Characteristics of integrated 18F-FDG PET/CT in Pulmonary Cryptococcosis

FDG-PET/CT of COVID-19 and Other Lung Infections

While not conventionally used as the first-line modality, [¹⁸F]-2-fluoro-2-deoxy-D-glucose (FDG) - positron emission tomography/computed tomography (PET/CT) can identify infection and inflammation both earlier and with higher sensitivity than anatomic imaging modalities [including chest X-ray (CXR), computed tomography (CT), and magnetic resonance imaging (MRI)]. The extent of inflammation and, conversely, recovery within the lungs, can be roughly quantified on FDG-PET/CT using maximum standardized uptake value (SUVmax) values. The Coronavirus disease 2019 (COVID-19) pandemic has highlighted the value of FDG-PET/CT in diagnosis, elucidation of acute pulmonary and extrapulmonary manifestations, and long-term follow up. Similarly, many other pulmonary infections such as previously documented coronaviruses, aspergillosis, blastomycosis, candidiasis, coccidioidomycosis, cryptococcosis, histoplasmosis, mucormycosis, and typical/atypical mycobacterial infections have all been identified and characterized using FDG-PET/CT imaging. The goal of this review is to summarize the actual and potential benefits of FDG-PET/CT in the imaging of COVID-19 and other lung infections. Further research is necessary to determine the best indications and clinical applications of FDG-PET/CT, improve its specificity, and ultimately ascertain how this modality can best be utilized in the diagnostic work up of infectious pathologies.

Radionuclide Imaging of Invasive Fungal Disease in Immunocompromised Hosts

Invasive fungal disease (IFD) leads to increased mortality, morbidity, and costs of treatment in patients with immunosuppressive conditions. The definitive diagnosis of IFD relies on the isolation of the causative fungal agents through microscopy, culture, or nucleic acid testing in tissue samples obtained from the sites of the disease. Biopsy is not always feasible or safe to be undertaken in immunocompromised hosts at risk of IFD. Noninvasive diagnostic techniques are, therefore, needed for the diagnosis and treatment response assessment of IFD. The available techniques that identify fungal-specific antigens in biological samples for diagnosing IFD have variable sensitivity and specificity. They also have limited utility in response assessment. Imaging has, therefore, been applied for the noninvasive detection of IFD. Morphologic imaging with computed tomography (CT) and magnetic resonance imaging (MRI) is the most applied technique. These techniques are neither sufficiently sensitive nor specific for the early diagnosis of IFD. Morphologic changes evaluated by CT and MRI occur later in the disease course and during recovery after successful treatment. These modalities may, therefore, not be ideal for early diagnosis and early response to therapy determination. Radionuclide imaging allows for targeting the host response to pathogenic fungi or specific structures of the pathogen itself. This makes radionuclide imaging techniques suitable for the early diagnosis and treatment response assessment of IFD. In this review, we aimed to discuss the interplay of host immunity, immunosuppression, and the occurrence of IFD. We also discuss the currently available radionuclide probes that have been evaluated in preclinical and clinical studies for their ability to detect IFD.

Use of 18F-FDG PET/CT to Differentiate Ectopic Adrenocorticotropic Hormone-Secreting Lung Tumors From Tumor-Like Pulmonary Infections in Patients With Ectopic Cushing Syndrome

Background

Ectopic adrenocorticotropic hormone (ACTH)-secreting lung tumors represent the most common cause of ectopic Cushing syndrome (ECS). Pulmonary opportunistic infections are associated with ECS. The present study aimed to evaluate the usefulness of ¹⁸F-FDG PET/CT for differentiating ectopic ACTH-secreting lung tumors from tumor-like pulmonary infections in patients with ECS.

Methods

We retrospectively reviewed the imaging data of 24 patients with ECS who were suspected to have ACTH-secreting lung tumors and underwent ¹⁸F-FDG PET/CT between 2008 and 2019. Eleven patients with lung tumors and 4 with pulmonary infections also had additional somatostatin receptor imaging (^99mTc-HYNIC-TOC SPECT/CT or ⁶⁸Ga-DOTATATE PET/CT).

Results

In total, 18 patients had lung tumors and six had pulmonary infections. The primary source of ECS remained occult in the six patients with pulmonary infections. The maximum standardized uptake value (SUV_max) for pulmonary infections was significantly higher than that for tumors (P = 0.008). Receiver operating characteristic analysis revealed that a cut-off SUV_max of 4.95 helped in differentiating ACTH-secreting lung tumors from infections with 75% sensitivity and 94.4% specificity. For the 11 patients with ACTH-lung tumors, somatostatin receptor imaging (SRI) was positive in 6; while for the 4 with pulmonary infections, SRI was positive in 2. The sensitivity and specificity of somatostatin receptor imaging (SRI) for detecting ACTH-secreting lung tumor was 54.5% and 50%.

Conclusions

Our findings suggest that pulmonary infections exhibit significantly higher FDG uptake than ACTH-secreting lung tumors in ¹⁸F-FDG PET/CT. An SUV_max cut-off value of 4.95 may be useful for differentiating the two conditions. Our results also suggested that SRI may not be an effective tool for differentiating the two conditions given the relatively low specificity.

Granulomatous Lung Nodule Mimicking as Metastasis on F18 Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography in a Case of Adrenocortical Carcinoma

A variety of fungal pulmonary infections can produce radiologic findings that mimic malignancy. Distinguishing these infectious lesions from malignancy remains challenging for physicians. We describe one such case where fungal lung nodule mimicked metastasis on fluorodeoxyglucose positron emission tomography/computed tomography scan.

The clinical and radiological characteristics of pulmonary cryptococcosis in immunocompetent and immunocompromised patients

Background

We characterized the clinical features, radiographic characteristics, and response to treatment of immunocompetent and immunocompromised patients with pulmonary cryptococcosis (PC).

Methods

We retrospectively reviewed the medical records and radiological profiles of patients diagnosed with PC who received surgical resection between May 2015 and November 2020 in a tertiary referral center.

Results

A total of 21 males and 18 females were included in the study. 23 patients were immunocompetent and 20 out of the 39 were asymptomatic. Immunocompetent patients were diagnosed with PC at a younger age than immunocompromised patients (48.9 vs 57.1 years, P = 0.02). Single nodule pattern was the most frequent lesion pattern (33 out of 39, 84.6%) and right upper lobe was the most common site of location (15 out of 47, 31.9%). The majority of lesions were located peripherally (38 out of 47, 80.9%) and most lesions were 1–2 cm in diameter (30 out of 47, 63.8%). Cavitation was more likely to occur in immunocompromised patients (5 out of 11, 45.5%) than in immunocompetent patients (6 out of 36, 16.7%) (P = 0.04) and there was complete resolution of PC in all patients treated with anti-fungal therapy.

Conclusions

Immunocompetent patients were diagnosed with PC at a younger age than immunocompromised patients. Single nodule pattern was the most frequent lesion pattern in PC patients. Cavitation was more likely to occur in immunocompromised patients than in immunocompetent patients.

Cryptococcus infection with asymptomatic diffuse pulmonary disease in an immunocompetent patient: A case report

BACKGROUND

Cryptococcus presenting as an opportunistic pathogen mainly affects immunocompromised patients, but the disseminated form of infection is rare among immunocompetent populations. The partial radiographic characteristics of pulmonary cryptococcosis mimic lung carcinoma, leading to unnecessary open chest exploratory surgery, and the lack of a gold-standard noninvasive diagnostic increases the risk of misdiagnosis. Positron emission tomography/computed tomography (PET/CT), a sensitive method for distinguishing malignant tumors, coupled with cryptococcal latex agglutination test showing a high positive rate may overcome these issues.

CASE

A 36-year-old man presented for general examination, without health complaints. Routine CT showed multiple pulmonary nodules and a mass with high maximum standardized uptake value. Initially, we suspected primary malignancy with hematogenous metastasis. Although his routine fungal analysis had been negative, subsequent CT-guided percutaneous core needle biopsy and histopathology examination indicated a diagnosis of pulmonary cryptococcosis. Fluconazole (200 mg/d) antifungal drug treatment was initiated, and 1 mo later the pulmonary mass had reduced in size markedly (on chest CT scan) without any complications.

CONCLUSION

Serologic and PET/CT examinations may not rule out cryptococcosis, and percutaneous lung puncture is critical under all circumstances.

Thoracic Endemic Fungi in the United States: Importance of Patient Location

The digitization of radiographic studies along with high-speed transmission of images has formed the basis of teleradiology, which has become an integral component in the workflow of a contemporary radiology practice. It is with this advent and growing utilization of teleradiology that the significance of the source location of images has gained importance. Specifically, the importance of where the patient resides and what endemic fungi occur in that location cannot be underestimated. In the United States, histoplasmosis, coccidioidomycosis, blastomycosis, and cryptococcosis are caused by endemic fungi occurring in the Ohio and Mississippi river valleys, the Southwest, the Upper Midwest, and the Pacific Northwest, respectively. All of these organisms enter the body through the respiratory system and have the potential to cause significant morbidity and mortality. Patients infected with these fungi are often asymptomatic but may present with acute flulike symptoms such as fever, cough, or dyspnea. Patients may also present with vague chronic symptoms including cough, fever, malaise, and weight loss. Thoracic manifestations at radiography and CT include consolidation, nodules, cavities, lymphadenopathy, and pleural disease. PET may show fluorine 18-fluorodeoxyglucose uptake with active acute or chronic infections, and it is difficult to distinguish infections from malignancy. Imaging findings may be nonspecific and can be confused with other disease processes, including malignancy. The patient demographics, clinical history, and location are clues that may lead to a proper diagnosis of endemic fungal disease. The radiologist should be cognizant of the patient location to provide a correct and timely radiologic diagnosis that helps guide the clinician to initiate appropriate therapy. ^©RSNA, 2021.

Pleural fluid secondary to pulmonary cryptococcal infection: a case report and review of the literature

Background

Pulmonary Cryptococcosis (PC) is diagnosed with increasing incidence in recent years, but it does not commonly involve the pleural space. Here, we report a HIV-negative case with advanced stage IIIB non-small cell lung cancer (NSCLC) treated with radiation therapy presented with dyspnea, a new PET-positive lung mass and bilateral pleural effusion suspecting progressive cancer. However, the patient has been diagnosed as pulmonary cryptococcal infection and successfully treated with oral fluconazole therapy.

Case presentation

A 77-year-old male with advanced stage non-small cell lung cancer treated with combined chemo-radiation therapy who presented with progressive dyspnea, a new PET-positive left lower lobe lung mass and bilateral pleural effusions. Initial diagnostic thoracentesis and bronchoscopy yielded no cancer, but instead found yeast forms consistent with cryptococcal organisms in the transbronchial biopsies of the left lower lobe lung mass. Subsequent to this, the previously collected pleural fluid culture showed growth of Cryptococcus neoformans. The same sample of pleural effusion was tested and was found to be positive for crytococcal antigen (CrAg) by a lateral flow assay (LFA). The patient has been treated with oral fluconazole therapy resulting in gradual resolution of the nodular infiltrates.

Conclusion

PC should be considered in immunosuppressed cancer patients. Additionally, concomitant pleural involvement in pulmonary cryptococcal infections may occur. The incidence of false positive ¹⁸FDG-PET scans in granulomatous infections and the use of CrAg testing in pleural fluid to aid in diagnosis are reviewed.

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.

Cryptococcus gattii Infection Presenting as an Aggressive Lung Mass

Cryptococcus gattii is an endemic fungus predominantly isolated in the tropical and subtropical regions, causing predominantly pulmonary disease with a predilection for the central nervous system. Herein, we report a case of rapidly progressing C. gattii pneumonia in an immune-deficient but virologically suppressed host with underlying human immunodeficiency viral (HIV) infection, exhibiting various fungal morphologies from bronchoalveolar lavage (BAL) cytological specimens. A 51-year-old Chinese male with known HIV disease was admitted to the Singapore General Hospital for evaluation of functional decline, febrile episodes, and a left hilar mass on chest radiograph. Computed tomography (CT) showed consolidation in the apical segment of the left lower lobe. He underwent bronchoscopy and BAL. Positron emission tomography-computed tomography done 10 days after the initial CT showed approximate doubling of the pulmonary lesion. Cytological examination of the fluid revealed yeasts of varying sizes. Subsequent fungal culture from BAL fluid grew C. gattii 10 days later.

18F-FDG PET/CT and contrast-enhanced CT findings of pulmonary cryptococcosis

PURPOSE

Pulmonary cryptococcosis is an uncommon cause of pulmonary nodules in non-AIDS patients. This study reports the ¹⁸F-fluorodeoxyglucose-positron emission tomography (¹⁸F-FDG PET/CT) and contrast-enhanced CT (CE-CT) findings of 42 patients with pulmonary cryptococcosis.

MATERIALS AND METHODS

A retrospective review of the ¹⁸F-FDG PET/CT and CE-CT findings of 42 patients with histologically proven pulmonary cryptococcosis was conducted. All patients underwent PET/CT and CE-CT in the same session. The CT diagnosis was based on the location, morphological features, and enhancement of lesions. The PET/CT findings were recorded, and clinical data and surgical and histopathological findings were collected.

RESULTS

The results of the PET scans revealed that 37 (88%) of 42 patients showed higher FDG uptake, and 5 (12%) patients demonstrated lower FDG uptake than the mediastinal blood pool. The maximum standardized uptake value (SUV) of pulmonary cryptococcosis ranged from 1.4 to 13.0 (average: 5.7±3.3, median 4.9). A single nodular pattern was the most prevalent pattern observed and was found in 29 (69%) patients. This pattern was followed by scattered nodular (n=4, 10%), clustered nodular (n=3, 7%), mass-like (n=3, 7%), and bronchopneumonic (n=3, 7%) patterns. The most frequent pattern of immunocompetent patients was the single nodular pattern (29 of 33, 88%). Immunocompromised patients most frequently pattern exhibited mass-like (3 of 9, 33%) and bronchopneumonic (3 of 9, 33%) patterns.

CONCLUSION

Pulmonary cryptococcosis most commonly appears as single nodules in immunocompetent patients. Mass-like and bronchopneumonic patterns were common in immunocompromised patients. In 88% of patients, lung lesions showed high FDG uptake, thus mimicking a possible malignant condition.

An Avid Imitator

We present a case of disseminated cryptococcal disease, coexisting with and mimicking lymphoma. Determination of serum cryptococcal antigen should be considered for lymphopenic patients with hematologic malignancies, presenting with unexplained fever, and/or lymphadenopathy and/or pulmonary findings. Patients with hematologic malignancies treated with chemotherapy regimens are susceptible to diverse opportunistic infections. Therefore, in this patient population, it is often necessary to obtain a definitive pathologic diagnosis, to diagnose uncommon syndromes and guide management.

Potential role of 18F-FDG PET/CT in patients with fungal infections

OBJECTIVE

Combined anatomic and functional imaging with (18)F-FDG PET/CT is slowly gaining foothold in the management of various infective pathologic abnormalities. However, limited literature is available regarding the role of FDG PET/CT in patients with fungal infections.

CONCLUSION

Here, we briefly review the available literature and highlight the potential role that FDG PET/CT can play in the diagnosis and management of fungal infections.

Pulmonary cryptococcosis with trachea wall invasion in an immunocompetent patient: a case report and literature review

Cryptococcosis causes significant morbidity and mortality in the world. Pulmonary cryptococcosis is a kind of subacute or chronic pulmonary fungal disease. We present a case of pulmonary cryptococcosis with a trachea wall invasion-like malignant tumor in an immunocompetent patient and a literature review. The 44-year-old man, a nonsmoker, suffered from mild dyspnea and white sputum with intermittent blood streaks. A computed tomography (CT) scan of his chest showed two possibly malignant lesions in the right hilum and upper-right field of his lung, which have higher uptake values of fluorodeoxyglucose on positron emission tomography (PET)/CT. Lung biopsy pathology showed scattered fungal spores and positive periodic acid-Schiff (PAS) staining. The immune status and blood tumor markers were all normal in this patient. The titer of Cryptococcus antigen latex agglutination test was 1:1,280. Under fiberoptic bronchoscopy, a prominent new mass on the right wall of the trachea blocked most of the right main bronchus. To reduce the symptoms of airway obstruction, treatment by bronchoscopy, i.e. ablation and endotracheal stent, was used. As his symptoms were aggravated by the use of itraconazole, amphotericin B liposome was used as antifungal treatment. All these methods led to a better prognosis. We conclude that pulmonary cryptococcosis may mimic lung neoplasms radiologically and bronchoscopically, even in immunocompetent patients.

The use of (18)F-FDG-PET/CT for diagnosis and treatment monitoring of inflammatory and infectious diseases

FDG-PET, combined with CT, is nowadays getting more and more relevant for the diagnosis of several infectious and inflammatory diseases and particularly for therapy monitoring. Thus, this paper gives special attention to the role of FDG-PET/CT in the diagnosis and therapy monitoring of infectious and inflammatory diseases. Enough evidence in the literature already exists about the usefulness of FDG-PET/CT in the diagnosis, management, and followup of patients with sarcoidosis, spondylodiscitis, and vasculitis. For other diseases, such as inflammatory bowel diseases, rheumatoid arthritis, autoimmune pancreatitis, and fungal infections, hard evidence is lacking, but studies also point out that FDG-PET/CT could be useful. It is of invaluable importance to have large prospective multicenter studies in this field to provide clear answers, not only for the status of nuclear medicine in general but also to reduce high costs of treatment.

Case of pulmonary cryptococcosis mimicking hematogeneous metastases in an immunocompetent patient: value of absent 18F-fluorodeoxyglucose uptake on positron emission tomography/CT scan

The radiologic appearance of multiple discrete pulmonary nodules in immunocompetent patients, with cryptococcal infection, has been rarely described. We describe a case of pulmonary cryptococcosis, presenting with bilaterally and randomly distributed nodules on a computed tomography, mimicking hematogeneous metastases. Positron emission tomography does not demonstrate 18F-fluorodeoxyglucose (FDG) uptake, suggesting a low probability for malignancy, which is a crucial piece of information for clinicians when making a management decision. We find the absence of FDG uptake correlates with the pathologic finding of an infectious nodule, composed of fibrosis and necrosis.

Not all that shines is cancer: pulmonary cryptococcosis mimicking lymphoma in [(18)] F fluoro-2-deoxy-D-glucose positron emission tomography

We report of a case of pulmonary cryptococcosis mimicking lymphoma in a positron emission tomography (FDG-PET) scan. A 62-year old man with diffuse large B-cell lymphoma had complete resolution of abdominal and pulmonary lesions after three cycles of rituximab-based chemotherapy (R-CHOP). However, FDG-PET showed new pulmonary nodules, suggesting active lymphoma. Chronic inflammatory granuloma was seen in the histopathological exam, with round-shaped structures compatible with fungus, later identified as Cryptococcus neoformans on culture. The lesions disappeared after 6 weeks of fluconazole therapy, and the patient could continue chemotherapy without further infectious complications.

Extensive cryptococcal tracheitis mimicking lymphoma in an AIDS patient

We describe a case of a 35-year-old man with human immunodeficiency virus infection/acquired immune deficiency syndrome presenting from an outside hospital with a diagnosis of non-Hodgkin's B-cell lymphoma. Radiologic imaging showed an infiltrative process with significant tracheal involvement and increased uptake of 18-fluoro-2-deoxyglucose on positron emission tomography. These findings were suspicious for non-Hodgkin's B-cell lymphoma. Flexible bronchoscopy and tissue sampling revealed cryptococcal infection of the trachea. This case presentation is of extensive cryptococcal tracheitis, an extremely rare presentation of endobronchial cryptococcosis. It also emphasizes the difficult radiologic distinction between such unusual endobronchial infections and malignancy.

Combined PET and X-ray computed tomography imaging in pulmonary infections and inflammation

PURPOSE OF REVIEW

This review addresses issues relating to the use of the relatively new combined PET and X-ray computed tomography (PET/CT) modality for imaging pulmonary infections and inflammation, as well as assessing its potential for this purpose.

RECENT FINDINGS

Accurate definition and monitoring of the extent of lung infection is difficult using conventional chest radiograph, CT scan, MRI, and radioisotope scintigraphy. In the last decade, PET/CT using radiolabeled fluorodeoxyglucose has been added to the imaging armamentarium, mostly for imaging lung cancer. To date, very few data are available on the application of this technique for imaging pulmonary infections and inflammation; however, this situation is changing, and there is now more interest in using PET/CT for this purpose. In addition, there are new tracers on the horizon which remain to be exploited.

SUMMARY

This review addresses some of these issues and outlines the potential to use PET/CT for noncancer pulmonary indications.

Pulmonary cryptococcosis: imaging findings in 23 non-AIDS patients

Objective

We aimed to review the patterns of lung abnormalities of pulmonary cryptococcosis on CT images, position emission tomography (PET) findings of the disease, and the response of lung abnormalities to the therapies in non-AIDS patients.

Materials and Methods

We evaluated the initial CT (n = 23) and 18F-fluorodeoxyglucose (FDG) PET (n = 10), and follow-up (n = 23) imaging findings of pulmonary cryptococcosis in 23 non-AIDS patients. Lung lesions were classified into five patterns at CT: single nodular, multiple clustered nodular, multiple scattered nodular, mass-like, and bronchopneumonic patterns. The CT pattern analyses, PET findings, and therapeutic responses were recorded.

Results

A clustered nodular pattern was the most prevalent and was observed in 10 (43%) patients. This pattern was followed by solitary pulmonary nodular (n = 4, 17%), scattered nodular (n = 3, 13%), bronchopneumonic (n = 2, 9%), and single mass (n = 1, 4%) patterns. On PET scans, six (60%) of 10 patients showed higher FDG uptake and four (40%) demonstrated lower FDG uptake than the mediastinal blood pool. With specific treatment of the disease, a complete clearance of lung abnormalities was noted in 15 patients, whereas a partial response was noted in seven patients. In one patient where treatment was not performed, the disease showed progression.

Conclusion

Pulmonary cryptococcosis most commonly appears as clustered nodules and is a slowly progressive and slowly resolving pulmonary infection. In two-thirds of patients, lung lesions show high FDG uptake, thus simulating a possible malignant condition.