Aortic Dissection: Teaching Points

Case Details: 48 yrs old lady  with tearing pain chest  on CT angiography  shows large, dissection of the  entire aorta , including  Ascending aorta , with celiac, SMA, renal arising from  true lumen (cerebral vessels showing no dissection) with cobweb sign and beak signs  positive.

Teaching points by Dr MGK Murthy, Dr Pritam, CT Technologist: Mr Shekhar

1. Aortic dissection  occurs when the blood enters medial layer through a  penetrating ulcer or tear of intima 

2.  Two types: Acute,  when clinical symptoms <14 and="" chronic="" days="" when="">14 days 

More useful , Stanford A:  involvement of ascending  aorta & or  arch, possibly descending as well (requires surgery)   

Stanford B:  Descending aorta and / arch distal  to left subclavian and beyond (medial management unless complications ) 

Debakey's I- ascending  aorta/ arch and possibly beyond

Debakey's II- only ascending aorta 

Debkey's III-- descending aorta 

3. If it  involves coronaries , it may produce  tamponade and death with Becks Traid positive  (a) low blood pressure or narrow pulse pressure, (b) muffled heart sounds  and  (c) raised JVP

4. Usually presents with tearing pain chest  or end organ schema .  CT angiography helpful 

(disadv = does not detect site of intimal tear)  

Signs- Dilated aorta, double lumen,   Intimal flap , intramural hematoma,  Mercedes-Benz sign(three distinct intimal flaps that have a triradiate configuration similar to the Mercedes-Benz logo ) (supposed to indicate secondary dissection in the dissected segment)(triple-barreled aortic dissection )  and Windsock sign(intimo-intimal intussusception between the true and false dissected lumens of the thoracic aorta(potentially fatal  sign)

5. Differences between false lumen (blood filled channel)  and true lumen (lined by intima) important . Exit tear produces the two lumens. 

How to identify on CT angio?

False lumen

a)  Larger

(b) cobweb sign (slender linear areas of low attenuation specific to the false lumen due to residual ribbons of media that have incompletely sheared away )

(c) Beak sign( an acute angle between the dissection flap and the outer wall) represents the end of the false lumen and propagating region  (can be high density or low density) 

(d) low contrast density (delayed contrast entry) 

(e) may be low density if completely thromboses

(f) Left renal artery usually arises from it  

True Lumen

(a) compressed and smaller 

(b) Outer wall calcification

(c) celiac,SMA, right renal arise from it 

6 Usually elderly chronic hypertensives ( etiology medial  layer degeneration). Others connective tissue disorders/ atherosclerosis( aetiology penetrating ulcer)  / Pregnancy/ vasculitis 

7 CXR - widened superior mediastinum more than 8cm , irregular aortic contour/ pushing of the  calcification inside(more than 1cm) and double aortic contour  etc. Repair of dilated ascending aorta more than 60mm  (more than 45mm when connective tissue disorders present)  may prevent  potential dissection.