EM · CT interpretation and usage (approach)
Computed tomography — the emergency department interpretation and usage approach
Also known as CT interpretation · CT usage · CT angiography · CT perfusion · pan-scan
The systematic approach to requesting and interpreting computed tomography in the emergency department — the appropriate-versus-inappropriate decision, contrast versus non-contrast phases, CT angiography for pulmonary embolism and aortic dissection, CT perfusion for the stroke penumbra, the early ischaemic stroke signs with the ASPECTS score, subarachnoid haemorrhage sensitivity within six hours, renal colic and appendicitis imaging, the contrast premedication and contrast-induced nephropathy drug doses, and the 2 to 10 mSv radiation dose per scan. ACEM-primary, globally tagged.
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Target exams
Red flags
- A normal non-contrast head CT does not exclude subarachnoid haemorrhage after six hours of headache — perform a lumbar puncture
- A subtle early ischaemic sign — the hyperdense MCA sign, loss of the insular ribbon, or an ASPECTS under 7 — signals established infarction and demands urgent reperfusion
- An intimal flap on CT angiography of the aorta is an acute aortic dissection until proven otherwise — a surgical or endovascular emergency
- A filling defect in a pulmonary artery on CT pulmonary angiography is a pulmonary embolism — assess right ventricular strain before disposition
- Sending an unstable, unmonitored or unescorted patient to the CT scanner is a preventable death in the radiology department
Meet the patient
A 52-year-old woman arrives an hour after a thunderclap headache she calls the worst of her life, maximal within seconds while lifting the shopping. She is alert, neurologically intact, with a stiff neck and a blood pressure of 158 over 92. The clinical question is narrow and time-critical — is there subarachnoid blood?[4]
The request has to be exactly right: a non-contrast head CT to find the blood (contrast would obscure it), read on the brain and subdural windows within the six-hour window when sensitivity peaks, with a lumbar puncture standing by if the scan is normal. Hold that one patient and the request she forces, and every phase-selection rule in this topic falls into place.[4]
References26ShowHide
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