Aortic dissection

Discussion:

An acute aortic dissection classically presents with severe chest, abdominal, or back pain, of maximum intensity at or shortly after its appearance, and qualitatively described as "ripping" or "tearing." Concomitant appearance of pathology affecting disparate systems is also frequently described, such as focal neurologic deficits or acute limb ischemia 4.

Common risk factors include hypertension, bicuspid aortic valves, connective tissue diseases and vascular inflammation. It is defined by a disruption in the vascular intima which results in the creation of two vascular conduits (true and false lumens) separated by an intimal flap. The Stanford classification is often used to clinically subdivide patients based on the intimal flap's entry point proximal (type A) or distal (type B) to the left subclavian origin.

Bedside transthoracic echocardiography is often the first imaging modality employed in the emergency department, and while incompletely sensitive can quickly identify complications requiring intervention and/or emergent consultation. While transesophageal echocardiography has remarkable test characteristics for the diagnosis of aortic dissection, the urgency of the clinical situation often precludes an invasive procedure requiring sedation 4

Sonographic features of an acute aortic dissection include:

  • subdivision of the vessel by a hyperechoic, mobile, linear intraluminal structure (intimal flap)
    • the true lumen tends to be smaller, increasing in diameter during systole 1
    • the larger false lumen may demonstrate intraluminal thrombus or spontaneous echocontrast
    • color flow Doppler interrogation may reveal alternation of filling corresponding to the cardiac cycle, as well as aliasing at intraluminal points of communication
  • aortic root dilation

Complications should be specifically sought, including:

  • aortic valve regurgitation
    • may also occur due to leaflet prolapse
  • myocardial ischemia
    • secondary to coronary involvement, most often the right coronary artery
    • failure of (or delayed) systolic thickening of the myocardium pertaining to the affected distribution is suggestive
  • pericardial effusion with or without tamponade
    • often with some degree of mixed echogenicity

The case patient had well filled cardiac chambers without an effusion, normal valvular coaptation and aortic root diameter, and visualized left ventricular segments (basal to mid anteroseptum and inferolateral walls) were normokinetic, lowering the suspicion for incipient complications to arise.

Contrast enhanced CT should be sought expeditiously as the modality of choice to to evaluate for an acute aortic dissection. As with this case it allows identification of the true and false lumens, noting the following salient features:

  • the beak sign, quite distinct just caudad to the diaphragmatic hiatus in the above CT, identifies the sharp angulation at the periphery of the false lumen
  • lower intraluminal density with patchy thrombosis and delayed opacification are notable in the false lumen in the above case
  • the left renal artery is also seen to characteristically arise from the false lumen 

 

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