Aortic dissections are difficult to diagnose in a timely manner for a variety of reasons, chief among those being the variability in presenting symptoms from one patient to the next: “I have chest pain, and my right side doesn’t work” or “I have abdominal cramping and my foot is cold.” This “vague symptomatology” becomes not so vague or surprising if you familiarize yourself with the anatomy of the aortic dissection and the many malperfusion syndromes that complicate up to 20-30% of all aortic dissections.[1]
There is a common paradigm in emergency medicine regarding aortic dissections known as “chest pain plus…”–that patients with chest pain complicated by another (often seemingly unrelated) complaint, such as chest pain PLUS arm weakness, should raise your index of suspicion for aortic dissection. The following post will elucidate the pathophysiology of the “plus” symptoms one can expect to see in complicated aortic dissections.
Figure 1. Illustration of potential sites of dissection along the aorta and likely dissection morphology predicated on proximity to major branching vessels.[2]
Figure 2. (A) Static prolapse of intimal dissection flap into vessel branch ostium with secondary clot formation. (B) Mobile intimal dissection flap with intermittent prolapse into vessel branch ostium (more common).[4]
Cerebral Malperfusion
Incidence: 6-14% of Type A Aortic Dissections (TAAD)[5]
Mechanism:
– Occlusion of arch vessels (either brachiocephalic artery or left carotid) by dissection flap
– False lumen thrombus embolizing to the brain
– Hypoperfusion event as a result of profound hypotension or cardiac tamponade
Figure 3. Evolution of ischemic stroke in a patient with occlusion of left carotid by an aortic dissection flap. (A) Dissection flap visualized in all vessels of the aortic arch. (B) Dissection flap involving the left carotid with partial occlusion. (C) Subacute ischemia pre-extra-anatomic bypass. (D) Ischemic stroke with hemorrhagic conversion post-intervention.[6]
Myocardial Malperfusion Syndrome
Incidence: 10-15% of TAAD[5]
Mechanism:
– Coronary artery occlusion by dissection flap or extension
– Coronary artery disruption
Right Coronary Artery Involvement
There are three mechanisms by which coronary artery involvement can result in coronary malperfusion: obstruction of the coronary artery by the dissection flap, extension of the dissection into the coronary artery (as pictured below), and coronary artery disruption (or rupture).
In a retrospective study at a single, tertiary care hospital, only five patients out of 159 patients (3.1%) with acute type A aortic dissections were found to have involvement of the RCA. All five of those patients, however, followed the predictable pattern of RCA malperfusion/occlusion with ST-segment elevations in II, III, and aVF, making it easily mistakable for an OMI.[7] Although the sample size was quite small, this ECG pattern has been observed in numerous other case reports of aortic dissections with RCA involvement.[8-11]
Figure 4a. Dissection into valve with flap occluding right coronary artery. [12]
Figure 4b. ECG notable for ST-elevations in leads II, III, aVF. Patient found to have a type A aortic dissection with disruption of the right coronary artery.[7]
Left Coronary Artery Involvement
Dissections with left coronary involvement are less likely, and although they also tend to show ST-elevations on ECG, they are less predictable than RCA occlusions in their pattern.[7,13]
Figure 5. ECG of a patient with aortic dissection into the left coronary artery with ST-elevations in aVL, aVR, V2, and V6 and depressions in II, III, and avF.[13]
Special Cases
Cardiac tamponade
Incidence: 20-36% of TAAD[14]
Mechanism:
– Rupture of adventitia in the ascending aortic artery
– Cardiac rupture
Figure 6. Rupture of the adventitia creating a contiguous space between the pericardium and the false lumen of the ascending aorta.[15] Small-volume, controlled pericardiocentesis can be used to improve hemodynamics, but one should expect the hemopericardium to reaccumulate.
Renal Malperfusion
Incidence: Approximately 8% of all aortic dissections[18,19]
Mechanism:
– Dissection into the renal artery
– Occlusion of vessel by dissection flap
– Thrombus
– Compression of the left renal vein by the enlarged aorta (“Nutcracker Syndrome”)
Symptoms and signs of renal artery involvement include flank pain and hematuria. In a patient with known renal artery involvement, keep a high index of suspicion for renal malperfusion, especially in the context of worsening kidney function or progressively uncontrolled hypertension.
Figure 7. Left renal artery arising from the false lumen with subsequent poor perfusion of the left kidney as evidenced by non-enhancement.[20]
Mesenteric Malperfusion
Incidence: 4-6% of all aortic dissections[5,21]
Mechanism:
– Occlusion of Celiac and Mesenteric Arteries by the dissection flap[22]
– Thrombus in false lumen
– Dissection into the Celiac and/or Mesenteric Arteries
The most common symptoms of malperfusion due to aortic dissection include abdominal pain, nausea, vomiting, and diarrhea; however, up to 40% of patients with this malperfusion syndrome do not have any abdominal pain. This is especially concerning when considering that mesenteric malperfusion is a strong predictor of mortality with up to two-thirds of patients dying during hospitalization.[5]
Figure 8. Total collapse of the true lumen with malperfusion of the celiac and superior mesenteric arteries.[5]
Spinal Malperfusion
Incidence: 4% of all aortic dissections[23]
Mechanism:
– Radiculolumbar arteries originating in the false lumen. The anterior cord at the T10-T12 level (Artery of Adamkiewisz) is a watershed area and most often involved[24]
– Thrombosis
– Hypoperfusion event as a result of profound hypotension
Figure 9. Illustration of the territory supplied by the Artery of Adamkiewicz and subsequent tracts that might be involved in spinal cord ischemia.[25]
Figure 10a. CTA shows thrombus in the thoracic aorta in a patient who presents with mild neck pain, bilateral lower extremity numbness & flaccid paralysis, poor rectal tone, and urinary retention.[27]
Figure 10b. MR is notable for abnormal signal in the conus medullaris, likely indicative of spinal ischemia.[27]
Limb Malperfusion
Limb ischemia secondary to aortic dissection typically presents with pain, signs of decreased perfusion, paresthesias, and/or weakness. The lower extremities are more often involved than the upper extremities.[28] In over half of cases with lower limb ischemia due to aortic dissection, both lower extremities are involved.[29] Pulse deficits are only 30% sensitive in detecting thoracic aortic dissection and should not be used to rule out dissection.[30]
Upper Limb Ischemia
Incidence: 1-4% of TAAD and more likely to involve the right rather than the left upper extremity[28]
Mechanism:
– Obstruction of vessel by flap
– Thrombosis
– Decreased flow due to blood supply from false lumen
Figure 11. Absent filling of the brachiocephalic trunk in a patient with a proximal aortic dissection.[31]
Lower Limb Ischemia
Incidence: 4-23% of TAAD[19,28] and 6% of Type B dissections[32]
Mechanism:
– Obstruction of iliac artery or aortic obstruction by dissection flap
– Thrombosis
– Decreased flow due to origination of artery in false lumen
Figure 12. A patient presenting with right leg pain found to have a type A dissection and right common iliac artery thrombosis with complete occlusion.[33]
Final Words
– Consider aortic dissection in “chest pain + ____” patients.
– Physical exam findings (such as weakness and pulse deficits) can be waxing and waning.
– Malperfusion syndromes complicate 25-30% of all aortic dissections.
– Symptoms of malperfusion syndromes can overlap and more than one major vascular bed can be involved.
– Although type B dissections are typically managed non-operatively, the presence of a concurrent malperfusion syndrome warrants evaluation for operative management.
Extra
– EM:RAP’s March 2021 Aortic Dissection Update
– Features of acute vs chronic dissection on CT
– Hounsfield units as a means to spot extravasation on CT
– Case-based learning from presentation to management
– The utility of d-dimers in the diagnosis of aortic dissection
References
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