Virtual Hospital: Radiology Resident Case of the Week: Disease: Aortic Dissection

Radiology Resident Case of the Week

Aortic Dissection

October 27, 1995

Ronald W. Fuller M.D.
Peer Review Status: Not reviewed

Clinical Sx:
Aortic dissection occurs in 5 to 10 cases per million population per year or 1 per 10,000 hospital admissions, and has a high rate of rupture, estimated as high as 77%, many of which occur within days of diagnosis. Complications include rupture which can lead to death in approximately 90% of untreated patients with aortic dissection, dissection into branch vessels, vascular occlusion, organ infarction, fistula formation and aortic insufficiency. Symptoms include sudden thoracic or abdominal pain which may radiate to head, back, pelvic region, lower extremities, and rarely arms. Varying degrees of shock with loss of consciousness can occur. Moderate fever, leukocytosis, and death can occur from rupture.

Causes of dissection include hypertension, MarfanÕs syndrome, trauma, EhlerÕs Danlos, coarctation, bicuspid aortic valve and relapsing polychondritis.

Etiology/Pathophysiology
Dissection refers to a tear or defect in the intima of the aorta which allows blood to enter the media, separating it into two layers. The tear occurs most frequently 1-2 cm above the aortic valve and at the isthmus near the attachment of the ligamentum arteriosum. Dissection begins as an intramural hematoma arising from ruptured vasa vasorum. Ischemia of the aortic media is the primary factor in medionecrosis.

Pathology:

Miscellaneous
Dissection can be described by either the De Bakey or Stanford classifications. De Bakey separates aortic dissections into three subtypes. Type1 dissections involve the entire thoracic aorta: ascending, transverse and descending. Type1 are surgical emergencies and account for 30% of dissections. Type2 involve only the ascending and account for 12-21% ( ie MarfanÕs syndrome). Type3 are limited to the descending aorta, originating distal to the left subclavian artery and account for 50% of the cases. Stanford A involves the ascending and B involves the descending aorta.

Imaging
The gold standard has long been angiography which is invasive and has associated morbidity and high radiation exposure. It remains popular at many institutions, primarily because of its preference by referring surgeons. In the acutely injured patient with a high suspicion of Type1 or 2 dissections, angiography remains the initial study of choice.

Ultrafast CT can produce high quality axial images of the aorta and surrounding structures when there is a low suspicion of dissection, chronic dissection or post operative surveillance.

Radiographic signs of dissection include 1) inward displacement of the Intimal calcifications 2) Intimal flap separating the true and false lumens 3) differential contrast opacification between the true an false lumens 4) presence of lower density material within the false lumen indicating the presence of a thrombus. The Intimal tear signifying the entry or exit site are usually not seen by CT. Paraaortic hematoma or fluid may signify aortic rupture or leak

DDX

Key references

ACR Code

Keywords:

References
Thompson, B. , Stanford, W. , Utility of Ultrafast Computed Tomography in the Detection of Aortic Aneurysms or Dissection Seminars in Ultrasound, CT , and MRI. Vol. 14, no 2 (April), 1993. p.117-128.

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