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Spiral CT in acute non-cardiac chest pain
Clinical Radiology (1999) 54, 38-45
Spiral CT in Acute Non-Cardiac T. B. OLIVER*,
J. T. MURCHISON”,
Chest Pain J. H. REID?
*Department of Clinical Imaging, Royal Infirmary of Edinburgh, Lauriston Place, Edinburgh, EH3 9W, TDepartment of Radiology, Borders General Hospital, Melrose, Roxburghshire, TD6 3BS, UK Received: 12 March 1998 Revised: 6 August 1998
UK and
Accepted: 20 August 1998
Aim: Spiral CT in acute non-cardiac chest pain is usually requested to diagnose aortic dissection but a spectrum of other cardiovascular diseases may simulate this. The purpose of this study was to assess the impact of spiral computed tomography (CT) in patients with suspected aortic dissection and to determine the nature and frequency of other disorders simulating it. Methods: Over a 26-month period, all patients undergoing CT for suspected acute aortic dissection were recruited. CT was performed using a standard protocol. The CT examinations and reports were reviewed along with other relevant imaging, clinical data, surgical findings and post-mortem results. The pattern of diagnoses and their associations were evaluated. Results: Seventy-six CT examinations were performed on 70 patients of whom 47 were male. The age of the patients ranged from 24 to 84. Seven patients had previously undergone cardiothoracic surgery. Twenty-four patients had normal CT findings; 46 patients (66%) had abnormal findings. Seventy-three significant pathologies were identified including thoracic aortic aneurysm (16 cases), aortic dissection (14 cases), acute intramural aortic haematoma (nine cases), aortic rupture (eight cases), atherosclerosis (four cases) and penetrating atheromatous ulcer (two cases), pulmonary embolus (four cases), pericardial disease (12 cases) and complications following surgery (three cases). The majority of patients had a life-threatening disease. Five patients without dissection had CT findings that explained clinical pulse deficits. Conclusion: Sudden onset non-cardiac, non-pleuritic chest pain is common to several acute cardiovascular disorders. Patients have a high incidence of life-threatening disease. Of this group, classic aortic dissection is the most common diagnosis but comprises a minority of cases. Spiral CT is a reliable diagnostic test but requires conscientious technique for optimum sensitivity and accuracy. Most patients will have abnormal CT findings. Oliver T. B. et al. (1999) Clinical Radiology 54,38-45. Key words: spinal CT, aortic dissection,haematoma, chest pain, differential diagnosis.
Patients presenting with sudden onset non-cardiac chest pain are commonly suspected of having thoracic aortic dissection but may harbour various other acute cardiovascular pathologies. These include acute intramural aortic haematoma, leaking aortic aneurysm, atherosclerotic ulcer, pericarditis and pulmonary embolus. Spiral computed tomography (CT) is fast, widely available and is established as a first line investigation in the work-up of these disorders. In the radiological literature, these entities are usually studied in isolation but in reality form a spectrum of related diseases which often co-exist. This observation along with the difficulty in separating these disorders on clinical grounds suggests that they should be considered together. The aim of this study was to assessthe impact of spiral CT in patients with suspected acute aortic dissection, to determine the prevalence of abnormal examinations, to characterize the spectrum and relative frequency of the diseasesencountered and to record associations between these diseases and the radiological findings useful in distinguishing them. Correspondence University Hospital 0009-9260/99/010038+08
to: Dr T. B. Oliver, Department of Clinical Imaging, of Wales, Heath Park, Cardiff, CF4 4XW, UK. $12.00/O
METHODS
AND MATERIALS
In our institution, a large teaching hospital and regional thoracic surgical referral centre, scans with this indication are performed using a standardprotocol on a GE HiSpeed Advantage scanner.An initial precontrast spiral CT through the great vessles and thoracic aorta using 1Omm collimation is followed by a second spiral CT with intravenous contrast medium using 5 mm collimation over a similar distribution. Ninety mililitres of contrast (300 mgI/nil) is administered by pump at 3 ml/s and optimal aortic contrast achieved using a ‘smart’ software algorithm, centred on the aortic arch. If aortic dissection is demonstrated, the inferior extent is delineated with a further spiral scan, using another injection of contrast if necessary.Images are reviewed at a workstation. This allows multiplanar reformats to be viewed if desired. A CT examination typically takes lessthan 15 min. All patients scanned as an emergency for suspected acute aortic dissection over a 26-month period were included. This simple inclusion criterium was chosen to produce an unbiased reflection of local clinical practice. All CT examinations and reports were retrospectively reviewed along with other relevant imaging, clinical data, 0 1999 The Royal
College
of Radiologists
SPIRAL
Table
1 - Spiral
CT for suspected
aortic
dissection-diagnoses
CT IN ACUTE
CHEST
PAIN
(n = 73)
Diagnosis
Number of cases
Comments
Aortic dissection Acute intramural aortic haematoma Thoracic aortic aneurysm Pulmonary embolus Pericardial collection Mediastinal haematoma Simple atheroma Penetrating atheromatous ulcer Other diagnoses
14 9 16 4 12 9 4 2
I type A, I type B 4 type A, 5 type B 4 simple, 12 complex 7 fluid, 5 high density 8 with aortic rupture
3
surgical findings and autopsy results. The pattern of diseases and their associations were recorded. RESULTS Seventy-six CT examinations were performed acutely in 70 patients of whom 47 were male. The age of the patients ranged from 24 to 84. Seven patients had previously undergone cardiothoracic surgery, 46 patients (66%) had abnormal CT findings and 73 significant pathologies were identified among these (Table 1).
(4
Aortic Dissection Fourteen aortic dissections were diagnosed. Seven were type A and seven were type B. In two patients (one type A and one type B), the aortic dissection was associated with acute intramural haematoma within the ascending aorta (type A) (Fig. la,b). Acute Intramural
Aortic Haematoma
Nine patients had acute intramural haematoma defined as crescentic or circumferential high density aortic wall thickening on the pre-contrast scan which failed to enhance following contrast (Fig. 2a,b). Four patients had type A haematomas and five had type B. Two patients had a coexisting classic dissection. Aortic Aneurysm Sixteen patients had aneurysmal dilatation of the thoracic aorta. Complications had arisen in 12 of these (11 dissections or acute intramural haematomas and one spontaneous rupture). Pulmonary
Embolus
Four patients had pulmonary emboli (Fig. 3). In two of these, large pulmonary artery thrombus loads were associated with occlusion of a great vessel by serpiginous material and a paradoxical embolus was presumed to have occurred. Pericardial
Disease
Five patients had high density pericardial collections, suggestive of pericardial haematoma. In four, this was associated
(b) Fig. 1 - Mixed type A aortic dissection and acute intramural haematoma. (a) Axial CT without contrast medium through aortic root. A triangular hyperdense region representing acute intramural haematoma is visible within the dilated aorta (small arrows). (b) Following contrast medium the haematoma fails to opacify but a dissection flap and false lumen are demonstrated. Pericardial haematoma is also present.
with acute aortic disease (two type A dissections, one type A mixed haematoma/dissection and one aortic root rupture due to cystic medial necrosis). In one case, a subsequent diagnosis of myocardial infarct was made. Magnetic resonance imaging (MRI) in this case showed left ventricular wall thinning but no evidence of wall rupture. Seven patients had fluid density pericardial collections. In three, there was associated aortic disease (one type A
Fig. 3 - Pulmonary embolus. Axial CT following contrast medium through the main pulmonary artery demonstrating extensive tubular thrombus, typical of material of systemic venous origin.
Atheroma Two cases of penetrating atheromatous aortic ulcer were identified (Fig. 4a,b). One presented with aortic rupture and the other, in a surgically unfit patient with pain but no CT evidence of acute rupture was treated conservatively, serial follow-up demonstrating no interval change. In three cases atheromatous disease of the aorta or great vessels, which resulted in a clinical pulse deficit was noted.
‘Pseudo-Dissection’: @I Fig. 2 - Acute intramural aortic haematoma. Axial CT through aortic arch. In (a), prior to contrast medium a hyperdense rind of haematoma encircles the aortic arch (arrows). (b) Following contrast medium this fails to enhance.
CT Findings Responsible for Pulse Deficits
In five cases described above (two paradoxical great vessel emboli, two atheromatous great vessels and one aortic occlusion) abnormalities which accounted for clinical pulse deficits were observed (Fig. 5a-c). Other Abnormalities
haematoma and two type B dissections). In four, the effusion was an isolated abnormality which subsequently resolved and was ascribed to pericarditis. Mediastinal
Haematoma
This was identified in nine cases. In one case, the haematoma was due to oozing following mitral valve replacement and it became infected necessitating drainage. In eight cases, haematoma resulted from aortic rupture, which was sometimes found to be contained at surgery. Underlying diagnoses were type A dissection (two cases), type A haematoma (two cases), type B haematoma, cystic medial necrosis, penetrating atheromatous ulcer and aortic aneurysm.
One patient who had had surgery for aortic coarctation in childhood presented with a calcified stenosis at the operation site but no evidence of dissection. Another patient with a perforated duodenal ulcer was retrospectively diagnosed after developing an upper abdominal abscess.A few bubbles of free gas on the lowest image of the initial aortic CT had been missed. A third patient who had an aortic graft for previous aortic dissection developed a pseudoaneurysm due to leakage at the anastomosis site (Fig. 6a,b).
DISCUSSION
This study emphasizes the utility of spiral CT in the investigation of patients with suspected aortic dissection.
SPIRAL
CT IN ACUTE
(b) Fig. 4 - Penetrating atheromatous aortic ulcer. (a) Axial CT demonstrating a large ulcer protruding laterally from an atheromatous descending thoracic aorta (arrow). Earlier leakage has resulted in a left pleural collection. (b) Aortographic correlation from the same patient showing the typical angiographic appearances.
CHEST PAIN
41
Although aortic dissection or haematoma were the disorders most frequently encountered (21 of 46 abnormal scans), a spectrum of other acute diseases sharing the same clinical features were identified. A high proportion of patients had abnormal scans. This reflects both the sensitivity of spiral CT and the high level of clinical suspicion behind requests for imaging, many of which were made outside normal working hours. Several technical points merit discussion. Use of a pump injector and ‘smart’ timing allows consistent and optimal enhancement of the aortic lumen. Windowing should be chosen so that dense contrast within true and false lumens does not obscure a thin dissection flap. Several causesof falsepositive CT diagnosis of dissection have been described [1,2]. These include enhancement of pulmonary veins, atelectatic lung or perianeurysmal fibrosis adjacent to the descending aorta which may simulate type B dissection and movement of the ascending aorta which produces a double image of the wall which may simulate a type A dissection. This latter artefact can be abolished by reconstruction of an additional single level scan series into short (100 ms) acquisition images [3]. In practice we have not found it troublesome, as it is characteristically visible on both sides of the aorta, has a flattened internal margin which is not typical for a dissection and is not identified on sequential slices through the adjacent aorta. We found multiplanar reformats useful to delineate the origin of some dissections and this is consistent with the experience of other workers (Fig. 7a,b) [4]. Three-dimensional reconstructions may be preferred by clinicians but due to the density thresholds used in producing these images, acute haematoma, thrombosed false lumens or established mural thrombus may not be demonstrated on such images. We believe a precontrast CT is mandatory. This optimally demonstrates calcification, which may be seen in association with atheroma, within longstanding luminal thrombus or in the intimal flap of a dissection. Furthermore, acute haematoma, either within the aortic wall or leaking into the mediastinum is best visualized before contrast due to its high density compared to flowing blood or mural thrombus. Acute haematoma may be seen in up to 44% of casesof acute dissection [I]. Acute intramural aortic haematoma is an important entity that has recently received attention in the literature [5-71. Although previously recognized as a distinct imaging appearance, it has usually been ascribed to atypical or thrombosed dissection. In large surgical series, intramural haematoma without intimal disruption is often described in a proportion of cases.Thus, whilst some cases of acute intramural haematoma may be due to thrombosis of a classical dissection, others must be regarded as the primary event. Spontaneous bleeding from aortic vasa vasora is thought to be the causeof the haemorrhage which may be complicated by aortic rupture or progression to classic aortic dissection or aneurysm. Previous reports have suggested that between 13 and 41% of acute dissections have CT features compatible with intramural haematoma [3,5,8,9]. The high proportion (42%) in our series may reflect increased awareness of the condition or the imaging advantages and greater coverage allowed by spiral CT. The close relationship between acute haematoma and dissection is reflected in our series which included two patients where intramural haematoma and dissection occurred together. In a further patient,
42
CLINICAL
RADIOLOGY
serial scans showed development of a contrasting false lumen where non-enhancing haematoma had been present on a scan the day before. Haematoma proximal to the left subclavian artery origin (type A) carries a similar prognosis to type A dissection and complications are more likely when the aortic root diameter is greater than 5cm or serial imaging shows failure of the haematoma to resolve [5,6,9,10]. The high mortality which accompanies untreated aortic dissection (80% at 1 month) makes early identification critical. Depending on available resources CT, MR, angiography or transoesophageal echocardiography (TOE) may be used in diagnosis and all have been reported to be reliable [ 1 l- 141. Although the traditional gold standard, angiography has been replaced by CT or TOE as the primary imaging modality in most centres, largely because of its invasive nature and inability to detect dissecting haematomas when there is no flap. Some surgeons may still request angiography, either because of familiarity with the images produced or where information is required about aortic valve function, the integrity of coronary arteries or involvement of the great vessels. A recent comparative study of spiral CT, multiplanar TOE and MR showed no difference in sensitivity (100% for all modalities) or specificity (100, 94 and 94% respectively) between the three techniques in the detection of thoracic aortic dissection. However, spiral CT was more sensitive and specific than TOE or MR in the assessment of great vessel involvement [ 151. Spiral CT has the advantages of speed, wide availability and ease of monitoring of sick patients. It readily distinguishes acute intramural aortic haematoma from atheroma or mural thrombus whereas TOE does not. CT provides no information about the coronary arteries or aortic valve function thus angiography or echocardiography may be required. The wide coverage permitted by spiral CT allows some assessmentof the distal aortic branches however and provides other diagnostic possibilities, as illustrated by this series. TOE is accurate in experienced hands and can be performed at the bedside of critically ill patients. Blind areas in the ascending aorta and arch due to the major airways initially led to false-negative examinations. The advent of multiplanar TOE has reduced this problem considerably. A low incidence of false-positive examinations persists due to reverberation artefact encountered in dilated or ectatic aortas. TOE is limited to evaluation of disease of the aorta and heart. The biggest drawback with TOE, however, is availability as even in larger centres, provision of a comprehensive out of hours service can be difficult. MR along with CT provides reproducible, measurable images which facilitate follow up of dissections, aneurysms
5 - ‘Pseudodissection’. CT findings explaining clinical pulse deficits. Paradoxical embolus. (a) Sagittal oblique reformatted CT image through the aorta following contrast. A serpiginous filling defect representing a paradoxical embolus extends from an occluded left subclavian artery origin into the descending aorta. Large central pulmonary emboli were seen on axial images. Key: LCA = left carotid artery; LSA = left subclavian artery; DA = descending aorta; PA = main pulmonary artery. Reprinted with permission of British Journal of Radiology. Atheroma. (6) Axial CT following contrast through proximal left subclavian artery demonstrating a focal concentric stenosis due to atheroma (arrow). (c) A more cephalad slice from the same examination shows normal opacifaction of the artery. Fig.
SPIRAL
CT IN ACUTE
(b)
CHEST
PAIN
(4
Fig. 6 - Pseudoaneurysm. (a) Axial CT following contrast through the aortic root demonstrates contrast within the sac of a pseudoaneurysm arising at the site of previous surgery for aortic dissection (arrow). A pericardial haematoma is present and a dissection flap persists in the descending aorta. (b) Tl weighted axial MR image at the same site showing turbulent flow within the pseudoaneurysm sac (arrow) and high signal intensity methaemoglobin in the haematoma periphery.
or intramural aortic haematoma (Fig. 8) [16]. The signal returned from haematoma in the acute phase is not specific for this entity however [7]. High field strength systems and the use of both spin echo and gradient echo sequenceswhich allows distinction of slow flow from haematoma have been advocated for maximum accuracy [ 151. The long examination time and difficulties in monitoring unstable patients are disadvantages of MR although satisfactory results have been reported using MR as the initial imaging modality in suspected acute dissection u71.
Choice of modality reflects accuracy and availability. In most hospitals, this will mean spiral CT, however TOE, MR or Fig. 7 - Type B aortic dissection. (a) Sagittal reformatted post-contrast thoracic CT images demonstrating origin of great vessels from the true lumen which is compressed distally by the poorly enhancing false lumen. (b) Aortographic correlation from the same patient.
(b)
44
CLINICALRADIOLOGY
Fig. 8 - Subacuteintramuralhaematoma. Tl weightedsagittalobliqueMR imageof thoracicaorta,3 weeksfollowing acuteintramuralhaemorrhage demonstrates diffusethickeningof the aorticwall (arrows)whichreturnsa typicalhigh signal.Acute intramuralhaematomahasa non-specificMR appearance. angiography may be added where additional information is required or for follow-up [ 181. The CT characteristics of classic acute dissection are a double lumen with intervening intimal flap (70%), internal displacement of calcified intima (17%), compression or distortion of the true lumen and haematoma within pericardium, mediastinum or pleural space [ 1,2]. Dissection originates at sites of maximum intimal stress. Approximately two-thirds arise on the anterior wall of the ascending aorta within 4cm of the aortic valve. Most of the remainder occur on the posterior wall of the descending aorta, just distal to the left subclavian artery origin. At both these sites shearing stressesoccur where the mobile aorta meets the relatively fixed heart or descending aorta. The often larger false lumen, tends to spiral round the outer curve of the aortic arch. Dilated aortas tend to dissect more readily. A minority (11 of 23) of dissections and intramural haematomas identified in our series occurred in aneurysmal aortas, however 75% of the 16 aneurysms encountered were complicated by dissection and/or rupture. Two patients had penetrating atheromatous ulcers. These have been defined as ‘atherosclerotic lesions with ulceration that penetrate the internal elastic lamina and allow haematoma formation within the media of the aortic wall’ [19]. The description covers a spectrum of lesions from asymptomatic
ones discovered incidentally to aggressive deeply penetrating ulcers that cause pain and lead to pseudoaneurysm formation with its attendant risk of rupture [20]. They typically occur in the distal descending aorta, are associated with acute, but localized intramural haemorrhage and ulcers may protrude eccentrically from the aortic lumen. Surgical repair has been advocated in symptomatic patients and requires more extensive grafting than is necessary with aortic dissection [19]. Medical treatment only may be successful in haemodynamically stable patients [20]. Two disorders not usually considered in the differential diagnosis of aortic dissection but frequently observed in our series are pericardial disease and pulmonary embolus. High density pericardial collections, which suggest haemopericardium were associated with significant proximal aortic disease in all but one of our cases. Conversely a majority of seven fluid density pericardial collections had no underlying cause and only one had ascending aortic pathology. Although a clinical pulse deficit occurs in a minority of dissections, it is an important sign which suggestsmajor branch vessel compromise. In several patients in our series, abnormalities unrelated to dissection which explained clinically apparent pulse deficits were identified. These included two casesof paradoxical embolism which occurs when material of systemic venous or right heart origin traverses a right to left cardiac or pulmonary shunt and occludes a systemic artery. In both our cases, patients with acute great vessel ishaemia had a corresponding serpiginous arterial filling defect, typical of venous thrombus in association with numerous pulmonary emboli. Autopsy studies have recorded an incidence of patent foramen ovale in 25 to 34% of cases, depending on the age at autopsy [21]. In patients with massive pulmonary embolism, hypoxaemia and systemic emboli are commoner where a patent foramen ovale can be demonstrated by contrast echocardiography [22]. Although an intracardiac shunt was not definitively proven in our cases, it is a reasonable hypothesis that an abrupt rise in right heart pressure due to pulmonary embolus promoted shunting of blood and clot through such a foramen. In conclusion, sudden onset non-cardiac, non-pleuritic chest pain is a non-specific manifestation of several acute cardiovascular disorders. Patients with this complaint have a high incidence of lifethreatening disease. Spiral CT is a rapid and reliable diagnostic test in this situation. The majority of patients will have abnormalities detectable by CT. Conscientious technique is important to maximize the sensitivity and accuracy of CT. The commonest disease encountered is classic aortic dissection but this comprises only a minority of patients with lifethreatening disease. Acute intramural aortic haematoma may be found with classic dissection but most cases occur in isolation. Recognition is important as the untreated prognosis is similar to that of classic dissection. Disease involving the great vesselssuch as atheroma and paradoxical pulmonary embolus can result in pulse deficits that clinically simulate dissection.
REFERENCES
1 GodwinJD.ConventionalCTof the aorta.Journalof Thoracic Imaging 1990;5(4):18-31. 2 DemosTC,PosniakHV, MarsanRE.CT of aorticdissection.Seminars in Roentgenology 1989;VolXXIV(1):22-37.
SPIRAL
CT IN ACUTE
3 Small JH, Dixon AK, Coulden RA et al. Fast CT for aortic dissection. British Journal ofRadiology 1996;69:900-905. 4 Zeman RK, Berman PM, Silverman PM et al. Diagnosis of aortic dissection: value of helical CT with multiplanar reformation and threedimensional rendering. American 1995;164:1375-1380. 5 Nienaber CA, von Kodolitsch Y, Petersen B et al. Intramural haemorrhage of the thoracic aorta. Diagnostic and therapeutic implications. Circulation 1995;92: 1465-1472. 6 Ide K, Uchida H, Otsuji H et al. Acute aortic dissection with intramural haematoma: possibility of transition to classic dissection or aneurysm. Journal of Thoracic Imaging 1996;11:46-52. 7 Wambeek NDK, Cameron DC, Holden A. Intramural aortic dissection. Australasian Radiology 1996;40:442-446. 8 Williams MP, Farrow R. Atypical patterns in the CT diagnosis of aortic dissection. Clinical Radiology 1994;49:686-689. 9 Yamada T, Tada S, Harada J. Aortic dissection without intimal rupture: diagnosis with MR imaging and CT. Radiology 1988;168:347-352. 10 Robbins RC, McManus RP, Mitchell RS et al. Management of patients with intramural haematoma of the thoracic aorta. Circulation 1993;88[part 2]:1-10. ! 1 Vasile N, Mathieu D, Keita K et al. Computed tomography of thoracic aortic dissection: accuracy and pitfalls. Journal of Computed Assisted Tomography 1986;10:211-215. !2 Kersting-Sonnnerhoff BA, Higgins CB, White RD et al. Aortic dissection: sensitivity and specificity of MR imaging. Radiology 1988;166:651-5. 13 Itzchak T, Rosenthal T, Adar R et al. Dissecting aneurysm of the
CHEST
14
15
16
17
18 19
20
21
22
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thoracic aorta: reappraisal of radiologic diagnosis. American Journal of Radiology 1975;125:559-570. Ballal RS, Nande NC, Galewood R et al. Usefulness of transoesophageal echocardiography in assessment of aortic dissection. Circulation 1991;84:1903-14. Sommer T, Fehske W, Holzknecht N et al. Aortic dissection: A comparative study of diagnosis with spiral CT, multiplanar transoesophageal echocardiography and MR imaging. Radiology 1996;199:347-352. Oliver TB, Murchison JT, Reid JH. Serial MRI in the management of intramural haemorrhage of the thoracic aorta. British Journal of Radiology 1997;70:1288-1290. Panting JR, Norell MS, Baker C, Nicholson AA. Feasibility, accuracy and safety of magnetic resonance imaging in acute aortic dissection. Clinical Radiology 1995;50:455-458. Reid JR. Imaging the thoracic aorta. Heart 1996;76:3-5. Stanson AW, Kazmier FJ, Lhollier LG et al. Penetrating atherosclerotic ulcer of the thoracic aorta: natural history and clinicopathologic correlation. Annals of Vascular Surgery 1986;l: 15-23. Kazerooni EA, Bree RL, Williams DM. Penetrating atherosclerotic ulcers of the descending thoracic aorta: evaluation with CT and distinction from aortic dissection. Radiology 1992;183:759-765. Hagen PT, Scholz DG, Edwards WD. Incidence and site of patent foramen ovale during the first ten decades of life: an autopsy study of 965 normal hearts. Mayo Clinic Proceedings 1984;59: 17-24. Kasper W, Giebel A, Tiede N et al. Patent foramen ovale in patients with haemodynamically significant pulmonary embolism. Luncet 1992;340:561-4.
Spiral CT in Acute Non-Cardiac T. B. OLIVER*,
J. T. MURCHISON”,
Chest Pain J. H. REID?
*Department of Clinical Imaging, Royal Infirmary of Edinburgh, Lauriston Place, Edinburgh, EH3 9W, TDepartment of Radiology, Borders General Hospital, Melrose, Roxburghshire, TD6 3BS, UK Received: 12 March 1998 Revised: 6 August 1998
UK and
Accepted: 20 August 1998
Aim: Spiral CT in acute non-cardiac chest pain is usually requested to diagnose aortic dissection but a spectrum of other cardiovascular diseases may simulate this. The purpose of this study was to assess the impact of spiral computed tomography (CT) in patients with suspected aortic dissection and to determine the nature and frequency of other disorders simulating it. Methods: Over a 26-month period, all patients undergoing CT for suspected acute aortic dissection were recruited. CT was performed using a standard protocol. The CT examinations and reports were reviewed along with other relevant imaging, clinical data, surgical findings and post-mortem results. The pattern of diagnoses and their associations were evaluated. Results: Seventy-six CT examinations were performed on 70 patients of whom 47 were male. The age of the patients ranged from 24 to 84. Seven patients had previously undergone cardiothoracic surgery. Twenty-four patients had normal CT findings; 46 patients (66%) had abnormal findings. Seventy-three significant pathologies were identified including thoracic aortic aneurysm (16 cases), aortic dissection (14 cases), acute intramural aortic haematoma (nine cases), aortic rupture (eight cases), atherosclerosis (four cases) and penetrating atheromatous ulcer (two cases), pulmonary embolus (four cases), pericardial disease (12 cases) and complications following surgery (three cases). The majority of patients had a life-threatening disease. Five patients without dissection had CT findings that explained clinical pulse deficits. Conclusion: Sudden onset non-cardiac, non-pleuritic chest pain is common to several acute cardiovascular disorders. Patients have a high incidence of life-threatening disease. Of this group, classic aortic dissection is the most common diagnosis but comprises a minority of cases. Spiral CT is a reliable diagnostic test but requires conscientious technique for optimum sensitivity and accuracy. Most patients will have abnormal CT findings. Oliver T. B. et al. (1999) Clinical Radiology 54,38-45. Key words: spinal CT, aortic dissection,haematoma, chest pain, differential diagnosis.
Patients presenting with sudden onset non-cardiac chest pain are commonly suspected of having thoracic aortic dissection but may harbour various other acute cardiovascular pathologies. These include acute intramural aortic haematoma, leaking aortic aneurysm, atherosclerotic ulcer, pericarditis and pulmonary embolus. Spiral computed tomography (CT) is fast, widely available and is established as a first line investigation in the work-up of these disorders. In the radiological literature, these entities are usually studied in isolation but in reality form a spectrum of related diseases which often co-exist. This observation along with the difficulty in separating these disorders on clinical grounds suggests that they should be considered together. The aim of this study was to assessthe impact of spiral CT in patients with suspected acute aortic dissection, to determine the prevalence of abnormal examinations, to characterize the spectrum and relative frequency of the diseasesencountered and to record associations between these diseases and the radiological findings useful in distinguishing them. Correspondence University Hospital 0009-9260/99/010038+08
to: Dr T. B. Oliver, Department of Clinical Imaging, of Wales, Heath Park, Cardiff, CF4 4XW, UK. $12.00/O
METHODS
AND MATERIALS
In our institution, a large teaching hospital and regional thoracic surgical referral centre, scans with this indication are performed using a standardprotocol on a GE HiSpeed Advantage scanner.An initial precontrast spiral CT through the great vessles and thoracic aorta using 1Omm collimation is followed by a second spiral CT with intravenous contrast medium using 5 mm collimation over a similar distribution. Ninety mililitres of contrast (300 mgI/nil) is administered by pump at 3 ml/s and optimal aortic contrast achieved using a ‘smart’ software algorithm, centred on the aortic arch. If aortic dissection is demonstrated, the inferior extent is delineated with a further spiral scan, using another injection of contrast if necessary.Images are reviewed at a workstation. This allows multiplanar reformats to be viewed if desired. A CT examination typically takes lessthan 15 min. All patients scanned as an emergency for suspected acute aortic dissection over a 26-month period were included. This simple inclusion criterium was chosen to produce an unbiased reflection of local clinical practice. All CT examinations and reports were retrospectively reviewed along with other relevant imaging, clinical data, 0 1999 The Royal
College
of Radiologists
SPIRAL
Table
1 - Spiral
CT for suspected
aortic
dissection-diagnoses
CT IN ACUTE
CHEST
PAIN
(n = 73)
Diagnosis
Number of cases
Comments
Aortic dissection Acute intramural aortic haematoma Thoracic aortic aneurysm Pulmonary embolus Pericardial collection Mediastinal haematoma Simple atheroma Penetrating atheromatous ulcer Other diagnoses
14 9 16 4 12 9 4 2
I type A, I type B 4 type A, 5 type B 4 simple, 12 complex 7 fluid, 5 high density 8 with aortic rupture
3
surgical findings and autopsy results. The pattern of diseases and their associations were recorded. RESULTS Seventy-six CT examinations were performed acutely in 70 patients of whom 47 were male. The age of the patients ranged from 24 to 84. Seven patients had previously undergone cardiothoracic surgery, 46 patients (66%) had abnormal CT findings and 73 significant pathologies were identified among these (Table 1).
(4
Aortic Dissection Fourteen aortic dissections were diagnosed. Seven were type A and seven were type B. In two patients (one type A and one type B), the aortic dissection was associated with acute intramural haematoma within the ascending aorta (type A) (Fig. la,b). Acute Intramural
Aortic Haematoma
Nine patients had acute intramural haematoma defined as crescentic or circumferential high density aortic wall thickening on the pre-contrast scan which failed to enhance following contrast (Fig. 2a,b). Four patients had type A haematomas and five had type B. Two patients had a coexisting classic dissection. Aortic Aneurysm Sixteen patients had aneurysmal dilatation of the thoracic aorta. Complications had arisen in 12 of these (11 dissections or acute intramural haematomas and one spontaneous rupture). Pulmonary
Embolus
Four patients had pulmonary emboli (Fig. 3). In two of these, large pulmonary artery thrombus loads were associated with occlusion of a great vessel by serpiginous material and a paradoxical embolus was presumed to have occurred. Pericardial
Disease
Five patients had high density pericardial collections, suggestive of pericardial haematoma. In four, this was associated
(b) Fig. 1 - Mixed type A aortic dissection and acute intramural haematoma. (a) Axial CT without contrast medium through aortic root. A triangular hyperdense region representing acute intramural haematoma is visible within the dilated aorta (small arrows). (b) Following contrast medium the haematoma fails to opacify but a dissection flap and false lumen are demonstrated. Pericardial haematoma is also present.
with acute aortic disease (two type A dissections, one type A mixed haematoma/dissection and one aortic root rupture due to cystic medial necrosis). In one case, a subsequent diagnosis of myocardial infarct was made. Magnetic resonance imaging (MRI) in this case showed left ventricular wall thinning but no evidence of wall rupture. Seven patients had fluid density pericardial collections. In three, there was associated aortic disease (one type A
Fig. 3 - Pulmonary embolus. Axial CT following contrast medium through the main pulmonary artery demonstrating extensive tubular thrombus, typical of material of systemic venous origin.
Atheroma Two cases of penetrating atheromatous aortic ulcer were identified (Fig. 4a,b). One presented with aortic rupture and the other, in a surgically unfit patient with pain but no CT evidence of acute rupture was treated conservatively, serial follow-up demonstrating no interval change. In three cases atheromatous disease of the aorta or great vessels, which resulted in a clinical pulse deficit was noted.
‘Pseudo-Dissection’: @I Fig. 2 - Acute intramural aortic haematoma. Axial CT through aortic arch. In (a), prior to contrast medium a hyperdense rind of haematoma encircles the aortic arch (arrows). (b) Following contrast medium this fails to enhance.
CT Findings Responsible for Pulse Deficits
In five cases described above (two paradoxical great vessel emboli, two atheromatous great vessels and one aortic occlusion) abnormalities which accounted for clinical pulse deficits were observed (Fig. 5a-c). Other Abnormalities
haematoma and two type B dissections). In four, the effusion was an isolated abnormality which subsequently resolved and was ascribed to pericarditis. Mediastinal
Haematoma
This was identified in nine cases. In one case, the haematoma was due to oozing following mitral valve replacement and it became infected necessitating drainage. In eight cases, haematoma resulted from aortic rupture, which was sometimes found to be contained at surgery. Underlying diagnoses were type A dissection (two cases), type A haematoma (two cases), type B haematoma, cystic medial necrosis, penetrating atheromatous ulcer and aortic aneurysm.
One patient who had had surgery for aortic coarctation in childhood presented with a calcified stenosis at the operation site but no evidence of dissection. Another patient with a perforated duodenal ulcer was retrospectively diagnosed after developing an upper abdominal abscess.A few bubbles of free gas on the lowest image of the initial aortic CT had been missed. A third patient who had an aortic graft for previous aortic dissection developed a pseudoaneurysm due to leakage at the anastomosis site (Fig. 6a,b).
DISCUSSION
This study emphasizes the utility of spiral CT in the investigation of patients with suspected aortic dissection.
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(b) Fig. 4 - Penetrating atheromatous aortic ulcer. (a) Axial CT demonstrating a large ulcer protruding laterally from an atheromatous descending thoracic aorta (arrow). Earlier leakage has resulted in a left pleural collection. (b) Aortographic correlation from the same patient showing the typical angiographic appearances.
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Although aortic dissection or haematoma were the disorders most frequently encountered (21 of 46 abnormal scans), a spectrum of other acute diseases sharing the same clinical features were identified. A high proportion of patients had abnormal scans. This reflects both the sensitivity of spiral CT and the high level of clinical suspicion behind requests for imaging, many of which were made outside normal working hours. Several technical points merit discussion. Use of a pump injector and ‘smart’ timing allows consistent and optimal enhancement of the aortic lumen. Windowing should be chosen so that dense contrast within true and false lumens does not obscure a thin dissection flap. Several causesof falsepositive CT diagnosis of dissection have been described [1,2]. These include enhancement of pulmonary veins, atelectatic lung or perianeurysmal fibrosis adjacent to the descending aorta which may simulate type B dissection and movement of the ascending aorta which produces a double image of the wall which may simulate a type A dissection. This latter artefact can be abolished by reconstruction of an additional single level scan series into short (100 ms) acquisition images [3]. In practice we have not found it troublesome, as it is characteristically visible on both sides of the aorta, has a flattened internal margin which is not typical for a dissection and is not identified on sequential slices through the adjacent aorta. We found multiplanar reformats useful to delineate the origin of some dissections and this is consistent with the experience of other workers (Fig. 7a,b) [4]. Three-dimensional reconstructions may be preferred by clinicians but due to the density thresholds used in producing these images, acute haematoma, thrombosed false lumens or established mural thrombus may not be demonstrated on such images. We believe a precontrast CT is mandatory. This optimally demonstrates calcification, which may be seen in association with atheroma, within longstanding luminal thrombus or in the intimal flap of a dissection. Furthermore, acute haematoma, either within the aortic wall or leaking into the mediastinum is best visualized before contrast due to its high density compared to flowing blood or mural thrombus. Acute haematoma may be seen in up to 44% of casesof acute dissection [I]. Acute intramural aortic haematoma is an important entity that has recently received attention in the literature [5-71. Although previously recognized as a distinct imaging appearance, it has usually been ascribed to atypical or thrombosed dissection. In large surgical series, intramural haematoma without intimal disruption is often described in a proportion of cases.Thus, whilst some cases of acute intramural haematoma may be due to thrombosis of a classical dissection, others must be regarded as the primary event. Spontaneous bleeding from aortic vasa vasora is thought to be the causeof the haemorrhage which may be complicated by aortic rupture or progression to classic aortic dissection or aneurysm. Previous reports have suggested that between 13 and 41% of acute dissections have CT features compatible with intramural haematoma [3,5,8,9]. The high proportion (42%) in our series may reflect increased awareness of the condition or the imaging advantages and greater coverage allowed by spiral CT. The close relationship between acute haematoma and dissection is reflected in our series which included two patients where intramural haematoma and dissection occurred together. In a further patient,
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serial scans showed development of a contrasting false lumen where non-enhancing haematoma had been present on a scan the day before. Haematoma proximal to the left subclavian artery origin (type A) carries a similar prognosis to type A dissection and complications are more likely when the aortic root diameter is greater than 5cm or serial imaging shows failure of the haematoma to resolve [5,6,9,10]. The high mortality which accompanies untreated aortic dissection (80% at 1 month) makes early identification critical. Depending on available resources CT, MR, angiography or transoesophageal echocardiography (TOE) may be used in diagnosis and all have been reported to be reliable [ 1 l- 141. Although the traditional gold standard, angiography has been replaced by CT or TOE as the primary imaging modality in most centres, largely because of its invasive nature and inability to detect dissecting haematomas when there is no flap. Some surgeons may still request angiography, either because of familiarity with the images produced or where information is required about aortic valve function, the integrity of coronary arteries or involvement of the great vessels. A recent comparative study of spiral CT, multiplanar TOE and MR showed no difference in sensitivity (100% for all modalities) or specificity (100, 94 and 94% respectively) between the three techniques in the detection of thoracic aortic dissection. However, spiral CT was more sensitive and specific than TOE or MR in the assessment of great vessel involvement [ 151. Spiral CT has the advantages of speed, wide availability and ease of monitoring of sick patients. It readily distinguishes acute intramural aortic haematoma from atheroma or mural thrombus whereas TOE does not. CT provides no information about the coronary arteries or aortic valve function thus angiography or echocardiography may be required. The wide coverage permitted by spiral CT allows some assessmentof the distal aortic branches however and provides other diagnostic possibilities, as illustrated by this series. TOE is accurate in experienced hands and can be performed at the bedside of critically ill patients. Blind areas in the ascending aorta and arch due to the major airways initially led to false-negative examinations. The advent of multiplanar TOE has reduced this problem considerably. A low incidence of false-positive examinations persists due to reverberation artefact encountered in dilated or ectatic aortas. TOE is limited to evaluation of disease of the aorta and heart. The biggest drawback with TOE, however, is availability as even in larger centres, provision of a comprehensive out of hours service can be difficult. MR along with CT provides reproducible, measurable images which facilitate follow up of dissections, aneurysms
5 - ‘Pseudodissection’. CT findings explaining clinical pulse deficits. Paradoxical embolus. (a) Sagittal oblique reformatted CT image through the aorta following contrast. A serpiginous filling defect representing a paradoxical embolus extends from an occluded left subclavian artery origin into the descending aorta. Large central pulmonary emboli were seen on axial images. Key: LCA = left carotid artery; LSA = left subclavian artery; DA = descending aorta; PA = main pulmonary artery. Reprinted with permission of British Journal of Radiology. Atheroma. (6) Axial CT following contrast through proximal left subclavian artery demonstrating a focal concentric stenosis due to atheroma (arrow). (c) A more cephalad slice from the same examination shows normal opacifaction of the artery. Fig.
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(b)
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Fig. 6 - Pseudoaneurysm. (a) Axial CT following contrast through the aortic root demonstrates contrast within the sac of a pseudoaneurysm arising at the site of previous surgery for aortic dissection (arrow). A pericardial haematoma is present and a dissection flap persists in the descending aorta. (b) Tl weighted axial MR image at the same site showing turbulent flow within the pseudoaneurysm sac (arrow) and high signal intensity methaemoglobin in the haematoma periphery.
or intramural aortic haematoma (Fig. 8) [16]. The signal returned from haematoma in the acute phase is not specific for this entity however [7]. High field strength systems and the use of both spin echo and gradient echo sequenceswhich allows distinction of slow flow from haematoma have been advocated for maximum accuracy [ 151. The long examination time and difficulties in monitoring unstable patients are disadvantages of MR although satisfactory results have been reported using MR as the initial imaging modality in suspected acute dissection u71.
Choice of modality reflects accuracy and availability. In most hospitals, this will mean spiral CT, however TOE, MR or Fig. 7 - Type B aortic dissection. (a) Sagittal reformatted post-contrast thoracic CT images demonstrating origin of great vessels from the true lumen which is compressed distally by the poorly enhancing false lumen. (b) Aortographic correlation from the same patient.
(b)
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Fig. 8 - Subacuteintramuralhaematoma. Tl weightedsagittalobliqueMR imageof thoracicaorta,3 weeksfollowing acuteintramuralhaemorrhage demonstrates diffusethickeningof the aorticwall (arrows)whichreturnsa typicalhigh signal.Acute intramuralhaematomahasa non-specificMR appearance. angiography may be added where additional information is required or for follow-up [ 181. The CT characteristics of classic acute dissection are a double lumen with intervening intimal flap (70%), internal displacement of calcified intima (17%), compression or distortion of the true lumen and haematoma within pericardium, mediastinum or pleural space [ 1,2]. Dissection originates at sites of maximum intimal stress. Approximately two-thirds arise on the anterior wall of the ascending aorta within 4cm of the aortic valve. Most of the remainder occur on the posterior wall of the descending aorta, just distal to the left subclavian artery origin. At both these sites shearing stressesoccur where the mobile aorta meets the relatively fixed heart or descending aorta. The often larger false lumen, tends to spiral round the outer curve of the aortic arch. Dilated aortas tend to dissect more readily. A minority (11 of 23) of dissections and intramural haematomas identified in our series occurred in aneurysmal aortas, however 75% of the 16 aneurysms encountered were complicated by dissection and/or rupture. Two patients had penetrating atheromatous ulcers. These have been defined as ‘atherosclerotic lesions with ulceration that penetrate the internal elastic lamina and allow haematoma formation within the media of the aortic wall’ [19]. The description covers a spectrum of lesions from asymptomatic
ones discovered incidentally to aggressive deeply penetrating ulcers that cause pain and lead to pseudoaneurysm formation with its attendant risk of rupture [20]. They typically occur in the distal descending aorta, are associated with acute, but localized intramural haemorrhage and ulcers may protrude eccentrically from the aortic lumen. Surgical repair has been advocated in symptomatic patients and requires more extensive grafting than is necessary with aortic dissection [19]. Medical treatment only may be successful in haemodynamically stable patients [20]. Two disorders not usually considered in the differential diagnosis of aortic dissection but frequently observed in our series are pericardial disease and pulmonary embolus. High density pericardial collections, which suggest haemopericardium were associated with significant proximal aortic disease in all but one of our cases. Conversely a majority of seven fluid density pericardial collections had no underlying cause and only one had ascending aortic pathology. Although a clinical pulse deficit occurs in a minority of dissections, it is an important sign which suggestsmajor branch vessel compromise. In several patients in our series, abnormalities unrelated to dissection which explained clinically apparent pulse deficits were identified. These included two casesof paradoxical embolism which occurs when material of systemic venous or right heart origin traverses a right to left cardiac or pulmonary shunt and occludes a systemic artery. In both our cases, patients with acute great vessel ishaemia had a corresponding serpiginous arterial filling defect, typical of venous thrombus in association with numerous pulmonary emboli. Autopsy studies have recorded an incidence of patent foramen ovale in 25 to 34% of cases, depending on the age at autopsy [21]. In patients with massive pulmonary embolism, hypoxaemia and systemic emboli are commoner where a patent foramen ovale can be demonstrated by contrast echocardiography [22]. Although an intracardiac shunt was not definitively proven in our cases, it is a reasonable hypothesis that an abrupt rise in right heart pressure due to pulmonary embolus promoted shunting of blood and clot through such a foramen. In conclusion, sudden onset non-cardiac, non-pleuritic chest pain is a non-specific manifestation of several acute cardiovascular disorders. Patients with this complaint have a high incidence of lifethreatening disease. Spiral CT is a rapid and reliable diagnostic test in this situation. The majority of patients will have abnormalities detectable by CT. Conscientious technique is important to maximize the sensitivity and accuracy of CT. The commonest disease encountered is classic aortic dissection but this comprises only a minority of patients with lifethreatening disease. Acute intramural aortic haematoma may be found with classic dissection but most cases occur in isolation. Recognition is important as the untreated prognosis is similar to that of classic dissection. Disease involving the great vesselssuch as atheroma and paradoxical pulmonary embolus can result in pulse deficits that clinically simulate dissection.
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