CT Interpretation: Head

The emergency physician should be adept at the interpretation of computed tomography of the head, particularly for life-threatening processes where awaiting a radiologist interpretation may unnecessarily delay care.

As with the approach detailed previously for imaging of the abdomen and pelvis, a similar structured method for interpretation of head imaging exists and follows the mnemonic “Blood Can Be Very Bad”.

Normal Neuroanatomy

Brainstem
Posterior Fossa
High Pons
Cisterns
Ventricles

Blood: Blood

Density
Acute: hyperdense (50-100HU)
1-2wks: isodense with brain
2-3wks: hypodense with brain

Types/Locations

Intraparenchymal Hemorrhage/Contusions
Sudden deceleration of the head causes the brain to impact on bony prominences (e.g., temporal, frontal, occipital poles).
Non-traumatic hemorrhagic lesions seen more frequently in elderly and located in basal ganglia.
Intraventricular Hemorrhage
White density in otherwise black ventricular spaces, can lead to obstructive hydrocephalus and elevated ICP.
Associated with worse prognosis in trauma.
Subarachnoid Hemorrhage
Hemorrhage into subarachnoid space usually filled with CSF (cistern, brain convexity).
Extracranial Hemorrhage
Presence of significant extracranial blood or soft-tissue swelling should point examiner to evaluation of underlying brain parenchyma, opposing brain parenchyma (for contrecoup injuries) and underlying bone for identification of fractures.

Can: Cisterns


Evaluating the cisterns is important for the identification of increased intracranial pressures (assessed by effacement of spaces) and presence of subarachnoid blood.

  • Circummesencephalic: CSF ring around midbrain and most sensitive marker for elevated ICP
  • Suprasellar: Star-shaped space above the sella
  • Quadrigeminal: W-shaped space at the top of the midbrain
  • Sylvian: Bilateral space between temporal/frontal lobes

Be: Brain

Evaluate the brain parenchyma, including an assessment of symmetry of the gyri/sulci pattern, midline shift, and a clear gray-white differentiation.

Very: Ventricles

Evaluate the ventricles for dilation or compression. Compare the ventricle size to the size of cisterns, large ventricles with normal/compressed cisterns and sulcal spaces suggests obstruction.

Bad: Bone

Switch to bone windows to evaluate for fracture. The identification of small, linear, non-depressed skull fractures may be difficult to identify as they are often confused with sutures – surrogates include pneumocephalus, and abnormal aeration of mastoid air cells and sinuses. The Presence of fractures increases the suspicion for intracranial injury, search adjacent and opposing parenchyma and extra-axial spaces.

Example #1

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CT Head Interpretation

  • Ill-defined lesion in right parietal white matter with a large amount of surrounding vasogenic edema with midline shift and right uncal herniation.
  • Acute on subacute right extra-axial subdural hematoma.
  • Effacement of basilar cisterns.

Example #2

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CT Head Interpretation

  • Bilateral subacute subdural hematomas, left larger than right and associated with rightward midline shift.
  • Left lateral ventricle is partially effaced.

Example #3

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CT Head Interpretation

Subdural hematoma with significant herniation

References

  1. Perron A. How to read a head CT scan. Emergency Medicine. 2008.
  2. Arhami Dolatabadi A, Baratloo A, Rouhipour A, et al. Interpretation of Computed Tomography of the Head: Emergency Physicians versus Radiologists. Trauma Mon. 2013;18(2):86–89. doi:10.5812/traumamon.12023.