Abnormal accumulation of [18F]fluorodeoxyglucose in the aortic wall related to inflammatory changes: Three case reports

Feasibility of Assessing Inflammation in Asymptomatic Abdominal Aortic Aneurysms With Integrated 18F-Fluorodeoxyglucose Positron Emission Tomography/Magnetic Resonance Imaging

OBJECTIVE

This study aimed to evaluate the feasibility of 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) combined with contrast enhanced magnetic resonance imaging (MRI) to identify inflammation in asymptomatic abdominal aortic aneurysms (AAA).

METHODS

FDG PET/MRI was performed on 15 patients with asymptomatic infrarenal AAAs >45 mm diameter. Prevalence of FDG uptake and MRI findings of inflammatory changes (oedema, wall thickening, and late gadolinium enhancement [LGE]) in the aortic wall were investigated at three levels: suprarenal aorta; non-aneurysmal aortic neck; and AAA.

RESULTS

The median diameter of the AAAs was 54 mm (range 47-65 mm) and the median expansion rate in the last 12 months was 3 mm (range 1-13 mm). The standard uptake value (SUV) of FDG in the aneurysmal wall (SUVmax 2.5) was higher than the blood pool (SUVmax 1.0; p < .001). The maximum target to background ratio was higher in the suprarenal aorta (mean ± SD; 3.1 ± 0.6) and aortic neck (2.7 ± 0.5) than in the aneurysmal aorta (2.5 ± 0.5; p < .001). Thirty-six FDG hotspots were observed in the aneurysmal wall of 13 patients. Wall thickening and LGE were identified in eight patients. The number of FDG hotspots correlated with recent AAA growth (r = 0.62, p = .01). The recent aneurysm expansion rate was higher in aneurysms with LGE than in those without (7 mm vs. 2 mm; p = .03). MRI inflammatory changes were observed in nine of 36 hot spots (25%) and in three of 13 patients with focal FDG uptake.

CONCLUSION

Fully integrated FDG PET/MRI can be used to study inflammation in asymptomatic AAAs. Heterogenous uptake of FDG in the aneurysmal wall indicates increased glucose metabolism, suggesting an ongoing inflammation. However, these FDG hotspots rarely correspond to MRI findings of inflammation, raising the question of which type of cellular activity is present in these areas. The presence of LGE and FDG hotspots both correlated to recent aneurysm growth, and their usefulness as clinical markers of aneurysm growth warrant additional investigation.

Role of PET/CT in the Evaluation of Aortic Disease

Positron emission tomography (PET) /computed tomography (CT) has been established as a standard imaging modality in the evaluation of malignancy. Although PET/CT has played a major role in the management of oncology patients, its clinical use has also increased for various disorders other than malignancy. Growing evidence shows that PET/CT images have many advantages in aortic disease as well. This review article addresses the potential role of PET/CT in diseases involving the aorta, emphasizing its usefulness with regard to acute thoracic aortic syndromes, aortic aneurysm, atherosclerotic lesions, aortitis and aortic tumors.

18F-FDG PET/MRI in the diagnosis of an infected aortic aneurysm

We report a case where an integrated whole body ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET)/magnetic resonance imaging (MRI) is performed in the diagnostic work-up of a saccular aortic aneurysm. The integrated whole body ¹⁸F-FDG PET/MRI study answered all relevant diagnostic questions, clearly marking an infected aortic aneurysm, depicting the extent of the infected area in relation to the aortic branch vessels, and indicating the aortic lesion as the primary site of infection. The patient was successfully treated by open type V TAAA repair and pericardial graft replacement. Aortic wall infection was proven in cultures of the surgical specimen.

The value of (18)F-FDG PET/CT in the assessment of active idiopathic retroperitoneal fibrosis

PURPOSE

The different stages in idiopathic retroperitoneal fibrosis (IRF) are generally assessed by assay of inflammatory markers and analysis of contrast-enhanced CT images of the retroperitoneal mass. We investigated the potential role of (18)F-FDG PET/CT in this clinical setting.

METHODS

(18)F-FDG uptake was assessed visually and semiquantitatively (using maximum standardized uptake values, SUVmax) in images of the abdominal mass in 22 patients prospectively enrolled from June 2008 to December 2010 who underwent a total of 33 PET/CT studies. The accuracy in discriminating active from inactive disease was calculated assuming as reference a biochemical instrumental evaluation of patients with IRF mostly based on the level of inflammatory indices and contrast enhancement (CE) of the mass at the time of each PET study. In particular, the relationship between SUVmax and CE, the latter calculated from the change in radiodensity (Hounsfield units) between the basal and postcontrast venous portal phases, was evaluated on a three-point scale (0 <20 HU, 1 20-30 HU, 2 ≥ 30 HU). SUVmax and CE scores were correlated with the erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels. The value of PET/CT in assessing the variation of disease activity over time was also investigated by analysing the changes in metabolic volume (MV) of the retroperitoneal lesion between repeat patient studies.

RESULTS

PET/CT accurately discriminated (93.9 %) active from inactive disease. Significant agreement (p < 0.01) was observed between visual and semiquantitative analysis of (18)F-FDG uptake, and CE score. A significant correlation (p < 0.01) was found among SUVmax, CRP levels (rho = 0.54) and ESR (rho = 0.55). Corresponding variations in MV and CE score were observed in patients with multiple studies (p < 0.01; rho = 0.68).

CONCLUSION

(18)F-FDG PET/CT may be considered an alternative imaging method for the assessment of different stages of IRF.

[¹⁸F]FDG-PET/CT in patients affected by retroperitoneal fibrosis: a bicentric experience

PURPOSE

The aim of our study was to assess the feasibility and usefulness of 2-[(18)F]-fluoro-2-deoxy-D: -glucose positron emission tomography computed tomography ([(18)F]FDG-PET/CT) in patients affected by retroperitoneal fibrosis.

MATERIALS AND METHODS

We retrospectively evaluated 25 patients studied in two centers: 18 underwent [(18)F]FDG-PET/CT as initial evaluation, three during follow-up, three during steroid therapy, and one to re-evaluate the disease. Among the group who underwent initial evaluation, ten underwent a second [(18)F]FDG-PET/CT after steroid therapy.

RESULTS

[(18)F]FDG-PET/CT was positive in 18 patients and negative in seven. Among the ten patients who underwent a second study after steroid therapy, six showed complete metabolic response, three partial response, and one no significant maximum standardized uptake value (SUV(max)) reduction.

CONCLUSION

Our preliminary results show that [(18)F]FDG-PET/CT is feasible and suitable for evaluating retroperitoneal fibrosis and is useful in assessing therapy response. Larger studies are desirable to confirm these findings and to determine the appropriate position of [(18)F]FDG-PET/CT in the diagnostic flow chart for this disease.

Infected aortic aneurysm and inflammatory aortic aneurysm--in search of an optimal differential diagnosis

Infected aortic aneurysm and inflammatory aortic aneurysm each account for a minor fraction of the total incidence of aortic aneurysm and are associated with periaortic inflammation. Despite the similarity, infected aortic aneurysm generally shows a more rapid change in clinical condition, leading to a fatal outcome; in addition, delayed diagnosis and misuse of corticosteroid or immunosuppressing drugs may lead to uncontrolled growth of microorganisms. Therefore, it is mandatory that detection of aortic aneurysm is followed by accurate differential diagnosis. In general, infected aortic aneurysm appears usually as a saccular form aneurysm with nodularity, irregular configuration; however, the differential diagnosis may not be easy sometimes for the following reasons: (1) symptoms, such as abdominal and/or back pain and fever, and blood test abnormalities, such as elevated C-reactive protein and enhanced erythrocyte sedimentation rate, are common in infected aortic aneurysm, but they are not found infrequently in inflammatory aortic aneurysm; (2) some inflammatory aortic aneurysms are immunoglobulin (Ig) G4-related, but not all of them; (3) the prevalence of IgG4 positivity in infected aortic aneurysm has not been well investigated; (4) enhanced uptake of 18F-fluorodeoxyglucose (FDG) by 18F-FDG-positron emission tomography may not distinguish between inflammation mediated by autoimmunity and that mediated by microorganism infection. Here we discuss the characteristics of these two forms of aortic aneurysm and the points of which we have to be aware before reaching a final diagnosis.

(18)F-fluorodeoxyglucose position emission tomography (FDG-PET) for monitoring disease activity and treatment response in idiopathic retroperitoneal fibrosis

OBJECTIVE

To evaluate the value of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) in monitoring disease activity and predicting treatment response in idiopathic retroperitoneal fibrosis (iRPF).

PATIENTS AND METHODS

This prospective study was approved by the institutional review board. Informed consent was obtained from all patients. Twenty-six patients with iRPF receiving tamoxifen monotherapy underwent repeated FDG-PET (baseline and, if positive, at 3 months) and computed tomographic (CT) scanning (baseline, 4 and 8 months). Maximal RPF mass thickness in 3 different view directions was measured on each CT scan; FDG-uptake was semi-quantified using a visual 4-point scale. Initial and follow-up PET scan results were correlated with clinical, laboratory and CT scan follow-up data. Treatment outcome was the aggregate measure of clinical, laboratory and CT-documented response to tamoxifen.

RESULTS

FDG-PET was positive in 20 patients. Patients with positive PET scan result had higher C-reactive protein level (P=0.02) and larger mass size (P=0.01) compared with patients with negative PET scan result. Visual PET score correlated with C-reactive protein level (P=0.002) and CT-documented mass thickness (P=0.04). Visual PET score decreased following treatment (P<0.01). This decrease correlated with decrease in ESR (P<0.001) but not with CT-documented mass regression. Positive predicting value (PPV) of initial positive PET scan result was 0.63; PPV of negative follow-up PET scan result in patients with initial positive PET scan result was 0.66.

CONCLUSION

FDG-PET is valuable in detecting (recurrent) disease activity. Short-term follow-up with FDG-PET cannot be routinely recommended for the therapeutic evaluation of RPF disease in tamoxifen-treated patients.

F-18 FDG PET-CT findings in Mikulicz disease and systemic involvement of IgG4-related lesions

A 72-year-old woman with Mikulicz disease with pathogically proven sclerosing sialadenitis showed systemic abnormal F-18 FDG uptake in the bilateral lacrimal and submandibular glands, pancreas, abdominal aortic wall, and a retroperitoneal fibroid mass on PET/CT scan, with marked elevation of the serum IgG4 level. This case supports Mikulicz disease being included as 1 of the disorders associated with a new clinical entity of systemic IgG4-related plasmacytic syndrome. A whole-body FDG-PET/CT scan can be expected as a useful tool for detecting systemic involvement in systemic IgG4-related plasmacytic syndrome.

Increased metabolic activity in abdominal aortic aneurysm detected by 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT)

OBJECTIVES

Abdominal aortic aneurysms (AAAs) are associated with an inflammatory cell infiltrate and enzymatic degradation of the vessel wall. The aim of this study was to detect increased metabolic activity in the wall of the AAA with 18F-fluorodeoxyglucose ((18)F-FDG), mediated by glucose transporter protein (GLUTs), using a dedicated hybrid PET/64-detector CT. DESIGN, METHOD AND MATERIALS: 14 patients (All male, mean age 73.6 years, range 61-82) with AAA under surveillance underwent PET/CT scanning with 175 MBq of intravenous (18)F-FDG. The maximum aneurysm diameter and calcification score were determined on the attenuation correction CT. A volume of interest was placed on the aneurysm sac and the maximum Standardised Uptake Value (SUV(max)) measured.

RESULTS

The mean aneurysm diameter was 5.4 cm (SD+/-0.8). Two aneurysms had the CT characteristics of inflammatory aneurysms. Twelve aneurysms showed increased FDG uptake (SUV(max)>2.5). There was no significant difference in FDG uptake between heavily calcified aneurysms and non-heavily calcified aneurysms (t-test). There was a significant increase in the FDG uptake in the two inflammatory aneurysms compared to the other twelve aneurysms (t-test; P=0.04).

CONCLUSION

The findings in this study offer in vivo evidence that the AAA wall shows increased glucose metabolism, mediated by the GLUTs: this increased metabolic activity as detected by PET/CT may be present in most AAAs.

Avid FDG uptake in a rapidly enlarging common carotid artery mycotic aneurysm, mimicking lymphadenopathy

We present a case of mycotic pseudoaneurysm of the right common carotid artery, which demonstrated avid FDG uptake mimicking lymphomatous involvement on a non-contrast FDG-PET/CT scan. Within 6 days of initial presentation, the pseudoaneurysm enlarged rapidly and required emergent surgical repair. To the best of our knowledge, this is the first reported case both of a PET-positive non-aortic aneurysm and a rapidly enlarging common carotid artery pseudoaneurysm. This case highlights the importance of contrast administration with PET/CT and the heralding nature of FDG uptake in an aneurysm wall for impending aneurysm rupture.

F-18-fluorodeoxyglucose positron emission tomography-computed tomography for the diagnosis of Takayasu's arteritis in stroke: a case report

INTRODUCTION

Diagnosis of Takayasu's arteritis as the cause of stroke is often delayed because of non-specific clinical presentation. F-18-fluorodeoxyglucose positron emission tomography-computed tomography may help to accurately diagnose and monitor Takayasu's arteritis in stroke patients.

CASE PRESENTATION

We report the case of a left middle cerebral artery stroke in a 39-year-old man. Laboratory data were consistent with an inflammatory reaction. While abdominal contrast-enhanced computed tomography showed an aneurysm of the infrarenal aorta, only F-18-fluorodeoxyglucose positron emission tomography-computed tomography revealed pathology (that is, intense F-18-fluorodeoxyglucose accumulation) in the carotid arteries, ascending aorta and the abdominal aorta cranial to the aneurysm. After treatment with high-dose prednisone followed by cyclophosphamide, the signs of systemic inflammation decreased and F-18-fluorodeoxyglucose uptake was reduced as compared with the initial scan.

CONCLUSION

F-18-fluorodeoxyglucose positron emission tomography-computed tomography showed inflammatory activity in the aorta and carotid arteries, suggestive of Takayasu's arteritis in a young stroke patient, and follow-up under immunosuppressive therapy indicated reduced F-18-fluorodeoxyglucose uptake. F-18-fluorodeoxyglucose positron emission tomography-computed tomography appears to be useful in detecting and quantifying the extent of vascular wall activity in systemic large-vessel vasculitis.

Increased 18F-fluorodeoxyglucose uptake in abdominal aortic aneurysms in positron emission/computed tomography is associated with inflammation, aortic wall instability, and acute symptoms

OBJECTIVE

With the established computed tomographic (CT)- morphologic parameters, only the relative, but not the individual rupture risk of abdominal aortic aneurysm (AAA), can be determined. So far, increased aortic 18F-fluorodeoxyglucose (FDG) metabolism measured by positron emission tomography (PET) has been reported in AAA with increased rupture risk. The aim of the study was to analyze the histopathologic changes in AAA wall correlated with increased FDG uptake for further implications on aortic wall stability and AAA rupture risk.

METHODS

Fifteen patients with asymptomatic (n = 12) and symptomatic (n = 3) AAA underwent FDG-PET/CT, followed by open AAA repair. FDG-PET/CT was used for precise localization of maximum FDG uptake, and the maximum standard uptake values (SUV(max)) were calculated. Biopsies of the AAA wall were operatively collected from areas with maximum FDG uptake, immunohistologically stained, and semiquantitatively analyzed for inflammatory infiltrates, vascular smooth muscle cells (VSMC), matrix metalloproteinase (MMP)-2 and -9 expression, as well as for elastin and collagenous fibers.

RESULTS

Symptomatic AAA showed significantly increased FDG uptake compared with asymptomatic AAA (SUV(max), 3.5 +/- 0.6 vs 7.5 +/- 3; P < .001). Thus, increased FDG uptake was correlated with higher densities of inflammatory infiltrates (r = +0.87, P < .01) and macrophage and T-cell infiltrations (r = +0.95, P < .01 and r = +0.66, P < .05), with higher MMP-9 expressions (r = +0.86; P < .01), and with reduction of collagen fiber (r = -0.76; P < .01) and VSMCs (r = -0.71; P < .01). Consecutive correlations were found for total inflammatory infiltrates, T lymphocytes, and macrophages with MMP-9 expression (r = +0.79, +0.79 and +0.74; P < .01). Moreover, MMP-9 expression was correlated with decreasing collagen fiber content (r = -0.53, P < .05) and VSMC density (r = -0.57, P < .05).

CONCLUSIONS

Maximum aortic FDG uptake correlated significantly with inflammation, followed by increased MMP expression and histopathologic characteristics of aneurysm wall instability and clinical symptoms. Therefore, FDG-PET/CT might be a new diagnostic technique to study AAA disease in vivo and may contribute to improve prediction of individual AAA rupture risk.

Application of PET/SPECT imaging in vascular disease

BACKGROUND

Nuclear medicine imaging differs from other imaging modalities by showing physiological processes instead of anatomical details.

OBJECTIVE

To describe the current applications of positron emission tomography (PET) and single photon emission computed tomography (SPECT) as a diagnostic tool for vascular disease as relevant to vascular surgeons.

METHODS

A literature search identified articles focussing on vascular disease and PET or SPECT using the Pubmed database. Manual cross referencing was also performed.

RESULTS

PET and SPECT may be used to assess plaque vulnerability, biology of aneurysm progression, prosthetic graft infection, and vasculitis. The ability to combine computerized tomography scanning or magnetic resonance imaging with PET or SPECT adds detailed anatomical information and enhances the potential of nuclear medicine imaging in the investigation of vascular disease.

DISCUSSION

Considerable further information will be needed to define whether and where PET or SPECT will fit in a clinical strategy. The necessary validation studies represent an exciting challenge for the future but also may require the development of interdisciplinary imaging groups to integrate expertise and optimize nuclear diagnostic potential.

Acute intramural hematoma of the aorta as a cause of positive FDG PET/CT

Type A acute intramural hematoma (IMH) of the ascending aorta is defined as hemorrhage in the aortic wall in the absence of intimal disruption. Proximity to the adventitia may explain the higher incidence of rupture in IMH. We present a case of IMH, diagnosed by the presence of linear intense uptake of FDG on PET/CT, in a 70-year-old woman undergoing staging for colorectal cancer. There is no current role for FDG-PET in the diagnosis of IMH. This case demonstrates that incidental focal FDG activity in the wall of the aorta may indicate the life-threatening diagnosis of IMH.

FDG-PET/CT for diagnosis and follow-up of vasculitis

We report three cases of vasculitis evaluated by FDG-PET/CT. Vasculitis is defined as inflammatory changes and necrosis in the aterial wall. The patients presented with non-specific symptoms such as fever up or elevated inflammatory markers. FDG-PET/CT clearly demonstrated intense FDG uptake in vessel walls. A 72-year-old female patient with a one month history of pyrexia had abnormal laboratory data suggesting an inflammatory process. FDG-PET/CT was very useful for the diagnosis of vasculitis. Steroid therapy was introduced. Normalization of laboratory data and symptomatic improvement correlated with normalization of FDG uptake in the vessels.