First Night on Call: A Resident's Head CT Checklist

The overnight non-contrast head CT is the highest-stakes routine study a first-year resident reads. The good news: it rewards a fixed search pattern more than almost any other exam. Read every head CT the same way, in the same order, every time, and the misses that end up in morbidity conference mostly stop being possible.

The classic mnemonic is Blood Can Be Very Bad — Blood, Cisterns, Brain, Ventricles, Bone. Use it, but use it as six deliberate passes, not a vibe.

Pass 1 — Blood, in every compartment

Acute blood is hyperdense (roughly 50–100 HU). Interrogate each compartment by name, out loud if it helps:

• Epidural: lens-shaped, bounded by sutures, usually with an overlying fracture. Look at the temporal region specifically — middle meningeal territory.
• Subdural: crescentic, crosses sutures, does not cross the falx. Trace the entire inner table, including along the falx and tentorium, where thin subdurals hide in plain sight.
• Subarachnoid: dense sulci and basal cisterns. In the "worst headache of life" patient, look hard at the suprasellar cistern, sylvian fissures, and interpeduncular fossa — a small aneurysmal bleed can be a few slices of subtle density.
• Intraparenchymal and intraventricular: don't stop at finding one bleed. Hemorrhage in an unusual location (isolated sylvian, inferior frontal) should make you consider an underlying aneurysm, and blood layering in the occipital horns is easy to dismiss as artifact.

Change your windows. On standard brain windows (roughly W80/L40), a thin subdural against bright bone is nearly invisible. A subdural window around W200/L70 separates blood from calvarium. This one habit finds more misses than any other on this list.

Pass 2 — Cisterns

Four questions: are the basal cisterns open, symmetric, blood-free, and normal in density? Effaced cisterns are the radiographic voice of raised intracranial pressure and impending herniation — and they can be the only finding early in diffuse edema. If the suprasellar cistern looks like a smile that stopped smiling, escalate.

Pass 3 — Brain

• Gray–white differentiation is your early-infarct detector. Loss of the insular ribbon and obscuration of the lentiform nucleus are the classic early MCA-territory signs.
• A hyperdense vessel (dense MCA sign, or a dense basilar tip) can precede any parenchymal change. Compare side to side.
• Symmetry: measure midline shift at the septum pellucidum, in millimeters, and say the number in the report — "7 mm leftward midline shift," never "some shift."
• Hypodensity that respects a vascular territory is an infarct until proven otherwise; hypodensity with mass effect and edema out of proportion suggests something subacute or non-vascular.

Pass 4 — Ventricles

Too big, too small, or asymmetric — each means something. Dilated temporal horns are the earliest sign of hydrocephalus and are frequently the finding residents skip. Small, slit-like ventricles in the wrong clinical context are diffuse swelling. Asymmetry with a trapped horn suggests an obstructing lesion at the foramen of Monro or atrium.

Pass 5 — Bone and air

Switch to bone windows for the whole calvarium and skull base — do not diagnose fractures on brain windows. Then look for what fractures bring with them: pneumocephalus, opacified mastoid air cells (temporal bone fracture until excluded in trauma), and air–fluid levels in the sphenoid sinus (a skull-base fracture marker in the trauma patient who "just fainted").

Pass 6 — The edges and the scout

The corners of the field kill quietly: the sellar and pineal regions, the craniocervical junction, the orbits, the scalp hematoma that tells you where to look harder inside. And read the scout view — a C1/C2 fracture or a displaced nasal bone lives there, and nowhere else on your stack.

The classic overnight misses, named

1. Isodense subacute subdural (1–3 weeks old): same density as cortex. The clue is the gray–white interface displaced inward from the skull.
2. Thin subdural along the tentorium read as "normal dural density."
3. Subtle SAH in a single sulcus in the anticoagulated fall patient.
4. Early hydrocephalus called "prominent ventricles for age."
5. Dense basilar artery in the unresponsive patient sent for "altered mental status."

When to call your attending

Call for: any new hemorrhage, midline shift, effaced cisterns, dense vessel with a matching deficit, pneumocephalus, or a fracture crossing a venous sinus or the carotid canal. Nobody remembers the resident who called about a subtle finding that turned out fine. Everyone remembers the one who didn't.

When you dictate the negative study, keep the structure fixed too — a consistent report is a searchable report. If you want to see what a disciplined structured report looks like assembled automatically, run a sample case in the browser or browse the free guideline calculators for the systems you'll be asked about on rounds.