Clinical imaging: Neuroimaging — head, brain and spine

• Basics: Choosing Neuroimaging - CT or MRI? | Reading a CT Head
• Trauma and bleeding: Head Injury - Who Needs a CT? | Extradural and Subdural Haematoma | Subarachnoid Haemorrhage | Intracerebral Haemorrhage
• Stroke: Imaging in Acute Ischaemic Stroke | TIA and Carotid Imaging
• Other brain disease: Raised Pressure, Hydrocephalus and Herniation | Brain Tumours and Ring-enhancing Lesions | Infection, Lumbar Puncture and Encephalitis | MRI in Multiple Sclerosis and White Matter Disease | Venous Sinus Thrombosis and PRES | Dementia, Epilepsy and Movement Disorders
• Spine: Cauda Equina and Spinal Cord Compression | Cervical Spine Injury
• Revision: Neuroimaging at a Glance | Spot the Diagnosis | Exam-style Scenarios | Key Points | Guidelines and Further Reading

🩻 Neuroimaging - head, brain and spine - page 4 of the Clinical Imaging chapter. CT head is one of the commonest emergency scans in the NHS - after falls, in stroke, with confusion and headache - and many decisions depend on it within minutes (thrombolysis, neurosurgery, lumbar puncture). MRI is far better for most non-acute brain and spinal problems. Spinal emergencies - cauda equina and malignant cord compression - need MRI the same day.
Your four questions for every neuroimaging decision: Is this an emergency where minutes matter (stroke, bleed, raised pressure, cord compression)? Does this patient need CT now, MRI later, or both? Has the scan answered the specific question? What happens next - thrombolysis, neurosurgery, LP, or MDT?

Choosing Neuroimaging - CT or MRI?

• CT strengths - fast, available 24/7, excellent for acute blood and bone; works for unstable patients.
• MRI strengths - far better for brain parenchyma, posterior fossa, spinal cord, white matter, small infarcts and tumours; no radiation.
• Contrast - CT or MRI contrast for tumours, abscesses, infection, metastases; CT angiography for vessels.

Reading a CT Head

• Densities - white (hyperdense): bone, acute blood, calcification, contrast; grey: brain (grey matter slightly brighter than white matter); dark (hypodense): CSF, oedema, infarct (after hours), fat, air (black).
• Blood over time - hyperdense when acute (first days), isodense to brain in the subacute phase (about 1–3 weeks - easily missed subdurals), hypodense when chronic.
• Systematic review - "Blood Can Be Very Bad":
  • Blood - extradural, subdural, subarachnoid, intraventricular, intraparenchymal.
  • Cisterns - basal cisterns open (effaced in raised pressure); blood in the cisterns (SAH).
  • Brain - symmetry, grey–white differentiation, mass, oedema, infarct, midline shift.
  • Ventricles - size (hydrocephalus or atrophy), symmetry, blood.
  • Bone - fractures (bone windows), sinuses and mastoid air cells (fluid suggests a skull base fracture), soft tissue swelling.
• Midline shift - measured at the septum pellucidum; significant mass effect needs neurosurgical discussion.
• Atrophy vs hydrocephalus - atrophy has enlarged sulci and ventricles in proportion; hydrocephalus has ventricles larger than expected with effaced sulci and dilated temporal horns.
• Normal calcification - pineal gland, choroid plexus, falx, basal ganglia (in older people).
• Windows - brain, subdural (wider window), bone; always review all.
• Compare with previous scans - small changes matter.

Head Injury - Who Needs a CT?

• Adults - CT head within 1 hour (NICE NG232) if any of:
  • GCS under 13 on initial assessment in the ED.
  • GCS under 15 at 2 hours after the injury.
  • Suspected open or depressed skull fracture.
  • Any sign of basal skull fracture - haemotympanum, "panda" eyes, CSF leak from ear or nose, Battle's sign (mastoid bruising).
  • Post-traumatic seizure.
  • Focal neurological deficit.
  • More than one episode of vomiting.
• Adults - CT head within 8 hours if there has been loss of consciousness or amnesia since the injury and any of: age 65 or over, history of bleeding or clotting disorder, dangerous mechanism (pedestrian struck, ejection from vehicle, fall from over 1 metre or 5 stairs), or more than 30 minutes' retrograde amnesia.
• Anticoagulants - people taking anticoagulants need careful assessment and usually CT (within 8 hours) even without other features - follow current NICE NG232 recommendations and local policy.
• Children - separate NICE criteria (e.g. suspicion of non-accidental injury, GCS under 14 in ED, under 1 year with bruise or swelling over 5 cm on the head).
• Skull X-rays have no role in adult head injury (except as part of a skeletal survey for suspected NAI in children).
• Discharge - written head injury advice, a responsible adult, safety-netting; delayed bleeds can occur (especially on anticoagulants).
• MRI - diffuse axonal injury (susceptibility-weighted imaging shows microhaemorrhages) when CT doesn't explain the clinical state.

Extradural and Subdural Haematoma

• Chronic subdural - often hypodense or mixed density (acute-on-chronic); isodense subacute subdurals are easy to miss - look for effaced sulci, midline shift and compressed ventricles on one side.
• Reversal of anticoagulation - vitamin K and prothrombin complex concentrate for warfarin; andexanet alfa or PCC for factor Xa inhibitors (local policy); idarucizumab for dabigatran.
• Discuss with neurosurgery - any haematoma with mass effect, falling GCS or pupillary change.

Subarachnoid Haemorrhage

• Thunderclap headache (peak within 1 minute), often with neck stiffness, vomiting, reduced consciousness, seizure - about 85% of non-traumatic SAH is from a ruptured berry aneurysm.
• Imaging (NICE NG228):
  • Non-contrast CT head as soon as possible - blood in the basal cisterns, sylvian fissures and sulci; hydrocephalus.
  • CT sensitivity is very high within 6 hours of onset and falls over time.
  • CT within 6 hours and normal - don't routinely do LP; consider alternative diagnoses.
  • CT after 6 hours and normal - lumbar puncture at least 12 hours after onset - xanthochromia (bilirubin on spectrophotometry).
  • SAH confirmed - CT angiography to find the aneurysm (or catheter angiography); urgent neurosurgical referral.
• Treatment - endovascular coiling (preferred for most) or surgical clipping; nimodipine (prevents delayed cerebral ischaemia from vasospasm); manage hydrocephalus (external ventricular drain), sodium (SIADH or cerebral salt wasting), BP.
• Complications - rebleeding (highest in the first 24 hours), vasospasm (days 3–14), hydrocephalus, hyponatraemia, seizures.
• Other causes - perimesencephalic (non-aneurysmal - benign), trauma (commonest cause of SAH overall), AVM, reversible cerebral vasoconstriction syndrome, dissection.
• Screening - MR angiography for relatives when two or more first-degree relatives have had aneurysms or SAH, and in ADPKD with a family history.

Intracerebral Haemorrhage

• Primary ICH - about 10–15% of strokes; CT shows a hyperdense parenchymal haematoma with surrounding oedema.
• Location gives clues:
  • Deep (basal ganglia, thalamus, pons, cerebellum) - hypertension.
  • Lobar (cortical) in older people - cerebral amyloid angiopathy (MRI - multiple lobar microbleeds, superficial siderosis).
  • Younger patients or atypical sites - AVM, cavernoma, aneurysm, tumour, cerebral venous thrombosis, drugs (cocaine, amphetamines).
• Further imaging - CT angiography (spot sign - active bleeding and expansion risk; vascular cause in under-70s or lobar bleeds); MRI later for underlying causes.
• Management (NICE NG128):
  • Reverse anticoagulation urgently.
  • Rapid BP lowering - systolic target 130–140 mmHg within 1 hour (if presenting within 6 hours and systolic 150–220), avoiding drops over 60 mmHg in 1 hour.
  • Neurosurgery - cerebellar haematomas (over 3 cm or brainstem compression), hydrocephalus (EVD), selected lobar bleeds.
• Haemorrhagic transformation of an infarct - after large infarcts or thrombolysis - repeat CT if deterioration.
• Intraventricular haemorrhage - hydrocephalus risk.

Imaging in Acute Ischaemic Stroke

• Non-contrast CT immediately (NICE NG128) - within 1 hour of arrival (sooner for thrombolysis candidates) if any of: indication for thrombolysis or thrombectomy, anticoagulant use or bleeding tendency, GCS under 13, unexplained progressive or fluctuating symptoms, papilloedema, neck stiffness or fever, severe headache at onset. Otherwise as soon as possible and within 24 hours.
• Purpose of the first CT - exclude haemorrhage and stroke mimics (tumour, subdural); early ischaemic signs:
  • Hyperdense artery sign (thrombus - e.g. hyperdense MCA).
  • Loss of grey–white differentiation - insular ribbon sign, obscured lentiform nucleus.
  • Sulcal effacement; established hypodensity (later - over 6 hours).
  • ASPECTS score (10 points for MCA territory - lower scores mean larger infarcts).
• CT angiography (aortic arch to vertex) - large vessel occlusion (ICA, MCA M1/M2, basilar) - for thrombectomy decisions; also shows carotid disease and dissection.
• CT perfusion or MRI - identify salvageable brain (penumbra) vs core infarct - selects patients for thrombectomy 6–24 hours after onset (or "wake-up" strokes) and thrombolysis beyond 4.5 hours in selected cases.
• Treatment windows (NICE NG128):
  • Thrombolysis (alteplase or tenecteplase) - within 4.5 hours of onset (or last known well).
  • Thrombectomy - anterior circulation LVO within 6 hours; 6–24 hours if imaging shows salvageable tissue; basilar occlusion up to 24 hours.
• MRI - DWI shows infarcts within minutes (bright on DWI, dark on ADC); FLAIR becomes positive after about 4.5 hours (DWI–FLAIR mismatch suggests onset under 4.5 hours - wake-up strokes); detects small and posterior fossa infarcts CT misses; also microbleeds.
• Posterior circulation stroke - CT is often normal - MRI DWI if clinically suspected (vertigo, ataxia, diplopia, dysarthria - HINTS exam).
• Repeat CT at 24 hours after thrombolysis or thrombectomy (before antiplatelets) and with any deterioration.

💡 Clinical Pearl: A normal CT doesn't rule out stroke - it rules out haemorrhage. Most acute infarcts are invisible on CT in the first hours. Thrombolysis decisions are made on the clinical picture plus a CT that shows no bleed, not on seeing the infarct.

TIA and Carotid Imaging

• Suspected TIA (NICE NG128):
  • Aspirin 300 mg (unless contraindicated) and refer for specialist assessment within 24 hours.
  • Don't routinely do CT for TIA unless an alternative diagnosis (e.g. tumour, subdural) or haemorrhage needs excluding (e.g. on anticoagulants - urgent CT).
  • MRI with DWI (after specialist assessment) - to confirm ischaemia, define the vascular territory, or find haemorrhage or alternative diagnoses.
• Carotid imaging - urgent carotid duplex ultrasound (or CTA or MRA) for people with anterior circulation TIA or non-disabling stroke who would be suitable for carotid endarterectomy.
  • Symptomatic stenosis 50–99% (NASCET) - refer for endarterectomy, ideally within 7 days of symptoms (benefit falls rapidly with delay).
  • Stenosis under 50% - best medical treatment.
  • Asymptomatic stenosis - best medical treatment in most.
• Cardiac imaging - ECG and ambulatory monitoring for AF; echocardiogram (bubble study for PFO in young cryptogenic stroke).
• Arterial dissection - neck pain, headache, Horner's syndrome after minor neck trauma - CTA or MRA (fat-suppressed MRI shows mural haematoma).

Raised Pressure, Hydrocephalus and Herniation

• Signs of raised intracranial pressure on CT - effaced sulci and basal cisterns, compressed ventricles, midline shift, loss of grey–white differentiation (diffuse oedema), herniation.
• Herniation syndromes:
  • Subfalcine - under the falx (midline shift) - anterior cerebral artery compression.
  • Transtentorial (uncal) - medial temporal lobe through the tentorium - ipsilateral third nerve palsy (fixed dilated pupil), contralateral hemiparesis, reduced consciousness.
  • Tonsillar ("coning") - cerebellar tonsils through the foramen magnum - brainstem compression, Cushing's response (hypertension, bradycardia, irregular breathing), respiratory arrest; LP is dangerous with significant mass effect.
• Hydrocephalus:
  • Obstructive (non-communicating) - blockage within the ventricular system (tumour, colloid cyst of the third ventricle, aqueduct stenosis, posterior fossa haemorrhage) - ventricles proximal to the block dilate - emergency drainage (EVD) or surgery.
  • Communicating - impaired CSF absorption (after SAH, meningitis) - all ventricles dilated.
  • Normal pressure hydrocephalus - older adults - triad of gait disturbance (magnetic gait), urinary incontinence and cognitive decline; ventricles enlarged out of proportion to sulci; CSF tap test (removal of 30–50 mL improves gait) predicts response to ventriculoperitoneal shunt.
  • Shunt malfunction - headache, vomiting, drowsiness - CT (compare ventricle size with baseline) and shunt series X-rays.
• Idiopathic intracranial hypertension - obese young women, headache, papilloedema, visual loss - MRI and MR venography normal (except empty sella, flattened globes, venous sinus narrowing) - exclude CVST; LP opening pressure raised.

Brain Tumours and Ring-enhancing Lesions

• Presentation - progressive focal deficit, seizures, headache with raised ICP features, personality change, cognitive decline.
• Imaging - MRI with gadolinium is the main test (CT with contrast if MRI unavailable); dexamethasone for symptomatic vasogenic oedema; neuro-oncology MDT.
• Common tumours:
  • Metastases - the commonest brain tumours in adults - often multiple, at the grey–white junction, with lots of oedema - lung, breast, melanoma, renal, colorectal; staging CT chest, abdomen and pelvis.
  • Glioblastoma - the commonest primary malignant tumour in adults - irregular ring-enhancing mass with necrosis, crossing the corpus callosum ("butterfly").
  • Low-grade glioma - non-enhancing T2/FLAIR bright mass (young adults with seizures).
  • Meningioma - extra-axial, dural-based, uniformly enhancing with a "dural tail", may calcify - often incidental (women; NF2).
  • Vestibular schwannoma - cerebellopontine angle - unilateral sensorineural hearing loss and tinnitus (MRI internal auditory meatus).
  • Pituitary adenoma - sellar mass - bitemporal hemianopia; microadenoma under 10 mm (dedicated pituitary MRI).
  • Primary CNS lymphoma - periventricular, homogeneously enhancing, restricted diffusion - immunosuppressed and older people - avoid steroids before biopsy if possible (they shrink lymphoma and hinder diagnosis).
• Ring-enhancing lesions - differential - metastases, abscess (smooth thin wall, restricted diffusion centrally - bright on DWI), glioblastoma, toxoplasmosis and lymphoma (HIV), subacute infarct, resolving haematoma, demyelination (incomplete or "open" ring), radiation necrosis, TB.
• Children - posterior fossa tumours (medulloblastoma, pilocytic astrocytoma, ependymoma), craniopharyngioma.

Infection, Lumbar Puncture and Encephalitis

• Suspected bacterial meningitis - don't delay antibiotics for imaging.
• CT before lumbar puncture is needed only if there are features suggesting raised pressure or a mass:
  • Focal neurological signs (not isolated cranial nerve palsy).
  • Reduced or fluctuating consciousness (GCS 12 or less, or a fall of 2 or more).
  • Papilloedema.
  • Recent or continuing seizures.
  • Severe immunocompromise (e.g. HIV with low CD4).
  • Also - relative bradycardia with hypertension, or other signs of shock (delay LP).
• A normal CT doesn't guarantee LP is safe - clinical signs of raised pressure still matter.
• Herpes simplex encephalitis - fever, confusion, seizures, behaviour change, dysphasia - MRI shows temporal lobe (often asymmetric, including insula) T2/FLAIR change; CT may be normal early - start IV aciclovir immediately; CSF HSV PCR.
• Brain abscess - ring-enhancing lesion with restricted diffusion; sources - sinusitis, otitis, dental, endocarditis, congenital heart disease - neurosurgical drainage and antibiotics.
• Subdural empyema - sinusitis in young people - neurosurgical emergency.
• Autoimmune encephalitis - MRI may show limbic (medial temporal) change or be normal (see Immunology chapter).
• Opportunistic infections (HIV) - toxoplasmosis (multiple ring-enhancing basal ganglia lesions), PML (non-enhancing white matter lesions), cryptococcus (dilated perivascular spaces).
• Discitis and spinal epidural abscess - back pain, fever, neurological signs, IV drug use or diabetes - MRI whole spine with contrast urgently.

MRI in Multiple Sclerosis and White Matter Disease

• MRI is the key test for MS - T2 and FLAIR hyperintense lesions:
  • Periventricular lesions perpendicular to the ventricles ("Dawson's fingers").
  • Juxtacortical or cortical, infratentorial (brainstem, cerebellum), spinal cord; optic nerve.
  • Enhancing lesions with gadolinium = active inflammation.
  • Central vein sign - supports MS over mimics.
• McDonald criteria (2017, revised 2024) - dissemination in space (lesions in typical areas) and dissemination in time (enhancing and non-enhancing lesions together, new lesions on follow-up, or CSF-specific oligoclonal bands) - allow diagnosis after a first episode.
• Clinically isolated syndrome (optic neuritis, transverse myelitis, brainstem syndrome) - MRI predicts conversion to MS.
• Monitoring - annual MRI on disease-modifying therapy; PML surveillance on natalizumab.
• Mimics:
  • Small vessel disease - very common in older people with vascular risk factors - patchy or confluent periventricular and deep white matter hyperintensities, lacunes.
  • NMOSD (longitudinally extensive cord lesions over 3 segments, area postrema), MOGAD, ADEM, migraine, vasculitis, sarcoidosis, CADASIL (anterior temporal poles), B12 deficiency (dorsal columns - subacute combined degeneration), HIV, PML.
• Incidental white matter lesions in older people are usually small vessel disease - interpret with the clinical picture.

Venous Sinus Thrombosis and PRES

• Cerebral venous sinus thrombosis (CVST):
  • Who - young women (pregnancy and postpartum, combined pill), thrombophilia, dehydration, infection, cancer, head injury; VITT (vaccine-induced - with low platelets).
  • Features - headache (often progressive), raised ICP (papilloedema), seizures, focal deficits, reduced consciousness.
  • Imaging - non-contrast CT may show a hyperdense sinus ("dense delta" or cord sign), venous infarcts (often haemorrhagic, not in arterial territories); contrast CT shows the "empty delta sign"; CT venography or MR venography confirms.
  • Treatment - anticoagulation (LMWH then warfarin or DOAC) even if there is haemorrhage; treat the cause; manage seizures and ICP.
• Posterior reversible encephalopathy syndrome (PRES):
  • Causes - severe hypertension, pre-eclampsia and eclampsia, calcineurin inhibitors (tacrolimus, ciclosporin), chemotherapy, renal failure, sepsis.
  • Features - headache, confusion, visual disturbance (cortical blindness), seizures.
  • MRI - symmetrical vasogenic oedema in the parieto-occipital white matter (T2/FLAIR bright, not restricted on DWI).
  • Treatment - control BP, stop the causative drug, treat seizures, magnesium in eclampsia - usually reversible.
• Reversible cerebral vasoconstriction syndrome - recurrent thunderclap headaches (postpartum, serotonergic drugs, cannabis) - "string of beads" vessels on CTA/MRA; may cause SAH or PRES.

Dementia, Epilepsy and Movement Disorders

• Dementia (NICE NG97):
  • Structural imaging (MRI preferred, or CT) to exclude reversible causes (subdural, tumour, NPH) and help subtype.
  • Alzheimer's - medial temporal lobe (hippocampal) atrophy, parietal atrophy.
  • Vascular dementia - extensive small vessel disease, infarcts.
  • Frontotemporal dementia - frontal and anterior temporal atrophy ("knife-edge").
  • FDG-PET or perfusion SPECT if subtype uncertain; DaTscan for suspected dementia with Lewy bodies; amyloid PET and CSF biomarkers increasingly used with anti-amyloid treatments (ARIA monitoring with MRI).
• Epilepsy (NICE NG217):
  • MRI for people with newly diagnosed epilepsy (unless typical idiopathic generalised epilepsy - e.g. childhood absence with classic EEG) - hippocampal sclerosis, cortical dysplasia, tumours, vascular malformations.
  • CT in the emergency setting (first seizure with head injury, focal signs, persistent confusion, anticoagulants, or when MRI isn't available).
• Parkinsonism - MRI usually normal in Parkinson's disease (used to exclude vascular parkinsonism, NPH, atypical syndromes - "hot cross bun" sign in MSA, midbrain atrophy "hummingbird" in PSP); DaTscan distinguishes degenerative parkinsonism from essential tremor and drug-induced parkinsonism.
• CJD - MRI DWI - cortical ribboning and basal ganglia restriction; "pulvinar sign" in variant CJD.
• Headache - most chronic headaches don't need imaging; image with red flags (thunderclap, new headache over 50, raised ICP features, focal signs, immunosuppression, cancer history, progressive pattern).

Cauda Equina and Spinal Cord Compression

• Cauda equina syndrome - compression of lumbosacral nerve roots (usually a large central L4/5 or L5/S1 disc prolapse):
  • Red flags - bilateral sciatica, saddle anaesthesia, new bladder dysfunction (retention, reduced sensation, incontinence), bowel dysfunction, sexual dysfunction, progressive neurological deficit.
  • Emergency MRI lumbar spine - as soon as possible, ideally within 4 hours of presentation, 24/7 (GIRFT national pathway) - then same-day decompressive surgery if confirmed.
  • Bladder scan for post-void residual supports but doesn't replace MRI.
• Metastatic spinal cord compression (MSCC) (NICE NG234):
  • Known or suspected cancer (breast, prostate, lung, kidney, myeloma) with back pain (thoracic, progressive, nocturnal, band-like) ± neurological symptoms.
  • MRI whole spine as soon as possible (within 24 hours) if neurological symptoms or signs; within 1 week for pain suggestive of spinal metastases without neurological features.
  • Dexamethasone 16 mg daily (with PPI) if neurological deficit; flat bed rest and spinal precautions if unstable; acute oncology - radiotherapy or surgery.
• Other causes of cord compression - epidural abscess, haematoma (anticoagulants), disc, trauma, tumour - whole spine MRI.
• Non-specific low back pain (NICE NG59) - don't routinely image in non-specialist settings; MRI only if it will change management (red flags or before specialist intervention).
• Osteoporotic vertebral fractures - X-ray or MRI (oedema on STIR = acute); DEXA and bone protection.

⚠️ Safety Pearl: New bladder symptoms or saddle numbness with back pain or sciatica is cauda equina until an MRI proves otherwise - arrange emergency MRI the same day, 24/7. Waiting for "retention" means waiting until the damage may be permanent.

Cervical Spine Injury

• Clinical decision rules - Canadian C-spine rule (adults - NICE NG232) identifies who needs imaging; NEXUS criteria elsewhere.
• Imaging:
  • CT cervical spine is the first-line imaging in adults (within 1 hour if indicated - e.g. GCS under 13, intubated, focal neurology, dangerous mechanism, age 65 and over with neck pain, or multiple region trauma).
  • Plain X-rays (3 views - lateral, AP, open-mouth peg) only in selected low-risk adults and in children (lower radiation; MRI for children when needed).
  • MRI - ligament injury, cord injury, disc herniation, neurological deficit with normal CT, before reducing facet dislocations.
• Lateral c-spine X-ray review - adequacy (C1 to the top of T1), alignment (anterior vertebral line, posterior vertebral line, spinolaminar line, spinous processes - smooth curves), bones (each vertebra, peg), soft tissues (prevertebral soft tissue - under 7 mm at C2, under 22 mm at C6).
• Older people - injuries from low-energy falls (peg fractures - type II), ankylosing spondylitis and DISH (rigid spine - fractures are unstable and easily missed - always CT, often whole spine).
• Spinal immobilisation - in-line immobilisation until cleared; avoid prolonged hard collars in older people (pressure damage, delirium).
• Thoracolumbar trauma - CT (often part of whole-body trauma CT); Chance fracture (seatbelt - flexion-distraction - associated bowel injury).

Neuroimaging at a Glance

Spot the Diagnosis