The clinical utility of FDG PET/CT among solid organ transplant recipients suspected of malignancy or infection

Outcomes of children treated for multiple Epstein-Barr virus-associated post-transplant tumors

BACKGROUND

After solid organ transplantation, children are at risk for Epstein-Barr virus-associated post-transplant lymphoproliferative disorder and smooth muscle tumors. Little is known about the clinical course, Epstein-Barr viral load variations, and optimal treatment for such patients. We set forth to understand the course of repeated episodes of post-transplant lymphoproliferative disorder and smooth muscle tumors.

METHODS

We performed a retrospective chart review of patients up to 21 years old with solid organ transplantation and post-transplant lymphoproliferative disorder at the Children's Hospital of Philadelphia from January 2003 through June 30, 2020.

RESULTS

Six patients had multiple episodes of Epstein-Barr virus-associated post-transplant lymphoproliferative disorder and smooth muscle tumors. When the second episode was discovered, only one patient was symptomatic. Histology differed from diagnosis in four patients. Treatment included viral-specific T-lymphocytes (2), rituximab (3), reduction in immunosuppression alone (1). Five patients had complete response, and one had stable disease, but three patients developed a subsequent tumor. Two patients developed Epstein-Barr virus-associated smooth muscle tumors. Of these six patients, four are alive. The deaths were not related to their tumors.

CONCLUSIONS

Despite a complete response to initial therapy, children are at risk for repeated episodes of Epstein-Barr virus-associated post-transplant lymphoproliferative disorder and smooth muscle tumors. Histology and location were not typically consistent with initial diagnosis, suggesting these are second primaries rather than recurrences. Disease may be managed with individualized treatment plans but EBV-specific T cells need further study in such tumors.

Clinical Utility of 18Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18F-FDG PET/CT) in Multivisceral Transplant Patients

Multivisceral transplant (MVTx) refers to a composite graft from a cadaveric donor, which often includes the liver, the pancreaticoduodenal complex, and small intestine transplanted en bloc. It remains rare and is performed in specialist centres. Post-transplant complications are reported at a higher rate in multivisceral transplants because of the high levels of immunosuppression used to prevent rejection of the highly immunogenic intestine. In this study, we analyzed the clinical utility of 28 ¹⁸F-FDG PET/CT scans in 20 multivisceral transplant recipients in whom previous non-functional imaging was deemed clinically inconclusive. The results were compared with histopathological and clinical follow-up data. In our study, the accuracy of ¹⁸F-FDG PET/CT was determined as 66.7%, where a final diagnosis was confirmed clinically or via pathology. Of the 28 scans, 24 scans (85.7%) directly affected patient management, of which 9 were related to starting of new treatments and 6 resulted in an ongoing treatment or planned surgery being stopped. This study demonstrates that ¹⁸F-FDG PET/CT is a promising technique in identifying life-threatening pathologies in this complex group of patients. It would appear that ¹⁸F-FDG PET/CT has a good level of accuracy, including for those MVTx patients suffering from infection, post-transplant lymphoproliferative disease, and malignancy.

Diagnostic Yield of 18F-FDG PET After Lung Transplantation: A Single-center, Retrospective Cohort Study

BACKGROUND

To investigate the diagnostic yield of 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) in lung transplant recipients.

METHODS

A single-center, retrospective cohort study including 234 18F-FDG PET examinations in 199 lung transplant recipients. Indication for PET referral, 18F-FDG PET diagnosis/findings and final clinical diagnosis were classified into 3 groups: malignancy, infection/inflammation not otherwise specified, and chronic lung allograft dysfunction with restrictive allograft syndrome phenotype. Sensitivity/specificity analysis was performed to determine accuracy of 18F-FDG PET in each group.

RESULTS

Sensitivity of 18F-FDG PET for malignancy was 91.4% (95% confidence interval, 82.5%-96.0%) and specificity was 82.3% (95% confidence interval, 74.5%-88.1%). Infection/inflammation not otherwise specified and restrictive allograft syndrome as indication for 18F-FDG PET comprised relatively small groups (14 and 31 cases, respectively). In addition, 18F-FDG PET revealed clinically relevant incidental findings in 15% of cases.

CONCLUSIONS

Referral for 18F-FDG PET after lung transplantation mainly occurred to confirm or rule out malignancy. In this specific setting, 18F-FDG PET has a high diagnostic yield. Accuracy of 18F-FDG PET for other indications is less clear, given small sample sizes. Clinically relevant diagnoses, unrelated to the primary indication for 18F-FDG PET, are found relatively often in this immunocompromised cohort.

SNMMI Procedure Standard/EANM Practice Guideline on Pediatric 18F-FDG PET/CT for Oncology 1.0

The Society of Nuclear Medicine and Molecular Imaging (SNMMI) is an international scientific and professional organization founded in 1954 to promote the science, technology, and practical application of nuclear medicine. The European Association of Nuclear Medicine (EANM) is a professional nonprofit medical association founded in 1985 to facilitate communication worldwide among individuals pursuing clinical and academic excellence in nuclear medicine. SNMMI and EANM members are physicians, technologists, and scientists specializing in the research and practice of nuclear medicine.

The SNMMI and EANM will periodically put forth new standards/guidelines for nuclear medicine practice to help advance the science of nuclear medicine and improve service to patients. Existing standards/guidelines will be reviewed for revision or renewal, as appropriate, on their fifth anniversary or sooner, if indicated. Each standard/guideline, representing a policy statement by the SNMMI/EANM, has undergone a thorough consensus process, entailing extensive review. The SNMMI and EANM recognize that the safe and effective use of diagnostic nuclear medicine imaging requires particular training and skills, as described in each document. These standards/guidelines are educational tools designed to assist practitioners in providing appropriate and effective nuclear medicine care for patients. These guidelines are consensus documents, and are not inflexible rules or requirements of practice. They are not intended, nor should they be used, to establish a legal standard of care. For these reasons and those set forth below, the SNMMI and the EANM cautions against the use of these standards/guidelines in litigation in which the clinical decisions of a practitioner are called into question.

The ultimate judgment regarding the propriety of any specific procedure or course of action must be made by medical professionals taking into account the unique circumstances of each case. Thus, there is no implication that action differing from what is laid out in the standards/guidelines, standing alone, is below standard of care. To the contrary, a conscientious practitioner may responsibly adopt a course of action different from that set forth in the standards/guidelines when, in the reasonable judgment 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 standards/guidelines.

The practice of medicine involves not only the science, but also the art of dealing with the prevention, diagnosis, alleviation, and treatment of disease. The variety and complexity of human conditions make it impossible for general guidelines to consistently allow for an accurate diagnosis to be reached or a particular treatment response to be predicted. Therefore, it should be recognized that adherence to these standards/guidelines will not ensure a successful outcome. All that should be expected is that the practitioner follows a reasonable course of action, based on their level of training, the current knowledge, the available resources, and the needs/context of the particular patient being treated.

PET and computerized tomography (CT) have been widely used in oncology. ¹⁸F-FDG is the most common radiotracer used for PET imaging. The purpose of this document is to provide imaging specialists and clinicians guidelines for recommending, performing, and interpreting ¹⁸F-FDG PET/CT in pediatric patients in oncology. There is not a high level of evidence for all recommendations suggested in this paper. These recommendations represent the expert opinions of experienced leaders in this field. Further studies are needed to have evidence-based recommendations for the application of ¹⁸F-FDG PET/CT in pediatric oncology. These recommendations should be viewed in the context of good practice of nuclear medicine and are not intended to be a substitute for national and international legal or regulatory provisions.

FDG PET/CT for Detection of Infectious Complications Following Solid Organ Transplantation

Infectious complications after solid organ transplantation (SOT) are often more severe and remain a diagnostic challenge due to vague and atypical clinical presentations. Diagnostic performance of conventional diagnostic tools is frequently inadequate which may lead to delayed diagnosis with the risk of poorer outcomes. This literature review aimed to investigate the current evidence on the use of ¹⁸F-fluoro-deoxy-glucose (FDG) Positron Emission Tomography (PET)/computer tomography (CT) in infectious complications after SOT. Based on search in PubMed, Medline, and Cochrane databases, 13 articles and 46 case reports were included. For inclusion, articles were to include data on patients with infectious complications after SOT, and where FDG PET/CT was part of the work-up. Final searches were conducted on 02 September 2020. Overall, in the absence of initial diagnostic clues, FDG PET/CT should be considered as the imaging technique of choice as it may guide further investigations and eventually reveal the diagnosis in most of the patients. However, the available literature of the role of FDG PET/CT in SOT recipients with infectious complications is scarce and well-designed prospective studies including control groups are warranted to establish the role of FDG PET/C/ in SOT recipients. The main drawback of FDG PET/CT is the lack of ability to differentiate between cancer and infectious diseases which are both highly prevalent in this patient group. Accordingly, the main reasons for "false" results of FDG PET/CT is the misdiagnosis of cancer in benign inflammatory or infectious processes, information which nonetheless can be useful.

Malignant Peripheral Nerve Sheath Tumor Arising From Transplanted Kidney Assessed by 18F-FDG PET/CT

Malignant peripheral nerve sheath tumor (MPNST) originates from Schwann cells or pluripotent perineural cells, which is an extremely rare tumor that occurs in the kidney. We report a case of MPNST in transplanted kidney that was diagnosed in a 32-year-old man with a history of kidney transplantation. Contrast-enhanced MRI and F-FDG PET/CT features of MPNST are described, which can accurately discriminate MPNST from infection and benign tumors. These features could potentially provide valuable information to distinguish it from other renal malignancies. F-FDG PET/CT may be a useful tool for the primary diagnosis and the initial staging of MPNST.

Assessment of Suspected Malignancy or Infection in Immunocompromised Patients After Solid Organ Transplantation by [18F]FDG PET/CT and [18F]FDG PET/MRI

Purpose

To study the value of 2-deoxy-2-[¹⁸F]fluoro-D-glucose([¹⁸F]FDG) positron emission tomography/computed tomography (PET/CT) and [¹⁸F]FDG positron emission tomography/magnetic resonance imaging (PET/MRI) in assessing immunocompromised patients with suspected malignancy or infection.

Methods

[¹⁸F]FDG-PET/CT and [¹⁸F]FDG-PET/MRI examinations of patients who were immunocompromised after receiving lung, heart, pancreas, kidney, liver, or combined kidney-liver transplants were analyzed in this retrospective study. Patients underwent whole-body hybrid-imaging because of clinical signs of malignancy and/or infection. Findings were assessed by molecular features ([¹⁸F]FDG-uptake) and morphological changes. The final diagnosis, which was arrived at after review of clinical, laboratory, and histopathologic analyses and follow-up imaging studies, served as the reference standard.

Results

Altogether, (i) 28 contrast-enhanced [¹⁸F]FDG-PET/CT scans (CE-PET/CT), (ii) 33 non-contrast [¹⁸F]FDG-PET/CT scans (NC-PET/CT), and (iii) 18 [¹⁸F]FDG-PET/MRI scans were included. Additionally, 12/62 patients underwent follow-up PET imaging to rule out vital tumor or metabolic active inflammatory processes. CE-PET/CT exhibited 94.4% sensitivity, 80.0% specificity, 89.5% positive predictive value (PPV), 88.9% negative predictive value (NPV), and 89.3% accuracy with regard to the reference standard. NC-PET/CT exhibited 91.3% sensitivity, 80.0% specificity, 91.3% PPV, 80.0% NPV, and 87.9% accuracy. PET/MRI exhibited 88.6% sensitivity, 99.2% specificity, 99.6% PPV, 81.3% NPV, and 94.4% accuracy. Exact McNemar statistical test (one-sided) showed significant difference between the CT-/MR-component alone and the integrated PET/CT and PET/MRI for diagnosis of malignancy or infection (p value < 0.001). Radiation exposure was 4- to 7-fold higher with PET/CT than with PET/MRI.

Conclusion

For immunocompromised patients with clinically unresolved symptoms, to rule out vital tumor manifestations or metabolic active inflammation, [¹⁸F]FDG-PET/MRI, CE-[¹⁸F]FDG-PET/CT, and NC-[¹⁸F]FDG-PET/CT exhibit excellent performance in diagnosing malignancy or infection. The main strength of PET/MRI is its considerably lower level of radiation exposure than that associated with PET/CT.

Diagnostic Performance of 18F-FDG PET or PET/CT for Detection of Post-Transplant Lymphoproliferative Disorder: A Systematic Review and a Bivariate Meta-Analysis

BACKGROUND

Some studies evaluated the diagnostic performance of fluorine-18-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography or positron emission tomography/computed tomography (PET or PET/CT) for the detection of post-transplant lymphoproliferative disorder (PTLD). As there is no clear consensus about the diagnostic accuracy of these imaging methods, we performed a meta-analysis on this topic.

METHODS

A comprehensive computer literature search of PubMed, Embase, and Cochrane library databases through December 2019 was performed. Pooled sensitivity, specificity, positive and negative likelihood ratios (LR+ and LR-), and diagnostic odds ratio (DOR) of ¹⁸F-FDG PET or PET/CT for detection of PTLD were calculated.

RESULTS

Five studies reporting data on the diagnostic performance of ¹⁸F-FDG PET or PET/CT in 336 transplant recipients were included in the systematic review and bivariate meta-analysis. Pooled sensitivity and specificity for detection of PTLD were 89.7% (95% confidence interval (95%CI): 84.6-93.2%) and 90.9% (95%CI: 85.9-94.3%), respectively. Pooled LR+, LR-, and DOR were 8.9 (95%CI: 5.7-14), 0.13 (95%CI: 0.08-0.2), and 70.4 (95%CI: 35.4-140), respectively. A significant heterogeneity among studies was not detected.

CONCLUSIONS

Despite limited literature data, ¹⁸F-FDG PET or PET/CT demonstrated good diagnostic performance for the detection of PTLD, but large prospective studies are needed to strengthen these findings.

18F-FDG PET/CT for invasive fungal infection in immunocompromised patients

BACKGROUND

Opportunistic invasive fungal infections (IFIs) comprise a heterogeneous spectrum of pathogens, whose early diagnosis remains challenging. Candida spp. and Aspergillus spp, the most frequent pathogens in immunocompromised patients, frequently affect lungs, liver, bone and skin.

AIM

To evaluate the impact of 18F-FDG PET/CT in the management of immunocompromised patients with IFI.

DESIGN

A single-center retrospective study included 51 immunocompromised patients with IFI diagnosis undergoing 83 18F-FDG PET/CTs.

METHODS

Twenty-nine 18F-FDG PET/CTs were performed for primary work-up in 29 treatment-naïve patients. Fifty-four PET/CTs were performed during follow-up to confirm IFI suspicion in 22 patients who had anti-fungal drug therapy before PET/CT. When available, histological and/or microbiological criteria were used to assess IFI diagnosis.

RESULTS

Aspergillus spp. and Candida spp. were the most frequent microorganisms responsible for IFI in our population. 18F-FDG PET/CT sensitivity, specificity, positive and negative predictive values, and global accuracy were 93%, 81%, 95%, 72% and 90%, respectively. 18F-FDG PET/CT influenced the diagnostic work-up at primary staging in 16/29 patients (55%) by assessing the extent of infection and targeting the diagnostic procedure. 18F-FDG PET/CT results during treatment induced anti-fungal drugs dosage increase and/or new drugs addition in 8/54 cases (15%) and contributed to the reduction of anti-fungal drugs dosage or treatment withdraws in 17 cases (31%).

CONCLUSIONS

We recommend the utilization of 18F-FDG PET/CT to improve the primary staging work-up of immunocompromised patients with IFI and to assess treatment effectiveness or disease relapse. Both 18F-FDG PET/CT and conventional imaging should be integrated into a well-defined imaging diagnostic algorithm considering the clinical context and both strengths and limitations of each diagnostic modality.

Application of animal and human PET in cardiac research

PURPOSE OF REVIEW

After a warm-up period of imaging research, several modalities of positron emission tomography (PET) are under development for evaluating ischemic heart disease.

RECENT FINDINGS

Several types of well-documented stem/progenitor PET imaging have been utilized for changes in myocardial blood flow and carbohydrate metabolism. Some recent experimental and human studies reported that these data may have beneficial effects on cardiac research.

SUMMARY

Although the role of PET in the pathology of ischemic heart disease has not been sufficiently elucidated, many studies attempting imaging research of myocardial metabolism and neural regulation have been reported. Further studies are needed to better evaluate the potential of PET in evaluating ischemic heart disease.

Identification of occult active infection using PET-CT in a combined liver-kidney transplant candidate

This case describes a patient being considered for combined liver-kidney transplantation for Caroli's disease with a failed renal transplant. A chronic septic focus could not be located with standard imaging techniques, such as ultrasonography and computed tomography. This case report highlights the observation that a retained non-functioning transplant can be the cause of fever of unknown origin and PET-CT can be useful in diagnosing these challenging cases.