Imaging of the aortic root on high-pitch non-gated and ECG-gated CT: awareness is the key!

Abstract

Abstract The aortic pathologies are well recognized on imaging. However, conventionally cardiac and proximal aortic abnormalities were only seen on dedicated cardiac or aortic studies due to need for ECG gating. Advances in CT technology have allowed motionless imaging of the chest and abdomen, leading to an increased visualization of cardiac and aortic root diseases on non-ECG-gated imaging. The advances are mostly driven by high pitch due to faster gantry rotation and table speed. The high-pitch scans are being increasingly used for variety of clinical indications because the images are free of motion artifact (both breathing and pulsation) as well as decreased radiation dose. Recognition of aortic root pathologies may be challenging due to lack of familiarity of radiologists with disease spectrum and their imaging appearance. It is important to recognize some of these conditions as early diagnosis and intervention is key to improving prognosis. We present a comprehensive review of proximal aortic anatomy, pathologies commonly seen at the aortic root, and their imaging appearances to familiarize radiologists with the diseases of this location.

Full text

E D U C A T I O N A L R E V I E W Open Access
Imaging of the aortic root on high-pitch
non-gated and ECG-gated CT: awareness is
the key!
Prashant Nagpal
1
, Mukta D. Agrawal
2,3
, Sachin S. Saboo
4*
, Sandeep Hedgire
5
, Sarv Priya
1
and Michael L. Steigner
2
Abstract
The aortic pathologies are well recognized on imaging. However, conventionally cardiac and proximal aortic
abnormalities were only seen on dedicated cardiac or aortic studies due to need for ECG gating. Advances in CT
technology have allowed motionless imaging of the chest and abdomen, leading to an increased visualization of
cardiac and aortic root diseases on non-ECG-gated imaging. The advances are mostly driven by high pitch due to
faster gantry rotation and table speed. The high-pitch scans are being increasingly used for variety of clinical
indications because the images are free of motion artifact (both breathing and pulsation) as well as decreased
radiation dose. Recognition of aortic root pathologies may be challenging due to lack of familiarity of radiologists
with disease spectrum and their imaging appearance. It is important to recognize some of these conditions as early
diagnosis and intervention is key to improving prognosis. We present a comprehensive review of proximal aortic
anatomy, pathologies commonly seen at the aortic root, and their imaging appearances to familiarize radiologists
with the diseases of this location.
Keywords: High-pitch CT, Aortic root, CT angiography, Aneurysm, Aortic valve
Key points
Advances in CT technology have allowed acquisition
of imaging without cardiac pulsation artifact even
without ECG gating.
Such protocols are being increasingly used for non-
aortic indications due to better image quality and
less patient radiation dose.
Aortic root and ascending aortic pathologies can be
incidentally seen in patients getting a CT for non-
aortic indications.
Knowledge of the pathologies specific to this part of
the aorta and their imaging appearance is useful for
diagnosis and early treatment.
Background
The diseases of the aorta are life threatening and are be-
ing increasingly diagnosed due to increased use and
availability of imaging [1]. Epidemiologically, the inci-
dence of the most life-threatening aortic disorder, aortic
dissection (AD), has increased over time, which could be
due to better detection with improved imaging or in-
creased longevity [1,2]. More importantly, the advances
in imaging technology have facilitated the assessment of
cardiac structures and proximal aorta on “routine”non-
electrocardiogram (ECG)-gated chest CTs. These ad-
vances are mostly driven by faster gantry rotations, faster
table speed, and sometimes by the use of more than one
X-ray source, allowing high-pitch exams. Such high-
pitch CT scans have allowed aortic evaluation even with-
out ECG gating [3–5]. The high-pitch scans are being
increasingly used for non-aortic clinical indications be-
cause of lack of motion (both breathing and pulsation)
artifacts as well as decreased radiation dose [3].
© The Author(s). 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License,
which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give
appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if
changes were made. The images or other third party material in this article are included in the article's Creative Commons
licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons
licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain
permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
* Correspondence: saboo_100@yahoo.com
4
Department of Radiology, University of Texas Health Center, San Antonio,
TX, USA
Full list of author information is available at the end of the article
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Nagpal et al. Insights into Imaging (2020) 11:51
https://doi.org/10.1186/s13244-020-00855-w

Studies comparing the high-pitch and routine scan-
ning for pulmonary embolism CT have shown improved
image quality, decreased artifacts, and decreased radi-
ation dose with high-pitch imaging [6,7]. This improve-
ment in image quality is associated with better
delineation of cardiovascular structures. A clinical trial,
Cardiac Pathologies in standard chest CT (CaPaCT)
study [8], and other studies [9,10] have highlighted that
there is increased detection of cardiovascular incidentals
on routine non-ECG-gated chest CTs. In a study, Ver-
dini et al. [10] showed that the sensitivity for detection
of cardiovascular incidentals correlates with the reader
experience with increased sensitivity if the reader has
dedicated cardiac training. In a single-center retrospect-
ive study, Seechi et al. [9] showed that incidental cardio-
vascular findings were seen in > 50% of retrospectively
evaluated cases (124/237), out of which aortic “inciden-
tal”finding was presented in 34.9% cases (80/229). Sig-
nificantly, they also remarked that cardiovascular
“incidentals”were not mentioned in nearly 70% of cases.
While these “incidental”findings without clinical context
have a concern of overdiagnosis and increase in patient
management burden, delayed diagnosis of a critical find-
ing (especially proximal aortic finding) may cause signifi-
cant morbidity and mortality.
The limitations to the diagnosis of the aortic root and
ascending aortic diseases include lack of familiarity of
the anatomy and the imaging appearance of specific con-
ditions among non-cardiothoracic radiologists. More-
over, improved visualization of the proximal aorta on
scans obtained on scanners with faster gantry rotation
and their interpretation by radiologists that may not be
familiar with these diseases has added to this challenge.
Although technological advances have happened in
other aortic imaging modalities like magnetic resonance
angiography, and trans-esophageal echocardiography [2],
incidentally seen aortic pathologies are mostly described
with CT. Hence, we aim to present a review of proximal
aortic anatomy, various disorders that affect the aortic
root, and their imaging appearances to familiarize radiol-
ogists with the diseases of this location.
Main text
Dedicated CT imaging for aortic root evaluation
While this review is focused on detection of aortic root
and proximal aortic pathologies on non-ECG-gated CT,
the knowledge of CT imaging dedicated for thoracic aortic
evaluation is important. CTA is the most commonly used
modality for aortic evaluation. The accuracy and hence
use of CTA for other vascular applications like coronary
artery imaging is also expanding [11]. CT is fast, non-
invasive, widely available, and allows evaluation of entire
aorta with very high (nearly 100%) sensitivity and specifi-
city for the diagnosis of aortic pathologies [2,4,12]. CT
imaging of the proximal aorta requires appropriate timing
for peak aortic contrast enhancement and conventionally
needs ECG gating to prevent artifacts from transmission
of cardiac pulsations. ECG-gated CTA is still considered
as the standard of care for follow-up and management de-
cisions of the aortic root and ascending aortic pathologies
[13,14]. The comparison of image quality of the heart and
proximal aorta on a routine non-ECG-gated exam, high-
pitch non-ECG-gated exam, and ECG-gated CTA exam is
shown in Fig. 1. ECG gating can be performed prospect-
ively or retrospectively. In prospective ECG triggering, the
tube current is switched on (equivalent to image acquisi-
tion) only during a specific phase (typically diastole) of the
cardiac cycle with significantly reduced radiation dose as
compared to retrospective ECG triggering whereby multi-
phase data is acquired through the cardiac cycle, and the
desired phases are selected for reconstruction afterward.
Retrospective triggering leads to higher radiation dose.
The use of ECG-based tube current (mA) modulation sig-
nificantly decreases the dose in retrospectively triggered
scans. The dedicated CT protocol for aortic pathologies is
summarized in Table 1.
3D imaging and centerline analysis
When evaluating relatively tortuous segments like aortic
arch, precise localization of pathology should be per-
formed using the double oblique technique. The aortic
diameters should always be assessed in the short axis to
the centerline using a double oblique technique on a 3D
workstation to prevent overestimation on raw axial CT
images. The maximum transverse diameter of the aorta
perpendicular to the centerline parallel to the wall of
that segment of the aorta is measured. These techniques
allow reproducible aortic measurements at specific ana-
tomic landmarks. The maximum diameter of the SOV is
measured in short axis from the sinus-to-trigon, and the
ascending aorta is typically measured at the level of the
right pulmonary artery [2,15]. Since the treatment and
follow-up of many aortic pathologies are based on size
cutoff, a standardized methodology is very important
(class A recommendation) [13]. Other 3D-techniques,
including volume rendering (VR) and maximum inten-
sity projections (MIP) images, can be reconstructed from
the raw CT images. These images are supplementary to
the primary CT angiography (CTA) images and are
helpful for surgical planning [2,16]. Cinematic rendering
(CR), a relatively new 3D technique which allows realis-
tic shadowing effects which enable clear representation
of the relative positions of objects within the imaged vol-
ume, is also being increasingly used for aortic pre-
surgical planning and differentiating pathologies from
normal variants [17,18]. As compared to VR, CR has
improved ability to visualize the spatial relations (par-
ticularly in the through-plane) [18].
Nagpal et al. Insights into Imaging (2020) 11:51 Page 2 of 14

Aortic anatomy—aortic root and ascending aorta
The left ventricle outflow tract (LVOT) continues into
the systemic circulation as thoracic aorta. The aortic
root is the bridge between the LVOT and the ascend-
ing aorta. Aortic root is the proximal-most segment
of the aorta from the aortic annulus to the sinotubu-
lar junction. In surgical literature, the aortic annulus
is described as the plane of attachment of aortic
cusps with the aortic wall [19]. In radiology and car-
diology literature, the aortic annulus is described as
the nadir of the attachment of the aortic leaflets.
Components of the aortic root include the aortic
annulus, aortic leaflets with their attachments and
trigones, the sinuses of Valsalva (SOV), and the sino-
tubular junction (STJ) (Fig. 2). The three leaflets form
the aortic valve and provide its main sealing mechan-
ism [20]. In healthy individuals, the aortic root is dir-
ectly anterior to the left atrium with no soft tissue in
between (Fig. 3). SOV are the three bulges in the aor-
tic root, between the valve and the sinotubular junc-
tion (Fig. 2). SOV are named based on the coronary
origin. The anterior bulge from which the right cor-
onary artery normally originates is the right SOV, and
theleftposteriorbulgefromwhichtheleftcoronary
artery normally originates is the left SOV. The right
posterior bulge which faces the interatrial septum and
has no coronary artery origin is called the non-
coronary SOV. The illustrative and CTA anatomy of
the SOV is highlighted in Fig. 4. The ascending aorta
is the part of the aorta between the sinotubular junc-
tion and the origin of the first arch vessel. Normally,
the proximal aorta lies posterior and to the right of
the pulmonary artery.
The normal diameter of the aortic root and ascending
aortic diameter is influenced by patient age, gender, and
body surface area. In 3431 Framingham Heart Study
participants, ECG-gated CT showed mean diameter of
34.1 ± 3.9 mm for the proximal thoracic aorta for men
and 31.9 ± 3.5 mm for women [21]. Similarly, a study on
SOV diameter in adults demonstrated that mean diam-
eter in end-diastole is 3.2 ± 0.6 cm for men and 2.9 ±
0.5 cm for women [22]. Due to variations in size with pa-
tient age, gender, and body surface area, having a single
diameter cutoff for abnormal diameter is frequently
Fig. 1 A 67-year-old man with medically managed type B aortic dissection and metastatic colon cancer. Conventional non-ECG-gated CT chest
image, high-pitch non-ECG-gated CT image, and ECG-gated CTA image highlighting improved visualization of heart and proximal aortic
structures with high-pitch exam even without ECG gating. Abbreviations: LA, left atrium; LV, left ventricle; RV, right ventricle; S, sinus of Valsalva;
DA, descending thoracic aorta
Table 1 Dedicated CT angiography protocol for thoracic aortic
pathology
Thoracic aorta CTA protocol at our institute
Scan range Full chest coverage from the thoracic outlet through
the lung base
Contrast
phases
1. Non-contrast high-pitch non-ECG-gated chest
(pitch factor > 3)
2. Contrast-enhanced ECG-gated chest
ECG gating Prospective with automatic single-phase selection
based on the HR (75% for low HR and 40% for high HR)
Radiation
exposure
kV automatically adjusted from the topogram otherwise
adjusted based on patient size 120 (BMI > 30), 100 (BMI
20–30), 80 (BMI < 20)
mA automatically adjusted from the topogram
Contrast Iopamidol 370 mg/mL (Bracco Diagnostic, Princeton, NJ,
USA)
Contrast dose 100 mL
Injection rate 4 cc/s
Slice thickness 3.0 mm thickness with 3.0 mm interval in axial, coronal,
and sagittal planes
1 mm thickness with 0.8 mm interval for 3D
postprocessing and double-oblique measurements
High-pitch scanning possible at dual-source scanners
CTA CT angiography, ECG electrocardiogram
Nagpal et al. Insights into Imaging (2020) 11:51 Page 3 of 14

inaccurate. However, the traditionally accepted values
for the upper limits of normal diameter for SOV and the
STJ are 4 cm and 3.6 cm for males and 3.6 cm and 3.2
cm for females respectively [23,24]. The maximum
transverse aortic diameters are measured in the short
axis using the double oblique method or centerline ana-
lysis at defined anatomical landmarks.
Lesions of the proximal aorta
Ascending aortic and sinuses of Valsalva aneurysm
An aortic aneurysm is defined as an abnormal perman-
ent dilatation of the aorta to greater than 1.5 times its
expected normal diameter [2]. Among all thoracic aortic
aneurysms, 60% comprises of the aortic root, ascending
aorta, or both [25]. True aneurysms involve all the layers
Fig. 2 Illustration demonstrating the anatomy of the aortic root
Fig. 3 Reformatted 3-chamber view (a) and axial (b) CTA of the heart and proximal aorta showing the normal relation of the aortic root to the
left atrium. No soft tissue should be present between the wall of the left coronary sinus and the left atrium (black arrow). In patients with aortic
root infection, this space (black arrow) is increased with soft tissue. Abbreviations: AA, ascending aorta; LA, left atrium; LV, left ventricle; PA,
pulmonary artery; An, annulus; S, sinus of Valsalva; STJ, sinotubular junction
Nagpal et al. Insights into Imaging (2020) 11:51 Page 4 of 14

of vessel wall while a false aneurysm/pseudoaneurysm
represent a disruption of layers of the wall of the aorta
with containment of extravasated blood by surrounding
tissues forming a pseudo-capsule [26]. Based on the nor-
mal variation in the size of the proximal aorta (described
in “Aortic anatomy—aortic root and ascending aorta”
section), the American College of Radiology (ACR) white
paper on management of incidentals on thoracic CT
suggest a size of 5 cm as the cutoff for a proximal aortic
aneurysm [27]. When using such approach of a cutoff
number, it should be kept in mind that aortic diameter
is a factor of sex, age, patient size, and the segment of
the aorta [13]. If the maximum aortic diameter is be-
tween the upper limits of normal (SOV, STJ: 4 cm, 3.6
cm for males and 3.6, 3.2 cm for females [23,24]) and
not meeting the criteria for aneurysm, the abnormal seg-
ment of the aorta should be reported as dilated [27]. For
increased accuracy, the maximum aortic diameter can
be indexed to body surface area. For proximal aorta, the
value of 2.1 cm/m
2
as an upper limit of normal and a
value of 2.75 cm/m
2
as a cutoff for aneurysm has been
described to have specificity of > 95% [14,23]. The pres-
ence of connective tissue disease can be an important
determinant in diagnosis and management of an aortic
aneurysm. As per American Heart Association and
European Society of Cardiology guidelines [13,14], pa-
tients with known connective tissue disease should be
treated early at smaller aortic diameters because of in-
creased risk of aortic dissection and rupture. In patients
without any aortopathy, guidelines suggest a cutoff of ≥
5.5 cm. For patients with bicuspid aortic valve or Marfan
syndrome, a cutoff for treatment is between 4.5 to 5.5
cm, depending on risk factors and clinical context [2,13,
14]. Loeys-Dietz syndrome patients either follow similar
criteria as Marfan syndrome patients or are treated at a
diameter ≥4.2 cm, given lack of consensus [2,13,25].
Within the aortic root, aneurysms may be seen iso-
lated at the SOV or involving the entire aortic root.
Combined involvement of aortic annulus, SOV, and
sinotubular junction, also known as annuloaortic ectasia,
is characteristic for connective tissue disorders like Mar-
fan syndrome and Ehlers-Danlos syndrome (Fig. 5)[15].
On the other hand, isolated SOV aneurysm is mostly
congenital and less commonly associated with infection,
atherosclerosis, degenerative disease, or trauma [28].
Congenital SOV aneurysm is seen in approximately 0.1%
of the population, is common in Asians, and is most
commonly seen at the right aortic sinus followed by the
noncoronary sinus (Fig. 6)[15]. SOV aneurysm can also
be associated with other congenital heart diseases like
ventricular septal defect (30–60%), aortic insufficiency
(20–30%), bicuspid aortic valve (10%), aortic stenosis, in-
fundibular pulmonary stenosis, patent ductus arteriosus,
left ventricular non-compaction, atrial septal defect, cor-
onary artery anomalies, and persistent left-sided superior
vena cava [15]. Commonly, these aneurysms are diag-
nosed incidentally. However, symptoms may be related
to aneurysm rupture or mass effect on the adjacent
structures [28]. The rupture most commonly happens
into the right ventricle and the right atrium. Other less
common sites include right ventricular outflow tract, left
ventricle, interventricular septum, or left atrium [15,28].
The rupture into the pericardium is very rare but has
high mortality [29]. The other sites of rupture have rela-
tively less mortality, with mean survival after diagnosis
being 3.9 years [28]. The treatment and follow-up for
Fig. 4 An illustration (a) and a CTA short axis image (b) through the sinuses of Valsalva highlighting the nomenclature and anatomy
Nagpal et al. Insights into Imaging (2020) 11:51 Page 5 of 14

unruptured SOV aneurysm are frequently debated. It is
suggested that unruptured SOV aneurysms should be
anticoagulated and followed up every 6 months [30].
Pseudoaneurysm
Blunt thoracic trauma (related to motor vehicle accidents,
falls, and sports injuries), post-surgical, and infection are
the most common cause of the pseudoaneurysms of the
heart or the thoracic aorta [31]. Pseudoaneurysms can be
complicated with fatal rupture, fistula formation, and com-
pression of surrounding structures (Fig. 7). Overt free rup-
ture can occur due to complete disruption of all of three
layers of the aortic wall leading to massive hematoma with
resultant hemodynamic instability. Patients with an aortic
pseudoaneurysm are characterized on imaging with peri-
vascular hematoma sealed off by periaortic structures like
mediastinum, pleura, or pericardium. Non-contrast scan is
helpful to identify areas of contrast enhancement and to
differentiate pseudoaneurysm from calcifications and prior
surgical changes. Management of aortic pseudoaneurysm
involves either endovascular intervention or open surgical
repair and is independent of its size [14]. Rarely, cardiac
pseudoaneurysm may be managed medically with serial im-
aging surveillance [31].
Aortic dissection (AD)
An AD is characterized by an intimomedial tear of the
aortic wall with subsequent separation of the layers. Dis-
sections most commonly arise in the ascending aorta 1
cm distal to the sinotubular junction or in the descend-
ing aorta at or just beyond the isthmus of thoracic aorta
because of maximum wall shear stress [32]. Spontaneous
dissections that originate in the aortic root are rare.
Most AD with aortic root involvement is due to retro-
grade dissection from the ascending aorta which in-
creases chances of rupture into the pericardial space
causing cardiac tamponade, dissect into coronary artery
origin, or create aortic valvular regurgitation [33]. These
complications are life-threatening and therefore warrant
Fig. 5 A 43-year-old man with Marfan syndrome and bicuspid aortic valve: sagittal (a) and axial (b) CTA images shows aortic root aneurysm with
dilatation centered at the sinuses of Valsalva (white arrow in a) with effacement of the sinotubular junction and normal caliber ascending aorta
and bicuspid aortic valve (black arrow in b). A “tulip-shaped”configuration of the aortic root is better appreciated on the volume rendered
image (c)
Fig. 6 A 41-year-old-man with incidentally detected sinus of Valsalva aneurysm. Non-contrast chest CT (a) obtained as a work-up for fever
showed an incidental dilatation (white arrow) of the aortic root (CT was done with high pitch, enabling the anatomic evaluation of aortic root
despite the lack of ECG gating). Follow-up contrast-enhanced-gated CTA images (band c) showing an incidental aneurysm of the noncoronary
sinus of Valsalva (black arrow)
Nagpal et al. Insights into Imaging (2020) 11:51 Page 6 of 14

urgent surgical repair. The involvement of the origin of
coronary arteries can lead to ischemia from extension of
the dissection into the ostia or by narrowing from the
intimomedial flap within the aorta without extension
into the coronary artery. The right coronary artery is
most commonly affected [32].
CTA with ECG synchronization is the standard of
care for the diagnosis of AD with very high sensitivity
and specificity [12,34]. However, the recent British
Society of Cardiovascular Imaging/British Society of
Cardiovascular CT guidelines mention that based on
scanner capabilities, motion-free CT imaging without
ECG synchronization on newer scanners may be
appropriate for suspected acute aortic syndrome
(AAS) [35]. On non-contrast or inappropriately timed
contrast-enhanced CT, diagnosis of AD may be chal-
lenging (Fig. 8a). On non-ECG-gated CT/MRI images,
complications of ascending aortic dissection (such as
extension of dissection into the coronaries, or rupture
into pericardial space) can be missed due to motion
artifact, and ECG-gated images or high-pitch CTA (if
scanner is capable) should be obtained whenever
there is high suspicion (Fig. 8b, c).
Intramural hematoma (IMH)
Aortic IMH is pathologically characterized by a
hematoma in the media of the aortic wall with an ab-
sence of a well-defined enhancing false lumen. Initially,
these were thought to be from rupture of vasa vasorum
but increasingly small intimal ulcer like projections are
being recognized which is proposed to lead to
hematoma within the wall [36]. As per the analysis of
the International Registry of Acute Aortic Dissection
[37], the clinical presentation and prognosis of type A
(aortic root and ascending aortic) IMH is similar to type
A AD. However, type A IMH patients were more likely
to have periaortic hematoma and pericardial effusion
which are important to recognize on imaging.
Non-contrast CT is very helpful in patients with IMH
as high attenuation of wall hematoma is characteristic
with an absence of intimal flap or enhancement on
contrast-enhanced CT (Fig. 9). MRI using vessel wall im-
aging, black blood, and cine gradient echo sequences
may be used as a problem-solving tool to differentiate
IMH from atherosclerotic wall thickening and thrombus
and to characterize the age of IMH [12,36]. The compli-
cations and management of IMH is similar to AD.
Fig. 7 A 55-year-old female with Staphylococcus aureus sepsis, cardiogenic shock, and pulmonary lesions concerning for septic emboli. Axial (a)
non-ECG-gated chest CT showed hyperdense purulent pericardial effusion (black arrow in a) with a contrast filled outpouching at the aortic root
(white arrow) and left pleural effusion (star). The contrast outpouching was not recognized by a non-cardiovascular imager. Follow-up axial (b)
and coronal (c) high-pitch CT images (venous phase) after 1 month of treatment showed resolution of pericardial effusion but enlarged
pseudoaneurysm (white arrow) exerting mass effect on the left anterior descending coronary stent. Surgical repair of the pseudoaneurysm with
coronary artery bypass grafting was performed due to continued chest pain
Fig. 8 A 75-year-old man with shortness of breath and chest pain that underwent high-pitch CTA pulmonary artery (a) that was negative for
pulmonary embolism but a concern for aortic dissection was raised by the cardiovascular radiologist. Aortic protocol CTA confirmed a type A
dissection with entry point adjacent to coronary bypass graft (arrow in band c) that was very subtle on the CTA pulmonary artery (a)
Nagpal et al. Insights into Imaging (2020) 11:51 Page 7 of 14

Proximal aortic infections
Most commonly, proximal aortic infections are periannular
and supraannular extensions from aortic valve endocarditis.
Sometimes, aortic root infection may be incidentally seen in
patients getting CT for fever or sepsis evaluation. Fat strand-
ing around the proximal aorta, obliteration of pericardial
and mediastinal fat, development of soft tissue attenuation
at the aortic root (especially between the aortic wall and the
left atrium, Fig. 10), and a frank fluid collection with enhan-
cing rim are often the imaging features of a perivalvular ex-
tension of the infection. The complications include an
extension to the mitral valve via aortomitral intervalvular
fibrosa, thrombosis, or narrowing of the coronary artery
(Fig. 10), fistulous connections with the adjacent cardiac
chambers, or rupture [38–40]. Aortic root involvement can
also be seen as wall thickening or a pseudoaneurysm.
Imaging plays an important role in the diagnosis of
these infections and is very helpful for pre-surgical plan-
ning. With an improved spatial and temporal resolution
of CT, even valve vegetations can sometimes be recog-
nized [41]. Although transthoracic and transesophageal
echocardiograms are often the first imaging modalities
in the diagnosis of infective endocarditis, ECG-gated
CTA provides a comparatively better anatomic assess-
ment in regards to the extension of periannular abscess
into adjacent cardiac valves, myocardium, coronary ar-
teries, and pericardial space which has been highlighted
in the recent studies and guidelines [42–45].
Aortitis
Inflammation of the aortic wall can be either infectious or
non-infectious. Both infectious and non-infectious etiolo-
gies can involve proximal aorta. Among the inflammatory
etiology, aortic involvement is classically seen with large
vessel vasculitis most commonly giant cell arteritis (GCA)
and Takayasu’s arteritis (TA). Chronic infectious causes of
aortitis, including HIV, tuberculosis, and syphilis, demon-
strate a non-specific imaging appearance of aneurysm
Fig. 9 A 72-year-old male with chest pain after conventional angiography done as a part of valve-in-valve surgical clearance. Non-contrast (a)
and contrast-enhanced (b) CTA images showing hyperdense aortic wall thickening at the sinotubular suggesting focal intramural hematoma,
related to intimal injury from difficult right coronary artery cannulation
Fig. 10 A 33-year-old male with a history of intravenous drug abuse with infectious endocarditis status post aortic valve replacement, presenting
with fever. Axial (aand b) and volume-rendered (c) CTA images showing soft tissue (star) between the aortic root and the left atrium consistent
with a paraaortic abscess. A pseudoaneurysm (white arrow) is also seen, and there is a mass effect on the left main coronary artery (black arrow)
with moderate narrowing
Nagpal et al. Insights into Imaging (2020) 11:51 Page 8 of 14

formation with or without wall thickening which in the
absence of other supporting imaging findings cannot be
reliably distinguished based on their imaging appearance
[46,47]. Other etiologies of aortic root aortitis include
radiation-induced vasculitis in patients with prior thera-
peutic radiation to the chest wall and are often encoun-
tered in the form of accelerated wall calcifications [48].
Within large vessel vasculitides, GCA is more likely to in-
volve the aortic root and ascending aorta [49] while TA
most commonly involves abdominal aorta followed by de-
scending thoracic aorta and aortic arch [50,51].
On imaging, it typically manifests as wall thickening
and enhancement. On CT, the wall thickening can
mimic intramural hematoma especially in the absence of
non-contrast images; the differentiation of which is cru-
cial. The inflammatory wall thickening is not hyperdense
(< 40 HU) on non-contrast images and reveals enhance-
ment on post-contrast and delayed images as compared
to non-enhancing hyperdense (> 50 HU) wall thickening
of IMH [52]. The pattern is also important; circumferen-
tial thickening is a feature of inflammatory aortitis while
incomplete crescentic thickening is a feature of IMH. If
confusion persists, T1-weighted black blood double in-
version recovery images before and after contrast
enhancement [53] or FDG-PET (Fig. 11) can be used as
a problem-solving tool [54,55]. Aortitis with coronary
involvement can present as ostia narrowing leading to
their ischemia or diffuse wall thickening. On imaging,
the sequelae of aortitis include calcifications, aneurysm,
pseudoaneurysm, and thrombosis [56].
Tumors and tumor-like conditions at the aortic root
Tumors and tumor-like conditions adjacent to the
proximal aorta can mimic aortic root pathologies and
may have overlapping clinical characteristics. Lymph-
omas, in particular, diffuse large B cell type, and mel-
anoma have a predilection to pericardial space while
the metastatic tumor deposits from these primary ma-
lignancies can be encountered at the aortic root in
the form of enhancing mass like nodularity with asso-
ciated pericardial effusion [57]. Mediastinal lymphoma
can be seen as isodense to hyperdense thickening on
CT with homogenous modest enhancement on post-
contrast images [58]. Aortopulmonary window para-
gangliomas adjacent to the aortic root arise from the
parasympathetic system and are rare tumors along the
proximal aorta. They are usually benign, arterially en-
hancing homogenous tumors (Fig. 12). They can
Fig. 11 A 47-year-old male with atypical chest pain. Axial CTA image (a) shows circumferential wall thickening (arrow) of the ascending aorta.
Axial fused and coronal maximum intensity projection (MIP) F-18 FDG PET-CT images (band c) shows increased FDG uptake in aortic wall (arrow)
consistent with active vasculitis (temporal artery biopsy showed giant cell arteritis)
Fig. 12 A 57-year-old male with chest pain. Axial (a) CTA image shows hypervascular mass between the ascending aorta and the main
pulmonary artery (arrow). Further characterization with MRI (b–d) was performed, the mass had bright T2 signal with increased perfusion and
wash out on delayed images. Pathology confirmed paraganglioma
Nagpal et al. Insights into Imaging (2020) 11:51 Page 9 of 14

recruit vascular supply from coronaries arteries and
maybe in close relation to the aortic root [59]. Their
intense vascularity should warrant against percutan-
eous biopsy. These can be differentiated from true
aortic root pathology based on maintenance of fat
planewithaorticwallwhileconfirmationofthediag-
nosis can reliably be obtained with an octreotide or
131
I-metaiodobenzylguanidine scan [60].
Non-neoplastic aortic root pathologies include aortic
valve pannus of the prosthetic valve and leaflet
thrombus. Pannus is a diffuse or mass-forming inflam-
matory process often originating from a suture [61]. The
fibrotic proliferation can often occur on the ventricular
side and appear as a focal round hypodensity [62]. The
distinction of pannus from thrombus may be difficult
but is important as both the entities have different thera-
peutic approaches. The pannus characteristically occurs
after 12 months, is underneath the valve surface extend-
ing from the sewing ring or the metal ring, may show
contrast enhancement, and has CT attenuation of > 145
Hounsfield units (HU) (Fig. 13). The thrombus, on the
other hand, can occur at any time, can be above or
below the aortic prosthetic aortic leaflets, does not en-
hance, and has an attenuation of < 145 HU (Fig. 14)
[63]. Thrombus with an attenuation of < 90 HU is asso-
ciated with the higher success of lysis [64]. A mimic of
aortic thickening and mediastinal lymph node is the
superior aortic recess. It is the most cephalad portion of
the transverse pericardial sinus. Fluid attenuation on
non-contrast CT images, absence of contrast enhance-
ment, and characteristic location (Fig. 15) helps to differ-
entiate this entity from other pathologies [65].
Post-surgical appearance
Normal post-surgical appearance
A detail description of various aortic surgeries and their
postoperative appearances is beyond the scope of this
article and is well described in literature dedicated to
this topic [66]. We discuss some expected post-surgical
appearance of the proximal aorta that general radiolo-
gists may encounter and should be familiar with, as it
may mimic abnormal conditions. Evaluation of post-
operative thoracic aorta is typically performed with
unenhanced and arterial phase CTA study. Knowledge
Fig. 13 A 64-year-old male status post aortic valve replacement using Hall tilting disc valve (Medtronic, Inc., Minneapolis, Minn) and shortness of
breath with increasing prosthetic aortic valve gradient on echocardiogram. Coronal oblique CTA reconstructed images reveal ovoid
hypoattenuating lesion (Hounsfield unit, 172) at the inferior surface of the valve ring causing restricted valve opening, consistent with
pannus formation
Fig. 14 A 67-year-old female status transcatheter aortic valve replacement (TAVR) using Sapiens valve (Edwards Lifesciences) with suspected
aortic valve lesion on echocardiogram. Axial (a) and coronal oblique (b) reconstructed CTA images reveal biconvex hypoattenuating (Hounsfield
unit, 74) leaflet and left cusp thickening causing restricted motion (seen on cine), consistent with thrombus
Nagpal et al. Insights into Imaging (2020) 11:51 Page 10 of 14

of pertinent clinical information, including surgical
notes, is important to recognize and differentiate normal
from abnormal post-surgical appearances.
Felt pledgets or sutures used during surgery can be
mistaken for small pseudoaneurysm on a contrast-
enhanced study. CT imaging can differentiate these en-
tities as felt appears hyperdense to blood pool on unen-
hanced CT (Fig. 16) while pseudoaneurysm appears
isodense to the blood, and felt sutures are typically sym-
metric at the anastomosis. If incidentally seen in a pa-
tient with chest pain, comparison with prior exam or a
repeat ECG-gated CT angiography (with non-contrast
images) should be obtained for differentiation as man-
agement of these entities is different.
The cardiopulmonary bypass cannula required dur-
ing various cardiothoracic surgical procedures is typ-
ically placed at the ascending aorta. An arterial
perfusion cannula may also be placed through a graft
side branch (if graft repair of ascending aorta is being
performed) to allow antegrade systemic perfusion dur-
ing the surgery till distal anastomosis is complete
[67]. The bypass cannula site may appear as an out-
pouching at CT (Fig. 17), thereby mimicking a pseu-
doaneurysm or leak. Correlation with the surgical
report or directly with the surgeon and correlation
with patient symptoms is critical to avoid this confu-
sion. On CT images, it appears as a well-defined,
broad-based, outpouching of contrast beyond the
Fig. 15 A 65-year-old male with acute chest pain. Contrast enhanced axial CTA (a) image shows asymmetrical hypodensity adjacent to right
lateral wall of ascending aorta (arrow). Non-contrast CT (b) confirmed hypodense fluid attenuation consistent with superior pericardial recess;
potential mimic of intramural hematoma
Fig. 16 A 89-year-old female patient with acute chest pain. Contrast enhanced axial CT (a) image was suspicious of a small pseudoaneurysm
(arrow); however, non-contrast CT (b) image identified the outpouching as surgical pledget (arrow)
Nagpal et al. Insights into Imaging (2020) 11:51 Page 11 of 14

normal contour of the aortic wall and in direct com-
munication with the aortic lumen (Fig. 17)[60].
Abnormal post-surgical appearance
Infections related to synthetic materials (e.g., suture) or
concomitant mediastinal infection may be seen on CT
imaging as the following: (a) focal saccular outpouching
(pseudoaneurysm), usually with a narrow neck, that con-
tains contrast material and arises from the aortic wall (Fig.
10); (b) periaortic soft tissue stranding or edema; and (c)
periaortic gas [66,67]. An aortic pseudoaneurysm close to
the aortic cannulation site may be difficult to differentiate
but is a surgical emergency with associated high operative
morbidity and mortality, given the high likelihood of a co-
existent infectious state. However, it is critical to differen-
tiate pseudoaneurysm from aortic cannulation because of
difference in management. Pseudoaneurysm shows irregu-
lar outline and is associated with a surrounding hematoma
(Fig. 18). Also, it is uncommon to develop a pseudoaneur-
ysm in the middle of a surgical graft as they most com-
monly occur at the anastomotic suture lines.
Conclusions
Aortic root pathologies are being increasingly recognized
with use of newer-generation CT scanners which allow
high-pitch exams with lower contrast and radiation dose.
Awareness of aortic root pathologies is essential for early
recognition and initiation of life-saving management. On
conventional routine chest CT exams, cardiac motion af-
fects precise delineation of the proximal aorta; therefore, in
patients with suspected aortic root pathology, ECG-gated
imaging or high-pitch CTA is recommended. Currently,
the use of ECG gating is the “standard of care”.Reviewof
operative record and comparison with non-contrast scan
can help to distinguish normal versus abnormal findings in
post-operative patients.
Fig. 17 A 58-year-old female post-op day 10 status post supracoronary ascending aorta replacement with graft repair and concern of
pseudoaneurysm on a pulmonary embolism rule-out CT (not shown). Axial (a) and sagittal (b) high-pitch CTA images show a smooth contrast
filled outpouching from proximal graft (white arrow) near to the anastomosis (black arrow in a). This smooth outpouching is a normal post-
operative appearance, related to over sewn reperfusion catheter stump from cardiopulmonary bypass during surgery
Fig. 18 A 69-year-old male, 6-week status post open ascending aortic aneurysm repair with chest pain, presented with acute chest pain. Axial (a),
coronal (b), and sagittal (c) CTA images show a smooth outpouching (black arrow) near graft repair consistent with perfusion catheter stump
(expected post-surgical finding). Additionally, there is another irregular outpouching (white arrow), and irregularity and associated anterior
pericardial hematoma (star) is concerning for a pseudoaneurysm. The patient had an emergent repeat surgical graft repair
Nagpal et al. Insights into Imaging (2020) 11:51 Page 12 of 14

Abbreviations
AAS: Acute aortic syndromes; AD: Aortic dissection; CT: Computed
tomography; CTA: CT angiography; CR: Cinematic rendering;
ECG: Electrocardiogram; HU: Hounsfield units; IMH: Intramural hematoma;
LVOT: Left ventricle outflow tract; MIP: Maximum intensity projection;
MRI: Magnetic resonance imaging; SOV: Sinuses of Valsalva; VR: Volume
rendering
Authors’contributions
All authors contributed for the elaboration, critical revision, and review of
intellectual content of the manuscript. All authors read and approved the
final manuscript.
Funding
None
Availability of data and materials
Not applicable
Ethics approval and consent to participate
Need for ethics approval and individual consent is waived for educational
review.
Consent for publication
Not applicable
Competing interests
None
Author details
1
Department of Radiology, University of Iowa Hospitals and Clinics, Iowa City,
IA, USA.
2
Department of Radiology, Non-invasive Cardiovascular Imaging,
Brigham and Women Hospital, Harvard Medical School, Boston, MA, USA.
3
Department of Radiology, Oklahoma University Health Sciences Center,
Oklahoma City, OK, USA.
4
Department of Radiology, University of Texas
Health Center, San Antonio, TX, USA.
5
Department of Radiology,
Cardiovascular Imaging, Massachusetts General Hospital, Harvard Medical
School, Boston, MA, USA.
Received: 7 December 2019 Accepted: 2 March 2020
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