      • → external carotid artery (supply head and neck outside cranium)
      • → internal carotid arteries (supply anterior 2/3 of brain)
    • Vertebral arteries, converge into:
      • → basilar artery (vertebrobasilar supply – posterior 1/3 of brain)
      • → feed into CIRCLE OF WILLIS
  • Identification of arteries on schematic or CT image
  • Identification from a CT image the arterial territory of COW and when pathology suggest specific artery affected

CTA's

  • Delineate vascular lumen, rather than organs themselves
  • IV contrast at peak enhancement (as much contrast as possible; highest density of contrast)
    • Larger volumes
    • Faster flow rates
    • Timing is critical
    • Bolus tracking
Clinical Indications for CTA Carotids/COW (4)
  • Acute ischaemic stroke protocol (Non Contrast CT head [to see ischaemic changes], CT Carotids/COW + perfusion study (to see specifically where arteries are blocked)
  • Subarachnoid haemorrhages
  • Transient Ischemic Attack
  • Berry aneurysms
CTA Carotids/COW Protocol
  • Patient prep:
    • remove metal objects in scan field
  • Patient positioning
    • Head first
    • Supine
    • Arms down by side on bed to reduce artefacts caused by shoulders
    • Straight on bed (no rotation + midline) *unless trauma then don’t move
    • Occlusal plane perpendicular to floor
    • Instruct patient to NOT SWALLOW during procedure (avoid movement of neck vessels
  • Scout view
    • AP
  • Contrast
    • 75mLs omnipaque 350 @5mls/sec
    • 50mLs saline chaser
  • Bolus tracking
    • Monitoring location at base of skull
    • Manual trigger when see a bit of contrast in ICA/vertebral arteries
  • Image reconstruction
    • 0.75/0.6mm axials → Axial/coronal/sagittal MIPS
    • VRT and bone removal - routine post contrast head 3/3mm → Axial/coronal/sagittal
  • Windowing
    • For CTA – WW 650, WL 150 IV contrast/calcified plaque/soft tissues
    • For post contrast CT head – Brain WW 80-90 WL 40-50
Pathologies on CT Image
  • COW occlusion (MCA) occlusion
  • Ruptured Aneurysm
  • Basilar artery aneurysm
  • Coronary Artery Stenosis (narrowing)

Venous Anatomy & CTV Head

  • Veins of the CNS drain deoxygenated blood from the cerebrum, cerebellum, brainstem, and spinal cord back into main system
    • → empty into the dural venous sinuses situated between the periosteal and meningeal layer of the dura
      • Sagittal → transverse → straight → signmoid sinuses → then into jugular veins → SVC → right atrium
  • Cerebral veins do not typically follow the arterial supply)
Timing difference between CTA and CTV of the head
  • Venous opacification required, so delay in commencing helical acquisition (only around 10-15 seconds difference from CTA)

Cerebral Venous Sinus Thrombosis (CVST)

  • Non contrast ct scans:
    • Filling defect in sinus or vein – thrombus within venous sinus or veins can appear as a hyperdense vein or sinus for the first 7-14 days
  • CTV:

Fascial Spaces of the Neck

  • Fascia = internal connective tissue which forms bands or sheets that surround and support muscles, vessels and nerves in the body
  • In the neck, it also helps to compartmentalise structures
  • Two fascias in the neck:
    • Superficial cervical fascia
    • Deep cervical fascia
SUPERFICIAL CERVICAL FASCIA
  • lies between dermis and the deep cervical
  • Contains neurovascular supply to skin, superficial veins, superficial lymph nodes, fat, platysma muscle
DEEP CERVICAL FASCIA
  • lies deep to superficial facia
  • Three separate but related fascial layers that encircle structures in the neck and allow anatomic compartmentalisation
CLINICAL RELEVANCE OF FACIAL SPACES OF THE NECK:
  • Compartmentalises structures within neck
  • These layers of fascia can limit spread of infection - e.g. superficial skin abscess prevented from spreading deeper into neck by other fascial layers
  • Many of the disease states that affect the deep structures of head and neck are confined to one compartment

Clinical Indications for CT Soft Tissue Neck

  • Lymphadenopathy
  • Thyroid
  • Salivary gland lesion
  • Inflammatory or infectious process
  • Head and neck neoplasms
  • Head and neck trauma
  • Treatment planning
  • Follow up imaging post treatment
  • Foreign bodies
  • Dysphagia
  • ?lump in throat
  • Tracheal stenosis
Contrast Timing for CT Soft Tissue Neck
  • Contrast: dual bolus biphasic injection = Two smaller amounts of contrast, with delays in between, to get biphasic information (arteries as well as veins)
    • 50mls Omnipaque 350 @ 2mls/sec; wait 120 seconds, then 2nd injection 50 mls omnipaque 350 @ 2mls/sec
    • Start scan 30 seconds after 2nd injection (2 min, 30 sec delay total)
Benign vs. Pathological Lymph Node Criteria
  • Size, shape, contour, number, and nodal morphology of lymph nodes
  • Nodal morphology = fat density, calcifications, heterogenous appearance, cystic, contrast enhancement
Abnormal Lymph Node Identification on CT Soft Tissue Neck Image
  • Non contrast image – enlarged lymph nodes:
  • Contrast image – compressed jugular vein due to enlarged lymph node
  • Biphasic image – enlargement compressing
Salivary Glands on CT Soft Tissue Neck Image
  • Non contrast: benign tumour – lipomas (made up of fat); low density = benign
  • Right carotid gland – normal lower density carotid parenchyma, hyperdense structure in between = benign parotid adenoma
  • Normal on the left vs high density on right – high density = tumour
  • Normal parotid (lower density compared to surrounding muscles), vs ill defined, margins infiltrating deep = squamous cell carcinoma
Thyroid on CT Soft Tissue Neck
  • Normal = Homogenous high attenuation on CT compared with adjacent muscles due to high iodine content
    • Vascular structure = avid IV contrast enhancement
  • Abnormal = Variable CT scan findings – e.g. calcifications, single or multiple nodules, cysts, or diffuse enlargement
Abnormal findings
  • Soft tissue neck, non contrast (a) and contrast (b)
    • Non contrast - Thyroid gland; homogenous high attenuation
    • Contrast – avid IV contrast enhancement, but diffuse enlargement = abnormal
    • Multiple nodules/cysts = abnormal
Anatomy for Soft Tissue Neck
  • Thyroid
  • Oesophagus
  • Trachea
  • Common carotid artery
  • Internal carotid artery
  • External carotid artery
  • Vertebral artery
  • Internal jugular vein
  • External jugular vein
  • Parotid gland
  • Submandibular gland