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KEY FACTS

Terminology
- Aneurysm arising from infection of arterial wall, usually bacterial
Imaging
- Rapidly growing focal saccular aneurysm arising eccentrically from aortic wall
- Periaortic soft tissue stranding, edema, and fluid
- Adjacent vertebral body or psoas abnormalities due to spread of infection
- Increased uptake of labeled leukocytes at site of aneurysm
Top Differential Diagnoses
- Atherosclerotic aneurysm
- Inflammatory aneurysm
- Contained rupture
- Aortoenteric fistula
Pathology
- Bacterial aortitis most commonly caused by Salmonella or Staphylococcus aureus
- Primary mycotic aneurysm arises from distant, unknown, or remote source of infection
- Secondary mycotic aneurysm arises from specific source of infection
Clinical Issues
- Fever, signs of sepsis
- Positive blood cultures in most cases
- Surgical resection/grafting following antibiotic therapy
Diagnostic Checklist
- Contrast-enhanced CTA or MRA with delayed images for evaluation
- Labeled leukocyte scan if indeterminate CTA and MRA

TERMINOLOGY

Synonyms
- Infectious aneurysm (more appropriate term)
Definitions
- Aneurysm arising from infection of arterial wall, usually bacterial

IMAGING

General Features

Best diagnostic clue

- Rapidly growing saccular aneurysm arising eccentrically from aortic wall

Location

- Anywhere in aorta or other vessels
        - Tends to occur at major branch points of aorta

Size
```
- Variable
```

Morphology

- Usually saccular with focal involvement of artery
- Periaortic inflammation, abscess, mass
- Periaortic gas
- Adjacent vertebral body abnormalities due to spread of infection

Radiographic Findings

Radiography

- May reveal increased size of aorta
- Lytic or sclerotic areas in adjacent bone

CT Findings

NECT

- Periaortic soft tissue stranding, edema, and fluid are frequent
- Periaortic gas
- Adjacent vertebral body or psoas abnormalities due to spread of infection
- Periaortic, high-attenuation fluid if ruptured
- Bacterial aortitis is rarely calcified
- Syphilitic aortitis shows curvilinear calcifications

CECT

- ≥ 1 saccular aneurysm(s) arising from aortic wall, usually focal
- Lobular contours of aneurysm
- Enhancement of periaortic soft tissue
- Rim enhancement in case of abscess

CTA

- Saccular, eccentric aneurysms of variable size
- Enhancing periaortic soft tissue or abscess

MR Findings

T1WI

- Periaortic low signal intensity in nonenhanced MR
- Aortic and periaortic enhancement following gadolinium, especially evident on fat-suppressed images
- Rim enhancement in case of abscess
- Adjacent bone abnormality if contiguous infection

T2WI

- Periaortic high signal intensity on fat-suppressed T2WI

Contrast-enhanced MRA - ≥ 1 saccular aneurysm(s) arising from aortic wall - Effacement of wall with possible leakage at rupture site - In addition to MRA, delayed source images need to be analyzed to identify areas of enhancement

Ultrasonographic Findings

Grayscale ultrasound

- Useful in children or if superficial arteries are involved
- Focal, eccentric pseudoaneurysm
- Perivascular soft tissue or abscess

Color Doppler

- Flow within aneurysm with typical yin-yang configuration

Echocardiographic Findings

Echocardiogram

- Used to rule out endocarditis as potential source of septic emboli

Angiographic Findings
- Conventional - Focal, saccular aneurysm - Irregularity of luminal surface
Nuclear Medicine Findings
- Labeled leukocyte scintigraphy
```
- Increased uptake at site of aneurysm
```

Imaging Recommendations

Best imaging tool

- Contrast-enhanced CT/CTA
- Labeled leukocyte scintigraphy

Protocol advice

- Obtain delayed images during contrast-enhanced CTA or MRA
- Review adjacent bones

DIFFERENTIAL DIAGNOSIS

Atherosclerotic Aneurysm
- Slow growing
- More often fusiform
- Often calcified
- No enhancement of aortic wall
Inflammatory Aneurysm
- Distal aorta and iliac involvement
- Thick rind of soft tissue around aorta
- Uniform, rim-like aortic wall enhancement on contrast CT/MR
- Fusiform aneurysm
- Retroperitoneal fibrosis
Contained Rupture
- Focal disruption or gap in aortic wall
- High attenuation in wall or in periphery of aneurysm
- Lack of enhancement
Aortoenteric Fistula
- Most involve duodenum
- Periaortic soft tissue with periaortic gas
- Active contrast material extravasation or pseudoaneurysm
- Presents as gastrointestinal bleed
Surgical material
- History of prior surgery
- Hyperdense on NECT

PATHOLOGY

General Features

Etiology

- Bacterial aortitis most commonly caused by *Salmonella* or *Staphylococcus aureus*
- Syphilitic aortitis involves ascending aorta but spares aortic sinus: Ascending aorta most common location
- Routes of infection
        - Most often caused by seeding of existing lesion (atheroma or aneurysm) via vasa vasorum
        - Direct extension from infection in vessel wall, i.e., bacterial endocarditis
        - Invasion of aortic wall by extravascular contiguous infection, such as spinal infection or intraabdominal abscess
        - Lymphatic spread
- *Burkholderia pseudomallei* (causing melioidosis), endemic in Southeast Asia and Northern Australia, is increasingly recognized as agent causing aortitis and mycotic aneurysms

Associated abnormalities

- Endocarditis
- Spinal or retroperitoneal infection
- Intraabdominal infection

Staging, Grading, & Classification
- Classification system - Primary mycotic aneurysm arises from distant, unknown, or remote source of infection - Secondary mycotic aneurysm arises from specific source of infection - Bacterial endocarditis (intravascular spread) - Tuberculosis (contiguous spread)
Gross Pathologic & Surgical Features
- Bacterial aneurysm - Noncalcified saccular aneurysm - Thinning of aortic wall with periaortic inflammatory changes
- Syphilitic aneurysm - Calcified lesion - Tree bark appearance when atheroma develops in infected areas
Microscopic Features
- Loss of intima and destruction of internal elastic lamina
- Varying degrees of destruction of media
- Bacteria present on histology
- Common bacteria: Pseudomonas, Clostridium, Salmonella, Streptococcus, Aspergillus

CLINICAL ISSUES

Presentation
- Most common signs/symptoms
```
- Fever, signs of sepsis
```
- Symptoms vary greatly
- Nonspecific findings
- Low-grade fever
- Localized pain
- Positive blood cultures - Blood cultures are negative in 25% of cases

Demographics

Epidemiology

- 0.7-2.6% of all aortic aneurysms
- Increased risk in
        - Intravenous drug abusers
        - Patients with history of bacterial endocarditis
                  - Occurs in 2% of patients with infective endocarditis
                  - Most common location is intracranial
                  - Rupture more easily and associated with poor prognosis
        - Immunocompromised patients
        - Patients with vascular prostheses (valves, grafts)

Natural History & Prognosis
- Nearly always fatal if untreated
- Acute rupture/hemorrhage seen in 75%
- Mortality rate estimated at 67%
Treatment
- Surgical resection/grafting following antibiotic therapy
- May need extraanatomic bypass grafting
- Endovascular repair in some cases

DIAGNOSTIC CHECKLIST

Consider
- Contrast-enhanced CTA or MRA with delayed images for evaluation
- Labeled leukocyte scan if CTA and MRA are indeterminate
Image Interpretation Pearls
- Focal, eccentric aneurysm of aorta
- Enhancing periaortic soft tissue
- Rim enhancement of periaortic abscess
Reporting Tips
- Include location, size, and involvement of branch vessels
- Check for and report extent of contiguous infection

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References

Selected References

Differential diagnosis

Dilated Aorta

DDX:9daee273-f1e9-4cf9-a979-8990a9b82e40

Dilated Aorta

DDX:bb8315f3-0893-4f17-aaf6-343fd5419b8e

Cases

{'cases': [{'authors': [{'key': 'bee1f359-33fb-4cba-9e6b-ed1ca1842439', 'value': 'Jeffrey S. Ross, MD'}], 'caseVersionId': 'cf6a6efe-995c-4a18-9cb2-5f3395aae678', 'description': "Variant case of a rare mycotic aneurysm presumably from extension from the adjacent thoracic osteomyelitis. The patient's hemoptysis was from the additional complication of an aortobronchial fistula. Patient was emergently treated with a covered stent within the descending aorta.\n\nCTA study of the thorax (#1-8) shows typical appearance of a midthoracic disc space infection with collapse of the disc space and endplate destruction (arrow, #1). Midline sagittal image (#1) also shows adjacent soft tissue mass within the posterior mediastinum (open arrows, #1). The contrast-enhanced images show a large, irregular, enhancing lesion consistent with pseudoaneurysm (open arrows, #2-5) within the posterior mediastinum that displaces the aorta anteriorly (curved arrows, #3-5). The vertebral body destruction from the osteomyelitis (arrows, #3-5) and the extension into the prevertebral soft tissues and mediastinum is seen on the axial views. Coronal images (#6-8) show the pseudoaneurysm (arrows) and the surrounding inflammatory mass as well as the disc space centered bony destruction (open arrow, #8).\n\nOblique aortogram shows contrast extravasating into the pseudoaneurysm with a broad neck (arrows, #9,10).", 'history': 'Presented with massive hemoptysis; history of back pain.', 'imagePoolId': 'd5da4f47-3ed7-4e07-9c88-8dcf8bb6ae26', 'name': 'Aortic vertebral fistula and aortobronchial fistula', 'teachingPoint': None, 'demographics': '59 Years old male'}], 'caseType': 'variant', 'name': 'VARIANT'}

Images

Selected Images

Axial CECT of the abdominal aorta shows periaortic, low-density soft tissue with rim enhancement of the aortic wall, which is consistent with an infected aortic wall and periaortic abscess.

Axial CECT of the aorta in the same patient shows an area of focal, small luminal outpouching (pseudoaneurysm) of the left lateral wall of the aorta with associated periaortic soft tissue swelling , consistent with a mycotic aneurysm.

Oblique CTA reconstruction in the same patient shows 2 focal contrast outpouchings consistent with mycotic pseudoaneurysms affecting the lateral wall of the abdominal aorta.

Coronal CTA of the aortoiliac arteries in the same patient following infrarenal aortic resection shows that the lower extremities are now perfused via a right axillary-femoral artery bypass graft and cross-femoral bypass graft . Note the absence of resected infrarenal aorta.

Axial CTA of the abdominal aorta shows a focal, eccentric pseudoaneurysm affecting the juxtarenal abdominal aorta . Note the minimal periaortic soft tissue.

Oblique CTA of the abdominal aorta in the same patient shows a focal, eccentric pseudoaneurysm . There is no significant soft tissue adjacent to the pseudoaneurysm. This patient had bacteremia and spinal infection (not shown). Surgical resection of the aorta confirmed the mycotic nature of the pseudoaneurysm.

Axial CTA of the thoracic aorta shows a focal, eccentric pseudoaneurysm arising from the anterior wall of the ascending aorta with associated periaortic soft tissue .

Oblique CTA of the thoracic aorta in the same patient shows a focal, eccentric pseudoaneurysm along the anterior wall of the ascending aorta with associated low-density soft tissue . These features are consistent with a mycotic aneurysm.

Axial CTA of the abdomen shows a pseudoaneurysm arising from a branch of the superior mesenteric artery. Note the perianeurysmal soft tissue .

Coronal CTA in the same patient confirms the pseudoaneurysm arising from a branch of the superior mesenteric artery. This was secondary to a septic embolus from valvular vegetations in a 30-year-old man with endocarditis secondary to intravenous drug abuse.

Additional Images

Oblique CTA shows a saccular aortic aneurysm with peripheral mural thrombus . Mycotic aneurysms are usually saccular and involve a focal arterial segment. Infection weakens the arterial wall and allows for the aneurysm formation.

Axial CECT shows a saccular aortic aneurysm with mural thrombus.

Axial CECT shows the saccular aneurysm with mural thrombus arising from the abdominal aorta . Mycotic aneurysms typically involve a diseased segment of the arterial wall.

Oblique MRA shows multiple small pseudoaneurysms following the ascending aortic aneurysm repair. Also note the enhancing soft tissue surrounding the aneurysms.

Axial NECT shows a saccular outpouching from the abdominal aorta . This eccentric saccular appearance is typical of a mycotic aneurysm.

Axial CECT shows a pseudoaneurysm and periaortic soft tissue following surgical repair of an ascending aortic aneurysm.

Axial CECT shows a saccular aortic aneurysm with mural thrombus and periaortic soft tissue .

Coronal CTA shows a saccular aortic aneurysm arising from the lateral wall of the abdominal aorta. Mycotic aneurysms account for ≤ 2.6% of all aortic aneurysms. There is an increased risk for this type of aneurysm in intravenous drug abusers, immunocompromised patients, and in cases of bacterial endocarditis.

28 KiB Raw Blame History

KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

Pathology

Clinical Issues

Diagnostic Checklist

TERMINOLOGY

Synonyms

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Size

Morphology

Radiographic Findings

Radiography

CT Findings

NECT

CECT

CTA

MR Findings

T1WI

T2WI

Ultrasonographic Findings

Grayscale ultrasound

Color Doppler

Echocardiographic Findings

Echocardiogram

Angiographic Findings

Nuclear Medicine Findings

Labeled leukocyte scintigraphy

Imaging Recommendations

Best imaging tool

Protocol advice

DIFFERENTIAL DIAGNOSIS

Atherosclerotic Aneurysm

Inflammatory Aneurysm

Contained Rupture

Aortoenteric Fistula

Surgical material

PATHOLOGY

General Features

Etiology

Associated abnormalities

Staging, Grading, & Classification

Gross Pathologic & Surgical Features

Microscopic Features

CLINICAL ISSUES

Presentation

Most common signs/symptoms

Demographics

Epidemiology

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Consider

Image Interpretation Pearls

Reporting Tips

References

Selected References

Differential diagnosis

Dilated Aorta

Dilated Aorta

Cases

Images

Selected Images

Additional Images

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