CT Head

Aka: CT Head, Head CAT Scan, Head CT, CT Brain, Contrast Staining on Non-Contrast Head CT

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II. Indications

  1. Cerebrovascular Accident
    1. Differentiate Hemorrhagic CVA from Ischemic CVA
    2. More sensitive than LP for Intracranial Hemorrhage
    3. Test Sensitivity diminishes from time of Hemorrhagic CVA
      1. Test Sensitivity 95-100% at 12 hours from onset
      2. Test Sensitivity 50% at 7 days from onset
      3. Hemorrhagic CVA is not detectable on CT Head at 2-3 weeks from onset
      4. Suarez (2006) N Engl J Med 354(4): 387-96 [PubMed]
  2. Brain Tumors (larger than 2-4 mm)
    1. Enhanced with iodinated Contrast Material
  3. Hydrocephalus
    1. Temporal horn of the Lateral Ventricle dilates (axial width >=5 mm) early in Hydrocephalus
      1. Appear rounded as Hydrocephalus develops (contrast with their normal curved-slit appearance)
    2. Third Ventricle appears O-Shaped when dilated from downstream CSF obstruction
      1. Third Ventricle is normally has a more slit-like appearance
  4. Intracranial Bleeding
    1. Epidural Hematoma
    2. Subdural Hematoma
    3. Intraparenchymal Hemorrhage
    4. Subarachnoid Hemorrhage (Thunderclap Headache)
  5. Evaluation of Traumatic Head Injury
    1. CT Head in every Severe Head Injury
    2. CT Head in every Moderate Head Injury
    3. See Head Injury CT Indications
    4. See Head Injury CT Indications in Children

III. Interpretation: General

  1. See CT Scan Window Width
    1. Describes CT Windows for Brain Window or Subdural Window
  2. Scout View (lateral head with 6 parallel lines delineating key slices)
    1. Skull Base
      1. Appears as an X dividing key structures
      2. Frontal Lobe and Frontal Sinuses
      3. Temporal Lobes (left and right)
      4. Mastoid Air Cells (bilateral appearance confirms symmetry of the imaging)
      5. Basilar Artery
      6. Fourth Ventricle
      7. Cerebellum
    2. Basic Slice 2
      1. Appears as a central 5-sided star (suprasellar cistern, superior to the sella turcica)
      2. Frontal Lobes
      3. Temporal Lobes
      4. Circle or Willis
      5. Brainstem (at Midbrain or Pons level)
      6. Cerebellum
    3. Basic Slice 3
      1. Appears as a smiling face
        1. Eyes = Lateral Ventricles
        2. Mouth = quadrigeminal cistern
      2. Frontal Lobes
      3. Putamen
      4. Parietal Lobes
    4. Basic Slice 4
      1. Appears as a frowning face
        1. Eyes = Lateral Ventricles
        2. Mouth = Lateral Ventricles
        3. Nose = Third Ventricle
      2. Frontal Lobes
      3. Thalamus (to either side of Third Ventricle)
      4. Internal Capsule
      5. Parietal Lobes
      6. Calcified structures
        1. Pineal Gland (central, near Third Ventricle)
        2. Choroid plexus (in posterior Lateral Ventricles)
        3. Colloid cysts may also appear in Third Ventricle (may cause obstructive Hydrocephalus)
    5. Basic Slice 5 (appears as 2 bananas, concave laterally = Lateral Ventricles)
      1. Cerebral Hemispheres
    6. Basic Slice 6 (appears as a coffee bean with 2 hemispheres with a central split)
      1. Cerebral Hemispheres

IV. Interpretation: Systematic Approach Mnemonics

  1. ABCS2
    1. A: Alignment and Abnormalities-Major
      1. Symmetry between sides using small well defined structures (e.g. eye lenses, masotid air cells)
      2. Basic slices (see above) are oriented correctly
    2. B: Blood and Brain
    3. C: CSF and Cisterns
    4. S: Skull and Subdural Windows
  2. "Blood Can Be Very Bad"
    1. B: Blood
      1. Background
        1. Recent Hemorrhage will appear bright white
          1. Darkens as it ages (isodense to brain at week 1-3, isodense to CSF at >3 weeks)
        2. Cerebral sulci flatten and become less apparent with Hemorrhage or brain edema
        3. Intraventricular Hemorrhage (e.g. SAH) may be best seen at the occipital horns of the Lateral Ventricles
        4. Use subdural windows (or lower contrast/brightness) to differentiate acute blood from bone (similar HU densities)
      2. Hemorrhages
        1. Epidural Hematoma (biconvex lens appearance)
        2. Subdural Hematoma (crescent moon appearance, cross Suture lines but not the falx or tentorium)
        3. Cerebral Intraparenchymal Hemorrhage or Traumatic Intracerebral Hemorrhage
        4. Subarachnoid Hemorrhage (SAH) or Traumatic Subarachnoid Hemorrhage
      3. Other findings
        1. Dense Vessel sign
          1. Bright white appearance of clotted vessel (e.g. MCA)
        2. Venous sinus thrombosis
          1. Venous clot (bright white) may be seen in some cases on non-enhanced CT
          2. If suspected, obtain CTV or MRV
    2. C: Cisterns
      1. See Cerebral Ventricle
    3. B: Brain
      1. Cerebral infarcts (black)
      2. Cerebral masses (or mass effect with midline shift)
      3. Edema
      4. Grey-white differentiation
        1. Homogeneous appearance is abnormal (e.g. anoxic brain injury, acute CVA)
        2. Zoom out of image (or move back away from monitor) to see regions of different attenuation
    4. V: Ventricles
      1. Abnormally large (Hydrocephalus)
      2. Abnormally small (slit-like ventricles)
      3. Sulcus effacement (lose contours, compressed against skull, when ICP increased)
      4. Herniation
        1. Subfalcine Herniation (midline shift, most common)
        2. Transtentorial Herniation (Uncal Herniation)
        3. Cerebellar Herniation (Tonsillar Herniation, least common)
    5. B: Bone (using bone windows)
      1. Skull Fracture
      2. Cancer (e.g. metastases, Multiple Myeloma)
      3. Pneumocephalus (more evident with bone windows)

V. Interpretation: Hemorrhage

  1. Hemorrhage appearance on CT changes with time
    1. Acute Hemorrhage: Hyperdense (light, white)
      1. Whiter than brain matter
    2. Subacute Hemorrhage: Isodense
      1. Similar density to brain matter and may be missed
    3. Chronic Hemorrhage: Hypodense (dark)
      1. Darker than brain matter
      2. Old Subdural Hematoma may appear as a hygroma
  2. Hemorrhage mimics: Contrast Staining
    1. Contrast staining refers to contrast deposition in extravascular brain parenchyma after IV contrast
      1. Non-contrast CT Head demonstrates a bright appearance similar to CNS Hemorrhage appearance
    2. Contrast staining occurs with transient increased blood brain permeability
      1. Intracranial neoplasm
      2. Ischemic CVA
      3. Intra-arterial clot extraction
    3. Contrast staining differs from CNS Hemorrhage in several ways
      1. Contrast staining typically resolves more quickly than Hemorrhage (24-48 hours)
      2. Contrast staining remains confined to the original lesion (while Hemorrhage extends)
      3. Contrast staining typically has attenuation <50 HU following endovascular thrombectomy
    4. Additional Imaging can also help distinguish between contrast staining and Hemorrhage
      1. Serial CT Head (repeated in 6 hours, traditional method)
      2. Dual energy CT
      3. MRI with susceptibility weighted imaging
    5. References
      1. Broder (2025) Crit Dec Emerg Med 39(10): 26-8

VI. References

  1. Ouellette and Tetreault (2015) Clinical Radiology, Medmaster, Miami, p. 92-106
  2. Broder (2024) Crit Dec Emerg Med 38(7): 22-3
  3. Broder (2021) Crit Dec Emerg Med 35(5): 10-1
  4. Haydel (2000) N Engl J Med 343:100-5 [PubMed]

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