Clinically important detection of infection as an ‘incidental’ finding during cancer staging using FDG-PET/CT

Acute Findings on FDG PET/CT: Key Imaging Features and How to Differentiate Them from Malignancy

PURPOSE OF REVIEW

To review acute findings commonly encountered during routine clinical FDG PET/CT studies and present key imaging features to differentiate them from malignant counterparts.

RECENT FINDINGS

FDG PET/CT is extensively used in routine clinical practice for oncology patients. Incidental acute findings in patients undergoing FDG PET/CT are increasingly common, and awareness of these findings and their mimics are important in delivering a clinically relevant and accurate radiological report for directing further management.

SUMMARY

This article will review examples of common acute findings encountered during routine FDG PET/CT scans, compare them against examples of FDG-avid malignancy that can mimic these findings and emphasize key imaging findings to differentiate acute findings from their malignant mimics.

The impact of infection and inflammation in oncologic 18F-FDG PET/CT imaging

Sites of infection and inflammation can be misleading in oncology PET/CT imaging because these areas commonly show ¹⁸F-FDG activity. Caution in the interpretation must be taken to avoid the misdiagnosis of malignancy. Utilization of both CT findings as well as patient history can help differentiate benign infectious and inflammatory processes from malignancy, although occasionally additional work-up may be required. This article discusses the mechanism of ¹⁸F-FDG uptake in infection and inflammation with illustrative examples.

Clinical value of FDG-PET/CT in bacteremia of unknown origin with catalase-negative gram-positive cocci or Staphylococcus aureus

INTRODUCTION

Bacteremia is associated with high mortality, especially when the site of infection is unknown. While conventional imaging usually focus on specific body parts, FDG-PET/CT visualizes hypermetabolic foci throughout the body.

PURPOSE

To investigate the ability of FDG/PET-CT to detect the site of infection and its clinical impact in bacteremia of unknown origin with catalase-negative Gram-positive cocci (excluding pneumococci and enterococci) or Staphylococcus aureus (BUOCSA).

METHODS

We retrospectively identified 157 patients with 165 episodes of BUOCSA, who subsequently underwent FDG-PET/CT. Data were collected from medical records. Decision regarding important sites of infection in patients with bacteremia was based on the entire patient course and served as reference diagnosis for comparison with FDG-PET/CT findings. FDG-PET/CT was considered to have high clinical impact if it correctly revealed site(s) of infection in areas not assessed by other imaging modalities or if other imaging modalities were negative/equivocal in these areas, or if it established a new clinically relevant diagnosis, and/or led to change in antimicrobial treatment.

RESULTS

FDG-PET/CT detected sites of infection in 56.4% of cases and had high clinical impact in 47.3%. It was the first imaging modality to identify sites of infection in 41.1% bacteremia cases, led to change of antimicrobial therapy in 14.7%, and established a new diagnosis unrelated to bacteremia in 9.8%. Detection rate and clinical impact were not significantly influenced by duration of antimicrobial treatment preceding FDG-PET/CT, days from suspicion of bacteremia to FDG-PET/CT-scan, type of bacteremia, or cancer.

CONCLUSION

FDG-PET/CT appears clinically useful in BUOCSA. Prospective studies are warranted for confirmation.

What, where and why: exploring fluorodeoxyglucose-PET's ability to localise and differentiate infection from cancer

PURPOSE OF REVIEW

To review the utility of FDG-PET imaging in detecting the cause of fever and infection in patients with cancer.

RECENT FINDINGS

FDG-PET has been shown to have high sensitivity and accuracy for causes of neutropenic fever, leading to higher diagnostic certainty in this group. Recent advances in pathogen-specific labelling in PET to identify Aspergillus spp. and Yersinia spp. infections in mice, as well as differentiating between Gram-positive, Gram-negative and mycobacterial infections are promising.

SUMMARY

Patients with cancer are vulnerable to infection and fever, and the causes of these are frequently unclear using conventional diagnostic methods leading to high morbidity and mortality, length of stay and costs of care. FDG-PET/CT, with its unique complementary functional and anatomical information as well as its whole-body imaging capability, has demonstrated use in detecting occult infection in immunocompromised patients, including invasive fungal and occult bacterial infections, as well as defining extent of infection. By demonstrating disease resolution following treatment and allowing earlier cessation of therapy, FDG-PET acts as a key tool for antimicrobial and antifungal stewardship. Limitations include at times poor differentiation between infection, malignancy and sterile inflammation, however, exciting new technologies specific to infectious pathogens may help alleviate that issue. Further prospective randomised research is needed to explore these benefits in a nonbiased fashion.

Bacterial Pneumonia in Patients with Cancer: Novel Risk Factors and Management

Bacterial pneumonias exact unacceptable morbidity on patients with cancer. Although the risk is often most pronounced among patients with treatment-induced cytopenias, the numerous contributors to life-threatening pneumonias in cancer populations range from derangements of lung architecture and swallow function to complex immune defects associated with cytotoxic therapies and graft-versus-host disease. These structural and immunologic abnormalities often make the diagnosis of pneumonia challenging in patients with cancer and impact the composition and duration of therapy. This article addresses host factors that contribute to pneumonia susceptibility, summarizes diagnostic recommendations, and reviews current guidelines for management of bacterial pneumonia in patients with cancer.

Cat-Scratch Disease: A Pitfall for Lymphoma Evaluation by FDG-PET/CT

FDG-PET/CT is a standard of care in staging and response assessment of Hodgkin lymphoma. Hence, it is important to recognize pitfalls owing to the potential therapeutic impact. We report a case of a 29-year-old woman affected by stage III bulky Hodgkin lymphoma. The interim FDG-PET/CT showed a complete metabolic response. After three new cycles of chemotherapy, the patient showed fever and lymphadenopathy at clinic examination, PET/CT revealed several FDG uptakes at lymph nodes in inguinal and iliac region. Pathologic analyses, after biopsy and serologic examinations, led to the diagnosis of cat-scratch disease.

Retrospektive Analyse von Zufallsbefunden, die bei Patienten mit kutanem malignen Malignom durch (18) F-Fluordeoxyglucose-PET/CT erhoben wurden

HINTERGRUND UND ZIELE

Bei der (18) F-Fluordeoxyglucose-Positronenemissionstomographie/Computertomographie (FDG-PET/CT) ergeben sich häufig Zufallsbefunde. In der vorliegenden Studie konzentrierten wir uns auf mittels FDG-PET/CT erhaltene Zufallsbefunde bei Patienten mit kutanem Melanom und überprüften deren Relevanz hinsichtlich weiterer diagnostischer Maßnahmen und Interventionen.

PATIENTEN UND METHODEN

Die Krankenakten von 181 konsekutiven Melanom-Patienten wurden retrospektiv ausgewertet, um das Management von Zufallsbefunden zu dokumentieren. Der Schwerpunkt lag dabei auf den histologischen Befunden.

ERGEBNISSE

Bei 33 von 181 (18 %) Patienten lagen 39 relevante Zufallsbefunde vor, und zwar im Kolorektalbereich (n = 15 Patienten), in der Schilddrüse (n = 8), der Prostata (n = 2), dem Bewegungsapparat (n = 2), in Lymphknoten (n = 2), der Parotis (n = 1), den Mandeln (n = 1), den Nieren (n = 1) und der Gallenblase (n = 1). Bei 25 Patienten schlossen sich weitere diagnostische Verfahren an, wobei in 21 Fällen ein klinisches Korrelat nachgewiesen wurde. Bei 16 von 21 Patienten ergab sich eine Neoplasie, darunter fünf maligne Läsionen (vier Kolonkarzinome und ein Prostatakarzinom). Die Malignome wurden frühzeitig diagnostiziert und in der Mehrzahl der Fälle erfolgreich entfernt.

SCHLUSSFOLGERUNGEN

Der Einsatz der FDG-PET/CT als Routine-Diagnostik wird in den Leitlinien empfohlen und ist indiziert bei malignem Melanom ab Stadium IIC. In dieser Studie wurden auf effektive Weise ansonsten nicht erkannte Krebserkrankungen, insbesondere Kolonkarzinome, detektiert. In den meisten Fällen war eine frühe Intervention möglich. Zufallsbefunde durch FDG-PET/CT sollten, unter Berücksichtigung des Zustands und der Wünsche des Patienten, mit den geeigneten diagnostischen Maßnahmen abgeklärt werden.

Impact of incidental findings on integrated 2-[18F]-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography in patients with gastric cancer

AIM

Since positron emission tomography/computed tomography (PET/CT) has been introduced, many incidental findings have been identified. The aim of this study was to assess the clinical significance of incidental findings on PET/CT in patients with gastric cancer.

METHODS

A total of 421 patients with gastric cancer underwent PET/CT for initial staging. Incidental findings on PET/CT were classified into five categories according to clinical significance--normal variant, benign, probably benign, probably malignant, and definitely malignant. We obtained information regarding follow-up examinations, additional visits, final diagnosis of incidental findings and short-term medical costs for further evaluation.

RESULTS

Eight hundred eighty-two incidental findings were detected in 386 (91.7%) patients. Of 274 incidental findings classified as probably benign, probably malignant or definitely malignant, 130 required one or more additional investigations. Finally, 12 (9.2%) were proved to be associated with second primary malignancy or metastasis of gastric cancer. One hundred twenty-nine additional outpatient visits and 10 additional hospitalizations were needed for evaluating the incidental findings. The treatment strategy for gastric cancer was changed in one patient. The estimated cost of additional investigations was $US283 (95% CI: $US248-$US311) per patient.

CONCLUSION

Incidental findings on PET/CT were common. Although the incidental findings were suspicious of malignancy, most were benign with high costs for additional investigations.

Late-onset Pneumocystis jirovecii pneumonia post-fludarabine, cyclophosphamide and rituximab: implications for prophylaxis

Objective

Fludarabine, cyclophosphamide and rituximab (FCR) therapy for lymphoid malignancies has historically been associated with a low reported incidence of Pneumocystis jirovecii pneumonia (PJP). However, prophylaxis was routinely used in early studies, and molecular diagnostic tools were not employed. The objective of this study was to review the incidence of PJP during and post‐FCR in the era of highly sensitive molecular diagnostics and ¹⁸F‐fluorodeoxyglucose (FDG) positron emission tomography (PET)–computerised tomography (CT).

Methods

All patients treated with standard FCR at the Peter MacCallum Cancer Centre (March 2009 to June 2012) were identified from a medications management database. Laboratory‐confirmed PJP cases during this time were identified from an electronic database.

Results

Overall, 66 patients were treated with a median of 5.5 FCR cycles. Eight PJP cases were identified, 6 of whom had received chemotherapy prior to FCR. In 5 cases, ¹⁸F‐FDG PET demonstrated bilateral ground‐glass infiltrates. Median CD4⁺ lymphocyte counts at time of PJP diagnosis and 9–12 months following FCR were 123 and 400 cells/μL, respectively. In patients receiving no prophylaxis, 9.1% developed PJP during FCR. The rate following FCR was 18.4%, with median onset at 6 months (2.4–24 months).

Conclusion

Given the high rate of late‐onset PJP, consideration should be given for extended PJP prophylaxis for up to 12 months post‐FCR, particularly in pretreated patients. Further evaluation of the role of CD4⁺ monitoring is warranted to quantify risk of disease development and to guide duration of prophylaxis.

Infectious and inflammatory complications of surgical management of cancer patients imaged with 18F-FDG PET/CT: a pictorial essay

The aim of this pictorial essay was to highlight the usefulness of fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in evaluating incidental infection or inflammation in cancer patients, related to surgical management. A retrospective review of 10,985 consecutive oncologic PET/CTs was done, and nine cases with suspected FDG positive infectious or inflammatory processes were selected for further review. PET/CT helped identify infections and inflammatory processes related to surgical management of cancer patients, define the extent of infection or inflammation, guide the management and, in some cases, evaluate response to therapy.

Impact of fluorine-18 fluorodeoxyglucose positron emission tomography on diagnosis and antimicrobial utilization in patients with high-risk febrile neutropenia

Early and targeted antimicrobial therapy improves outcomes in patients with febrile neutropenia (FN). We evaluated the impact of fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) on antimicrobial utilization in the management of FN. A cohort of patients with FN and hematological malignancy was identified. Cases (in whom FDG-PET was performed, n = 37) were compared with controls (in whom conventional investigations excluding FDG-PET were performed, n = 76). An underlying cause for FN was determined in 94.6% of cases, compared to 69.7% of controls. FDG-PET had a significant impact on antimicrobial utilization compared to conventional imaging (35.1% vs. 11.8%; p = 0.003), and was associated with shorter duration of liposomal amphotericin-B therapy for systemic fungal infection (median 4.0 days cases vs. 10.0 days controls; p = 0.001). Cases had a longer length of hospitalization (p = 0.016). In the management of patients with high-risk FN, FDG-PET improves diagnostic yield and allows rationalization of antifungal therapy. The impact upon healthcare costs associated with antimicrobial therapy for FN requires further evaluation.