(Radiology. 1999;211:81-85.)
© RSNA, 1999
Case 9: Mycotic Pseudoaneurysm of the Abdominal Aorta in Association with Mycobacterial Psoas Abscess—A Complication of BCG Therapy1
Jeanne M. LaBerge, MD,
Robert K. Kerlan, Jr, MD,
Linda M. Reilly, MD and
Timothy A. Chuter, MD
1 From the Departments of Radiology (J.M.L., R.K.K.) and Surgery (L.M.R., T.A.C.), University of California San Francisco, Box 0628, 505 Parnassus Ave, San Francisco, CA 94143-0628. Received April 23, 1998; revision requested June 8; revision received July 7; accepted July 31. Address reprint requests to J.M.L.
Index terms: Abscess, 44.2019 • Aneurysm, aortic, 981.457, 981.494 • Bacillus Calmette-Guérin (BCG), 44.2019, 83.2019 • Bladder neoplasms, therapy, 83.32, 83.499 • Diagnosis please • Muscles, abscess, 44.12912, 44.12916, 44.2019, 44.458 • Muscles, iliopsoas, 44.121, 44.12912, 44.12916, 44.459 • Mycobacteria, 44.2019, 981.458 • Stents and prostheses, 981.4522
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HISTORY
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A 75-year-old man underwent endovascular stent-graft repair of an infrarenal abdominal aortic aneurysm. A tapered aortic–unilateral iliac stent-graft was implanted, and a femoral-femoral crossover graft procedure was performed. One year later, he developed progressive back pain. An abdominal computed tomographic (CT) scan revealed a low-attenuation mass in the right iliopsoas muscle. CT-guided aspiration was performed, and antibiotics were begun for a presumed psoas abscess. The patient's pain persisted, and repeat CT was performed 2 months later. Contrast material–enhanced axial images (Fig 1), a coronal reconstruction image (Fig 2a), and a maximum intensity projection CT angiogram (Fig 2b) were obtained, followed by an abdominal aortogram (Fig 3). An operation was performed the next day.
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Figure 1a. Contrast-enhanced abdominal CT scans. (a) Axial image obtained through the proximal stent-graft shows a focal extraluminal contrast material collection (solid arrow) extending posterolaterally beyond the anticipated confines of and in continuity with the stent-graft and a low-attenuation mass (open arrow) in the left psoas muscle. (b) Axial image obtained through the midportion of the stent-graft. No contrast material leaks into the aneurysm, but a large, complex, rim-enhancing, low-attenuation mass (arrows) is seen within the psoas muscles bilaterally. The L4 vertebra is disrupted. (c) Axial image obtained through the lower abdominal aorta reveals a low-attenuation rim-enhancing mass (arrow) in the right iliac muscle.
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Figure 1b. Contrast-enhanced abdominal CT scans. (a) Axial image obtained through the proximal stent-graft shows a focal extraluminal contrast material collection (solid arrow) extending posterolaterally beyond the anticipated confines of and in continuity with the stent-graft and a low-attenuation mass (open arrow) in the left psoas muscle. (b) Axial image obtained through the midportion of the stent-graft. No contrast material leaks into the aneurysm, but a large, complex, rim-enhancing, low-attenuation mass (arrows) is seen within the psoas muscles bilaterally. The L4 vertebra is disrupted. (c) Axial image obtained through the lower abdominal aorta reveals a low-attenuation rim-enhancing mass (arrow) in the right iliac muscle.
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Figure 1c. Contrast-enhanced abdominal CT scans. (a) Axial image obtained through the proximal stent-graft shows a focal extraluminal contrast material collection (solid arrow) extending posterolaterally beyond the anticipated confines of and in continuity with the stent-graft and a low-attenuation mass (open arrow) in the left psoas muscle. (b) Axial image obtained through the midportion of the stent-graft. No contrast material leaks into the aneurysm, but a large, complex, rim-enhancing, low-attenuation mass (arrows) is seen within the psoas muscles bilaterally. The L4 vertebra is disrupted. (c) Axial image obtained through the lower abdominal aorta reveals a low-attenuation rim-enhancing mass (arrow) in the right iliac muscle.
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Figure 2a. Reformatted images from the same CT study shown in Figure 1. (a) Coronal reconstruction image through the retroperitoneum illustrates the extensive bilateral psoas and right iliac muscle involvement. Bone destruction of L4 and the L3 to L4 interspace (arrow) is also clearly demonstrated. (b) Maximum intensity projection CT angiogram shows the two Z-stents in the aortic portion of the stent-graft and a Wallstent extending into the left iliac artery. The upper part of a femoral-femoral crossover graft (arrowhead) is also visible. A saccular aneurysm at the top of the stent-graft (solid arrow) displaces the left renal artery (open arrow) superiorly.
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Figure 2b. Reformatted images from the same CT study shown in Figure 1. (a) Coronal reconstruction image through the retroperitoneum illustrates the extensive bilateral psoas and right iliac muscle involvement. Bone destruction of L4 and the L3 to L4 interspace (arrow) is also clearly demonstrated. (b) Maximum intensity projection CT angiogram shows the two Z-stents in the aortic portion of the stent-graft and a Wallstent extending into the left iliac artery. The upper part of a femoral-femoral crossover graft (arrowhead) is also visible. A saccular aneurysm at the top of the stent-graft (solid arrow) displaces the left renal artery (open arrow) superiorly.
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Figure 3a. Abdominal aortograms. (a) Image obtained in the early arterial phase shows a focal saccular aneurysm (solid arrow) adjacent to the proximal end of the stent-graft. Note the displacement of the left renal artery (open arrow) and a proximal left renal arterial stenosis. (b) Image obtained in the late arterial phase with opacification of the middle and distal portions of the graft. The stent-graft has Z-stents proximally within the aorta and distally within the iliac artery. A Wallstent has been deployed within the graft and extends through the distal iliac limb. An endovascular occluder is visible in the right common iliac artery.
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Figure 3b. Abdominal aortograms. (a) Image obtained in the early arterial phase shows a focal saccular aneurysm (solid arrow) adjacent to the proximal end of the stent-graft. Note the displacement of the left renal artery (open arrow) and a proximal left renal arterial stenosis. (b) Image obtained in the late arterial phase with opacification of the middle and distal portions of the graft. The stent-graft has Z-stents proximally within the aorta and distally within the iliac artery. A Wallstent has been deployed within the graft and extends through the distal iliac limb. An endovascular occluder is visible in the right common iliac artery.
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The patient's medical history revealed bladder cancer treated by means of intravesical instillation of bacille Calmette-Guérin (BCG) 8 months before aortic endograft placement and severe coronary artery disease treated by means of percutaneous transluminal coronary angioplasty 2 months before endograft repair.
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IMAGING FINDINGS
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Contrast-enhanced abdominal CT scans obtained 14 months after stent-graft repair (Fig 1) reveal the cause of this patient's back pain. There is a pseudoaneurysm at the proximal stent-graft insertion in association with a rim-enhancing low-attenuation mass in the left psoas muscle, which extends into the right psoas and iliac muscles. In addition, the diffuse psoas abnormality is associated with destruction of the L4 vertebral body. There is no evidence of a perigraft leak.
The reformatted CT images (Fig 2) display the abnormal findings to best advantage. The extent of the psoas and iliac muscle involvement is easily appreciated on the reconstructed coronal image (Fig 2a), and the bone destruction at L4 is apparent. The relationship of the contrast material–filled pseudoaneurysm to the proximal Gianturco Z-stents (Cook, Bloomington, Ind) of the stent-graft is well demonstrated on the maximum intensity projection CT angiogram (Fig 2b).
The focal saccular nature of the proximal stent-graft pseudoaneurysm is confirmed on the conventional aortogram (Fig 3). The tapered aortic–unilateral iliac stent-graft design is well displayed in this study.
The diagnosis was tuberculous psoas abscess induced by BCG therapy for bladder cancer and mycotic (tuberculous) pseudoaneurysm of the abdominal aorta in association with endovascular stent-graft. Results of cultures of the aspirate obtained 2 months before surgical exploration were positive for a Mycobacterium complex, and stains were positive for acid-fast bacillus. Surgical exploration revealed a mycotic pseudoaneurysm of the immediate infrarenal aorta with erosion into the spine and a large complex iliopsoas abscess. The patient was treated by means of excising the stent-graft, involved portion of the aorta, and left kidney; extraanatomic bypass; and excision and drainage of the iliopsoas abscess.
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DISCUSSION
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Aortic stent-grafts are a promising new therapy for the treatment of abdominal aortic aneurysms. These devices, implanted by using an endovascular approach, generally consist of a fabric graft supported either partially or completely by metallic stents. A variety of stent-graft designs have been proposed and are currently under investigation. Diagnostic radiologists are often involved with the pre- and postoperative imaging of stent-grafts and should therefore be familiar with the imaging characteristics of stent-grafts and their complications.
The stent-graft described in this article is of a partially supported, tapered, aortic–unilateral iliac design that is under investigation at our institution (T.A.C., principle investigator). The fabric graft is supported proximally and distally by Gianturco Z-stents. The contralateral iliac artery is occluded by placement of an occluder stent in the common iliac artery, and a femoral-femoral crossover graft procedure is performed. In addition, the body of the stent-graft is reinforced by a coaxial Wallstent placed inside the aortic component of the graft extending into the iliac segment. The follow-up protocol for patients treated with this device includes CT within 1 week, at 3 months, and every 6 months thereafter.
Continued perfusion of an abdominal aneurysm after stent-graft repair is a relatively uncommon but serious complication of endovascular stent-graft repair (1,2). Patients with continued perfusion, if untreated, are at continued risk of aortic rupture and death. Patients with "endoleaks" are usually asymptomatic, and therefore routine follow-up CT evaluation is performed at selected intervals. Patients with symptoms referable to the aneurysm, such as back pain, should be examined by means of additional CT.
In the case on which we report, symptoms of back pain 1 year after stent-graft repair raised the concern of persistent aneurysm perfusion. Surprisingly, there was no evidence of a leak visible on the CT scan initially obtained after stent-graft placement, nor was a leak into the true aneurysm observed on subsequent follow-up CT scans. The cause of this patient's back pain was not an aneurysmal leak, but rather a diffuse abnormality of the psoas muscle bilaterally extending into the right iliac muscle. The differential diagnosis of psoas disease includes abscess, tumor, and hematoma. Clinical history provides the key to ensuring a correct diagnosis, as the CT findings alone may not be specific enough to differentiate tumor or abscess from hematoma.
In a recent review of psoas abscesses, Lenchik et al (3) found three CT features useful in establishing the proper diagnosis: low attenuation of the lesion, irregular lesion margins, and diffuse involvement of the entire muscle by the lesion. Low attenuation was the most reliable indicator of infection (sensitivity, 100%; specificity, 43%; accuracy, 70%), irregular margins were the most reliable indicator of tumor (sensitivity, 67%; specificity, 52%; accuracy, 57%), and diffuse involvement of the whole muscle was the most reliable feature of hematoma (sensitivity, 88%; specificity, 78%; accuracy, 80%). In our case, the low attenuation of the psoas muscle, lack of diffuse involvement, and smooth margins favor the diagnosis of abscess.
Infection of the psoas muscle is most commonly pyogenic and is often due to Staphylococcus aureus. Pyogenic abscesses are frequently associated with adjacent inflammatory conditions of the bowel, such as appendicitis or diverticulitis. Tuberculosis is a less common cause of psoas abscess and may be due to extension of vertebral infection or hematogenous spread.
In this case, the extensive low-attenuation iliopsoas abnormality with associated bone destruction is suggestive of tuberculosis. These findings, along with the history of BCG exposure 8 months before stent-graft placement, make a mycobacterial iliopsoas abscess the leading diagnosis. The pseudoaneurysm of the abdominal aorta at the proximal stent-graft is in direct continuity with the psoas abscess, which suggests that it is a mycobacterial mycotic pseudoaneurysm.
BCG is an attenuated live strain of Mycobacterium bovis initially developed more than 80 years ago as a vaccine against tuberculosis (4). It is not currently used in the United States for this purpose because of the small but serious risk of systemic infection from the vaccine (4). BCG is a potent immune system stimulant and has been shown to be effective in the treatment of superficial bladder cancer when instilled within the bladder after tumor resection. Serious complications from BCG therapy for bladder cancer are infrequent but well documented (4). Adverse systemic reactions, including fever, prostatitis, pneumonitis, hepatitis, and sepsis, may occur in 1%–2% of patients (4).
Mycotic aneurysm and psoas abscess are rare complications of BCG therapy. To our knowledge, four cases of mycotic aneurysm from M bovis have been reported on (one in the thoracic aorta, two in the abdominal aorta, and one in the femoral artery) (5–8). The patients presented 15 months to 3 years after exposure. Regional lymphangitic spread was implicated as the route of spread of the organism from the bladder. Of note, two of these patients (50%) died of this complication. Two cases of psoas abscess, detected at 9 and 15 months after BCG exposure, have been reported on previously (9,10).
BCG-related infections can be treated with antituberculous drugs (4). M bovis is usually sensitive to isoniazid, rifampin, and ethambutol hydrochloride. In addition to antibiotics, drainage is usually necessary to cure psoas abscess. In the past, open surgical drainage was advocated for tuberculous psoas abscess (11). Several recent reports (12,13) have suggested that percutaneous drainage may also be effective. Mycotic aneurysm must be treated emergently with excision and bypass surgery.
In our case, the patient was initially too ill to undergo an open surgical procedure to treat his large abdominal aortic aneurysm and therefore underwent placement of an endovascular stent-graft, with successful exclusion of the aneurysm. He developed a psoas abscess and mycotic infection of the aorta above the stent-graft, which required removal of the stent-graft and infected portion of the aorta. These infections are likely the sequelae of the lymphangitic spread of BCG and are unrelated to the stent-graft.
Our congratulations to the 70 individuals who submitted the most likely diagnosis (mycotic pseudoaneurysm of the abdominal aorta in association with mycobacterial psoas abscess—a complication of BCG therapy) for Diagnosis Please, Case 9. Please note that credit was given only if both components of the diagnosis were mentioned. The names and locations of the individuals, as submitted, are as follows:
- Roger L. Antonelli, MD, Dayton, Ohio
- Lionel Arrivé, MD, Paris, France
- William W. Atherton, DC, Chesterfield, Mo
- Edward L. Baker, MD, San Francisco, Calif
- Adrian Brady, FFRRCSI, FRCR, Cork, Ireland
- Eric L. Bressler, MD, Minnetonka, Minn
- Michael P. Buetow, MD, Okemos, Mich
- Steve Burbidge, MD, St Louis Park, Minn
- Hearns W. Charles, MD, New York, NY
- Timothy Clark, MD, Greenville, NC
- Y-S Cordoliani, MD, Paris, France
- Jose L. Criales, MD, Mexico DF, Mexico
- Horacio D'Agostino, MD, Shreveport, La
- M.G. de Baets, MD, Lugano, Switzerland
- David R. DeLone, Madison, Wis
- Mark H. Depper, MD, Laurel, Md
- Paul H. Ellenbogen, MD, Dallas, Tex
- Keith D Epperson, MD, Milwaukee, Wis
- Namik Erdag, MD, Cambridge, Mass
- Ayþe Erden, MD, Ankara, Turkey
- Abigail Falk, MD, New York, NY
- Arnold C. Friedman, MD, New York, NY
- Ted A. Glass, MD, Fredericksburg, Va
- Bhaskar Golla, Floral Park, NY
- Daniel S. Gordon, MD, Sanford, NC
- Walter O. Grauer, MD, Zurich, Switzerland
- Ian Hammond, MD, Ottawa, Ontario, Canada
- Maureen Heldmann, MD, Shreveport, La
- Carlos Holguera Blazquez, MD, Madrid, Spain
- Douglas S. Katz, MD, Mineola, NY
- Mitchell A. Klein, MD, Milwaukee, Wis
- Arlene M. Klink, MD, Scotch Plains, NJ
- Dr Stewart Kribs, London, Ontario, Canada
- Glenn Krinsky, New York, NY
- Peter Leyman, MD, Aalst, Belgium
- David R. Ludwig, MD, Amherst, NY
- Marcus E. Luetolf, Chur, Switzerland
- N.B.S. Mani, MD, Chandigarh, India
- Kathlyn Marsot Dupuch, Paris, France
- Michael B. Martin, MD, Austin, Tex
- Steven F. Millward, MD, Ottowa, Ontario, Canada
- Manabu Minami, MD, Tokyo, Japan
- Hidetoshi Miyake, MD, Oita, Japan
- Sergio J. Moguillansky, MD, Rio Negro, Argentina
- S. Neuenschwander, Paris, France
- James A. Newcomb, MD, Allentown, Pa
- Orlando Ortiz, MD, Mineola, NY
- David M. Panicek, MD, New York, NY
- Narendrakumar P. Patel, MD, Newburgh, NY
- Tim Pendergrass, MD, Fairchild AFB, Wash
- Shawn P. Quillin, MD, Charlotte, NC
- Enrique Remartinez Escobar, Melilla, Spain
- Uri Rimon, MD, Rehovot, Israel
- Joel Rubenstein, MD A. Scherrer, Suresnes, France
- Pierre Schmit, L'Hay les Roses, France
- Steven M. Schultz, MD, Ft Worth, Tex
- Martin A. Schwartz, MD, Pacific Palisades, Calif
- Matt Shapiro, Boxborough, Mass
- L.H. Sie, MD, Beverwijk, the Netherlands
- Paolo Siotto, MD, Cagliari, Italy
- Michael S. Stecker, MD, Iowa City, Iowa
- Peter M. Stroz, MD, Toronto, Ontario, Canada
- Douglas L. Teich, MD, Hermosa Beach, Calif
- J. Keith Thompson, MD, Richmond, Va
- John To, MD, Iron Mountain, Mich
- H. Wouter van Es, MD, Nieuwegein, the Netherlands
- Jeffrey H. Watters, MD, Des Moines, Iowa
- Joseph T. Wroblicka, MD, Iowa City, Iowa
- Joe Yut, MD, Olathe, Kan
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Footnotes
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Abbreviation: BCG = bacille Calmette-Guérin
Several patents relating to stent-graft technology are licensed by T.A.C. to Cook, Bloomington, Ind, and others are licensed to Guidant, Menlo Park, Calif.
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References
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Lenchik L, Dovgan DJ, Kier R. CT of the iliopsoas compartment: value of differentiating tumor, abscess and hematoma. AJR 1994; 162:83-86.[Abstract/Free Full Text]
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Lamm DL, van der Meijden APM, Morales A, et al. Incidence and treatment of complications of bacillus Calmette-Guerin intravesical therapy in superficial bladder cancer. J Urol 1992; 147:596-600.[Medline]
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Gupta S, Gulati SSM, Singh P. Ilio-psoas abscesses: percutaneous drainage under imaging guidance. Clin Radiol 1997; 52:704-707.[Medline]
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TOP
HISTORY
IMAGING FINDINGS
