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Inflammatory aortic aneurysms: Characteristic appearance on magnetic resonance imaging
Eur J Vasc Surg 6, 399-402 (1992)
Inflammatory Aortic Aneurysms" Characteristic Appearance on Magnetic Resonance Imaging W. G. T e n n a n t 1, G. G. Hartnell 2, R. N. Baird I and M. H o r r o c k s I 1Vascular Studies Unit and 2 Department of Radiology, Bristol Royal Infirmary, Bristol, U.K. Ten to 15% of all aortic aneurysms show inflammatory change. They are characteristically covered on their anterior and lateral sides with thick white fibrous tissue. Peri-aortic fibrosis may spread into the retroperitoneum to encase and obstruct adjacent organs making operative treatment more difficult and increasing the operative morbidity and mortality. Fifteen patients with inflammatory aneurysms and 46 p~tients with simple non-inflammatory aneurysms were studied prospectively. Each patient underwent magnetic resonance imaging (MRI) using a Picker Vista MR2055 scanner operating at 0.5 tesla. Each scan was reviewed by a radiologist (G.G.H.) preoperatively and a diagnosis of inflammatory or non-inflammatory aneurysm made. At operation, the diagnosis of aneurysm type was made on macroscopic features of inflammatory change, and confirmed histologically using previously published criteria. The radiological diagnosis was found to correspond to the surgical and pathological diagnosis in all cases. In cases of inflammatory aortic aneurysm the aneurysm wall appeared laminated on MRI scan, showing three or more bright, high-signal layers. These appearances of inflammatory change are characteristic, and were present in all 15 patients with such aneurysms. There were no false positives among those patients with simple aneurysms, and no false negatives. Operative specimens of aortic wall were taken from four patients with inflammatory aortic aneurysms and four patients with simple non-inflammatory aortic aneurysms, and subjected to MRI scanning. The characteristic banding appeared only in the inflammatory aneurysm wall samples. Magnetic resonance imaging is a highly sensitive investigative technique for the detection of inflammatory aneurysms, showing characteristic changes. These changes are also seen in in vitro scans of wall samples from inflammatory aneurysms. In initial studies, these appearances would appear to correlate with histological findings. Key Words: Aortic aneurysm; Inflammatory aneurysm.
Introduction Inflammatory change is present in 10-15% of all abdominal aortic aneurysms. 1 Its presence often renders operative repair of such aneurysms difficult and hazardous. Characteristically, the anterior and lateral walls of the a n e u r y s m s are covered in a thick white layer of fibrous tissue which fixes the d u o d e n u m and other adjacent structures to the a n e u r y s m sac. 2 In florid cases, this tissue extends laterally into the retroperitoneum to involve nearby structures such as the ureters, the inferior vena cava, and the small bowel mesentery. The involved organs m a y be encased in a thick coat of fibrosis, and the resulting stenosis m a y lead to venous or ureteric obstruction. 3 In extreme cases, the appearances are of a h o m o g e n e o u s midabdominal mass of hard fibrous tissue containing the Please address all correspondence to: M. Horrocks, Department of Surgery, Royal United Hospital, Bath, BA1 3NG, U.K. 0950-821X/92/040399+04 $03.00/0 © 1992 Grune & Stratton Ltd.
aneurysm, inferior vena cava, left renal vein, ureters and d u o d e n u m within it. It is these features which give the operative treatment of inflammatory aneurysm a higher operative mortality than its simple noninflammatory counterpart, and such changes m a y require an alternative surgical approach. 4 It is clearly in the best interests of both patient and surgeon for the diagnosis of inflammatory change to be m a d e before, rather than at, operation. Specific clinical features and biochemical or haematological abnormalities are common, insensitive, and usually present only in advanced disease. Radiological detection b y ultrasound is unreliable with a sensitivity of u n d e r 20%. 5 Currently the most accurate radiological technique for the diagnosis of inflamm a t o r y a n e u r y s m is contrast enhanced c o m p u t e d tomography. Not only is it reliant on ionising radiation and intravenous contrast material, but its diagnostic accuracy has rarely exceeded 50% in prospective series. 6
400
W. G, Tennant et aL
We have investigated the characteristics of inflammatory aneurysms of magnetic resonance imaging (MRI) and describe previously unreported unique appearances of such aneurysms using this modality.
Patients and Methods
Sixty-one patients were studied prospectively. Each underwent preoperative MRI using a Picker Vista MR2055 scanner operating at 0.5 tesla. The images were acquired using saggital and coronal spin echo sequences (TE 26, TR 500-600 ms). Transverse images were ungated multi-echo and S.T.I.R. sequences. The multi-echo sequences had first-echo images at TE 20, TR 1800, and second image at TE 80, TR 1800. The (short-tall inversion recovery) S.T.I.R. sequences were acquired with a TE of 30, TI 100, and TR 1500. On the majority of the images slice thickness was 10 ram, with a field of view of 40-45 cm. The radiological diagnosis of inflammatory change was made preoperatively by a single observer (G.G.H.), who was blinded from the subsequent operative and histopathological findings. The diagnosis of inflammatory aneurysm was made on the basis of typical appearances at operation and histo-pathological examination of operative specimens according to previously published criteria. 7 Specimens of aortic wall were taken from the anterior part of the aneurysm in four of the patients with inflammatory aneurysms, and four with simple aneurysms. Adherent thrombus was removed, and the specimens stained using standard haematoxylin and eosin. The rest of each specimen was subjected to MRI. Specimens were prepared for MRI by immersing them in water, resting on a base of water-saturated foam rubber.
A constant finding in all cases of inflammatory aneurysms was a complex layered wall structure of concentric rings of high signal within the wall. Although seen on T 1 weighted images, this finding was most prominent on S.T.I.R. sequences. In all cases of inflammatory aneurysm there were three or more concentric layers of high signal density. Without exception, aneurysms classed as "simple" or noninflammatory lacked this characteristic, with walls displaying only one, or at most two rings of high signal density [(Fig. l(a) and (b)]. Eight samples of full-thickness aneurysm wall were scanned in vitro as described above. Four of the samples were taken from patients with inflammatory
(a)
(b)
Results
Sixty-one patients underwent MRI according to the protocol in the preoperative period. There were no instances in which the scan could not be completed. At operation, 15 aneurysms were classified as inflammatory, and this diagnosis was confirmed by postoperative histopathological examination. The remaining 46 were non-inflammatory. The mean age of the inflammatory group was 67 years (range 49-80, median 67) and it included two females. The group with simple aneurysms included five females and had a mean age of 72 (range 56-81, median 74). Eur J Vasc Surg Vol 6, July 1992
Fig. 1. (a) In vivo MRI scan of an inflammatory aneurysm. The area of the aorta is indicated within the arrowed bar. The wall can be seen to display four, and in places five, bright high signal density layers. (b) In vivo MRI scan of simple aneurysm. The area of the aorta is indicated within the arrowed bar. Only two bright high signal layers are seen in the wall.
MRI and Inflammatory Aortic Aneurysm
(a)
401
(b)
Fig. 2. (a) In vitro MRI scan of inflammatory aneurysm wall specimen. Layering is clearly demonstrated, and is most prominent in the images indicated by the arrows. (b) In vitro MRI scan of simple aneurysm wall specimen. Layering is absent, best seen in the images indicated by the arrows.
aneurysms, and four from patients with simple aneurysms. Inflammatory samples once again d e m o n strated a layered appearance, although this was less well-marked than w h e n seen in vivo. Simple aneurysms s h o w e d no such complex structure w h e n using in vitro scans [(Fig. 2(a) and (b)]. Routine staining of all in vitro a n e u r y s m samples was p e r f o r m e d using haematoxylin and eosin. Once again, inflammatory samples displayed layering. This appeared to be due to alternating layers of lymphocyte infiltrate and fibrosis (Fig. 3).
Fig. 3. Histological specimen of inflammatory aneurysm wall (haematoxylin and eosin stained). Layers of lymphocytes and fibrosis alternate.
Discussion
So-called " i n f l a m m a t o r y " aneurysms account for 10-15% of all aortic aneurysms. They are characterised b y peri-aneurysmal inflammatory change and fibrosis. The aetiology of the inflammation is u n k n o w n , but is thought to be due to an i m m u n e response to a c o m p o n e n t of atheroma. According to the w o r k of Mitchinson, oxidised lipoprotein or "ceroid" is extruded through the d a m a g e d medial coat of the aneurysm, presenting to the i m m u n e system. 8 The resulting fibrosis is responsible for the increased difficulty !n operative repair of inflammatory aneurysms, and the associated increased operative mortality. W h e n confined to the aorta, the fibrotic change m a y result in dense adhesions between the aorta and the d u o d e n u m . It m a y also extend superiorly to obscure the a n e u r y s m neck, encasing both the neck and the left renal vein in a mass of hard fibrotic tissue. In such cases, control of the aorta m a y have to be at the suprarenal or thoracic level. In florid cases, fibrosis m a y extend into the retrop e r i t o n e u m to involve the inferior vena cava, the ureters, and the mesentery of both the small bowel and transverse colon. The ureters are frequently d r a w n medially, and m a y be so stenosed as to cause post-renal failure. Adhesion of the inferior vena cava to the a n e u r y s m wall m a y cause obstruction, and m a y place it at risk during dissection of the a n e u r y s m sac. In our o w n recently reviewed retrospective series of 47 inflammatory aneurysms, the ureters were involved in 10 cases, the left renal vein in five and the Eur J Vasc Surg Vol 6, July 1992
402
W.G. Tennant et al.
inferior v e n a cava in two. Four patients required extension of the a b d o m i n a l incision into the chest to gain control of the aorta a b o v e the d i a p h r a g m because of u n e x p e c t e d l y extensive i n f l a m m a t o r y change. The operative (30 day) mortality for i n f l a m m a t o r y aortic a n e u r y s m s in this series w a s 13%, c o m p a r e d with 4.3% for simple n o n - i n f l a m m a t o r y a n e u r y s m s . The p r e o p e r a t i v e diagnosis of i n f l a m m a t o r y change is currently difficult. In s o m e cases, s y m p t o m s a n d signs exist, often the result of visceral stenosis or obstruction b y fibrosis, b u t in the vast majority of cases the i n f l a m m a t o r y change is a s y m p t o m a t i c . The only haematological investigation which m a y be useful is the E.S.R. D o c u m e n t e d reports of a n a e m i a and leukocytosis are rare. There are no reported specific biochemical abnormalities in i n f l a m m a t o r y a n e u r y s m disease. Preoperative diagnosis of i n f l a m m a t o r y a n e u r y s m s d e p e n d s u p o n the use of radiological methods. Plain r a d i o g r a p h y is unhelpful. I n t r a v e n o u s u r o g r a p h y m a y s h o w medial deviation of the ureters, but this is not a specific sign, 9 a n d d e p e n d s on the presence of uretic i n v o l v e m e n t in fibrosis. U l t r a s o u n d has been a d v o c a t e d in the past, but m o r e recently has been s u p e r s e d e d b y contrast enhanced c o m p u t e d tomography. U l t r a s o u n d is not sensitive e n o u g h to be of a n y clinical use, and is only able to detect i n f l a m m a tory a n e u r y s m s in 20% of cases. 5 Even in s o m e of the largest prospective studies of i n f l a m m a t o r y a n e u r y s m disease, c o m p u t e d t o m o g r a p h y has a diagnostic sensitivity of a p p r o x i m a t e l y 50% .6 The results presented here suggest that i n f l a m m a tory a n e u r y s m s h a v e a characteristic a n d specific a p p e a r a n c e on MRI. This is m o s t obvious on S.T.I.R. sequences, a m o d a l i t y which particularly enhances differences in tissue w a t e r content. The precise origin of the concentric layered a p p e a r a n c e in u n k n o w n . The l u m e n of the aorta is seen on MRI as a " f l o w v o i d " of low signal intensity, so it is likely that one of the con-
Eur J Vasc Surg Vol 6, July 1992
centric rings of high signal is attributable to thrombus. Initial studies, however, reveal that concentric layered a p p e a r a n c e s are also seen in in vitro MRI images, and suggest that MRI detects intramural structural changes not visible with other radiological modalities. There is initial evidence to suggest that these intram u r a l structural differences m a y be correlated with light microscopic changes. Magnetic resonance i m a g i n g does not use ionising radiation, is not d e p e n d a n t on the use of intravenous contrast material, a n d has a higher diagnostic sensitivity for i n f l a m m a t o r y change than that previously reported for other radiological modalities. We believe that MRI is n o w the investigation of choice for the detection o f i n f l a m m a t o r y change in a b d o m i n a l aortic aneurysms.
References
1 CRAWFORDJL, STOWECL, SAFIHJ, et al. Inflammatory aneurysms of the aorta. J Vasc Surg 1985; 2: 113-124. 20LCOTT C, HOLCROFTJW, STONEYRJ, WYLIEEJ. Unusual problems of abdominal aortic aneurysms. Am J Surg 1978; 135: 426-431. 3 DARKESG, GLASSRE, EADIEDGA. Abdominal aortic aneurysm: perianeurysmal fibrosis and ureteric obstruction and deviation. BrJ Surg 1977; 64: 649-652. 4 STERPETTIAV, HUNTERWJ, FELDHAUSRJ, et al. Inflammatory aneurysms of the abdominal aorta: incidence, pathologic and aetiologic considerations. J Vasc Surg 1989; 9: 643-650. 5 STRINGERMD, BENTLEYPG. Inflammatory aortic aneurysms. Br J Hosp Med 1987;June: 512-515. 6 FITZGERALDEJ, BLACKETTRL. "Inflammatory" abdominal aortic aneurysms. Clin Rad 1988; 39: 247-251. 7 MCMAHONJN, DAVIESJD, SCOTTDJA, et al. The microscopic features of inflammatory abdominal aortic aneurysms: discriminant analysis. Histopathology 1990; 16: 557-564. 8 MITCHINSONMJ. Chronic periaortitis and periarteritis. Histopathology 1984; 8: 589-600. 9 PECKDR, BHATTGM, LOWMANRL. Traction displacement of the ureter: a sign of aortic aneurysm. J Uro11973; 109: 983-986. Accepted 14 January 1992
Inflammatory Aortic Aneurysms" Characteristic Appearance on Magnetic Resonance Imaging W. G. T e n n a n t 1, G. G. Hartnell 2, R. N. Baird I and M. H o r r o c k s I 1Vascular Studies Unit and 2 Department of Radiology, Bristol Royal Infirmary, Bristol, U.K. Ten to 15% of all aortic aneurysms show inflammatory change. They are characteristically covered on their anterior and lateral sides with thick white fibrous tissue. Peri-aortic fibrosis may spread into the retroperitoneum to encase and obstruct adjacent organs making operative treatment more difficult and increasing the operative morbidity and mortality. Fifteen patients with inflammatory aneurysms and 46 p~tients with simple non-inflammatory aneurysms were studied prospectively. Each patient underwent magnetic resonance imaging (MRI) using a Picker Vista MR2055 scanner operating at 0.5 tesla. Each scan was reviewed by a radiologist (G.G.H.) preoperatively and a diagnosis of inflammatory or non-inflammatory aneurysm made. At operation, the diagnosis of aneurysm type was made on macroscopic features of inflammatory change, and confirmed histologically using previously published criteria. The radiological diagnosis was found to correspond to the surgical and pathological diagnosis in all cases. In cases of inflammatory aortic aneurysm the aneurysm wall appeared laminated on MRI scan, showing three or more bright, high-signal layers. These appearances of inflammatory change are characteristic, and were present in all 15 patients with such aneurysms. There were no false positives among those patients with simple aneurysms, and no false negatives. Operative specimens of aortic wall were taken from four patients with inflammatory aortic aneurysms and four patients with simple non-inflammatory aortic aneurysms, and subjected to MRI scanning. The characteristic banding appeared only in the inflammatory aneurysm wall samples. Magnetic resonance imaging is a highly sensitive investigative technique for the detection of inflammatory aneurysms, showing characteristic changes. These changes are also seen in in vitro scans of wall samples from inflammatory aneurysms. In initial studies, these appearances would appear to correlate with histological findings. Key Words: Aortic aneurysm; Inflammatory aneurysm.
Introduction Inflammatory change is present in 10-15% of all abdominal aortic aneurysms. 1 Its presence often renders operative repair of such aneurysms difficult and hazardous. Characteristically, the anterior and lateral walls of the a n e u r y s m s are covered in a thick white layer of fibrous tissue which fixes the d u o d e n u m and other adjacent structures to the a n e u r y s m sac. 2 In florid cases, this tissue extends laterally into the retroperitoneum to involve nearby structures such as the ureters, the inferior vena cava, and the small bowel mesentery. The involved organs m a y be encased in a thick coat of fibrosis, and the resulting stenosis m a y lead to venous or ureteric obstruction. 3 In extreme cases, the appearances are of a h o m o g e n e o u s midabdominal mass of hard fibrous tissue containing the Please address all correspondence to: M. Horrocks, Department of Surgery, Royal United Hospital, Bath, BA1 3NG, U.K. 0950-821X/92/040399+04 $03.00/0 © 1992 Grune & Stratton Ltd.
aneurysm, inferior vena cava, left renal vein, ureters and d u o d e n u m within it. It is these features which give the operative treatment of inflammatory aneurysm a higher operative mortality than its simple noninflammatory counterpart, and such changes m a y require an alternative surgical approach. 4 It is clearly in the best interests of both patient and surgeon for the diagnosis of inflammatory change to be m a d e before, rather than at, operation. Specific clinical features and biochemical or haematological abnormalities are common, insensitive, and usually present only in advanced disease. Radiological detection b y ultrasound is unreliable with a sensitivity of u n d e r 20%. 5 Currently the most accurate radiological technique for the diagnosis of inflamm a t o r y a n e u r y s m is contrast enhanced c o m p u t e d tomography. Not only is it reliant on ionising radiation and intravenous contrast material, but its diagnostic accuracy has rarely exceeded 50% in prospective series. 6
400
W. G, Tennant et aL
We have investigated the characteristics of inflammatory aneurysms of magnetic resonance imaging (MRI) and describe previously unreported unique appearances of such aneurysms using this modality.
Patients and Methods
Sixty-one patients were studied prospectively. Each underwent preoperative MRI using a Picker Vista MR2055 scanner operating at 0.5 tesla. The images were acquired using saggital and coronal spin echo sequences (TE 26, TR 500-600 ms). Transverse images were ungated multi-echo and S.T.I.R. sequences. The multi-echo sequences had first-echo images at TE 20, TR 1800, and second image at TE 80, TR 1800. The (short-tall inversion recovery) S.T.I.R. sequences were acquired with a TE of 30, TI 100, and TR 1500. On the majority of the images slice thickness was 10 ram, with a field of view of 40-45 cm. The radiological diagnosis of inflammatory change was made preoperatively by a single observer (G.G.H.), who was blinded from the subsequent operative and histopathological findings. The diagnosis of inflammatory aneurysm was made on the basis of typical appearances at operation and histo-pathological examination of operative specimens according to previously published criteria. 7 Specimens of aortic wall were taken from the anterior part of the aneurysm in four of the patients with inflammatory aneurysms, and four with simple aneurysms. Adherent thrombus was removed, and the specimens stained using standard haematoxylin and eosin. The rest of each specimen was subjected to MRI. Specimens were prepared for MRI by immersing them in water, resting on a base of water-saturated foam rubber.
A constant finding in all cases of inflammatory aneurysms was a complex layered wall structure of concentric rings of high signal within the wall. Although seen on T 1 weighted images, this finding was most prominent on S.T.I.R. sequences. In all cases of inflammatory aneurysm there were three or more concentric layers of high signal density. Without exception, aneurysms classed as "simple" or noninflammatory lacked this characteristic, with walls displaying only one, or at most two rings of high signal density [(Fig. l(a) and (b)]. Eight samples of full-thickness aneurysm wall were scanned in vitro as described above. Four of the samples were taken from patients with inflammatory
(a)
(b)
Results
Sixty-one patients underwent MRI according to the protocol in the preoperative period. There were no instances in which the scan could not be completed. At operation, 15 aneurysms were classified as inflammatory, and this diagnosis was confirmed by postoperative histopathological examination. The remaining 46 were non-inflammatory. The mean age of the inflammatory group was 67 years (range 49-80, median 67) and it included two females. The group with simple aneurysms included five females and had a mean age of 72 (range 56-81, median 74). Eur J Vasc Surg Vol 6, July 1992
Fig. 1. (a) In vivo MRI scan of an inflammatory aneurysm. The area of the aorta is indicated within the arrowed bar. The wall can be seen to display four, and in places five, bright high signal density layers. (b) In vivo MRI scan of simple aneurysm. The area of the aorta is indicated within the arrowed bar. Only two bright high signal layers are seen in the wall.
MRI and Inflammatory Aortic Aneurysm
(a)
401
(b)
Fig. 2. (a) In vitro MRI scan of inflammatory aneurysm wall specimen. Layering is clearly demonstrated, and is most prominent in the images indicated by the arrows. (b) In vitro MRI scan of simple aneurysm wall specimen. Layering is absent, best seen in the images indicated by the arrows.
aneurysms, and four from patients with simple aneurysms. Inflammatory samples once again d e m o n strated a layered appearance, although this was less well-marked than w h e n seen in vivo. Simple aneurysms s h o w e d no such complex structure w h e n using in vitro scans [(Fig. 2(a) and (b)]. Routine staining of all in vitro a n e u r y s m samples was p e r f o r m e d using haematoxylin and eosin. Once again, inflammatory samples displayed layering. This appeared to be due to alternating layers of lymphocyte infiltrate and fibrosis (Fig. 3).
Fig. 3. Histological specimen of inflammatory aneurysm wall (haematoxylin and eosin stained). Layers of lymphocytes and fibrosis alternate.
Discussion
So-called " i n f l a m m a t o r y " aneurysms account for 10-15% of all aortic aneurysms. They are characterised b y peri-aneurysmal inflammatory change and fibrosis. The aetiology of the inflammation is u n k n o w n , but is thought to be due to an i m m u n e response to a c o m p o n e n t of atheroma. According to the w o r k of Mitchinson, oxidised lipoprotein or "ceroid" is extruded through the d a m a g e d medial coat of the aneurysm, presenting to the i m m u n e system. 8 The resulting fibrosis is responsible for the increased difficulty !n operative repair of inflammatory aneurysms, and the associated increased operative mortality. W h e n confined to the aorta, the fibrotic change m a y result in dense adhesions between the aorta and the d u o d e n u m . It m a y also extend superiorly to obscure the a n e u r y s m neck, encasing both the neck and the left renal vein in a mass of hard fibrotic tissue. In such cases, control of the aorta m a y have to be at the suprarenal or thoracic level. In florid cases, fibrosis m a y extend into the retrop e r i t o n e u m to involve the inferior vena cava, the ureters, and the mesentery of both the small bowel and transverse colon. The ureters are frequently d r a w n medially, and m a y be so stenosed as to cause post-renal failure. Adhesion of the inferior vena cava to the a n e u r y s m wall m a y cause obstruction, and m a y place it at risk during dissection of the a n e u r y s m sac. In our o w n recently reviewed retrospective series of 47 inflammatory aneurysms, the ureters were involved in 10 cases, the left renal vein in five and the Eur J Vasc Surg Vol 6, July 1992
402
W.G. Tennant et al.
inferior v e n a cava in two. Four patients required extension of the a b d o m i n a l incision into the chest to gain control of the aorta a b o v e the d i a p h r a g m because of u n e x p e c t e d l y extensive i n f l a m m a t o r y change. The operative (30 day) mortality for i n f l a m m a t o r y aortic a n e u r y s m s in this series w a s 13%, c o m p a r e d with 4.3% for simple n o n - i n f l a m m a t o r y a n e u r y s m s . The p r e o p e r a t i v e diagnosis of i n f l a m m a t o r y change is currently difficult. In s o m e cases, s y m p t o m s a n d signs exist, often the result of visceral stenosis or obstruction b y fibrosis, b u t in the vast majority of cases the i n f l a m m a t o r y change is a s y m p t o m a t i c . The only haematological investigation which m a y be useful is the E.S.R. D o c u m e n t e d reports of a n a e m i a and leukocytosis are rare. There are no reported specific biochemical abnormalities in i n f l a m m a t o r y a n e u r y s m disease. Preoperative diagnosis of i n f l a m m a t o r y a n e u r y s m s d e p e n d s u p o n the use of radiological methods. Plain r a d i o g r a p h y is unhelpful. I n t r a v e n o u s u r o g r a p h y m a y s h o w medial deviation of the ureters, but this is not a specific sign, 9 a n d d e p e n d s on the presence of uretic i n v o l v e m e n t in fibrosis. U l t r a s o u n d has been a d v o c a t e d in the past, but m o r e recently has been s u p e r s e d e d b y contrast enhanced c o m p u t e d tomography. U l t r a s o u n d is not sensitive e n o u g h to be of a n y clinical use, and is only able to detect i n f l a m m a tory a n e u r y s m s in 20% of cases. 5 Even in s o m e of the largest prospective studies of i n f l a m m a t o r y a n e u r y s m disease, c o m p u t e d t o m o g r a p h y has a diagnostic sensitivity of a p p r o x i m a t e l y 50% .6 The results presented here suggest that i n f l a m m a tory a n e u r y s m s h a v e a characteristic a n d specific a p p e a r a n c e on MRI. This is m o s t obvious on S.T.I.R. sequences, a m o d a l i t y which particularly enhances differences in tissue w a t e r content. The precise origin of the concentric layered a p p e a r a n c e in u n k n o w n . The l u m e n of the aorta is seen on MRI as a " f l o w v o i d " of low signal intensity, so it is likely that one of the con-
Eur J Vasc Surg Vol 6, July 1992
centric rings of high signal is attributable to thrombus. Initial studies, however, reveal that concentric layered a p p e a r a n c e s are also seen in in vitro MRI images, and suggest that MRI detects intramural structural changes not visible with other radiological modalities. There is initial evidence to suggest that these intram u r a l structural differences m a y be correlated with light microscopic changes. Magnetic resonance i m a g i n g does not use ionising radiation, is not d e p e n d a n t on the use of intravenous contrast material, a n d has a higher diagnostic sensitivity for i n f l a m m a t o r y change than that previously reported for other radiological modalities. We believe that MRI is n o w the investigation of choice for the detection o f i n f l a m m a t o r y change in a b d o m i n a l aortic aneurysms.
References
1 CRAWFORDJL, STOWECL, SAFIHJ, et al. Inflammatory aneurysms of the aorta. J Vasc Surg 1985; 2: 113-124. 20LCOTT C, HOLCROFTJW, STONEYRJ, WYLIEEJ. Unusual problems of abdominal aortic aneurysms. Am J Surg 1978; 135: 426-431. 3 DARKESG, GLASSRE, EADIEDGA. Abdominal aortic aneurysm: perianeurysmal fibrosis and ureteric obstruction and deviation. BrJ Surg 1977; 64: 649-652. 4 STERPETTIAV, HUNTERWJ, FELDHAUSRJ, et al. Inflammatory aneurysms of the abdominal aorta: incidence, pathologic and aetiologic considerations. J Vasc Surg 1989; 9: 643-650. 5 STRINGERMD, BENTLEYPG. Inflammatory aortic aneurysms. Br J Hosp Med 1987;June: 512-515. 6 FITZGERALDEJ, BLACKETTRL. "Inflammatory" abdominal aortic aneurysms. Clin Rad 1988; 39: 247-251. 7 MCMAHONJN, DAVIESJD, SCOTTDJA, et al. The microscopic features of inflammatory abdominal aortic aneurysms: discriminant analysis. Histopathology 1990; 16: 557-564. 8 MITCHINSONMJ. Chronic periaortitis and periarteritis. Histopathology 1984; 8: 589-600. 9 PECKDR, BHATTGM, LOWMANRL. Traction displacement of the ureter: a sign of aortic aneurysm. J Uro11973; 109: 983-986. Accepted 14 January 1992