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Basic Non-Contrast Head CT Interpretation

Imaging exam of choice for pts with acute CNS symptoms or traumatic head injury. High sensitivity for detection of neurosurgical emergencies (acute intracranial hemorrhage, mass effect, territorial infarct, brain herniation, or hydrocephalus).

Mnemonic for framework of quick Head CT review: Blood Can Be Very Bad.

Blood

  • Appearance of blood varies by timing. Acute blood is hyperdense (bright white). Subacute (~1 week) blood becomes isodense to brain parenchyma. Chronic (>2 weeks) blood is hypodense (dark).

  • Epidural Hemorrhage (extra-axial)

  • Bleeding between dura mater and skull

  • Does not cross skull sutures, expands inwards toward the brain parenchyma. Lentiform shape.

  • Often preceded by history of trauma, injury to middle meningeal artery (look for associated scalp injury, skull fracture)

  • Subdural Hemorrhage (extra-axial)

    • Bleeding between dura and arachnoid mater. o Does cross skull sutures. Crescent shape.
    • Typically secondary to trauma with injury to bridging cortical veins.
    • Subacute subdural hemorrhage can be difficult to identify as it tends to resemble grey matter.

  • Subarachnoid hemorrhage (extra-axial)

    • Bleeding into subarachnoid space between arachnoid and pia mater
    • Most apparent around the circle of Willis or in the Sylvian fissure.
    • CT sensitivity highly dependent on the amount of blood and time since hemorrhage.
    • Most commonly secondary to trauma or spontaneously from aneurysmal rupture

  • Intraventricular hemorrhage (extra-axial)

    • Blood within ventricular system
    • Can be primary (blood in ventricles with minimal parenchymal blood) or more commonly secondary (secondary extension of parenchymal or subarachnoid bleed into ventricles)
    • Tends to pool dependently, best seen in the occipital horns of the lateral ventricles

  • Intraparenchymal hemorrhage (intra-axial)

    • Can be spontaneous (no underlying lesion – hypertensive or amyloid-related hemorrhage) or due to an underlying lesion (tumor, vascular malformation, or cerebral venous thrombosis)
    • Traumatic intraparenchymal bleeding often is ipsilateral or directly contralateral to the site of injury, (coup-contrecoup mechanism).
    • Spontaneous bleeding related to uncontrolled hypertension classically occurs in the deep grey matter structures (like basal ganglia and thalamus).

Cisterns

  • Subarachnoid or basal cisterns = compartments within the subarachnoid space where CSF pools between arachnoid and pia mater. Contains vasculature and cranial nerves.

  • Assess for hemorrhage (subarachnoid), effacement, and asymmetry

  • Multiple, with major cisterns including

  • Sylvian cisterns: between frontal and temporal lobes

  • Suprasellar cistern: above the sella turcica, under the hypothalamus

  • Quadrigeminal cistern: between the tectum, splenium of the corpus callosum and the superior cerebellum

  • Prepontine cistern: anterior to the pons, posterior to the clivus

  • Cisterna magna

Brain

  • Gross evaluation of parenchymal structure, identification of major parenchymal abnormalities

  • Symmetry of bilateral sulci and gyri, sulcal effacement

  • Parenchymal attenuation

  • Acute blood, calcification, IV contrast = hyperdense.

  • Air, fat, ischemia, edema = hypodense.

  • Grey-white matter differentiation: compare to the contralateral side. Loss of grey-white matter differentiation is an early sign of ischemic insult.

  • Midline shift: evaluate the midline structures (falx cerebri, septum pellucidum) for mass effect

  • Edema

  • Cytotoxic edema: result of ischemia or infarction. Affects grey and white matter.

  • Vasogenic edema: Usually related to a lesion (tumor or abscess). Blood-brain barrier disrupted. Affects mainly white matter with preserved grey-white matter differentiation.

  • Herniation: shifts of cerebral tissue from normal location into adjacent space. Secondary to a change in intracranial volume and increase in intracranial pressure (edema, tumor, hemorrhage).

  • Masses: better assessed with intravenous contrast. Looks for associated hemorrhage, edema, calcification, mass effect

Ventricles

  • Intraventricular hemorrhage (described above).

  • Be aware that dense choroid plexus calcifications may resemble acute intraventricular hemorrhage

  • Asymmetry

  • Hydrocephalus: important to determine if it is obstructive or communicating to identify the underlying cause

  • Temporal horns tend to dilate first in the setting of hydrocephalus.

  • Ventricular effacement: thinning of ventricles; can be secondary to cerebral edema, space occupying lesion, hemorrhage

Bones

  • Important to evaluate bony structures with dedicated bone windows.

  • Fractures of the calvarium and skull base may be subtle. Use signs of superficial soft tissue injury as a clue for underlying fractures.

  • Presence of gas (pneumocephalus), blood, and opacification of sinuses may also hint at underlying fracture.

Additional Resources for Head CT Interpretation: https://radiopaedia.org/articles/ct-head-an-approach?lang=us https://radiologyassistant.nl/neuroradiology https://litfl.com/ct-head-interpretation/