Imaging in the Emergency Department
Imaging use in the Emergency Department has increased rapidly over the past few years due to technical advances and increasing pressure to move decision-making earlier in a patient’s journey, and to prevent unnecessary hospital admissions. Ultrasound is now a core skill for senior Emergency Department doctors and new hospitals often have a CT scanner in the Emergency Department.
Plain radiographs interpreted by the treating clinician are used for the majority of Emergency Department imaging. The advent of digital radiography has made real-time reporting by radiologists easier.
X-rays are ionising radiation and cause damage to tissues through which they pass. The energy released is proportional to the density of the tissue. Abdominal or thoracolumbar radiographs should not be performed in young people, especially females, without a very good reason, as the gonads are very radio- sensitive. In this book, X-ray doses are expressed in terms of chest radiographs (CXR). One CXR is approximately 3 days of back- ground radiation.
X-rays are not therapeutic. If the result will not change management, radiographs should not be taken. Examples include uncomplicated rib fractures (when not worried about a pneumothorax), coccyx pain and stubbed toes other than the big toe. Soft tissues are poorly shown by plain films, making it an insensitive examination for joints that rely on these for stability, e.g. knee, shoulder.
Reading plain radiographs
• Check the patient’s name and the date of the film, particularly on digital radiography systems, which offer many opportunities for confusion.
• There should be two good views of limbs: anterior-posterior and lateral.
• If requesting imaging of more than one area, ask yourself if this is necessary. If not urgent, it may be better to re-examine the patient once they have had some analgesia, or obtain a senior opinion.
• You will learn more from your radiology department if you engage with them and ask their advice rather than expecting a purely technical service.
• Many Emergency Departments operate a system whereby the radiographer can flag an abnormality on the radiograph. You should not dismiss something that the radiographer has flagged as abnormal without obtaining a senior opinion.
Clinical (bedside) ultrasound use has increased exponentially with the availability of cheap robust ultrasound machines, and is now a core skill for Emergency Department doctors. Ultrasound has been described as the ‘visual stethoscope’ and is revolutionising the assessment and management of patients in the Emergency Department.
Ultrasound was initially used in the Emergency Department in the resuscitation room for:
• Detecting abdominal aortic aneurysms (AAA).
• Focused abdominal scanning in trauma (FAST) scans, searching for blood in the peritoneal cavity.
• Central venous line placement.
However, ultrasound use is now expanding to include:
• Shock assessment: cardiac function, vascular filling, signs of pulmonary embolus, together with the AAA and FAST scans.
• Basic echocardiography.
• Deep vein thrombosis (DVT) scanning.
• Early pregnancy scanning.
• Hepato-biliary scanning.
Disadvantages are that ultrasound is operator dependent, requires training and skill validation, and can divert attention from more important problems.
Computed tomography scan
As resolution and availability have increased and acquisition times have dropped, computed tomography (CT) has become an increasingly useful tool for the Emergency Department. CT is very good for bony injuries, and the trauma CT has proved to be more sensitive and specific than clinical examination in major trauma, but requires a very large radiation dose (1000 CXR).
Neck imaging in high-risk trauma is routinely done by CT (100 CXR), as plain films are insufficiently sensitive at detecting significant injury. Examples of high-risk injuries are a high-speed rollover road traffic collision, and also the elderly patient who falls forward, hitting their face (‘fall on outstretched face’), who is at high risk of odontoid peg fracture, and in whom interpretation of plain radiographs is very difficult (see Chapter 11).
Modern CT scanners have enough resolution and speed to be able to resolve cardiac anatomy including the coronary arteries, pulmonary emboli and aortic dissection (400 CXR). CT brain scan (100 CXR) is an essential part of the assessment of stroke or the unconscious patient. CT KUB (kidneys, ureters and bladder; 400 CXRs) is the imaging of choice in renal colic.
Magnetic resonance scan
Magnetic resonance (MR) scanning is rarely used in the Emergency Department apart from possible cauda equina syndrome (acute central disc prolapse pressing on the cauda equina), giving bowel and bladder symptoms. MR scanning can be used to avoid the large radiation dose incurred by CT, e.g. investigating renal colic in young women.
Joints in which stability and function are mainly due to soft tissues, i.e. ligaments and cartilage such as the knee and shoulder, are well imaged by MR scanning, but it is generally difficult to access these directly from the Emergency Department.
Interventional imaging has an increasing role for a limited number of severe conditions. Interventional imaging is generally offered in larger hospitals, and together with trauma care, is one of the main drivers for centralisation of acute services into large hospitals.
• Primary percutaneous cardiac intervention with stenting has become the treatment of choice for patients with myocardial infarction.
• Endovascular treatments for patients with AAAs and aortic dissection are increasingly used. Neurosurgical bleeding from aneurysms is treatable by coils, as is otherwise uncontrollable bleeding in the pelvis, e.g. from pelvic fractures.