A 67-year-old male presented with sudden onset of mid- to lower back pain, weakness and paresthesia in both legs. CT of the lumbar spine was performed to exclude spinal nerve root compression or bone lesions, both of which were not present. Additional MRI of the spine was performed to exclude spinal cord pathology.
MRI of the spine showed an ovoid paravertebral mass, adjacent to the thoracic aorta. The mass had a thin wall and a very low central signal intensity on T1, T2 and T2 TIRM, closely mirroring the signal intensity of the thoracic aorta on all sequences. (Figure 1)
These findings were suggestive of a lesion in connection with the thoracic aorta, prompting a re-examination of recent previous imaging. Non-enhanced lumbar spine CT performed 2 days earlier showed displaced intimal calcifications, which indicate the presence of an aortic dissection. (Figure 2)
Urgent triphasic contrast-enhanced thoraco-abdominal CT confirmed the presence of a Stanford type B aortic dissection. The inferior mesenteric artery was supplied by the false lumen, all other visceral arteries and the iliac arteries were supplied by the true lumen (not shown). The para-aortic mass showed slightly delayed enhancement and wash-out relative to the aorta, indicative of a contained rupture/pseudoaneurysm arising from the false lumen. (Figure 3) These findings were confirmed on catheter angiography and endovascular stent grafting was performed.
Artic dissection (AD) is one of several acute aortic syndromes (AAS). AAS encompasses a spectrum of conditions presenting with acute aortic type pain, which are clinically difficult to distinguish. Traditionally AAS includes AD, intramural hematoma (IMH) and penetrating aortic ulcer (PAU). The incidence of PAU increases with age as it is related to intimal disease in advanced atherosclerosis. IMH is thought to be associated with a small intimal tear in the majority of cases but can also be occur in the setting of a PUA. 
Aortic dissection arises following an intimal tear with blood dissecting in the media, creating a false lumen. Dissections are classified as Stanford type A when starting at the ascending aorta and type B when starting distal to the left subclavian artery. Non-A, non-B dissections originate distal to the left subclavian artery and extend proximally, involving the arch. 
The typical patient profile is a male, in the 7th decade with a history of arterial hypertension presenting with acute severe chest pain, often irradiating to the (upper) back. Atypical presentation with mild pain and predominantly signs of branch vessel occlusions is rare. [3, 4]
Chest radiograph may show a widened mediastinum and inward displacement of atherosclerotic aortic calcification but is normal in 10-40% of patients. Transesophageal cardiac ultrasound has a higher sensitivity for AD than transthoracic ultrasound but is still limited in the evaluation of the aortic arch and extent of the dissection. [3, 5]
Triphasic CT angiography is the preferred imaging modality in suspected AD. Non-enhanced phase most clearly depicts endoluminal displacement of intimal calcifications and possible spontaneously hyperdense intramural hematoma. ECG-triggered arterial phase eliminates aortic root motion artefacts and allows for optimal assessment of extent and branch vessel involvement. Venous phase is helpful in evaluating (contained) rupture and signs of organ ischemia.
The false lumen is identifiable by the “beak sign” (acute angle between aortic wall and intimal flap), “cobweb sign” (linear hypodensities representing residual media) and is often larger and lower density on arterial phase than the true lumen. Important findings to mention include entry point (Stanford A vs B), extent in supra-aortic/visceral/iliac arteries and maximal diameter of the aorta. Possible complications include organ malperfusion by branch vessel occlusion, (contained) rupture and signs of cardiac tamponade in pericardial rupture of type A dissections. 
Signs of rupture include pleural, pericardial or mediastinal fluid which may show delayed enhancement/contrast extravasation. On MRI a contained rupture/pseudoaneurysm mirrors the signal of the aorta on all sequences, as demonstrated in this case report.
Stanford type A dissections are managed surgically. Management of type B dissections is often conservative but can require surgery or endovascular stent grafting in the presence of complications. 
Take-Home Message / Teaching Points
AD can present atypically with mild pain and predominantly signs of vessel occlusion. Displaced intimal calcifications on any non-contrast imaging should prompt investigation of possible AD. A juxta-aortic mass with signal characteristic mirroring the aorta on MRI can be seen in aortic contained rupture/pseudoaneurysm.
 Ueda T, Chin A, Petrovitch I, Fleischmann D. A pictorial review of acute aortic syndrome: discriminating and overlapping features as revealed by ECG-gated multidetector-row CT angiography. Insights Imaging. 2012 Dec;3(6):561-71. doi: 10.1007/s13244-012-0195-7. Epub 2012 Nov 6. (PMID: 23129238)
 Czerny M, Schmidli J, Adler S, van den Berg JC, Bertoglio L, Carrel T, Chiesa R, Clough RE, Eberle B, Etz C, Grabenwöger M, Haulon S, Jakob H, Kari FA, Mestres CA, Pacini D, Resch T, Rylski B, Schoenhoff F, Shrestha M, von Tengg-Kobligk H, Tsagakis K, Wyss TR; EACTS/ESVS scientific document group. Current options and recommendations for the treatment of thoracic aortic pathologies involving the aortic arch: an expert consensus document of the European Association for Cardio-Thoracic surgery (EACTS) and the European Society for Vascular Surgery (ESVS). Eur J Cardiothorac Surg. 2019 Jan 1;55(1):133-162. doi: 10.1093/ejcts/ezy313. (PMID: 30312382)
 Bossone E, LaBounty TM, Eagle KA. Acute aortic syndromes: diagnosis and management, an update. Eur Heart J. 2018 Mar 1;39(9):739-749d. doi: 10.1093/eurheartj/ehx319. (PMID: 29106452)
 Hdiji O, Bouzidi N, Damak M, Mhiri C. Acute aortic dissection presenting as painless paraplegia: a case report. J Med Case Rep. 2016;10:99. Published 2016 Apr 5. doi:10.1186/s13256-016-0881-z - : Roque A, Herédia V, Ramalho M, et al. (2012) MR findings of lithium-related kidney disease: preliminary observations in four patients. Abdom Imaging. 37(1):140-146. doi:10.1007/s00261-011-9745-6. (PMID: 21717136)
 McMahon MA, Squirrell CA. Multidetector CT of Aortic Dissection: A Pictorial Review. Radiographics. 2010 Mar;30(2):445-60. doi: 10.1148/rg.302095104. (PMID: 20228328)
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License.