Outline the advantages and disadvantages of a CT scan, Transoesophageal echocardiography, MRI and an aortogram for the evaluation of suspected aortic dissection.
• CT Advantages:
• easy availability on an emergency basis
• high sensitivity and specificity
• can pick up complications involving the branches ( e.g. ischaemic gut) and extent of dissection into abdominal aorta
• easier to monitor the patient than MRI
• detects pericardial effusion.
• have to move the patient
• iodinated contrast
• cannot assess for AR, LV function or coronaries
• TOE Advantages:
• bedside test
• can detect intimal flap, true and false lumen AR, tamponade
• assess LV function
• no contrast needed
• may need anaesthesia/intubation
• may cause undesirable hypertension
• not widely available
• special expertise required
• MRI Advantages:
• High sensitivity and specificity
• MR contrast (Gadolinium) has more favourable safety profile
• can detect AR
• Not readily available
• inconvenient (patient motionless for 30 minutes)
• access and monitoring difficult
• limited applicability (claustrophobia, pacemakers)
• will detect intimal flap, AR
• assess LV, tamponade, blocked coronaries (important for surgery in type A
• not readily available
• large contrast load
The college answer can be more easily reduced into a table:
A good article on this topic is available. It illuminates some of the finer points which the college answer has omitted:
- In high risk patients, all the modalities are more or less equal in accuracy
- In moderate risk patients, positive predicitive values are >90% for CT, MRI and TOE but only 65% for aortography
- MRI is the most sensitive of the lot - in low risk patients, it picks up close to 100% of the dissections
- All four modalities have a 85% negative predictive value.
Khan, Ijaz A., and Chandra K. Nair. "Clinical, diagnostic, and management perspectives of aortic dissection." Chest Journal 122.1 (2002): 311-328.
The canonical source for this information would have to be the most recent iteration of theACCF/AHA Guidelines for Diagnosis and Management of Patients With Thoracic Aortic Disease.