CT Head Interpretation for Nurses

Accurate interpretation of CT head scans for nurses involves understanding basic neuroanatomy, recognizing key pathologies like traumatic brain injuries and strokes, and differentiating between various types of bleeds and infarcts based on their CT appearance.

Core Principles

CT scans use X-rays absorbed by different tissues to create gray-scale images, with Hounsfield Units (HU) quantifying density (black for low density, white for high density).
Understanding the 7 key CT levels of the brain (Upper cortex, Lateral ventricle, Thalamus/Basal Ganglia, Quadrigeminal cistern, Midbrain, Suprasellar cistern, Base of skull) aids in anatomical localization.
Traumatic brain injuries are categorized by the location of extra-axial blood: Epidural (EDH) is lentiform/biconvex, Subdural (SDH) is crescentic/semi-lunar, and Subarachnoid (SAH) is in the sulci and cisterns.
Ischemic strokes appear as hypodense areas (not as black as CSF) with potential mass effect, while hemorrhagic strokes appear as hyperdense (white) lesions with mass effect.

Action Steps

Identify the CT level by recognizing characteristic anatomical structures (e.g., 'Boomerangs' for lateral ventricles, 'Pizza slice' for Thalamus/Basal Ganglia).
Assess for extra-axial blood by looking for hyperdense areas outside the brain parenchyma, noting their shape (lentiform for EDH, crescentic for SDH) and location.
Differentiate between acute and chronic infarcts by observing the degree of hypodensity and presence of volume loss (chronic infarcts are darker and show volume loss).
Identify acute hemorrhage as a hyperdense (white) lesion, noting its location and any associated mass effect (e.g., compression of ventricles).

Key Terms

Hounsfield Units (HU): A scale from -1000 to +1000 used in CT imaging to represent the X-ray attenuation of different tissues, where lower values (e.g., air at -300 HU) are darker and higher values (e.g., bone at 120 HU) are whiter.
Epidural Hematoma (EDH): A collection of blood between the dura mater and the skull, typically lentiform or biconvex in shape, often caused by arterial bleeding.
Subdural Hematoma (SDH): A collection of blood between the dura mater and the arachnoid mater, typically crescentic or semi-lunar in shape, often caused by tearing of bridging veins.
Subarachnoid Hemorrhage (SAH): Bleeding into the subarachnoid space, often appearing as hyperdense blood in the sulci and cisterns, commonly due to aneurysm rupture.
Ischemic Stroke: Brain tissue death due to lack of blood supply, appearing as a hypodense area on CT, which may be normal in the first few hours.
Hemorrhagic Stroke: Bleeding within the brain parenchyma, appearing as a hyperdense (white) area on CT.

Real World Examples

A patient presents with a head injury and the CT scan shows a biconvex collection of blood between the skull and the brain's outer membrane.: This is characteristic of an Epidural Hematoma (EDH), likely from damage to the middle meningeal artery.
A CT scan of a patient with a severe headache reveals hyperdense blood within the sulci and basal cisterns of the brain.: This pattern indicates a Subarachnoid Hemorrhage (SAH), often caused by a ruptured aneurysm.
A CT scan shows a hypodense area in the left basal ganglia that is 'not as black as CSF' and has caused some compression of the adjacent ventricle.: This suggests an acute infarct (ischemic stroke) in the left basal ganglia, with associated edema causing mass effect.