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

Potential applications of PET/MRI in non-oncologic conditions within the abdomen and pelvis

PET/MRI is a relatively new imaging modality with several advantages over PET/CT that promise to improve imaging of the abdomen and pelvis for specific diagnostic tasks by combining the superior soft tissue characterization of MRI with the functional information acquired from PET. PET/MRI has an established role in staging and response assessment of multiple abdominopelvic malignancies, but the modality is not yet established for non-oncologic conditions of the abdomen and pelvis. In this review, potential applications of PET/MRI for non-oncologic conditions of abdomen and pelvis are outlined, and the available literature is reviewed to highlight promising areas for further research and translation into clinical practice.

A role of FDG PET/CT for Response Assessment in Large Vessel Disease?

Currently, a large amount of evidence-based data clearly demonstrates the usefulness of [¹⁸F]FDG PET/CT in the diagnosis of several infectious and inflammatory diseases, including those related to the large vessels. The aim of this article is to clarify whether, beyond initial diagnosis, [¹⁸F]FDG PET/CT may have a role in treatment response assessment in inflammatory or infectious diseases of the large vessels, including large vessel vasculitis, vascular graft infection, retroperitoneal fibrosis/chronic periaortitis and infective native aortic aneurysms. Rapidly accumulating data suggest that [¹⁸F]FDG PET/CT could be a valuable imaging method for therapy monitoring in some infectious and inflammatory diseases of large vessels. The available data, albeit preliminary, indicate that [¹⁸F]FDG PET/CT could even play a pivotal role in the management of these diseases, leading to better drug dosage, confirmation of the usefulness of the treatment, and early modification of the therapeutic strategy. However, to date, the role of [¹⁸F]FDG PET/CT for treatment assessment in large vessel diseases, in particular large vessel vasculitis, is not clearly defined and well-designed prospective studies are needed to confirm its possible role in treatment monitoring and treatment guidance.

Retroperitoneal Fibrosis and its Differential Diagnoses: The Role of Radiological Imaging

Background Retroperitoneal fibrosis is a rare disease with an incidence of 0–1/100 000 inhabitants per year and is associated with chronic inflammatory fibrosis of the retroperitoneum and the abdominal aorta. This article sheds light on the role of radiological imaging in retroperitoneal fibrosis, names various differential diagnoses and provides an overview of drug and surgical treatment options.

Methods A literature search for the keywords “retroperitoneal fibrosis” and “Ormond’s disease” was carried out in the PubMed database between January 1, 1995 and December 31, 2019 (n = 1806). Mainly original papers were selected, but also reviews, in English and German language, with a focus on publications in the last 10 years, without excluding older publications that the authors believe are relevant to the topic discussed in the review (n = 40).

Results and Conclusion Ormond’s disease is a rare but important differential diagnosis for nonspecific back and flank pain. Imaging diagnostics using CT or MRI show a retroperitoneal mass, which must be differentiated from lymphoma, sarcoma, multiple myeloma and Erdheim-Chester disease. Patients have an excellent prognosis under adequate therapy. FDG-PET/CT or FDG-PET/MRT should be considered as potential modalities, as hybrid imaging can evaluate both the morphological changes and the inflammation.

Key Points: 

Citation Format

Impact of hybrid molecular imaging in retroperitoneal fibrosis: a systematic review

The aim of this article was to critically assess the usefulness of hybrid molecular imaging (FDG PET/CT and FDG PET/MR) procedures in the evaluation of inflammatory activity in retroperitoneal fibrosis (RPF). A systematic review of the literature was performed using PubMed without timeline restriction and using the following keywords: retroperitoneal fibrosis, disease activity, diagnostic techniques, PET/CT, PET/MR. We evaluated full text articles written in the English language. Case reports, review articles or editorials and articles not in the field of interest of this review were excluded. Nine articles comprising a total of 186 patients met the inclusion criteria and were included and described in this systematic review. The new hybrid molecular imaging methods give promising results in the evaluation of the activity of the disease, quantification and prediction of therapeutic response and in tailoring medical therapy in RPF. FDG PET/CT can be a valuable tool in detecting disease activity, particularly in asymptomatic patients with RPF with acute phase reactant increase. Hybrid imaging can predict therapy response outcome and the best time for stent removal. Although PET/MR has potential advantage in small lesions and has reduced radiation exposure in comparison to PET/CT, PET quantification parameters have potentially higher diagnostic value over MR parameters in the evaluation of RPF. Acute phase reactants alone may not be reliable for the management and follow-up assessment of the disease. Hybrid imaging in RFP could be more comfortable, more accurate, with less radiation burden than different separate imaging studies acquired at different points in time.

The value of 18F-FDG PET/CT in the distinction between retroperitoneal fibrosis and its malignant mimics

OBJECTIVE

To discuss the utility of ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography/computerized tomography (PET/CT) in the diagnosis of idiopathic retroperitoneal fibrosis (iRPF).

METHODS

IRPF patients diagnosed between September 2011 and June 2016 were included. Retroperitoneal malignancy patients were included as control. The morphological features and FDG uptake of retroperitoneal lesions were measured along with lymph node (LN) mapping.

RESULTS

Seventy-one iRPF patients were included. Fifteen lymphoma patients and 6 retroperitoneal metastatic malignancy patients were included as control. Significant differences in morphological features were observed between iRPF and lymphoma but not retroperitoneal metastatic carcinoma. Compared with malignancy, iRPF displayed a lower frequency of high-FDG-uptake retroperitoneal lesions (P = 0.017) and a lower mean maximum standardized uptake value (SUV_max) (P < 0.001). LNs located at axillary, retroperitoneal, supraclavicular, inguinal or peritoneal sites were more frequently observed in retroperitoneal malignancy, therefore, were defined as specific LNs. The area under the curve (AUC) for SUV_max was 0.893 with a sensitivity of 85.7% and a specificity of 80.3%, when the cut-off value of the SUV_max was 6.23. The AUC for the logistic regression model combining the lesions above renal arteries, the SUV_max and the number of specific LNs was 0.987 with a sensitivity of 90.5% and a specificity of 98.6%. The risk stratification model analysis indicated that most of the retroperitoneal malignancy patients were at moderate or high level, while most of the iRPF patients were at low risk.

CONCLUSIONS

Retroperitoneal malignancy can mimic iRPF morphologically. ¹⁸F-FDG PET/CT can help to distinguish iRPF from retroperitoneal lymphoma and metastatic malignancy.

[18F]-Fluorodeoxyglucose Positron Emission Tomography in the Diagnosis, Treatment Stratification, and Monitoring of Patients with Retroperitoneal Fibrosis: A Prospective Clinical Study

BACKGROUND

The ability to distinguish malignant from benign retroperitoneal fibrosis (RPF) and to select patients who are likely to respond to steroid treatment using a noninvasive test would be a major step forward in the management of patients with RPF.

OBJECTIVE

To prospectively evaluate the potential of [18F]-fluorodeoxyglucose positron emission tomography (FDG-PET) to improve clinical decision-making and management of RPF.

DESIGN, SETTING, AND PARTICIPANTS

A total of 122 RPF patients were assessed and managed by a multidisciplinary RPF service between January 2012 and December 2015. Of these, 78 patients underwent 101 FDG-PET scans, as well as computed tomography and blood tests. Management was based on the findings from these investigations. Median follow-up was 16 mo.

RESULTS AND LIMITATIONS

Of the 24 patients with negative [18F]-FDG-PET, none (0%) had malignancy on biopsy (negative predictive value 100%). [18F]-FDG-PET identified malignancy in 4/4 patients (100%) before biopsy. All four patients had highly avid PET (maximum standardised uptake value ≥4) with atypical avidity distribution. [18F]-FDG-PET revealed avidity in 19/38 patients (50%) with normal inflammatory markers and no avidity in 10/63 patients (16%) with raised marker levels. Patients with highly avid PET were significantly more likely to respond to steroids compared to those with low avidity (9/11 [82%] vs 3/24 [12%]; p<0.01) or negative PET (9/11 [82%] vs 0/14 [0%]; p<0.01). Limitations include the small number of patients and the predominance of tertiary referrals, which may represent patients with particularly problematic RPF.

CONCLUSIONS

This study has established a promising role for [18F]-FDG-PET in optimising and individualising the treatment of RPF.

PATIENT SUMMARY

This study shows that [18F]-fluorodeoxyglucose positron emission tomography scans could reduce the need for biopsy in patients with retroperitoneal fibrosis (RPF). This technique can distinguish cancer from noncancerous RPF, and may be better than blood tests in assessing and monitoring RPF. It also appears to predict a patient's response to steroids, which should allow more individualised treatment.

(18)F-FDG PET/MRI evaluation of retroperitoneal fibrosis: a simultaneous multiparametric approach for diagnosing active disease

PURPOSE

The aim of this study was to evaluate integrated (18)F-FDG PET/MRI as a one-stop diagnostic procedure in the assessment of (active) idiopathic retroperitoneal fibrosis (RPF) METHODS: A total of 22 examinations comprising a PET/CT scan followed by a PET/MRI scan in 17 patients (13 men, 4 women, age 58 ± 11 years) with histopathologically confirmed RPF at diagnosis or during follow-up under steroid therapy were analysed in correlation with laboratory inflammation markers (ESR, CRP). The patient cohort was subdivided into two groups: 6 examinations in untreated and 16 in treated patients. Tissue formations in typically periaortic localization suggestive of RPF were visually and quantitatively evaluated. The PET analysis included the assessment of SUVmax and a qualitative score for FDG uptake in RPF tissue in relation to the uptake in the liver. MRI analysis included evaluation of the T2-weighted image signal intensity, contrast enhancement and diffusion restriction (ADC values). Mean values were compared using the Mann-Whitney U test. ADC, SUVmax and ESR values were correlated using Pearson's correlation.

RESULTS

MRI analysis revealed restricted diffusion in 100 % and 56 %, hyperintense T2 signal in 100 % and 31 %, and contrast enhancement in the periaortic tissue formation suggestive of RPF in 100 % and 62.5 % in the untreated and treated patients, respectively. In the qualitative and quantitative PET analysis, statistically significant differences were found for mean FDG uptake scores (2.5 ± 0.8 in untreated patients and 1.1 ± 0.9 in treated patients) and mean SUVmax (7.8 ± 3.5 and 4.1 ± 2.2, respectively). A strong correlation was found between the ADC values and SUVmax (Pearson r   -0.65, P = 0.0019), and between ESR and CRP values and SUVmax (both r = 0.45, P = 0.061).

CONCLUSION

Integrated (18)F-FDG PET/MRI shows high diagnostic potential as a one-stop diagnostic procedure for the assessment of (active) RPF providing multiparametric supportive information.

A Rationale for the Use of F18-FDG PET/CT in Fever and Inflammation of Unknown Origin

This review focuses on the diagnostic value of hybrid F18-FDG Positron Emission Tomography/Computerized tomography (PET/CT) in fever of unknown origin (FUO) and inflammation of unknown origin (IUO). Due to the wide range of possible causes both FUO and IUO remain a clinical challenge for both patients and physicians. In addition, the aetiology of IUO shows the same variation in diseases as the FUO spectrum and probably requires the same diagnostic approach as FUO. There are numerous historically used diagnostic approaches incorporating invasive and non-invasive, and imaging techniques, all with relative high specificity but limited sensitivity. This hampers the generalization of these diagnostic approaches. However, recently published reports show that F18-FDG PET/CT in FUO and IUO has a high sensitivity and a relative non-specificity for malignancy, infection and inflammation. This makes F18-FDG PET/CT an ideal diagnostic tool to start the diagnostic process and to guide subsequent focused diagnostic approaches with higher specificity. In addition, F18-FDG PET/CT has a relative high negative predictive value. Therefore F18 FDG PET/CT should be incorporated in the routine diagnostic work-up of patients with FUO and IUO, preferably at an early stage in the diagnostic process.

Emerging role of Fluorine-18-fluorodeoxyglucose positron emission tomography in patients with retroperitoneal fibrosis: a systematic review

To systematically review the literature data on the role of Fluorine-18-fluorodeoxyglucose positron emission tomography and positron emission tomography/computed tomography (FDG-PET and PET/CT) in patients with retroperitoneal fibrosis (RF), PubMed/MEDLINE, Embase and Scopus databases were searched for articles that evaluated the usefulness of FDG-PET and PET/CT in patients with RF from inception to March 31, 2012. Review articles or editorials, articles not in the field of interest of this review, case reports and preclinical studies were excluded. Only studies including FDG-PET or PET/CT scans performed in at least three patients with RF were included. Ten studies comprising a total of 101 patients with RF were found. The main findings of the included studies are described. FDG-PET and PET/CT are feasible and suitable imaging methods for evaluating patients with RF. These functional imaging techniques seem to be useful both in the diagnosis (mainly in the assessment of activity and extent of the disease) and in evaluating the treatment response in patients with RF. Given the heterogeneity among the various studies for PET analysis and diagnostic criteria, a standardization of the technique is required in order to achieve reproducible and inter-observer independent results. Moreover, further studies are needed to substantiate the role of FDG-PET and PET/CT in patients with RF.

Fluorine-18-fluorodeoxyglucose positron emission tomography in assessing retroperitoneal fibrosis: a literature review

Background and Purpose. Several studies have evaluated the role of fluorine-18-fluorodeoxyglucose positron emission tomography and positron emission tomography/computed tomography (FDG-PET and PET/CT) in diagnosing and assessing disease activity in patients with retroperitoneal fibrosis (RF). The aim of our paper is to perform a literature review on this topic. Methods. Scientific articles that evaluated the usefulness of FDG-PET and PET/CT in patients with RF were searched and discussed. Results. Eleven studies were found, and the main findings of these articles were described. Conclusion. FDG-PET and PET/CT are useful functional imaging methods for assessing patients with RF both in the diagnosis and in the treatment response evaluation. Moreover, further studies are needed to substantiate the role of FDG-PET and PET/CT in patients with RF.