ORIGINAL Annals of Nuclear Medicine Vol. 6, No. 4, 235-239, 1992 Ga-67 citrate scan in vascular graft infection Ignacio BANZO. Remedios QUIRCE. Justo SERRANO, Julio JIMENEZ, Olga TABUENCA and Jose M. CARRIL Servicio de Medicina Nuclear, Hospital Universitario Valdecilla, Santander, Spain The clinical utility of the Ga-67 scan has been studied in 9 patients with clinical suspicion of vascular graft infection. Eleven grafts were analyzed : 4 aortobifemoral, 2 iliofemoral, 3 femoropopliteal, 1 axillofemoral, and 1 axillobifemoral. The Ga-67 scan was positive in 8 grafts with bacteriological proof of infection and negative in 3 grafts in which infection was ruled out by clinical follow-up. A Ga-67 scan also demonstrated the spread of infection to the thigh in two patients and to the pelvis in another two patients. In 4 patients CT was performed. The CT findings included graft thrombosis, perigraft fluid collection and thickened graft wall. No discrepancies were found between the CT scan and Ga-67 scan. In three patients a control Ga-67 scan was carried out after specific antibiotic and surgical treatment. Two of these showed increased Ga-67 uptake and spreading of infection along the graft; in the other patient, a Ga-67 scan revealed normalization after resolution of an abdominal abscess. In conclusion, the Ga-67 scan proved useful in the diagnosis of vascular graft infection, the definition of location of the extent of the disease and in the evaluation of the efficiency of treatment. Key words : vascular graft, infection, Ga-67 scan INTRODUCTION VASCULAR GRAFT INFECTION is an uncommon complication of vascular surgery, but results in high morbidity and mortality rates and an increase in the number of limb amputations required.1 Fever and 'suppuration from the surgical incision are usually the only clinical findings when graft infection is present.2 These non-specific symptoms do not help to locate and evaluate the extent of the infection, so an accurate diagnostic method is required. This paper presents our experience in the diagnosis of vascular graft infection by means of Ga-67 citrate scintigraphy. MATERIALS AND METHODS We made a retrospective study of the clinical records Received February 12, 1992, revision accepted May 22, 1992. For reprints contact : Ignacio Banzo, M.D., Servicio de Medicina Nuclear, Hospital Universitario Valdecilla, 39008 Santander, SPAIN. of 9 vascular graft patients given a Ga-67 scan on suspicion of vascular graft infection. Eleven grafts were analyzed : 4 aortobifemoral, 2 iliofemoral, 3 femoropopliteal, I axillofemoral, and I axillobifemoral. The graft infection was presented between six days and eleven years after the vascular surgery. Clinical manifestations were fever in three cases, suppuration through the surgical incision in four cases, one patient was admitted in a septic state, and one patient developed an abscess in the thigh. The Ga-67 scan was performed 48 hours after intravenous injection of 111-185 MBq of Ga-67 citrate. Images were obtained over the sites where vascular grafts were located and 450,000 to 650,000 counts per image were obtained. Two patients were scanned three times and one patient twice, so the total number of Ga-67 scintigraphies was 14. Ga-67 images were considered positive when uptake was found in any part of a vascular graft. Uptake found at a recient surgical incision was considered normal. In four patients CT scan was also performed concurrently with the Ga-67 scan. CT criteria for vascular graft infection were : thickened graft wall or increased perigraft soft tissue, perigraft fluid, pseudoaneurism at anatomosis, graft occlusion, and gas in the graft bed.3 RESULTS Infection was established in 8 of 11 vascular grafts studied, including 6 cases that had positive graft culture and two cases that had positive culture of the surgical incision exudate. In three cases clinical follow-up ruled out infection. Table I shows the microorganisms isolated. From a therapeutical point of view, three grafts were removed and three cases underwent limb amputation ; two patients were treated with antibiotics alone. Ga-67 scan was positive in all 8 infected grafts (Figs. 1, 2) and negative in the three non-infected grafts (Table 1). Apart from graft uptake, Ga-67 scan also revealed the s pread of infection to the thigh in two cases and the formation of abscesses in two patients (Fig. 3). In the four patients with graft infection that underwent paired CT and Ga-67 scan, no discrepancies were found. Ga-67 scan was performed previous to CT in 3 patients and the CT scan was ruled out to confirm Ga-67 findings. In these patients, CT findings included graft thrombosis in one patient and perigraft fluid in association with wall thickness in two patients. In the remaining patient. CT scan showed thickened wall, perigraft fluid and inflammatory changes adjacent to the graft ; Ga-67 scan was performed to evaluate the extent of infection. The CT likewise revealed abscesses in 3 out of the 4 patients. Three patients also were explored following the initiation of antibiotic and surgical treatment (Table 1). Patient No. 5 had a pelvis abscess after removal of an iliofemoral graft infected by S. epidermidis; two Ga-67 follow-up scans showed clearing of the abscess with antibiotic therapy. Ga-67 scan of patient No. 6 showed uptake on the right side of the aortobifemoral graft infected by Aspergillus; a follow-up scan 15 days after the initiation of Anphotericine treatment revealed a thigh abscess. In patient No. 7 an axillofemoral graft infected by Bacteroides fragilis was removed (Fig. 1) and in the same operation an aortobifemoral graft was done ; two control scans showed whole graft infection from the distal anastomosis of a femoral branch (Fig. 2). DISCUSSION Vascular graft infection is a complication of vascular surgery with an incidence of 1-6%, which is responsible for a high rate of morbidity and mortality, between 25-78%.1,4 Clinical signs of infection are non-specific and may manifest either immediately following surgery or some years later. Also they are not helpful in the evaluation of the extent of infection. Many techniques have been employed in order to detect vascular graft infection: angiography,5 ultrasonography,6 CT,3,7 RNM,8 In-111 IgG,9 In-111 leukocytes,10,11 Tc-99m-HMPAO leukocytes,12,13 and Ga-67 citrate scan.14,15 Although the Ga-67 scan has demonstrated a sensitivity of 78-1OO% and a specificity greater than 90% for graft infection,3,15 it has excited little interest and received only limited attention from a few researchers.6,16,17 In 1980, Causey et al.14 first reported Ga-67 uptake in 5 vascular grafts with proven infection. Subsequently. Thivolle et al.15 reported 11 patients with vascular grafts, 7 of which were infected; the Ga-67 scan correctly identify uptake in these grafts and it was negative in the four non-infected grafts. Moreover, Ga-67 scan and Tc-99m-HMPAO leukocytes were found useful in the detection of 8 infected vascular grafts in the series reported by Vorne et al.13 Our results are similar to previous reports; all infected vascular grafts were successfully identified by Ga-67 scan. The extent of infection in vascular grafts determines the treatment to be applied. In general, infection limited to the groin is treated with antibiotics; surgical therapy is employed in the cases in which medical treatment fails.1 The spread of infection to the retroperitoneum requires graft removal and extraanatomic revascularization of the lower limbs. 2,4 In our study, Ga-67 scan revealed the spread of infection beyond the graft in 4 patients. Figure 3 is a good example of these findings. The scan was performed on a patient carrying a left femoropopliteal graft that had undergone leg amputation below the knee. Scintigraphy revealed Ga-67 uptake along the vascular graft at which distal end Pseudomona aeruginosa was isolated. Right iliac fossa uptake related to a pelvis abscess was also noted. Therefore it may be considered from these findings that the Ga-67 scan is able to identify those patients with local graft infection which are susceptible to medical treatment, patients with infection involving the whole vascular graft which requires surgical treatment, as well the patients with infectious complications such abscess formation. The principal disadvantage of the Ga-67 scintigraphy in diagnosis of infection is the necessary period of waiting before the scan may be performed. This drawback resulted in an unfavourable comparison with the labelled leukocyte method, especially with Tc-99m-HMPAO leukocytes.18 We have always obtained images 48 hours after injection, although Thivolle et al.15 found Ga-67 uptake in vascular graft at 24 hours after radiotracer administration and Causey et al.14 were able to locate the infection site in all vasculsr grafts studied 6 hours after injection, but this uptake was more clearly seen at 24-48 hours. The physiological Ga-67 uptake in abdominal structures (liver, spleen and colon) and surgical incisions has been considered as a potential disadvantage of the Ga-67 scan.19 However thoroughly abdominal cleaning is carried out, the vascular graft is not close to the liver or spleen, and surgical incision uptake tends to decrease after the first week.3,14 CT utility for graft infection has also been demonstrated previously.3,7,20 CT is also able to detect other complications of vascular surgery such as retroperitoneal haematomas, aortoduodenal fistula, pseudoaneurism, vascular thrombosis, intestinal infarction, and postsurgical pancreatitis.21,22 We have found no discrepancies between CT and Ga-67 scan, but our experience is limited. However, Johnson et al.3 reported greater sensitivity of CT in the diagnosis of the retroperitoneal spread of infection. In a comparative study CT-Ga-67 scan, Ga-67 was negative in two patients with retroperitoneal infection; Ga-67 scan was more specific than CT in facilitating the differentiation between vascular graft infection and postsurgical infiammatory changes. From these results, the authors recommend the CT as the initial choice for exploration, leaving the Ga-67 scan to those cases where the results of the CT scan are not conclusive.3 In conclusion, vascular graft infection as a complication of vascular surgery is difficult to diagnose and may have dramatic consequences in terms of morbidity and mortality rates, and the need to carry out limb amputation. Several medical explorations are required to confirm its presence and extent. From our results, some conclusions can be drawn. First, Ga-67 scan was a useful technique in the diagnosis of vascular graft infection, with 100% specificity and sensitivity. Secondly, in all cases studied, Ga-67 scan identified the location and extent of the infection, including abscess formation beyond the graft area. Thirdly, the Ga-67 scan facilitated the evaluation of the treatment efficiency in patients who underwent surgical and/or antibiotic therapy. Fourthly, our limited experience with regard to the CT does not enable us to reach firm conclusions concerning its utility, and further investigations are therefore necessary. REFERENCES 1. Lorentzen JE, Nielsen OM. Arendrup H, et al: Vascular graft infection : An analysis of sixty two graft infections in 2411 consecutively implanted synthetic vascular grafts. Surgery 98 : 81-86, 1985 2. Bunt TJ, Haynes JL: Synthetic vascular graft infection: The continuing headache. Am Surg 50: 43-48, 1984 3. Johnson KK, Russ PD, Bair JH, et al: Diagnosis of synthetic vascular graft infection : Comparison of CT and gallium scans. AJR 1 54: 405-409, 1990 4. Bunt TJ: Synthetic vascular graft infections. I. Graft infections. Surgery 93 : 733-746, 1983 5. Vogelzang RL, Limpert JD, Yao JS: Detection of prosthetic vascular complications: Comparison of CT and angiography. AJR 148 : 819-823, 1987 6. Simpson AJ. Astin JK. Peck MR Diagnosis of an abdominal aortic graft abscess by combined ultrasonography and scintigraphy. Clin Nucl Med 4 : 338-340 1979 7. Haaga JR, Baldwin N, Reich NE, et al : CT detection of infected synthetic grafts: Preliminary report of a new sign. AJR 131 : 317-320, 1978 8. Justich E, Amparo EG, Hricak H, et al: Infected aortoiliofemoral grafts : Magnetic resonance imaging. Radiology 154: 133-136, 1985 9. LaMuraglia GM Fischman AJ, Strauss W, et al : Utility of the indium-111-labeled human immunoglobulin G scan for the detection of focal vascular graft infection. J Vasc Surg 10: 20-27, 1989 10. Wilson DG, Seabold JE, Lieberman LM : Detection of aortoarterial graft infections by leukocyte scintigraphy. Clin Nucl Med 8 : 421-423, 1983 11. Chung CJ, Hicklin OA, Payan JM, et al : Indium-111-labeled leukocyte scan in detection of synthetic vascular graft infection : The effect of antibiotic treatment. J Nucl Med 32: 13-15, 1991 12. Banzo J. Prats E, Azcona M, et al : The use of 99mTc-HMPAO-leukocyte scan in the diagnosis of vascular graft infections. Eur J Nucl Med 16: 503, 1990 13. Vorne M, Soini I, Lantto T, et al : Technetium-99m HMPAO-labeled leukocytes in detection of inflammatory lesions : Comparison with Gallium-67 citrate. J Nucl Med 30: 1332-1336, 1989 14. Causey DA, Fajman WA, Perdue GD, et al: 67Ga scintigraphy in postoperative synthetic graft infections. AJR 134: 1041-1045, 1980 15. Thivolle P, Varenne L, Heyden Y, et al : Gallium-67 citrate whole body scanning for the localization of infected vascular synthetic grafts. Clin Nucl Med 1O: 330-332, 1985 16. Silva J, Harvey WC: Detection of infections with gallium-67 and scintigraphic imaging. J Infect Dis 130: 125-131, 1974 17. Vorne M. Laitinen R. Lantto T, et al: Chronic prosthetic vascular graft infection visualized with Technetium-99m-Hexamethylpropylenearnine Oxime-labeled leukocytes. J Nucl Med 32 : 1425-1427, 1991 18. Lantto EH, Lantto TJ, Vorne M : Fast diagnosis of abdominal infections and inflammations with technetium-99m-HMPAO labeled leukocytes. J Nucl Med 32: 2029-2034, 1991 19. LaMuraglia GM: Chronic prosthetic vascular graft infection visualization with Gallium-67. J Nucl Med 32: 1427-1428, 1991 20. Mark AS, McCarthy SM Moss AA, et al : Detection of abdominal aortic graft infection : Comparison of CT and In-labeled white blood cell scan. AJR 144 : 315-318, 1985 21 . Hilton S, Megibow AJ, Naidich DP, et al: Computed tomography of the postoperative abdominal aorta. Radiology 145 : 403-407, 1982 22. Mark A, Moss AA, Lusby R, et al : CT evaluation of complications of abdominal aortic surgery. Radiology 145 : 409-414, 1982