How to Dictate a Noncontrast Head CT: A Search Pattern That Survives 3 AM

The noncontrast head CT is the study you will read most often under the worst conditions: 3 AM, a stroke page running, eleven more on the list. Under those conditions, perception fails before knowledge does — which is why the answer is not knowing more, it is a fixed search pattern you execute identically on the five-thousandth study as on the fifth. The classic mnemonic is Blood Can Be Very Bad: Blood, Cisterns, Brain, Ventricles, Bone. Steal it, keep it, and let your dictation follow it so the pattern audits itself.

Blood: four compartments, four shapes

Acute blood is hyperdense — roughly 50–70 HU — and each compartment has a shape:

• Epidural: lentiform (biconvex), bounded by sutures, can cross the midline. The classic story is a temporal fracture over the middle meningeal artery; look hard at the bone beneath every epidural.
• Subdural: crescentic, crosses sutures, does not cross dural reflections. Check the posterior falx and the tentorium — a thin layering subdural along the tentorial leaflet is a common subtle miss. And remember the isodense subacute subdural: at one to three weeks the collection matches gray matter, and the clue is effaced sulci that don't reach the inner table.
• Subarachnoid: blood in sulci and cisterns. The highest-yield single look is the interpeduncular and suprasellar cisterns — a small aneurysmal bleed pools there when the rest of the study looks clean.
• Intraparenchymal and intraventricular: describe location, size, and any intraventricular extension; a tiny hemorrhage layering dependently in the occipital horns is often the only sign of IVH, so look there deliberately.

Window discipline matters: a subdural hugging the inner table disappears on standard brain windows. Sweep once on subdural windows (roughly W150–200/L50–70) on every trauma head.

Cisterns: the herniation check

Four spaces, one question — are they open? Suprasellar, perimesencephalic, quadrigeminal, and the sylvian fissures. Effacement of the basal cisterns is the CT signature of herniation and raised intracranial pressure, and it outranks almost everything else on the study. If the cisterns are closing, that is the first line of the impression and a phone call, whatever else the scan shows.

Brain: gray-white and the early infarct signs

Scan the gray-white interface systematically — it is where the subtle findings live:

• Loss of the insular ribbon — the insular cortex fades into the external capsule; one of the earliest MCA-territory signs.
• Obscuration of the lentiform nucleus — the basal ganglia blur into the surrounding white matter.
• Cortical sulcal effacement with subtle loss of gray-white distinction in one territory. Compare side to side at the same level; symmetry is your control.

Say the honest sentence about timing: a normal noncontrast CT does not exclude acute ischemic stroke — early infarcts are commonly invisible in the first hours. The noncontrast study's actual job in the stroke pathway is to exclude hemorrhage before thrombolysis, and the report should answer that question explicitly.

The hyperdense vessel

A hyperdense MCA sign — one M1 denser than its mate — means intraluminal thrombus; its sylvian cousin, the MCA dot sign, is the same finding in an M2/M3 branch. The check is always comparative: dense relative to the contralateral vessel and other intracranial arteries, because elevated hematocrit and calcified atherosclerosis make all the vessels dense — bilateral density is usually physiologic, unilateral density is a clot. Look at the basilar tip too; a hyperdense basilar is an emergency that is routinely missed because nobody looks.

Ventricles: size, symmetry, and the temporal horns

The earliest, most reliable sign of hydrocephalus is dilation of the temporal horns, which are barely visible slits on a normal study. Then ask whether the picture is communicating (all ventricles enlarged) or obstructive (dilated above a blockage — classically enlarged lateral and third ventricles with a normal fourth). Distinguish hydrocephalus from ex vacuo enlargement by the company it keeps: prominent sulci favor atrophy; effaced sulci with ballooned temporal horns favor hydrocephalus.

If there is mass effect, measure the midline shift in millimeters at the septum pellucidum and name the level. "Mild shift" means nothing across serial exams; "7 mm leftward midline shift at the septum pellucidum, previously 4 mm" is a trajectory.

The posterior fossa deserves its own ten seconds

Beam-hardening streak between the petrous bones degrades exactly the region where the stakes are highest, so give the posterior fossa a deliberate look rather than an incidental one: the cerebellar hemispheres for hemorrhage or a wedge of low density, the brainstem for symmetry, and the fourth ventricle for position and patency. A cerebellar infarct or bleed that swells can obstruct the fourth ventricle and kill via hydrocephalus in hours — it is the one "small" finding on this exam with a neurosurgical tempo, and artifact is the standing excuse for missing it. If the study is degraded and the question is posterior circulation, say the honest sentence: evaluation is limited, MRI if clinical concern persists.

Bone and air: the last pass that catches the first injury

End every trauma head on bone windows, slice by slice, plus one deliberate look for the indirect signs: fluid in the mastoid air cells or sphenoid sinus in a trauma patient is a skull-base fracture until proven otherwise, and pneumocephalus means a fracture violated a sinus or the mastoid somewhere — find it or say you looked. The scout and the soft tissues get one glance each; scalp hematoma tells you where to stare on the bone pass.

Writing it for the ED at 3 AM

The emergency physician will read your impression on a phone, between patients, in about four seconds. Structure it as the answers to the four questions they are actually asking, in order:

1. Blood? Yes/no, compartment, size.
2. Mass effect? Midline shift in mm, cisterns open or effaced, herniation.
3. Hydrocephalus? Yes/no.
4. Fracture? Yes/no.

A negative study earns the precise negative, not the lazy one: "No acute intracranial hemorrhage, mass effect, or hydrocephalus" — not "normal head CT," because the study cannot promise "normal," only the absence of what CT can see. If the clinical question is stroke, add the timing caveat and, when the pattern fits, the next step: "No hemorrhage; no established infarct — early ischemia is not excluded on noncontrast CT."

A model report

EXAMINATION: CT head without contrast
HISTORY: 78-year-old male on apixaban, fall from
standing, GCS 14.
TECHNIQUE: Helical noncontrast CT of the head; brain,
subdural, and bone algorithm reconstructions.
COMPARISON: None.
FINDINGS:
Hemorrhage: Crescentic hyperdense extra-axial collection
along the right cerebral convexity, maximal thickness
9 mm, consistent with acute subdural hematoma. Trace
subarachnoid blood in two adjacent right frontal sulci.
No intraventricular extension.
Mass effect: 4 mm leftward midline shift at the septum
pellucidum. Basal cisterns patent. No herniation.
Brain: Gray-white differentiation preserved. No
established infarct. No hyperdense vessel.
Ventricles: Normal size; temporal horns not dilated.
Bone: No fracture. Mastoid air cells and paranasal
sinuses clear. Right parietal scalp hematoma.
IMPRESSION:
1. Acute right convexity subdural hematoma, 9 mm, with
   4 mm leftward midline shift. Basal cisterns patent.
2. Trace right frontal traumatic subarachnoid
   hemorrhage.
3. No hydrocephalus. No fracture.
Findings communicated to Dr. Chen in the ED at 03:41.

The findings follow the search pattern, the impression answers the four questions in order, and the communication line closes the loop on an anticoagulated head bleed. Keep the normal head CT template as your negative-study scaffold — its structure is this search pattern written down — and the template library has the rest of the call-night exams. Or push a head CT through the live demo: dictate "right subdural, nine millimeters, four millimeters of shift" and watch the full pattern — cisterns, ventricles, bone, communication line — build itself around the finding.