Computerized tomographic assessment of graft incorporation after aortic reconstruction

Evidence-based guideline of the European Association of Nuclear Medicine (EANM) on imaging infection in vascular grafts

Purpose

Consensus on optimal imaging procedure for vascular graft/endograft infection (VGEI) is still lacking and the choice of a diagnostic test is often based on the experience of single centres. This document provides evidence-based recommendations aiming at defining which imaging modality may be preferred in different clinical settings and post-surgical time window.

Methods

This working group includes 6 nuclear medicine physicians appointed by the European Association of Nuclear Medicine, 4 vascular surgeons, and 2 radiologists. Vascular surgeons formulated 5 clinical questions that were converted into 10 statements and addressed through a systematic analysis of available literature by using PICOs (Population/problem–Intervention/Indicator–Comparator–Outcome) strategy. Each consensus statement was scored for level of evidence and for recommendation grade, according to the Oxford Centre for Evidence-based Medicine criteria.

Results

Sixty-six articles, published from January 2000 up to December 2021, were analysed and used for evidence-based recommendations.

Conclusion

Computed tomography angiography (CTA) is the first-line imaging modality in suspected VGEI but nuclear medicine modalities are often needed to confirm or exclude the infection. Positron emission tomography/computed tomography (PET/CT) with 2-deoxy-2-[¹⁸F]fluoro-D-glucose ([¹⁸F]FDG) has very high negative predictive value but it should be performed preferably at least 4 months after surgery to avoid false positive results. Radiolabelled white blood cell (WBC) scintigraphy, given its high diagnostic accuracy, can be performed at any time after surgery.

Preamble

The European Association of Nuclear Medicine (EANM) is a professional no-profit medical association that facilitates communication worldwide between individuals pursuing clinical and research excellence in nuclear medicine. The EANM was founded in 1985. EANM members are physicians, technologists, and scientists specializing in the research and practice of nuclear medicine. The EANM will periodically define new guidelines for nuclear medicine practice to help advance the science of nuclear medicine and to improve the quality of service to patients throughout the world. Existing practice guidelines will be reviewed for revision or renewal, as appropriate, on their fifth anniversary or sooner, if indicated. Each practice guideline, representing a policy statement by the EANM, has undergone a thorough consensus process in which it has been subjected to extensive review. The EANM recognizes that the safe and effective use of diagnostic nuclear medicine imaging requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guideline by those entities not providing these services is not authorized. These guidelines are an educational tool designed to assist practitioners in providing appropriate care for patients. They are not inflexible rules or requirements of practice and are not intended, nor should they be used, to establish a legal standard of care. For these reasons and those set forth below, the EANM suggests caution against the use of the current consensus document in litigation in which the clinical decisions of a practitioner are called into question. The ultimate judgement regarding the propriety of any specific procedure or course of action must be made by the physician or medical physicist in the light of all the circumstances presented. Thus, there is no implication that an approach differing from the consensus document, standing alone, is below the standard of care. To the contrary, a conscientious practitioner may responsibly adopt a course of action different from that set forth in the consensus document when, in the reasonable judgement of the practitioner, such course of action is indicated by the condition of the patient, limitations of available resources, or advances in knowledge or technology subsequent to publication of the consensus document. The practice of medicine includes both the art and the science of the prevention, diagnosis, alleviation, and treatment of disease. The variety and complexity of human conditions make it impossible to always reach the most appropriate diagnosis or to predict with certainty a particular response to treatment. Therefore, it should be recognized that adherence to this consensus document will not ensure an accurate diagnosis or a successful outcome. All that should be expected is that the practitioner will follow a reasonable course of action based on current knowledge, available resources, and the needs of the patient, to deliver effective and safe medical care. The sole purpose of this consensus document is to assist practitioners in achieving this objective.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-022-05769-x.

Aortic Fistulas: Pathophysiologic Features, Imaging Findings, and Diagnostic Pitfalls

Fistulas between the aorta and surrounding organs are extremely rare but can be fatal if they are not identified and treated promptly. Most of these fistulas are associated with a history of trauma or vascular intervention. However, spontaneous aortic fistulas (AoFs) can develop in patients with weakened vasculature, which can be due to advanced atherosclerotic disease, collagen-vascular disease, vasculitides, and/or hematogenous infections. The clinical features of AoFs are often nonspecific, with patients presenting with bleeding manifestations, back or abdominal pain, fever, and shock. Confirmation with invasive endoscopy is often impractical in the acute setting. Imaging plays an important role in the management of AoFs, and multiphasic multidetector CT angiography is the initial imaging examination of choice. Obvious signs of AoF include intravenous contrast material extravasation into the fistulizing hollow organ, tract visualization, and aortic graft migration into the adjacent structure. However, nonspecific indirect signs such as loss of fat planes and ectopic foci of gas are seen more commonly. These indirect signs can be confused with other entities such as infection and postoperative changes. Management may involve complex and staged surgical procedures, depending on the patient's clinical status, site of the fistula, presence of infection, and anticipated tissue friability. As endovascular interventions become more common, radiologists will need to have a high index of suspicion for this entity in patients who have a history of aneurysms, vascular repair, or trauma and present with bleeding. Online supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article. ^©RSNA, 2021.

Perspective: options in managing aortic graft infections

Thoracic aortic graft infections are infrequent, but are associated with high mortality and morbidity risk. To prevent these life-threatening infections, one must be aware of pathogenesis. When it occurs, a multidisciplinary (surgeon, radiologist, microbiologist, nuclear specialist, infectiologist, anesthesiologist, intensive care specialist) cascade must be initiated. A fast and accurate diagnosis using diagnostic criteria is vital. The appropriate treatment consists of a combination of antibiotics and surgery. Whether or not the vascular prosthesis is preserved depends on a case-by-case basis (tailor-made). Several graft preservation strategies have proven their effectiveness.

Perigraft air mimicking infection on CT angiography following open abdominal aortic aneurysm repair

Aortic graft infection is a feared complication after open abdominal aortic aneurysm repair secondary to its high mortality. Perigraft air is a common finding after open aortic aneurysm repair; however, it is also associated with aortic graft infection. Delineating between graft infection and common postoperative finding is a challenge. This is further complicated by use of hemostatic agents such as Gelfoam, which is also documented to cause perigraft air. Correct diagnosis has crucial implications in management of potential aortic graft infection, which is a vascular emergency. We report a case of perigraft air in a patient status after open aortic aneurysm repair with associated clinical manifestations of infection in whom conservative management and surveillance was selected for treatment. We then discuss the timeline of perigraft air, potential causation, importance of history, and physical examination, and finally, we discuss how specific findings on computed tomography imaging for infection in other areas may be useful in aortic graft infection.

The "3M" Approach to Cardiovascular Infections: Multimodality, Multitracers, and Multidisciplinary

Cardiovascular infections are associated with high morbidity and mortality. Early diagnosis is crucial for adequate patient management, as early treatment improves the prognosis. The diagnosis cannot be made on the basis of a single symptom, sign, or diagnostic test. Rather, the diagnosis requires a multidisciplinary discussion in addition to the integration of clinical signs, microbiology data, and imaging data. The application of multimodality imaging, including molecular imaging techniques, has improved the sensitivity to detect infections involving heart valves and vessels and implanted cardiovascular devices while also allowing for early detection of septic emboli and metastatic infections before these become clinically apparent. In this review, we describe data supporting the use of a Multimodality, Multitracer, and Multidisciplinary approach (the 3M approach) to cardiovascular infections. In particular, the role of white blood cell SPECT/CT and [¹⁸F]FDG PET/CT in most prevalent and clinically relevant cardiovascular infections will be discussed. In addition, the needs of advanced hybrid equipment, dedicated imaging acquisition protocols, specific expertise for image reading, and interpretation in this field are discussed, emphasizing the need for a specific reference framework within a Cardiovascular Multidisciplinary Team Approach to select the best test or combination of tests for each specific clinical situation.

Multidisciplinary Treatment Approach for Prosthetic Vascular Graft Infection in the Thoracic Aortic Area

Prosthetic vascular graft infection in the thoracic aortic area is a rare but serious complication. Adequate management of the complication is essential to increase the chance of success of open surgery. While surgical site infection is suggested as the root cause of the complication, it is also related to decreased host tolerance, especially as found in elderly patients. The handling of prosthetic vascular graft infection has been widely discussed to date. This paper mainly provides a summary of literature reports published within the past 5 years to discuss issues related to multidisciplinary treatment approaches, including surgical site infection, timing of onset, diagnostic methods, causative pathogens, auxiliary diagnostic methods, antibiotic treatment, anti-infective structures of vascular prostheses, surgical treatment, treatment strategy against infectious aortic aneurysms, future surgical treatment, postoperative systemic therapy, and antimicrobial stewardship. A thorough understanding of these issues will enable us to prevent prosthetic vascular graft infection in the thoracic aortic area as far as possible. In the event of its occurrence, the early introduction of appropriate treatment is expected to cure the disease without worsening of the underlying pathological condition.

Aortoenteric fistula as a complication of open reconstruction and endovascular repair of abdominal aorta

The paper intends to present a review of imaging characteristics of secondary aortoenteric fistula (AEF). Mechanical injury, infection, and adherence of a bowel segment to the aorta or aortic graft are major etiologic factors of AEF after open aortic repair. The pathogenesis of AEF formation after endovascular abdominal aortic repair is related to mechanical failure of the stent-graft, to stent graft infection, and to persistent pressurization of the aneurysmal sac. The major clinical manifestations of AEF comprise haematemesis, melaena, abdominal pain, sepsis, and fever. CT is the initial diagnostic modality of choice in a stable patient. However, the majority of reported CT appearances are not specific. In case of equivocal CT scans and clinical suspicion of AEF, scintigraphy, (67)Ga citrate scans or (18)F-FDG PET/CT is useful. Diagnostic accuracy of endoscopy in evaluation of AEF is low; nevertheless it allows to evaluate other than AEF etiologies of gastrointestinal bleeding. Without adequate therapy, AEF is lethal. Conventional surgical treatment is associated with high morbidity and mortality. The endovascular repair may be an option in hemodynamically unstable and high-risk surgical patients. We also illustrate an example of a secondary AEF with highly specific albeit rare radiologic picture from our institution.

Aneurysms of the ascending aorta and arch: the role of imaging in diagnosis and surgical management

Thoracic aortic aneurysms tend to be asymptomatic and were previously often diagnosed only after a complication such as dissection or rupture occurred. Better imaging techniques and an increase in the use of cross-sectional imaging has led to an increase in the diagnosis of aortic aneurysms, which has allowed for elective treatment prior to the development of a complication. The location, size and etiology of an aneurysm all impact the clinical outcomes and these factors are used to determine the appropriate timing of surgical replacement. Surgeons often rely on the information obtained from preoperative imaging to determine when to intervene and what type of procedure will be necessary, making it important for the radiologist to understand these issues in order to provide the necessary information. Postoperative imaging after surgical replacement of the aorta is also important, as there are some common findings that occur in this patient population that can impact how they are treated. The purpose of this article is to review the etiology and associated findings of aneurysms of the ascending aorta and arch, with a focus on how computed tomography angiography and magnetic resonance angiography findings are used to determine the appropriate timing for elective replacement and the type of surgical procedure, as well as the role of follow-up imaging. This will include a review of the most commonly performed types of surgical procedures, to provide an understanding of how the findings of preoperative imaging studies impact what the surgeon does in the operating room, as well as the expected findings of postoperative imaging studies.

MDCT angiography after open thoracic aortic surgery: pearls and pitfalls

OBJECTIVE

The purpose of this article is to review open thoracic aortic surgical techniques and to describe the range of postoperative findings on CT angiography (CTA).

CONCLUSION

An understanding of surgical thoracic aortic procedures will allow appropriate differentiation of normal from abnormal CTA findings on postoperative imaging.

Perigraft air is not always pathological: a case report

Background

The presence of perigraft air is a common finding in the immediate post-operative phase following abdominal aortic aneurysm repair whilst the later appearance of air, in association with elevated inflammatory markers, is regarded as being indicative of the serious complication of graft infection. What is not known is at what timepoint following surgery does the perigraft air become a significant finding.

Case Presentation

We report the case of a 71 year old man who underwent a computed tomography scan 15 days following repair of an abdominal aortic aneurysm because of the presence of unexplained pyrexia. The scan showed the presence of perigraft air and a small haematoma. The patient was managed conservatively and after 6 weeks the air and haematoma had resolved completely.

Conclusion

The presence of perigraft air in the early postoperative phase is probably a normal finding, is not associated with graft infection and can be managed non-operatively.

Leakage of the Arterial Prosthesis of an Impella RVAD

Seromas occurring around a vascular graft are a rare complication. We report a life-threatening plasma leakage that occurred through the polytetrafluoroethylene vascular prosthesis of an Impella right ventricular assist device (Impella RD [Impella Cardiosystems GmbH, Aachen, Germany]) implanted in a 62-year-old patient with acute right ventricular failure after cardiac transplantation. The leakage became progressively massive. Weaning the patient from the right ventricular assist device was not possible. The prosthesis was thus wrapped within a pericardial patch to contain the leakage. Three days later the patient could be successfully weaned and the pump was removed. The clinical evolution was favorable.

CT of acute abdominal aortic disorders

Aortic aneurysm rupture, aortic dissection, PAU, acute aortic occlusion, traumatic aortic injury, and aortic fistula represent acute abdominal aortic conditions. Because of its speed and proximity to the emergency department, helical CT is the imaging test of choice for these conditions. MR imaging also plays an important role in the imaging of aortic dissection and PAU, particularly when the patient is unable to receive intravenous contrast material. In this era of MDCT, conventional angiography is used as a secondary diagnostic tool to clarify equivocal findings on cross-sectional imaging. Ultrasound is helpful when CT is not readily available and the patient is unable or too unstable to undergo MR imaging.

Aortic prosthetic graft infections: radiologic manifestations and implications for management

Prosthetic graft infections are an uncommon complication of aortic bypass. These infections may have serious sequelae such as limb loss and can be lethal. They are hard to eradicate and, under certain circumstances, difficult to diagnose. Usually, computed tomography (CT) is the most efficacious imaging method for diagnosis of graft infections due to its quick availability. The sensitivity of magnetic resonance imaging in detection of perigraft infection has not been thoroughly investigated but is probably similar to that of CT. After the early postoperative period, persistent or expanding perigraft soft tissue, fluid, and gas are the CT findings of graft infection. Aortoenteric fistula should be considered a subset of aortic graft infection; however, perigraft air is more likely to be seen with an aortoenteric fistula. Other conditions associated with graft infection include pseudoaneurysm, hydronephrosis, and osteomyelitis. Adjunctive studies such as sinography, ultrasonography, gallium scanning, and labeled white blood cell scanning can be quite useful in diagnosis, determination of the extent of disease, and selection of the treatment modality. White blood cell scanning is an important complementary test to CT in ambiguous cases, such as in the early postoperative period, and may be more sensitive in detection of early graft infection.

Management of Patients with Prosthetic Vascular Graft Infection

Management of patients with infected prosthetic vascular grafts is one of the most difficult challenges faced by the vascular surgeon. Patients often present with nonspecific symptoms, but delay in treatment can lead to life-threatening sepsis and/or hemorrhage. Fortunately, prosthetic vascular graft infection is uncommon, with the incidence varying between 1 and 6 per cent, depending on the location of the graft. Initially, the potentially infected vascular graft should be imaged using either CT or magnetic resonance imaging, with radionuclide studies being reserved for those instances in which imaging studies do not confirm or exclude the diagnosis of infection. Current treatments for prosthetic vascular graft infection include attempted graft preservation, graft removal with in situ graft replacement (using autogenous or new prosthetic grafts), and graft removal with extra-anatomic bypass. Morbidity and mortality associated with treatment, likelihood of long-term limb salvage, and likelihood of persistent or recurrent infection vary among these types of treatment. Therefore, in an individual patient with a prosthetic vascular graft infection, many things must be considered to appropriately determine the treatment most likely to achieve eradication of the infection and long-term limb salvage with the lowest risk. Regardless, with appropriate application of the techniques currently available for treatment of prosthetic vascular graft infection, long-term elimination of infection and limb preservation can be achieved in the great majority of patients with this grave problem.

Can knitting structure affect dilation of polyester bifurcated prostheses? A randomized study with the use of helical computed tomography scanning

PURPOSE

The aim of this study was to prospectively evaluate the postoperative dilation of two types of knitted polyester arterial prostheses with the use of helical computed tomographic scanning.

METHODS

Thirty-four patients who underwent aortoiliac or aortofemoral bifurcation grafting were randomized to receive a collagen-sealed warp-knitted polyester graft (n = 16 patients) or a gelatin-sealed Köper-knitted polyester graft (n = 18 patients). Alterations in size of all parts of the grafts were evaluated by helical computed tomographic scanning at postoperative day 8, at 3 months, and at 6 months.

RESULTS

On postoperative day 8, the mean dilation of the Köper-knitted grafts was 18% +/- 8% for the stem and 15% +/- 12% for the limbs. At the same time period, the mean dilation of warp-knitted grafts was 27% +/- 13% for the stem and 33% +/- 18% for the limbs. No increase in graft dilation was observed at 3 and 6 months. Despite the wide range of values among patients with the same graft type, at each time interval, the Köper-knitted grafts dilated significantly less than the warp-knitted grafts (P <. 05).

CONCLUSION

In this randomized study, helical computed tomographic scanning was an accurate technique with which to assess graft dilation. For a 6-month follow-up interval, the Köper-knitted polyester structure dilated less than the warp-knitted structure. Longer-term serial scans should allow a better understanding of the clinical significance of graft dilation.

Heparin as a risk factor for perigraft seroma complicating the modified Blalock-Taussig shunt

OBJECTIVE

The purpose of this study was to determine the risk factors associated with the occurrence of perigraft seromas complicating systemic-to-pulmonary polytetrafluoroethylene grafts.

METHODS

Clinical and perioperative variables were reexamined, blinded for the outcome variable perigraft seroma, in 60 patients undergoing 67 consecutive graft procedures in a 3.5-year period.

RESULTS

Eight cases of perigraft seroma were diagnosed in six patients. Univariate analysis revealed age (p = 0.02), a diagnosis of pulmonary atresia with ventricular septal defect and systemic-pulmonary collaterals (p = 0.001), reimplantation of collaterals during the procedure (p < 0.001), and intravenous heparin administered after operation (p < 0.0001) as risk factors for symptomatic perigraft seroma. Multivariable analysis defined heparin as the only significant factor associated with symptomatic perigraft seroma. Consolidation of the upper lobe on chest radiograph, ipsilateral to the shunt, directly after operation (p = 0.01), but especially 8 to 10 days after operation (p < 0.0001), or the need for prolonged drainage of pleural fluid (p < 0.0001) were correlated with the occurrence of perigraft seroma. Perigraft seroma led to four early rethoracotomies in three patients and to accelerated corrective surgery in three cases. Consolidation and absent perfusion of lung segments persisted in two patients.

CONCLUSIONS

Our data suggest that the use of heparin leads to an increased risk of perigraft seroma, complicating systemic-pulmonary polytetrafluoroethylene grafts. Prolonged pleural drainage and/or postoperative consolidation of the upper lobe indicate the development of symptomatic perigraft seroma. Treatment is controversial and results are unpredictable. Expectative management seems to be justified so long as permitted by the clinical condition.

The surgical management of aortoenteric fistulas

Aortoenteric fistulas are serious and life-threatening complications of aortic surgery. Their exact pathogenesis is unknown, but mechanical erosion or infection leading to suture line failure are likely mechanisms. The presentation of an aortoenteric fistula can be seen months to years following the original operation, and clinical suspicion remains the cornerstone for diagnosis. When it is suspected, a prompt diagnostic work-up should be pursued in the absence of a readily recognizable source of hemorrhage. Once it is found, either by diagnostic studies or emergency laparotomy, repair can be accomplished by in situ graft replacement or extra-anatomic bypass with closure of the aortic stump. Thorough debridement of the aorta and perigraft tissues is essential for success and patient survival. As perioperative preparation and surgical techniques evolve, so too will the controversy concerning the optimal method for repair.

Successful treatment of early postoperative aortic graft infection by percutaneous catheter drainage

Successful treatment by percutaneous catheter drainage of an acute aortic graft infection with an associated pancreatic fistula is reported. Percutaneous catheter drainage can be considered in selected patients when the risk of reoperation is deemed unacceptable or when other reasonable treatment options do not exist.

Healing of aortic prosthetic grafts: a study by magnetic resonance imaging

Thirty-six patients with aortoiliac reconstruction were studied by magnetic resonance imaging (MRI) to determine the diameter, baseline signal, and subsequent magnetic signal characteristics of postoperative periprosthetic collection (PPC). Our study confirmed the presence of PCC in most cases (32/36). The diameter was significantly (p < 0.05) correlated with the type of disease being treated, the type of proximal anastomosis created, and whether or not drainage and postoperative transfusion were used. PPC usually disappeared within 3 to 6 months postoperatively. Modifications of magnetic signals T1 and T2 require approximately the same amount of time to diminish. During follow-up investigations in this series, there was one case of prosthetic infection characterized by the persistence of PPC and a strong T2 signal 6 months after surgery, the latter corresponding to incomplete or delayed healing. The MRI aspects of normal healing of aortic grafts were analyzed to correctly interpret the MRI aspects of complications in surgery of the aorta.

The isolation of a fibroblast growth inhibitor associated with perigraft seroma

PURPOSE

Perigraft seroma is a rare complication of reconstructive vascular surgery characterized by a clear, sterile fluid collection confined within a fibrous pseudomembrane around a prosthetic graft. The exact cause of this disease is unknown but involves failure of surrounding connective tissue to incorporate the graft. To understand why this occurs, we studied sera from patients with perigraft seroma for their effect on human fibroblasts. Sera from control subjects, patients with uninfected prosthetic grafts, and patients with prosthetic grafts were tested for comparison.

METHODS

Fibroblast growth was measured by radioactive thymidine uptake and hexosaminidase colorimetric cell proliferation assays. We fractionated sera with gel filtration columns and measured each fraction's effect on fibroblast growth.

RESULTS

Serum samples from patients with perigraft seroma inhibited fibroblast growth in a dose-dependent manner. In contrast, a postseroma sample, normal human sera, and sera from patients with infected and uninfected grafts showed no significant fibroblast inhibition. An inhibitory factor with a molecular weight of 2000 d was isolated from serum of patients with perigraft seroma.

CONCLUSIONS

Perigraft seroma is associated with a fibroblast inhibitor with a molecular weight of 2000 d. Further identification and characterization of this protein may lead to clinical applications in preventing and treating perigraft seroma.

Postoperative graft incorporation after aortic reconstruction--comparison between computerised tomography and Tc-99m-HMPAO labelled leucocyte imaging

Aortic graft infection may result in high mortality ranging up to 88%. Therefore, early diagnosis is imperative in the treatment of this serious complication. Computerised tomography (CT) is considered as a sensitive tool in the diagnosis of aortic graft infection. Some findings used as the criteria for infection, such as periprosthetic gas and fluid are, however, normal postoperative findings. The aim of this prospective study was to compare CT-scan and Tc-99m-HMPAO labelled leucocytes in the early diagnosis of aortic graft infection. The present study includes 24 consecutive patients (all men, age 70 +/- 8 years, range 55-85 years), who were operated on for abdominal aortic aneurysm. Prosthetic and suture materials were the same in all operations. Each patient was examined with the aid of CT-scan and imaged with Tc-99m-HMPAO labelled leucocytes 2 weeks and 3, 6 and 12 months after the reconstructive aortic surgery. Two radiologists and two specialists in nuclear medicine examined the data independently without knowing the clinical picture of the results of any other examinations of the patients. Seven patients (7/24; 29%) showed significant accumulation of labelled leucocytes in the first imaging (2 weeks postoperatively) with Tc-99m-HMPAO labelled leucocytes. Three months after the surgery only four patients (4/24; 17%) were positive in this respect. One of these patients had clinically proven aortic graft infection and another positive was a patient with resected and reconstructed mycotic aneurysm. CT-examination in all scans was suggestive for aortic graft infection in two cases (2/24; 8%), but neither of these patients showed any signs of infection.(ABSTRACT TRUNCATED AT 250 WORDS)

STIR imaging of synthetic vascular graft infection

Nine patients with suspected prosthetic vascular graft infection were studied with axial spin echo (SE) and short TI inversion recovery (STIR) magnetic resonance imaging. Images were assessed for presence and extent of abnormality. All patients had either surgical (8/9) or bacteriologic (6/9) confirmation of infection. STIR images better defined the extent of infection and had greater fat-fluid contrast than SE images in 6/9 studies. In 3 cases with peri-graft fluid alone, T2-weighted images had slightly greater contrast, although the STIR images were still diagnostic. STIR imaging can offer improved accuracy in evaluation of suspected prosthetic graft infection when used in conjunction with SE techniques.

Evaluation of hematoma by MRI in follow-up of aorto-femoral bypass

We selected a population of 20 patients with atherosclerotic disease, submitted to implantation of aorto-femoral bypass graft. These patients were studied by MRI with T1- and T2-weighted sequences (w.s.) using a 0.5 T superconductive magnet. Investigation was performed at 1 wk, 1, 3, and 6 mo after dacron implantation, to evaluate the normal evolution of hematoma and the potential development of complications. At the first week examination, hematoma presented medium signal intensity on T1 w.s. and high signal intensity on T2 w.s.; at 1 mo control the amount of hematoma was slightly reduced and we found persistence of high signal intensity on T2 w.s.; progressive reduction of size and signal intensity on T2 w.s. was noted at 3 mo control, in patients operated for peripheral vascular disease; on the other hand we found persistence of high signal intensity in T2 w.s. in patients treated for abdominal aortic aneurysms; only after 6 mo it was evident in all patients fibrotic evolution of the collection and low signal intensity in both T1 and T2 w.s. Thus, MRI study was useful in the evaluation of patency, morphology, and in detection of intraluminal thrombosis, but also in the characterization of periprosthetic hematoma.

Role of magnetic resonance imaging in the evaluation of aortic graft healing, perigraft fluid collection, and graft infection

The authors report their preliminary experience in the use of Magnetic Resonance Imaging (MRI) in ten patients who underwent aortic reconstruction. Examinations were performed 1, 4, 12 and 24 weeks after surgery, to examine the presence, size, magnetic characteristics and evolution of periprosthetic collections. The results have shown that periprosthetic collection can be considered normal after aortic reconstructive surgery, because such a perigraft collection (PFC) was present in 90% of the patients studied 1 week after operation, and had disappeared within 24 weeks in all cases. The magnetic characteristics were evaluated by T1 [repetition time (TR) = 480 msec and echo time (TE) = 20 msec] and T2 weighted spin-echo sequences (TR = 1800 msec and TE = 70/120 msec). Variations in the magnetic characteristics, found in sequential examinations, correlated with modifications of the collection and suggested that it was originally blood. The MRI examination performed 24 weeks after surgery gave a low signal intensity in T1 and T2 weighted sequences (w.s.) suggesting periprosthetic fibrosis. These preliminary observations may constitute a starting point for better evaluation of the normal appearance and evolution of the periprosthetic fluid collections following aortic graft implantation and, may be useful for the early detection of infection especially in asymptomatic patients.

Perigraft seroma: clinical, histologic, and serologic correlates

A 14 year retrospective study of perigraft seroma, defined as an enlarging sterile fluid collection at the site of a prosthetic graft, revealed well-documented cases in 5 of 118 extraanatomical bypasses (4.2 percent), 3 of 248 aortic reconstructive procedures (1.2 percent), and 1 of 395 femoropopliteal bypasses (0.3 percent). These nine cases involved four polytetrafluoroethylene and five Dacron grafts. There were five graft thromboses, one instance of limb loss, two graft infections, two deaths, and 13 separate surgical procedures related to the perigraft seroma. Histologic studies revealed a fibrous pseudomembrane lining the perigraft seroma wall and immature fibroblasts lining the graft. Sera from three patients with perigraft seroma, five patients with well-incorporated prosthetic grafts, and three healthy volunteer subjects were tested for in vitro evidence of fibroblast inhibition against fibroblast tissue cultures derived from the pseudomembrane of a perigraft seroma. Control fetal calf serum, sera from all three healthy subjects, and sera from all five patients with well-incorporated grafts allowed fibroblast proliferation. In contrast, sera from all three patients with perigraft seroma inhibited fibroblast growth. Furthermore, sera collected 1, 2, and 3 months after graft removal from one patient and serum collected 3 months after spontaneous resolution of a perigraft seroma from another patient failed to inhibit fibroblasts. We have concluded that patients with perigraft seroma have a high rate of graft and limb loss and require multiple reoperations. The pathogenesis of perigraft seroma appears to involve a humoral fibroblast inhibitor which prevents maturation and proliferation of perigraft fibroblasts, leading to poor graft incorporation. The decrease of inhibition below detectable levels after graft removal or spontaneous resolution of the perigraft seroma suggests that the graft may induce host production of the inhibitor. Effective therapy of perigraft seroma may include fibroblast modulation, removal of the inciting graft, or both.