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Case report: Legionella infected thoracic aortic graft
I
0895-61 l/93 56.M) + .I0 Copyright 0 1993 Pergamon Press Ltd.
Computerized Medrcal Imaging and Graphics, Vol. 17, No. I, pp. 61-67, 1993 Rinted in the U.S.A. All ri&s reserved.
CASE REPORT:
LEGIONELLA
INFECTED
THORACIC
AORTIC
GRAFT
Richard Tello*, Thomas Hill, George Hartnell, Philip Costello, and Ken Stokes New
England
Deaconess
Hospital and Harvard Medical School, Department 185 Pilgrim Road, Boston, MA 022 15
of Radiology,
(Received 9, July 1992) Abstract-A case of a tboracic aortic graft in a patient with Marfan’s syndrome infected with legionella is presented. The pathogenesis of graft infection and aspects of examination with aortography, gallium scanning, magnetic resonance imaging (MRI), and spiral volumetric computed tomography (CIJ are presented, and the pathophysiology and management of thoracic aortic graft infections is briefly discussed. Key Words:
Magnetic resonance imaging (cardiac), Computed tomography, Aortic graft (infected), SPECT, Legionella pneumophillia
INTRODUCIION
The CT signs of mycotic aneurysm include irregular dilatation of the aorta, and periarotic abscess. However, streak artifacts that emanate from valve prosthesis or surgical clips often confound the detail of the CT image obtained, and thus may prove a difficult diagnostic challenge (3). Thus, examination with alternate imaging modalities, such as nuclear pharmaceutical scintigraphy, or MRI, where thrombosis of the false channel, or perigraft infection, is identified by a decrease in signal intensity on the second echo image, may be necessary to establish a definitive diagnosis (4).
The consequences of aortic dissection are potentially fatal, depending upon the location of the intimal tear. In type A aortic dissection the intimal tear occurs in the ascending aorta, and may extend distally. In a great number of patients, the dissection also proceeds proximally. Disastrous sequelae may occur when this second, or false, lumen occludes the ostia of the major arterial branches, including the coronary, carotid, renal, and mesenteric vasculature. The clinical presentation may, therefore, include myocardial infarction, arrhythmias, stroke, mesenteric infarction, acute renal failure, or cardiac tamponade. Type A aortic dissection occurs primarily in patients under 65 yr of age, and is the most lethal form of the disease. Type B dissection also involves the ascending aorta, but the dissection does not extend to the origin of the great vessels. Marfan’s syndrome and other connective tissue disorders are the major predisposing factors. The diagnosis should be confirmed by contrast arteriography, computed tomography (CT), or magnetic resonance imaging (MRI), which will demonstrate a false lumen or narrowing of the true lumen (1). In these cases, surgical repair often consists of simple Dacron graft placement, as has been described by Carpentier (2). Unfortunately, the placement of foreign material into the body carries the small, but real, risk of potential infection, either at surgery, or from subsequent hematogenous seeding. Thus, diagnosing infection of a graft becomes a serious diagnostic dilemma.
CASE
REPORT
A 58-yr-old white female with a diagnosis of Marfan’s syndrome, a patent ductus arteriosus ligation at age 25, and who had repair of a type A dissecting aneurysm at age 55, was in her usual good health until 2 mo prior to admission, when she developed fevers of 10 1- 102°F with chills and rigors. Laboratory tests indicated that she had positive legionella titers, and was treated with erythromycin for 10 days. She noted increasing fatigue, and was admitted to a local hospital where blood cultures were negative. She was treated with intravenous vancomycin and gentamicin for 3 1 days. This was complicated by development of “Redman” syndrome, and increasing renal insufficiency leading to heart failure. She then developed increasing upper abdominal pain, and a gallium scan demonstrated increased activity in the left upper lung and right lower quadrant of the abdomen, which subsequently resulted in the resection of a villous adenoma of the colon at the hepatic flexure. At that time, CT was interpreted as demonstrating no change in her aortic graft, compared with CT scan 1 year previously,
* Correspondence should be addressed to: Richard Tello, Department of Radiology, Farr-2, New England Deaconess Hospital, I85 Pilgrim Road. Boston, MA 022 15. 61
62
Computerized Medical Imaging and Graphics
January-February/
1993, Volume 17, Number 1
MRI, and contrast aortography. Surgical debridement was undertaken, and although she survived surgery, her course rapidly deteriorated over the ensuing 2 wk with her demise secondary to uncontrollable sepsis. METHODS The gallium scan was acquired 72 h after the intravenous administration of 9.7 mCi of gallium 67. Planar and SPECT images were obtained on a Siemens Orbiter with MicroDelta controller (Erlangen, Germany) with planar images obtained with a medium energy collimator to 800 K counts. SPECT acquisition was also with a medium energy collimator at 6” increments over 360” for 30 s/view at 100/K counts. Images were reconstructed with a Butterworth filter of order 6, with frequency cut-off of 0.5. Spiral CT was performed with the use of two consecutive 24 s breathholding spiral examinations of the thorax using a Siemens Somatom Plus (Erlangen, Germany) with a total of 120 cc of intravenous contrast (iopamidol 300 mg/ mL, Squibb, NJ), and use of an 8 mm-thick collimation and 8 mm/s table feed. The details of the single breathhold technique have been described elsewhere (5). The
Fig. 1. Planar gallium scan, anterior view, with increased avidity in the left upper thorax (arrow).
and she was discharged. She then progressively developed increasing fatigue, shortness of breath, and a ventilation/perfusion (V/Q) scan was remarkable for decreased perfusion to both lungs. She was, at that time, transported to our facility. On admission, physical examination showed diminished breath sounds on the left without wheezing, and a 4/6 holosystolic murmur at the apex, with an additional 4/6 systolic ejection component at the aortic root. Imaging investigations included gallium scan with planar and single photon emission computed tomography (SPECT) acquisition, spiral volumetric CT, tine
Fig.
2. Planar gallium scan, left lateral view, demonstrating the arching posterior
region of avidity (arrow).
Legionella infected thoracic aortic graft
Fig. 3. Multiple
axial images from gallium SPECT, demonstrating
??
63
R. TELLO et al.
avidity along the course of the aorta (arrows).
loss of calcification, opacification Fig. 4. Axial image from spiral CT, demonstrating lumens, and soft tissue inflammation (arrow).
of true (T) and false (F)
64
Computerized Medical Imaging and Graphics
January_February/l993,
Volume 17, Number 1
Fig. 5. 3D spiral CT reconstruction, LAO viewing perspective, demonstrating communication and false (F) lumens in the ascending and descending aorta.
contrast aortogram was performed using single wall technique and a 5-Fr pigtail catheter with advancement into the proximal aortic arch, and an injection of intravenous contrast at 20 cc/s for a total of 40 cc, and acquisition of images in the left anterior oblique (LAO) projection. MRI of the aorta was acquired using ECGgated axial and oblique T l-weighted spin-echo images, and multi-angulated flow compensated tine-fast imaging with steady procession (FISP) images using a Siemens 1.O T Magnetom (Erlangen, Germany). RESULTS Gallium study demonstrated increased activity in the left upper lung zone as is demonstrated in Fig. 1, and posteriorly as in Fig. 2, SPECT analysis confirmed that this activity correlated with the course of the dissections false lumen, as can be seen in Fig. 3. CT demonstrates a large mass adjacent to the site of the previously repaired dissection with two contrast opacified channels, as is seen in Fig. 4. Three dimensional reconstruction, shown in Fig. 5, indicates the nature of these channels as being a false and true lumen. The
between
true (T)
MRI aortogram, shown in parasagittal view in Fig. 6, demonstrates communication between the false lumen, or pseudoaneurysm, and the true lumen to the ascending aorta and the descending aorta, and thus clarifies the communications between these channels which CT and aortography could not readily resolve. Contrast aortography, shown in Fig. 7, corroborated an inferior communication between the two channels. However, ambiguity regarding the more proximal communication could not be ascertained by this study. Coronary angiography demonstrated no compromise to the myocardial perfusion and the patient underwent surgical resection and debridement, and subsequently died 2 wk later. Pathology confirmed the diagnosis of cystic medial necrosis, and although legionella cultures were negative once therapy was instituted, her serum titers were highly positive. DISCUSSION The diagnosis and assessment of the extent of a graft infection is difficult on clinical grounds. In a prospective study that compared CT and indium-labeled
Legionella infected thoracic aortic graft
Fig. 6. Parasagittal
MRI demonstrating
??
R. TELLO etul.
communication between true (T) and false (F) lumens consistent with inflammatory process.
white blood cell scans in the diagnosis of aortic graft infection, CT correctly detected the retroperitoneal extension of the infection in 60% of those with groin infection; indium scans diagnosed the extension in only 20% of the cases. The study suggested that CT is more sensitive in evaluating the extent of aortic graft infection, and should be the imaging method of choice (6). However, to our knowledge, there have been no specific assessments of the utility of gallium nor MRI in thoracic graft infections. The CT features of infected aortic aneurysm repairs include the disappearance of aortic calcifications, and an irregular, thickened aortic wall with peripheral enhancement (7). The nonspecific clinical presentation and high mortality make mycotic aneurysm an important consideration in the differential diagnosis of abnormal soft tissue contiguous with the aorta. The
65
with loss of signal
presence of air in the per&raft space is highly suggestive of an infection, and, after the initial postoperative month, it must be considered an abnormal finding. Other findings in infection include the presence of a saccular aneurysm with an irregular lumen, perianeurysmal fluid, gas and/or hematoma, osteomyelitis in adjacent vertebral bodies, and disruption of intimal calcification. Thus, CT has been of substantial benefit in the identification and characterization of infected aortic aneurysms (8). The size and extent of pseudoaneurysm or anastomotic dilatation, the presence of thrombus and vessel occlusion, the extent of abscesses, and the effect of pseudoaneurysms and abscesses on adjacent structures can be readily demonstrated by MR. The size of the residual lumen in the case of thrombosis can easily be assessed by MR angiography. Abscesses may be iden-
66
Computerized
Medical Imaging and Graphics
January-February/l
993, Volume
17, Number
1
In one review, there was a reported overall operative mortality of 50% in the treatment of infected grafts. In these studies, graft cultures were positive in 84% of patients, and were commonly gram-positive cocci and gram-negative enteric organisms (11). Systemic antibiotics are essential, but no one knows how long treatment should be continued. SUMMARY This case report presents a broad spectrum of imaging of an infected thoracic aortic graft in a patient with Marfan’s syndrome with legionella, which is an unusual organism because of its etiology. REFERENCES
Fig. 7. Aortogram demonstrating ambiguity regarding communication of both lumens along the descending aorta.
tified by their characteristic signal increase with long repetition rates and long echo delays. MR has also been able to exclude suspected complications such as hemorrhage and graft occlusion (9). Aortic graft infections are uncommon, but potentially lethal complications of aortic graft surgery. In some cases, if the infection is limited to the groin, local therapy and preservation of the graft may be possible, whereas infections extending into the retroperitoneum require removal of the graft and revascularization of the lower limbs. Late infections will develop in 1.9% of patients who receive prosthetic grafts in the chest or mediastinum. Organisms such as staph epidermis, enterococcus, and Aspergillus may be isolated (10). However, to our knowledge, no case related to legionella has been reported. Several guidelines, which are useful in the management of these infections, have evolved: Prompt reoperation with complete debridement of infected and necrotic tissue, removal of infected prosthetic material if suture lines are involved, local antiseptic irrigation, and appropriate, specific systemic antibiotics, rerouting of blood flow through clean operative fields, and the use of pedicle flaps ( 11).
I. Fishman, M.C.; Hoffmann, A.R.; Kalusner, R.D.; Thaler, MS. Medicine, 2nd ed. Philadelphia, PA: Lippincott; 1985. 2. Carpentier, A.; Deloche, A.; Fabiani, J.N.; Chauvaud, S.; Relland, J. Nottin, R.; Vouhe, P.; Massoud, H.; Dubost, C. New surgical approach to aortic dissection: Flow reversal and thrombo-occlusion. J. Thorac. Cardiovasc. Surg. 81(5):659-668; 3. Guthaner, D.F. The use of CT in assessing aneurysms and dissecting hematomas of the thoracic aorta. In: Taveras, J.M.; Ferrucci, J.T., eds. Radiology. Philadelphia, PA: Lippincott; 1990: ch.35. 4. Pemes, J.M.; Grenier, P.; Desbleds, M.T.; de Brux, J.L. MR evaluation of chronic aortic dissection. J. Comput. Assist. Tomogr. 11(6):975-81; 1987. 5. Costello, P.; Dupuy, D.E.; Ecker, C.P. Spiral CT of the thorax with small volumes of contrast material: A comparative study. Radiology 18l(P):274; 1991. 6. Mark, A.S.; McCarthy, S.M.; Moss, A.A.; Price, D. Detection of abdominal aortic graft infection: Comparison of CT and inlabeled white blood cell scans. Am. J. Roentgen01 144(2):3158; 1985. 7. Blair, R.H.; Resnik, M.D.; Polga, J.P. CT appearance of mycotic abdominal aortic aneurysms. J. Comput. Assist. Tomogr. I3( 1): 101-4; 1989. 8. Vogelzang, R.L.; Sohaey, R. Infected aortic aneurysms: CT appearance. J. Comput. Assist. Tomogr. 12(1):109-12; 1988. 9. Auffermann. W.; Olofsson, P.; Stoney, R.; Higgins, C.B. MR imaging of complications of aortic surgery. J. Comput. Assist. Tomogr. 11(6):982-9; 1987. of infected thoracic 10. Hargrove, A.; Edmunds, A. Management aortic prosthesis grafts. Ann. Thorac. Surg. 37:72-77; 1984. Il. Yeager, R.A.; Moneta, G.L.; Taylor, L.M.; Harris, E.J.; McConnell, D.B.; Porter. J.M. Improving survival and limb salvage in patients with aortic graft infection. Am. J. Surg. 159:466-469; 1990.
About the Author-RICHARD
TELLO, M.D., graduated from MIT with a BS in mathematics, and a BSE in mechanical engineering in 1982, an MSME in mechanical engineering in 1983, and is pursuing his Ph.D. He received the MD from Stanford in 1989, and interned at St. Mary’s Hospital in San Francisco. He is currently a resident in radiology at New England Deaconess Hospital-Harvard Medical school, and is an RSNA research resident award recipient. Research interests include cardiovascular and three-dimensional imaging. About the Author-THOMAS HILL, M.D., is an associated professor of radiology at Harvard Medical School, and the director of the nuclear radiology section at the New England Deaconess Hospital. He is a
Legionella infected thoracic aortic graft graduate of Washington University Medical School, St. Louis, MO. He has been a staff radiologist at Deaconess since 1976. His publications in nuclear medicine have mainly focused on SPECT, especially in the area of brain and cardiovascular imaging. About the Author-GEORGE HARTNELL,FRCR, MRCP, graduated
from Bristol University in 1976, and trained in cardiology at Havefield Hospital. He subsequently trained in radiology at the Royal postgraduate Medical School, London. He is associate professor of radiology at Harvard Medical School, and his research interests are cardiovascular MRI and vascular interventional radiology. About the Author-PHILIP COSTELLO,M.D., graduated from the University of London Medical School. He pursued his radiology and postgraduate work at the University of Toronto, Canada. Since 1976 he has been a staff radiologist at the New England Deaconess Hospital,
??
R. TELLOet al.
67
and is currently an associate professor of radiology at Harvard Medical School. He has published extensively in areas related to thoracic radiology and computed tomography. About the Author--KEN STOKES,M.D., obtained his BA in Biology at Washington University, St. Louis in 1975. He attended St. Louis University Medical school obtaining his MD in 1979. An internship in general surgery, and residency in radiology at St. Louis University Hospitals was followed by a fellowship in vascular and interventional radiology at New England Deaconess Hospital in 1983. He then joined the staff at the Deaconess, and later took a position in Virginia where he was appointed assistant professor of radiology at Eastern Virginia Medical School. He returned to the Deaconess to become director of interventional radiology in 1988. Dr. Stoke’s writings cover a wide range of interests, from transluminal angioplasty, and femoropopliteal angioplasty in the diabetic patient, to abdominal MR angiography.
0895-61 l/93 56.M) + .I0 Copyright 0 1993 Pergamon Press Ltd.
Computerized Medrcal Imaging and Graphics, Vol. 17, No. I, pp. 61-67, 1993 Rinted in the U.S.A. All ri&s reserved.
CASE REPORT:
LEGIONELLA
INFECTED
THORACIC
AORTIC
GRAFT
Richard Tello*, Thomas Hill, George Hartnell, Philip Costello, and Ken Stokes New
England
Deaconess
Hospital and Harvard Medical School, Department 185 Pilgrim Road, Boston, MA 022 15
of Radiology,
(Received 9, July 1992) Abstract-A case of a tboracic aortic graft in a patient with Marfan’s syndrome infected with legionella is presented. The pathogenesis of graft infection and aspects of examination with aortography, gallium scanning, magnetic resonance imaging (MRI), and spiral volumetric computed tomography (CIJ are presented, and the pathophysiology and management of thoracic aortic graft infections is briefly discussed. Key Words:
Magnetic resonance imaging (cardiac), Computed tomography, Aortic graft (infected), SPECT, Legionella pneumophillia
INTRODUCIION
The CT signs of mycotic aneurysm include irregular dilatation of the aorta, and periarotic abscess. However, streak artifacts that emanate from valve prosthesis or surgical clips often confound the detail of the CT image obtained, and thus may prove a difficult diagnostic challenge (3). Thus, examination with alternate imaging modalities, such as nuclear pharmaceutical scintigraphy, or MRI, where thrombosis of the false channel, or perigraft infection, is identified by a decrease in signal intensity on the second echo image, may be necessary to establish a definitive diagnosis (4).
The consequences of aortic dissection are potentially fatal, depending upon the location of the intimal tear. In type A aortic dissection the intimal tear occurs in the ascending aorta, and may extend distally. In a great number of patients, the dissection also proceeds proximally. Disastrous sequelae may occur when this second, or false, lumen occludes the ostia of the major arterial branches, including the coronary, carotid, renal, and mesenteric vasculature. The clinical presentation may, therefore, include myocardial infarction, arrhythmias, stroke, mesenteric infarction, acute renal failure, or cardiac tamponade. Type A aortic dissection occurs primarily in patients under 65 yr of age, and is the most lethal form of the disease. Type B dissection also involves the ascending aorta, but the dissection does not extend to the origin of the great vessels. Marfan’s syndrome and other connective tissue disorders are the major predisposing factors. The diagnosis should be confirmed by contrast arteriography, computed tomography (CT), or magnetic resonance imaging (MRI), which will demonstrate a false lumen or narrowing of the true lumen (1). In these cases, surgical repair often consists of simple Dacron graft placement, as has been described by Carpentier (2). Unfortunately, the placement of foreign material into the body carries the small, but real, risk of potential infection, either at surgery, or from subsequent hematogenous seeding. Thus, diagnosing infection of a graft becomes a serious diagnostic dilemma.
CASE
REPORT
A 58-yr-old white female with a diagnosis of Marfan’s syndrome, a patent ductus arteriosus ligation at age 25, and who had repair of a type A dissecting aneurysm at age 55, was in her usual good health until 2 mo prior to admission, when she developed fevers of 10 1- 102°F with chills and rigors. Laboratory tests indicated that she had positive legionella titers, and was treated with erythromycin for 10 days. She noted increasing fatigue, and was admitted to a local hospital where blood cultures were negative. She was treated with intravenous vancomycin and gentamicin for 3 1 days. This was complicated by development of “Redman” syndrome, and increasing renal insufficiency leading to heart failure. She then developed increasing upper abdominal pain, and a gallium scan demonstrated increased activity in the left upper lung and right lower quadrant of the abdomen, which subsequently resulted in the resection of a villous adenoma of the colon at the hepatic flexure. At that time, CT was interpreted as demonstrating no change in her aortic graft, compared with CT scan 1 year previously,
* Correspondence should be addressed to: Richard Tello, Department of Radiology, Farr-2, New England Deaconess Hospital, I85 Pilgrim Road. Boston, MA 022 15. 61
62
Computerized Medical Imaging and Graphics
January-February/
1993, Volume 17, Number 1
MRI, and contrast aortography. Surgical debridement was undertaken, and although she survived surgery, her course rapidly deteriorated over the ensuing 2 wk with her demise secondary to uncontrollable sepsis. METHODS The gallium scan was acquired 72 h after the intravenous administration of 9.7 mCi of gallium 67. Planar and SPECT images were obtained on a Siemens Orbiter with MicroDelta controller (Erlangen, Germany) with planar images obtained with a medium energy collimator to 800 K counts. SPECT acquisition was also with a medium energy collimator at 6” increments over 360” for 30 s/view at 100/K counts. Images were reconstructed with a Butterworth filter of order 6, with frequency cut-off of 0.5. Spiral CT was performed with the use of two consecutive 24 s breathholding spiral examinations of the thorax using a Siemens Somatom Plus (Erlangen, Germany) with a total of 120 cc of intravenous contrast (iopamidol 300 mg/ mL, Squibb, NJ), and use of an 8 mm-thick collimation and 8 mm/s table feed. The details of the single breathhold technique have been described elsewhere (5). The
Fig. 1. Planar gallium scan, anterior view, with increased avidity in the left upper thorax (arrow).
and she was discharged. She then progressively developed increasing fatigue, shortness of breath, and a ventilation/perfusion (V/Q) scan was remarkable for decreased perfusion to both lungs. She was, at that time, transported to our facility. On admission, physical examination showed diminished breath sounds on the left without wheezing, and a 4/6 holosystolic murmur at the apex, with an additional 4/6 systolic ejection component at the aortic root. Imaging investigations included gallium scan with planar and single photon emission computed tomography (SPECT) acquisition, spiral volumetric CT, tine
Fig.
2. Planar gallium scan, left lateral view, demonstrating the arching posterior
region of avidity (arrow).
Legionella infected thoracic aortic graft
Fig. 3. Multiple
axial images from gallium SPECT, demonstrating
??
63
R. TELLO et al.
avidity along the course of the aorta (arrows).
loss of calcification, opacification Fig. 4. Axial image from spiral CT, demonstrating lumens, and soft tissue inflammation (arrow).
of true (T) and false (F)
64
Computerized Medical Imaging and Graphics
January_February/l993,
Volume 17, Number 1
Fig. 5. 3D spiral CT reconstruction, LAO viewing perspective, demonstrating communication and false (F) lumens in the ascending and descending aorta.
contrast aortogram was performed using single wall technique and a 5-Fr pigtail catheter with advancement into the proximal aortic arch, and an injection of intravenous contrast at 20 cc/s for a total of 40 cc, and acquisition of images in the left anterior oblique (LAO) projection. MRI of the aorta was acquired using ECGgated axial and oblique T l-weighted spin-echo images, and multi-angulated flow compensated tine-fast imaging with steady procession (FISP) images using a Siemens 1.O T Magnetom (Erlangen, Germany). RESULTS Gallium study demonstrated increased activity in the left upper lung zone as is demonstrated in Fig. 1, and posteriorly as in Fig. 2, SPECT analysis confirmed that this activity correlated with the course of the dissections false lumen, as can be seen in Fig. 3. CT demonstrates a large mass adjacent to the site of the previously repaired dissection with two contrast opacified channels, as is seen in Fig. 4. Three dimensional reconstruction, shown in Fig. 5, indicates the nature of these channels as being a false and true lumen. The
between
true (T)
MRI aortogram, shown in parasagittal view in Fig. 6, demonstrates communication between the false lumen, or pseudoaneurysm, and the true lumen to the ascending aorta and the descending aorta, and thus clarifies the communications between these channels which CT and aortography could not readily resolve. Contrast aortography, shown in Fig. 7, corroborated an inferior communication between the two channels. However, ambiguity regarding the more proximal communication could not be ascertained by this study. Coronary angiography demonstrated no compromise to the myocardial perfusion and the patient underwent surgical resection and debridement, and subsequently died 2 wk later. Pathology confirmed the diagnosis of cystic medial necrosis, and although legionella cultures were negative once therapy was instituted, her serum titers were highly positive. DISCUSSION The diagnosis and assessment of the extent of a graft infection is difficult on clinical grounds. In a prospective study that compared CT and indium-labeled
Legionella infected thoracic aortic graft
Fig. 6. Parasagittal
MRI demonstrating
??
R. TELLO etul.
communication between true (T) and false (F) lumens consistent with inflammatory process.
white blood cell scans in the diagnosis of aortic graft infection, CT correctly detected the retroperitoneal extension of the infection in 60% of those with groin infection; indium scans diagnosed the extension in only 20% of the cases. The study suggested that CT is more sensitive in evaluating the extent of aortic graft infection, and should be the imaging method of choice (6). However, to our knowledge, there have been no specific assessments of the utility of gallium nor MRI in thoracic graft infections. The CT features of infected aortic aneurysm repairs include the disappearance of aortic calcifications, and an irregular, thickened aortic wall with peripheral enhancement (7). The nonspecific clinical presentation and high mortality make mycotic aneurysm an important consideration in the differential diagnosis of abnormal soft tissue contiguous with the aorta. The
65
with loss of signal
presence of air in the per&raft space is highly suggestive of an infection, and, after the initial postoperative month, it must be considered an abnormal finding. Other findings in infection include the presence of a saccular aneurysm with an irregular lumen, perianeurysmal fluid, gas and/or hematoma, osteomyelitis in adjacent vertebral bodies, and disruption of intimal calcification. Thus, CT has been of substantial benefit in the identification and characterization of infected aortic aneurysms (8). The size and extent of pseudoaneurysm or anastomotic dilatation, the presence of thrombus and vessel occlusion, the extent of abscesses, and the effect of pseudoaneurysms and abscesses on adjacent structures can be readily demonstrated by MR. The size of the residual lumen in the case of thrombosis can easily be assessed by MR angiography. Abscesses may be iden-
66
Computerized
Medical Imaging and Graphics
January-February/l
993, Volume
17, Number
1
In one review, there was a reported overall operative mortality of 50% in the treatment of infected grafts. In these studies, graft cultures were positive in 84% of patients, and were commonly gram-positive cocci and gram-negative enteric organisms (11). Systemic antibiotics are essential, but no one knows how long treatment should be continued. SUMMARY This case report presents a broad spectrum of imaging of an infected thoracic aortic graft in a patient with Marfan’s syndrome with legionella, which is an unusual organism because of its etiology. REFERENCES
Fig. 7. Aortogram demonstrating ambiguity regarding communication of both lumens along the descending aorta.
tified by their characteristic signal increase with long repetition rates and long echo delays. MR has also been able to exclude suspected complications such as hemorrhage and graft occlusion (9). Aortic graft infections are uncommon, but potentially lethal complications of aortic graft surgery. In some cases, if the infection is limited to the groin, local therapy and preservation of the graft may be possible, whereas infections extending into the retroperitoneum require removal of the graft and revascularization of the lower limbs. Late infections will develop in 1.9% of patients who receive prosthetic grafts in the chest or mediastinum. Organisms such as staph epidermis, enterococcus, and Aspergillus may be isolated (10). However, to our knowledge, no case related to legionella has been reported. Several guidelines, which are useful in the management of these infections, have evolved: Prompt reoperation with complete debridement of infected and necrotic tissue, removal of infected prosthetic material if suture lines are involved, local antiseptic irrigation, and appropriate, specific systemic antibiotics, rerouting of blood flow through clean operative fields, and the use of pedicle flaps ( 11).
I. Fishman, M.C.; Hoffmann, A.R.; Kalusner, R.D.; Thaler, MS. Medicine, 2nd ed. Philadelphia, PA: Lippincott; 1985. 2. Carpentier, A.; Deloche, A.; Fabiani, J.N.; Chauvaud, S.; Relland, J. Nottin, R.; Vouhe, P.; Massoud, H.; Dubost, C. New surgical approach to aortic dissection: Flow reversal and thrombo-occlusion. J. Thorac. Cardiovasc. Surg. 81(5):659-668; 3. Guthaner, D.F. The use of CT in assessing aneurysms and dissecting hematomas of the thoracic aorta. In: Taveras, J.M.; Ferrucci, J.T., eds. Radiology. Philadelphia, PA: Lippincott; 1990: ch.35. 4. Pemes, J.M.; Grenier, P.; Desbleds, M.T.; de Brux, J.L. MR evaluation of chronic aortic dissection. J. Comput. Assist. Tomogr. 11(6):975-81; 1987. 5. Costello, P.; Dupuy, D.E.; Ecker, C.P. Spiral CT of the thorax with small volumes of contrast material: A comparative study. Radiology 18l(P):274; 1991. 6. Mark, A.S.; McCarthy, S.M.; Moss, A.A.; Price, D. Detection of abdominal aortic graft infection: Comparison of CT and inlabeled white blood cell scans. Am. J. Roentgen01 144(2):3158; 1985. 7. Blair, R.H.; Resnik, M.D.; Polga, J.P. CT appearance of mycotic abdominal aortic aneurysms. J. Comput. Assist. Tomogr. I3( 1): 101-4; 1989. 8. Vogelzang, R.L.; Sohaey, R. Infected aortic aneurysms: CT appearance. J. Comput. Assist. Tomogr. 12(1):109-12; 1988. 9. Auffermann. W.; Olofsson, P.; Stoney, R.; Higgins, C.B. MR imaging of complications of aortic surgery. J. Comput. Assist. Tomogr. 11(6):982-9; 1987. of infected thoracic 10. Hargrove, A.; Edmunds, A. Management aortic prosthesis grafts. Ann. Thorac. Surg. 37:72-77; 1984. Il. Yeager, R.A.; Moneta, G.L.; Taylor, L.M.; Harris, E.J.; McConnell, D.B.; Porter. J.M. Improving survival and limb salvage in patients with aortic graft infection. Am. J. Surg. 159:466-469; 1990.
About the Author-RICHARD
TELLO, M.D., graduated from MIT with a BS in mathematics, and a BSE in mechanical engineering in 1982, an MSME in mechanical engineering in 1983, and is pursuing his Ph.D. He received the MD from Stanford in 1989, and interned at St. Mary’s Hospital in San Francisco. He is currently a resident in radiology at New England Deaconess Hospital-Harvard Medical school, and is an RSNA research resident award recipient. Research interests include cardiovascular and three-dimensional imaging. About the Author-THOMAS HILL, M.D., is an associated professor of radiology at Harvard Medical School, and the director of the nuclear radiology section at the New England Deaconess Hospital. He is a
Legionella infected thoracic aortic graft graduate of Washington University Medical School, St. Louis, MO. He has been a staff radiologist at Deaconess since 1976. His publications in nuclear medicine have mainly focused on SPECT, especially in the area of brain and cardiovascular imaging. About the Author-GEORGE HARTNELL,FRCR, MRCP, graduated
from Bristol University in 1976, and trained in cardiology at Havefield Hospital. He subsequently trained in radiology at the Royal postgraduate Medical School, London. He is associate professor of radiology at Harvard Medical School, and his research interests are cardiovascular MRI and vascular interventional radiology. About the Author-PHILIP COSTELLO,M.D., graduated from the University of London Medical School. He pursued his radiology and postgraduate work at the University of Toronto, Canada. Since 1976 he has been a staff radiologist at the New England Deaconess Hospital,
??
R. TELLOet al.
67
and is currently an associate professor of radiology at Harvard Medical School. He has published extensively in areas related to thoracic radiology and computed tomography. About the Author--KEN STOKES,M.D., obtained his BA in Biology at Washington University, St. Louis in 1975. He attended St. Louis University Medical school obtaining his MD in 1979. An internship in general surgery, and residency in radiology at St. Louis University Hospitals was followed by a fellowship in vascular and interventional radiology at New England Deaconess Hospital in 1983. He then joined the staff at the Deaconess, and later took a position in Virginia where he was appointed assistant professor of radiology at Eastern Virginia Medical School. He returned to the Deaconess to become director of interventional radiology in 1988. Dr. Stoke’s writings cover a wide range of interests, from transluminal angioplasty, and femoropopliteal angioplasty in the diabetic patient, to abdominal MR angiography.