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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.

Head CT Non-Contrast

📋 Indications

⛔ Contraindications & Cautions

🧑‍⚕️ Patient Preparation

⚙️ Technique & Parameters

🔎 Systematic Review

🩻 Key Findings & Significance

🧠 Differential Considerations

💡 Pearls & Pitfalls

📝 Structured Report

📚 References