738 CLINICAL RADIOLOGY

Materials and Methods: 64 patients (M:F 39:25, age range 18-83) with proven acute pancreatitis were evaulated by CT. Unenhanced and enhanced studies were performed concurrently using 5 mm sections. Three blinded readers performed an ROC analysis to evaluate the CT grade (A-E), presence of necrosis (no necrosis, 0-30%, 31 50%, > 50% necrosis) and presence and number of peripancreatic fluid collections.

Results: ROC curves for necrosis, CT grade, presence and number of peripancreatic collections were calculated. Mean concordance for the 3 observers between enhanced and unenhanced scans for presence of necrosis was 86%, CT grade 59%, presence of peripancreatic collec- tions 85% and number of collections 66%. No significant interobserver variation was noted for all features analysed.

Conclusions: Detection of necrosis is identified in over 85% of unenhanced cases indicating that contrast-enhanced CT may not be required in the majority of cases. Lower concordance for CT grade and number of collections reflects the difficulty of using the current CT grading system in routine clinical practice.

IS BARIUM TRAPPING IN RECTOCOELES SIGNIFICANT? S. HALLIGAN and C. I. BARTRAM Department of Radiology, St Mark's Hospital, London

Introduction: During Evacuation Proctography (EP), contrast may be retained in a rectocoele at the end of evacuation. Barium trapping is not a feature of small rectocoeles and is thought to be functionally significant. However, not all large rectocoeles retain contrast. We compared patients who retained barium with a group who did not, to determine any additional feature associated with this phenomenon.

Methods: 11 women with barium trapping were identified prospec- tively & compared to 11 controls, matched for lateral rectocoele area on EP, who did not retain contrast. From EP the lateral rectocoele area was measured planimetrically by computerised video capture. Evacua- tion time/completeness & rectal structural abnormality were noted. Patients also attempted to expel a noncompliant, 1.5cm diameter intrarectal balloon, connected to a transducer to record intrarectal pressure.

Results: No significant difference from controls was found with evacuation time (P - 0.466), completeness of evacuation (P = 0.717), pelvic floor descent (P -0 .532 ) , maximum anal canal width (P=0.621) , anorectal angle at rest (P=0.277) & straining (P - 0.398), ability to evacuate the balloon (P = 1.41) or maximum intrarectal pressure achieved (P = 0.430).

Conclusions: Barium trapping in rectocoeles has not been shown to be associated with impairment of evacuation generally, or to prevent the expulsion of a small solid bolus. It is therefore doubtful that this sign is of any clinical significance.

THE VALUE OF THE SUPINE CHEST RADIOGRAPH IN THE DIAGNOSIS OF TRAUMATIC RUPTURE OF THE AORTA J. J. BHATTACHARYA, M. WALSH, P. KESSAR, A. WILSON and O. CHAN The Royal London Hospital, London

Introduction: The Helicopter Emergency Medical Service (HEMS) manages poly-traumatised patients using advanced trauma life-sup- port protocols (ATLS). The supine trauma radiograph is used to screen the chest and numerous radiological signs have been described to diagnose traumatic rupture of the aorta. Unfortunately previous reviews have questioned the value of many of these signs and most have been found to have a low predictive value.

Design: Retrospective study. Subject and Methodology: We performed a retrospective study

reviewing supine chest radiographs taken in the resuscitation room in all patients managed by HEMS in a three year period. 339 chest radiographs were reviewed by two experienced trauma radiologists. The presence of each of these signs was recorded and the predictive value determined using aortography, surgery and/or clinical out- c o m e .

Results and Conclusion: Initial impressions and preliminary findings confirm that the supine radiographic signs for aortic rupture are unreliable. Supporting statistical data is anticipated and will be presented at the meeting.

VASCULAR

SPIRAL CT ANGIOGRAPHY AND 3D DISPLAY OF ABDOMINAL AORTIC ANEURYSMS A. R. PADHANI, M. FARRUGIA, S. RANKIN, J. REIDY, J. ZHAO, P. E. SUMMERS, D. HAWKES and P. TAYLOR Departments of Radiology, Radiological Sciences, Vascular Surgery and Neurology, Guy's Hospital, London

Introduction: Spiral CT angiography shows promise as an imaging technique for the routine preoperative evaluation of abdominal aortic aneurysms (AAA). This study determines its clinical utility and compares five visualisation modes.

Design: Prospective. Subjects and Methods: Twenty five patients with AAA were evaluated

on a Phillips SR7000 scanner. Single or twin spirals with breath-holding were performed. Images were acquired following the injection of 50 100mls of intravenous iopromide at a rate of 3ml/second. The reconstructed data was displayed as axial images, multiplanar refor- mats, shaded surface displays (SSD), maximum intensity projections (MIP) and true volume renderings. The images were assessed by two radiologists and a vascular surgeon. Information obtained included aneurysm extent, diameter, necks and run-off vessels as well as status of renal and visceral arteries. Images were assessed with regard to quality and accuracy of information obtained. Surgical and conventional angiographic correlation was obtained when available.

Results: Axial images with multiplanar reformats revealed maximum detail but anatomical features are difficult to appreciate in three dimensions. SSD showed excellent anatomical detail without over- lapping structures. MIP depicted calcification well. Volume rendered images permitted the simultaneous display vascular lumen, calcification and mural thrombus.

Conclusions: CT angiography can replace conventional arteriography for the routine evaluation of AAA. All five display modes should be included as they provide complementary information.

ABDOMINAL AORTIC ANEURYSM; RESULTS OF A 10 YEAR SCREENING PROGRAMME A N D THE IMPLICATIONS FOR RADIOLOGY D. N. KAY St Richard's Hospital, Royal West Sussex NHS Trust, Chichester, West Sussex

The implications of screening by ultrasound for abdominal aortic aneurysms (AAA) have been debated for several years and further interest has been aroused by the development of new techniques for elective repair using endovascular stents. A prospective study is in progress in which patients aged 65 or over identified from general practice registers, are screened for AAA by ultrasound, and are fol- lowed, together with age-matched controls, with regard to aneurysm development and mortality. Ten thousand people have been screened to date. Those with aneurysms of more than 6 cm are considered for elective repair, those with intermediate enlargement have regular follow-up scans to assess possible expansion.

Results 1) Numbers of patients with aortic diameters; at first examination.

> 6 cm 28 5-5.9cm 28 4-4.9 cm 69 3 -3.9 cm 231 < 3 cm 8588

2) Expansion monitored at follow-up Reaching 6 cm 27 Expanding at > 1 cm/year 95 3) Risk of Rupture Risk of rupture of aneurysm < 6cm and not expanding: 0.08%. Thus the risk of rupture is less than the risk of elective surgery in this group provided regular follow-up scans are performed.

Conclusions. 1) Ultrasound screening presents a simple and acceptable method of identifying a lethal condition in which elective rather than emergency intervention is preferable. 2) Criteria for surgery can be applied which balance the risk of intervention against the mortality from rupture, provided follow-up scans are performed. 3) There are implications for radiology in terms of workload, clinical advice and the supervision of screening programmes.