CT Head Interpretation: Systematic Approach

Overview

The Non-Contrast Computed Tomography (NCCT) of the head is the frontline radiological investigation for acute neurological emergencies. It is unmatched in its speed and sensitivity for detecting acute hemorrhage and gross structural abnormalities.

The Blood Can Be Very Bad Mnemonic

Interpreting a CT Head requires rigorous discipline to avoid missing subtle findings. The most widely taught and reliable systematic approach uses the mnemonic "Blood Can Be Very Bad":

• Blood - Evaluate for acute hemorrhage (EDH, SDH, SAH, IPH).
• Cisterns - Assess the basal cisterns for effacement or blood.
• Brain - Differentiate gray/white matter, look for edema, mass effect, or midline shift.
• Ventricles - Check for hydrocephalus, asymmetry, or intraventricular hemorrhage.
• Bone - Evaluate the skull vault and skull base for fractures.

B - Blood (Acute Hemorrhage)

Acute extravascular blood appears hyperdense (bright white) on a non-contrast CT, typically measuring between 50-90 Hounsfield Units (HU). You must systematically rule out the four main compartments of intracranial hemorrhage:

• Extradural Hematoma (EDH): Biconvex (lens-shaped) hyperdensity that does not cross cranial sutures. Almost always arterial in origin, classically from a torn middle meningeal artery secondary to a temporal bone fracture.
• Subdural Hematoma (SDH): Crescent-shaped accumulation of blood that can cross sutures but cannot cross the dural attachments (falx cerebri, tentorium). Often venous, arising from torn bridging veins in the elderly or alcoholic populations.
• Subarachnoid Hemorrhage (SAH): Hyperdense blood filling the basal cisterns, Sylvian fissures, and cortical sulci. Trauma is the most common cause, but an aneurysmal rupture MUST be clinically suspected if non-traumatic.
• Intraparenchymal Hemorrhage (IPH): Bleeding directly into the brain substance. Often hypertensive (basal ganglia, thalamus, pons) or secondary to amyloid angiopathy in the elderly (lobar hemorrhages).

C - Cisterns

The basal cisterns reflect the pressure status of the cranial vault. Effacement (closing off) of these critical CSF spaces is a dire warning sign of impending herniation.

• Quadrigeminal Cistern: W-shaped cistern posterior to the midbrain. Effacement suggests upward or downward transtentorial herniation.
• Suprasellar Cistern: Star-shaped cistern above the sella turcica. Obliteration here strongly suggests severe diffuse cerebral edema or a massive anterior mass.
• Ambient Cisterns: Hug the lateral aspects of the midbrain. Asymmetric effacement occurs in early uncal herniation.
• Pre-pontine Cistern: Space anterior to the pons.

B - Brain Parenchyma

Evaluate the cerebral and cerebellar hemispheres for symmetry, mass effect, and the preservation of the gray-white matter interface. A loss of this interface is a massive red flag.

• Midline Shift: Draw a line from the crista galli to the internal occipital protuberance. Measure any deviation of the septum pellucidum or pineal gland.
• Loss of Gray-White Differentiation: This is the earliest CT sign of acute cytotoxic edema (infarction or severe hypoxic injury). Edema increases tissue water content, drastically lowering its Hounsfield Unit value until it resembles white matter.
• Insular Ribbon Sign: Loss of the gray-white interface at the lateral margins of the insular cortex is a classically early, subtle sign of an evolving Middle Cerebral Artery (MCA) infarct.

V - Ventricles

Assess the lateral, third, and fourth ventricles for size, symmetry, and the presence of hyperdense material.

• Hydrocephalus: Dilation of the ventricular system. Differentiating communicating from non-communicating hydrocephalus is vital for neurosurgical planning.
• Intraventricular Hemorrhage (IVH): Blood layering within the dependent portions of the ventricles (often the occipital horns in a supine patient).

B - Bones & Scalp

Switch to a dedicated bone window (e.g., Width: 3000, Level: 500) to search for fractures. Never skip reviewing the soft tissues of the scalp!

• A dense scalp hematoma or "boggy swelling" points you directly to the site of impact. Always rigorously inspect the bone underlying this exact location for subtle linear or depressed fractures.
• Trace all cranial sutures to avoid mistaking a normal suture for a fracture line. Remember: Sutures have sclerotic (white) edges, whereas acute fractures have sharp, lucent (black) unsclerotic margins.

High Yield Facts