Imaging decisions in the emergency department — pan-scan, stroke, and the thunderclap headache

(a) Trauma imaging — pan-scan versus selective CT (5 marks).

^[2]- He is a polytrauma patient with a significant mechanism, hypotension, a tender abdomen, and a major long-bone injury — a candidate for immediate imaging.

• Resuscitate first and escort to CT: secure the airway, two large-bore cannulae, activate the massive transfusion protocol, splint the femur, and send him monitored and escorted — the CT suite is a hostile environment for the unstable patient.
• The REACT-2 randomised trial compared immediate total-body CT with conventional imaging and selective CT in blunt trauma and showed no difference in in-hospital mortality at the cost of a higher radiation dose.^[2] Routine pan-scan is therefore not a default.
• In this patient the mechanism and the hypotension justify a truncated pan-scan — non-contrast head and cervical spine, then contrast-enhanced CT of the chest, abdomen and pelvis — because the suspected polytrauma makes selective imaging likely to miss injury and the clinical picture cannot localise the bleeding.
• The selective principle still applies at the margins: clear the cervical spine with the Canadian C-spine rule where applicable, and avoid re-scanning regions already adequately imaged. The decision is driven by mechanism and physiology, not by reflex.
• A FAST at the bedside may confirm free fluid in the unstable patient and, if positive with a clear source, may avert the scanner and proceed to theatre.

(b) Thunderclap headache — interpretation and the lumbar-puncture decision (4 marks).

• The headache began 10 hours ago, she is now pain-free with a normal examination and a normal non-contrast head CT.
• CT sensitivity for subarachnoid haemorrhage is 100 percent within six hours of onset (121 of 121 in Perry's cohort, 95 per cent CI 97 to 100), but it falls with time as blood is diluted and degrades (92.9 per cent overall).^[4]
• At 10 hours, a normal CT does not reliably exclude subarachnoid haemorrhage — the next investigation is a lumbar puncture to detect xanthochromia (bilirubin from lysed red cells).
• A negative CT within six hours, in the right patient, may exclude the diagnosis without a lumbar puncture; after six hours, or with any persistent suspicion, the lumbar puncture is required. Discharge without it is a classic error.

(c) ASPECTS (3 marks).

• ASPECTS is the Alberta Stroke Program Early CT Score, a ten-point territorial score applied to two standardised slices of the middle cerebral artery territory on the non-contrast head CT.^[3]
• A normal territory scores ten; one point is subtracted for each of the ten regions showing early ischaemic change (M1 through M6 cortex, the caudate, lentiform, internal capsule, and insula), for a worst score of zero.
• A hyperdense MCA sign is acute thrombus in the vessel; a low ASPECTS (7 or below) indicates a large established infarct core, predicts poor functional outcome, and (with a large core on perfusion) argues against reperfusion of non-salvageable tissue. The next step is CT angiography to find the vessel and, if within window, to trigger thrombolysis or thrombectomy transfer.

(d) Contrast-induced nephropathy — risk and hydration (3 marks).

^[9]- Contrast-induced nephropathy is an acute kidney injury arising within days of iodinated contrast, defined as a rise in creatinine, in a patient with pre-existing renal impairment, diabetes, or volume depletion; the risk is stratified by the eGFR. (AMACING enrolled eGFR 30 to 59 and excluded eGFR below 30, dialysis and unreferred patients, so the below-30 patient was not studied.)

• The AMACING trial showed that in high-risk patients undergoing an elective procedure, no prophylaxis was non-inferior to intravenous hydration (2.6 versus 2.7 per cent) for preventing nephropathy, and hydration itself caused complications (5.5 per cent).^[9]
• The implication is that prophylactic intravenous hydration is reserved for the genuinely high-risk patient (markedly reduced eGFR, diabetes, volume depletion) rather than every patient who receives contrast — and that withholding a necessary diagnostic contrast CT purely to avoid nephropathy is not justified when the answer changes management.