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Head CT Non-Contrast

Non-contrast CT of the head is the first-line neuroimaging study in acute care because it is fast, widely available, and highly sensitive for acute hemorrhage, mass effect, and large territorial infarction. It is the pivotal decision point in acute stroke pathways, distinguishing hemorrhagic from ischemic stroke before thrombolysis, and in trauma triage. Sensitivity for subtle early ischemia and small posterior fossa lesions is limited, and follow-up MRI is often required.

Indications

  • Suspected acute stroke to exclude hemorrhage before thrombolysis or thrombectomy
  • Acute head trauma, especially with GCS <15, focal deficit, or Canadian CT Head Rule criteria
  • Sudden severe (thunderclap) headache to exclude subarachnoid hemorrhage
  • New-onset seizure, first seizure, or seizure with focal deficit
  • Altered mental status or unexplained acute neurological decline
  • Suspected raised intracranial pressure or hydrocephalus / shunt malfunction
  • Postoperative or post-procedural neurosurgical surveillance

Contraindications & Cautions

  • No absolute contraindications; the study is non-contrast and rapid
  • Pregnancy: justify on clinical grounds; fetal dose is negligible with the head out of the primary beam, but document justification
  • Radiation stewardship (ALARA) in children and in patients requiring serial scans; consider MRI where time permits
  • Uncooperative or moving patient may require sedation, degrading study quality
  • If contrast is later needed (mass, infection), screen renal function and contrast allergy history

Patient Preparation

  • No fasting or specific preparation for standard non-contrast head CT
  • Remove metallic hairpins, earrings, hearing aids, and dentures from the scan field
  • Position supine with head in the head holder, chin tucked, and the head immobilized
  • Confirm patient identity and the clinical question; document last-known-well time in stroke cases
  • For agitated patients, arrange nursing or sedation support; monitor unstable trauma patients
  • In acute stroke, coordinate with the stroke team so CT angiography/perfusion can follow seamlessly

Technique & Parameters

  • Helical or sequential acquisition from skull base (foramen magnum) to vertex
  • Typical 120 kVp; mAs modulated to patient size; reconstruct 5 mm axial brain images with 1-2 mm thin recons for reformats
  • Reconstruct both soft-tissue (brain) and bone algorithms; review at brain (W80/L40), subdural (W150-200/L50-80), and bone (W2000-3000/L400-600) windows
  • Gantry angulation along the orbitomeatal line to minimize lens dose where sequential technique is used
  • Multiplanar sagittal and coronal reformats for midline structures, vertex, and skull base
  • No IV contrast for the standard study; stone/bone algorithm reconstructions for suspected fractures

Systematic Review

  • Assess symmetry and gray-white matter differentiation across both hemispheres
  • Evaluate for intra- and extra-axial blood: subdural, epidural, subarachnoid, intraparenchymal, intraventricular
  • Trace the ventricular system for size, symmetry, and effacement; assess basal cisterns for effacement or blood
  • Check for midline shift, mass effect, and herniation (subfalcine, uncal, tonsillar)
  • Review the posterior fossa and brainstem, allowing for beam-hardening artifact
  • Examine the calvarium, skull base, and facial bones on bone windows for fractures
  • Inspect the extracranial soft tissues, orbits, mastoids, and paranasal sinuses (air-fluid levels)

Key Findings & Significance

  • Hyperdense acute blood (50-80 HU) indicating hemorrhage; location defines subtype
  • Loss of gray-white differentiation, insular ribbon sign, or hyperdense vessel sign suggesting acute ischemia
  • Effaced sulci, compressed ventricles, or basal cistern loss indicating mass effect / raised ICP
  • Midline shift quantified at the septum pellucidum, signaling herniation risk
  • Hydrocephalus with dilated temporal horns and periventricular hypodensity (transependymal flow)
  • Skull fractures, pneumocephalus, or foreign bodies in trauma
  • Established (hypodense) versus acute infarction; chronic encephalomalacia and small-vessel changes

Differential Considerations

  • Hyperdense extra-axial collection: crescentic subdural vs lentiform epidural hematoma
  • Diffuse basal cistern hyperdensity: aneurysmal SAH vs traumatic SAH vs pseudo-SAH (diffuse edema)
  • Focal hypodensity: acute infarct vs vasogenic edema around tumor/abscess vs demyelination
  • Ring or masslike lesion: primary tumor vs metastasis vs abscess (correlate with contrast/MRI)
  • Ventricular enlargement: obstructive hydrocephalus vs communicating vs ex-vacuo atrophy
  • Hyperdense vessel: acute thrombus vs high hematocrit vs calcified atheroma

Pearls & Pitfalls

  • Early ischemic change is subtle; scrutinize the insular ribbon, lentiform nucleus, and use narrow stroke windows
  • Isodense subacute subdural hematomas can be missed; look for inward buckling of the gray-white junction and sulcal effacement
  • Beam-hardening (Hounsfield dark bands) in the posterior fossa can mimic or obscure infarct and hemorrhage
  • Small posterior fossa and brainstem lesions are frequently occult on CT; low threshold for MRI
  • Check the scalp and orbits; injuries and foreign bodies are commonly overlooked
  • In suspected SAH with a negative CT beyond 6 hours, lumbar puncture or CTA/MRI may still be needed

Structured Report

  • State study type, comparison, and technique (non-contrast head CT)
  • Report intracranial hemorrhage: presence, type, location, and volume where relevant
  • Describe parenchyma: gray-white differentiation, infarction, edema, mass effect, and midline shift in millimeters
  • Comment on ventricles, cisterns, and evidence of hydrocephalus or herniation
  • Report extra-axial spaces, calvarium/skull base fractures, and paranasal sinus/mastoid findings
  • Impression: prioritize acute, actionable findings (hemorrhage, herniation, large infarct) and recommend follow-up imaging where indicated (CTA, MRI)

References

  • ACR Appropriateness Criteria: Head Trauma; Cerebrovascular Disease (Suspected Stroke)
  • Osborn's Brain: Imaging, Pathology, and Anatomy (2nd ed.)
  • American Heart Association/American Stroke Association Guidelines for the Early Management of Acute Ischemic Stroke
  • Royal College of Radiologists, iRefer: Making the Best Use of Clinical Radiology

Educational clinical decision support only. Protocols vary by institution and equipment; always confirm with a qualified radiologist and local guidelines before clinical use.