Dissection Detection
Author: Ari Nutovitz MD, Editor: Jeffery Greco
Aortic dissection
Case: 68 yo Male with a hx of HTN coming in complaining of epigastric abdominal pain radiating to his back. He describes the pain as tearing, worst at onset, 8/10 on pain scale and associated with nausea. He reports that he was lifting heavy boxes when he noticed the pain start. He is now also complaining of difficulty walking, due to pain in his left leg. BP 130/80, HR 60, RR 16, Pulse Ox:98% on RA. The remained of physical exam was unremarkable, no pulse deficit. You happen to have an ultrasound machine right next to you and you decide to look at the aorta..
POCUS Thoracic Aorta
● Sonographic views of the thoracic aorta viewed best with the phased array probe for adequate depth and frequency.
● Begin evaluation by obtaining the parasternal long axis (PSLA) view.
○ With the cardiac setting, the phased array probe is placed along the left sternal border, approximately in the third to fourth intercostal space. Probe marker should be pointed toward the patient's right shoulder.
● Measurement of the aortic root is obtained from the PSLA view at end diastole (AV valves should be open)
● Measurement taken from the sinus of Valsalva is recommended by the American Society of Echocardiography.[i] However, measurement of the largest diameter obtained may be more practical.
Measurements >4 cm is indicative of dilation and thoracic aneurysm.[ii]
Be sure to measure from “leading edge to leading edge” à anterior edge of anterior wall to anterior edge of posterior wall
● Other sonographic findings that may increase or decrease the likelihood of a dissection include the presence of an intimal flap or a pericardial effusion (especially a complex effusion)
● The descending thoracic aorta is difficult to fully evaluate on TTE. However, a portion of the descending thoracic aorta can be seen from the PSLA view and can also be evaluated for dilation, with a diameter no greater than 3 cm being normal.[i]
How about Suprasternal Notch View (SSNV)?
· You can also take the phased array probe that you used for the PSLA view and get an additional window to view the thoracic aorta from the suprasternal notch
· With this view you are able to visualize the aortic arch, the innominate artery, the left common carotid, and the left subclavian artery[i]
· Using a maximal normal thoracic aortic diameter of 40 mm, diagnostic accuracy in detecting dilation of the aorta was found to be 100% in certain studies[ii]
POCUS of Transabdominal Aorta
To start get the curvilinear probe from your ultrasound machine and place it on the patient epigastrium. You want the probe indicator on the side to be facing the patient’s right side and the probe itself in the transverse (horizontal) plane.
The clinician after placing the probe on the epigastrium should identify the vertebral body, aorta and IVC as shown below.
Once you obtain your orientation you could differentiate the aorta and IVC by position, and Doppler flow. The aorta typically lies anterior to the vertebral body, is circular in shape, thick-walled and pulsatile on Doppler. Whereas the IVC is less circular, thin-walled, and to the right of the aorta (Note given the IVCs close proximity to the aorta in may appear pulsatile as well).
After you get the transverse measurement of your aorta, look to see if you have an intimal flap (a line segregating the aorta). This could be better seen by flipping your probe 90 degrees with the indicator pointing towards the patients head at 12 o’clock as seen below. Now that you know the different planes to capture the view of the aorta, you scan through the aorta paying close attention to size and if there’s an intimal flap. The aorta should taper or decrease in size as you scan caudally.
Key structures you want to identify as your scanning down would be the “seagull sign”, which is the celiac artery with branches of the splenic and common hepatic as seen in image 2 above or below. (Proximal Aorta)
As you scan down you will encounter your next key structure, which is the “mantle sign” composed of the SMA, splenic vein and left renal vein as shown below. (Mid-Aorta)
Finally, you will scan down until you get to the bifurcation of the aorta where the common iliacs form. Just proximal to this is considered the distal aorta, where the diameter should be additionally measured. Additionally measure the bilateral common iliacs (normal diameter 1cm, aneurysmal >1.5cm)
Our Patient ended up having a proximal aortic dissection that radiated down the common iliac arteries and had vascular surgery consult and medical management.
Key points
1. Incidence of aortic dissection in general population ranges from 2.6->3.5 per 100,000 person-years.[i]
2. Most important high risk condition is HTN[ii]
3. Clinical triad- up to 96% of acute aortic dissections are identified[iii]
a. Abrupt onset of thoracic or abdominal pain with a sharp, tearing, and/or ripping character
b. A variation in pulse (absence of a proximal extremity or carotid pulse) and/or blood pressure (>20 mmHg difference between the right and left arm)
c. Mediastinal and/or aortic widening on chest radiograph
4. Modalities to choose and the sensitivity (sens) and specificity (spec):[iv]
a. MRA- sens-95%, spec-100%
b. CT- sens-83-95%, spec-97-100%
c. TEE- sens-98%, spec-63-96%
d. TTE-sens-77-80%, spec-93-96%
e. Aortography-sens-94%, spec-88%
f. Transabdominal US- sens-99%, spec-98%[v]
5. High clinical suspicion, along with your POCUS ultrasound can help you identify aortic dissection in a majority of cases. BUT don’t forget to still get a CTA as the gold standard until more studies on ultrasound come out.
[1] https://bostoncityem.com/2017/09/19/thoracic-aortic/
[1] https://www.nuemblog.com/new-page
[1] Goldstein SA, et al. Multimodality imaging of diseases of the thoracic aorta in adults: from the American Society of Echocardiography and the European Association of Cardiovascular Imaging: endorsed by the Society of Cardiovascular Computed Tomography and Society for Cardiovascular Magnetic Resonance. J Am Soc Echocardiogr 2015;28:119–182.
[1] Taylor RA, Oliva I, Van Tonder R, Elefteriades J, Dziura J, Moore CL. Point-of-care focused cardiac ultrasound for the assessment of thoracic aortic dimensions, dilation, and aneurysmal disease. Acad Emerg Med.
[1] https://www.sah.org.au/critical-care-ultrasound-aorta
[1] 3 AronbergDJ, Glazer HS, Madsen K, Sagel SS. Normal thoracic aortic diameters by computed tomography. J Comput Assist Tomogr1984; 8: 247–250
[1] https://umem.org/educational_pearls/2359/
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4814212/
[1] https://umem.org/educational_pearls/
[1] https://fpnotebook.com/surgery/Rad/UltrsndInAbdmnlArtcAnrysm.htm
[1] https://www.pinterest.com/pin/288230444896100575/
[1] https://www.saem.org/cdem/education/online-education/m3-curriculum/bedside-ultrasonagraphy/aaa-exam
[1] https://www.mdedge.com/emergencymedicine/article/88824/imaging/aortic-dissection
[1] https://www.saem.org/cdem/education/online-education/m3-curriculum/bedside-ultrasonagraphy/aaa-exam
[1] https://www.saem.org/cdem/education/online-education/m3-curriculum/bedside-ultrasonagraphy/aaa-exam
[1] https://www.pinterest.com/pin/51228514483911860/
[1] https://ultrasound.guide/lesson/62/Abdominal-aorta-transverse-plane
[1] https://ultrasoundregistryreview.com/abdominalTrial2.html