Mediastinal Histoplasmosis: F-18 FDG PET and CT Findings Simulating Malignant Disease

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.

Periprosthetic seroma with false-positive FDG PET-CT reactive nodes mistaken for metastases in a patient previously treated of metastasic melanoma. Potential source of diagnostic errors

INTRODUCTION

FDG PET/CT is believed to be crucial in oncology, but its limited specificity represents a challenge. Prosthetic meshes used for repair abdominal defects may lead to false-positives FDG PET/CT uptake, over staging malignancies and inducing inappropriate treatments. A false-positive FDG PET/CT uptake mimicking metastatic disease during the follow-up of a previously treated metastatic melanoma patient is presented.

Imaging fungal infections in children

Fungal infections in children rarely occur, but continue to have a high morbidity and mortality despite the development of newer antifungal agents. It is essential for these infections to be diagnosed at the earliest possible stage so appropriate treatment can be initiated promptly. The addition of high-resolution computer tomography (HR CT) has helped in early diagnosis making; however, it lacks both sensitivity and specificity. Metabolic changes precede anatomical changes and hybrid imaging with positron emission tomography (PET) integrated with imaging modalities with high anatomical resolution such as CT or magnetic resonance imaging (MRI) is likely to detect these infections at an earlier stage with higher diagnostic accuracy rates. Several authors presented papers highlighting the advantages of PET/CT in imaging fungal infections. These papers, however, usually involve a limited number of patients and mostly adults. Fungal infections behave different in children than in adults, since there are differences in epidemiology, imaging findings, and response to treatment with antifungal drugs. This paper reviews the literature and explores the use of hybrid imaging for diagnosis and therapy decision making in children with fungal infections.

Staging and response of sternal histoplasmosis by 18F-FDG PET/CT

Histoplasmosis, a granulomatous mycosis caused by the fungus Histoplasma capsulatum, is known to primarily affect the lungs and the immune system, with involvement of skeletal system as a rare manifestation, in which case the disease usually assumes multifocality. We present a singular case of a young man diagnosed to have an isolated skeletal histoplasmosis involving the body of sternum where 18F-FDG PET/CT played major role in both diagnosis and in response evaluation to antifungal therapy.

A cytomorphometric analysis of pulmonary and mediastinal granulomas: differentiating histoplasmosis from sarcoidosis by fine-needle aspiration

BACKGROUND

Histoplasmosis and sarcoidosis are commonly included in the differential diagnosis of mass lesions at lung and mediastinal sites. Once cancer is excluded on aspiration biopsy, further classification is essential for proper treatment.

METHODS

A search identified patients with histoplasmosis and sarcoidosis for whom the diagnosis was made by clinicopathologic correlation. Cases were reviewed for various cytologic parameters along with patient demographic, clinical, and laboratory data.

RESULTS

Fifty-eight cases of histoplasmosis and 44 cases of sarcoidosis were reviewed. Thirty-seven of 58 (64%) Histoplasma cases exhibited abundant, bland necrosis, and 76% of cases contained <2 angular and ragged granulomas per slide. Yeasts were identified in 36 of 37 (97%) specimens with necrosis and in 44 of 58 (76%) cases overall. These cases had an acute (14%) and/or chronic (67%) inflammatory component and uncommonly had a giant cell infiltrate (12%). Sarcoid granulomas were round with crisp, sharp borders: 80% of these granulomas contained >3 granulomas per slide, and 32% contained >10 granulomas per slide. All sarcoid granulomas had a chronic inflammatory background without acute inflammatory cells, and 50% contained giant cell infiltrates.

CONCLUSIONS

Differentiation between histoplasmosis and sarcoidosis is possible in the majority of cases. Histoplasmosis usually exhibits few angular, ragged granulomas (<2 granulomas per slide) in a background of bland necrosis. Yeasts are identified on special stains performed in aspirate smears. Sarcoidosis typically contains many more granulomas (often >10 per slide) than histoplasmosis and has a rounded morphology with crisp and sharp borders. Typically, there is no necrosis or acute inflammation, and giant cell infiltrates are frequent.

Histoplasmosis presenting with multiple pulmonary nodules. A case mimicking radiological features of pulmonary metastasis

We present a case of histoplasmosis with multiple pulmonary nodules in a patient with a history of melanoma. This case closely simulated malignancy, including the presence of feeding vessel sign, which occurs in pulmonary metastasis. We emphasize the need to be aware of this infection in areas where histoplasmosis is endemic.

F-18 FDG PET/CT contributes to more accurate detection of lymph nodal metastasis from actively proliferating esophageal squamous cell carcinoma

PURPOSE

Evaluating the status of disease progression is critical for planning a therapeutic strategy for esophageal cancer. In this regard, F-18 fluorodeoxyglucose-labeled positron emission tomography (PET) is one of the most useful diagnostic modalities. However, there is room to improve its diagnostic performance, such as distinguishing lymph nodal metastases from false positives. In this study, we examined the diagnostic accuracy of fluorodeoxyglucose PET accompanied by computed tomography imaging (PET/CT) to detect regional lymph nodal metastasis from esophageal squamous cell carcinoma (ESCC).

METHODS

A total of 102 patients diagnosed as ESCC were subjected to this study. These patients had a preoperative PET/CT examination to evaluate the existence of metastasis. The values of maximum standardized uptake value (SUVmax) in primary tumors and in metastasized lymph nodes were measured to analyze their relationship with various clinicopathologic characteristics including the status of tumor cell proliferation, which was assessed by immunohistochemistry for Ki-67.

RESULTS

The SUVmax of the primary tumor was positively correlated with tumor size and vessel invasion, and was positively related with the SUVmax of lymph nodal metastasis, especially in cases of poorly differentiated ESCC. The SUVmax of metastasized lymph nodes was higher in larger-sized metastasized lymph nodes, whereas the Ki-labeling index of lymph nodal metastasis was positively related with the SUVmax per unit area (SUVmax/mm). The diagnostic accuracy of PET/CT (87.3%) was higher than that of conventional CT scans (78.4%).

CONCLUSIONS

The improved diagnostic accuracy of PET/CT can be explained by its ability to detect actively progressive metastasis at an early phase regardless of size.

Pseudometastasis secondary to histoplasmosis infection: false-positive PET/CT findings

Positron emission computed tomography (PET)/CT is a common modality used in the workup of neoplastic conditions. However, false-positive results may be produced by underlying infectious processes. We report two cases of false-positive PET/CT studies secondary to histoplasmosis infections in both a pediatric and a young adult patient. After the diagnoses, one patient was observed with no therapy and the other received a complete course of itraconazole. In both cases biopsy results were positive for fungal elements consistent with histoplasmosis. Both patients were successfully managed and have had follow-up histoplasmosis titers that reveal resolving infections.

Cutaneous and subcutaneous imaging on FDG-PET: benign and malignant findings

F-18 fluorodeoxyglucose positron emission tomography (F-18 FDG PET) has been shown to be useful in the evaluation of many tumors due to its high sensitivity and specificity. However, false-positive interpretations may occur from benign subcutaneous and cutaneous etiologies. At our institution we have encountered FDG-PET scans which demonstrated a variety of cutaneous and subcutaneous lesions including stomas, hernias, rhinophyma, dose infiltrations, physiologic muscle uptake, and tophaceous gout. Additionally, malignant cutaneous and subcutaneous malignant lesions may also demonstrate substantial F-18 FDG uptake on PET scans, including lymphoma, skin metastases, and melanoma. The purpose of this atlas article is to demonstrate and review key features of various cutaneous and subcutaneous lesions, both benign and malignant, which can result in hypermetabolism on FDG-PET or PET-CT scans.

PET/CT-MR Imaging in Head and Neck Cancer Including Pitfalls and Physiologic Variations

This article emphasizes the strengths and potential pitfalls of functional and anatomic imaging in patients who have head and neck cancer with an emphasis on the treated neck, including patients who have undergone surgery and/or radiation therapy. Anatomic and molecular imaging together allow optimal evaluation and interpretation of a patient who has cancer. Effective assessment of patients who have head and neck cancer can be achieved through a careful review of pertinent anatomy, with awareness of the physiologic variations (especially those in the treated head and neck) seen in PET imaging, and analysis of both the PET and cross-sectional images.

Utility of positron emission tomography in the mediastinum: moving beyond lung and esophageal cancer staging

PET and PET-CT are rapidly evolving as modalities of thoracic imaging. In the mediastinum, PET can provide information to distinguish thymic hyperplasia from neoplasia, although the use of this imaging for this purpose is not accepted uniformly as necessary. PET is the standard of care in staging and follow-up of mediastinal lymphoma and in follow-up of metastatic seminomas after chemotherapy. Mycobacterial/fungal infections, sarcoidosis, and brown fat can mimic malignant findings on PET in the mediastinum.

Role of modern imaging techniques for diagnosis of infection in the era of 18F-fluorodeoxyglucose positron emission tomography

During the past several years, it has become quite evident that positron emission tomography (PET) with 18F-fluorodeoxyglucose (FDG) imaging can play a major role in the management of patients with suspected infection. Particularly, several groups have demonstrated that this powerful imaging methodology is very effective in the evaluation of osteomyelitis, infected prostheses, fever of unknown origin, and AIDS. In view of its extraordinary sensitivity in detecting disease activity and the ability to quantitate the degree of FDG uptake, PET might prove to be an appropriate modality for monitoring disease activity and evaluating response to therapy. FDG-PET has many advantages over existing imaging techniques for the diagnosis of infectious diseases. These include feasibility of securing diagnostic results within 1.5 to 2 h, excellent spatial resolution, and accurate anatomical localization of sites of abnormality. The availability of PET/computed tomography as a practical tool has further enhanced the role of metabolic imaging in many settings. In the future, this modality is very likely to be employed on a routine basis for detecting, characterizing, and monitoring patients with suspected and proven infection.

PET/CT of esophageal cancer: its role in clinical management

Positron emission tomography (PET)/computed tomography (CT) has important utility and limitations in the initial staging of esophageal cancer, evaluation of response to neoadjuvant therapy, and detection of recurrent malignancy. Esophageal cancer is often treated by using a combined modality approach (chemotherapy, radiation therapy, and esophagectomy); correct integration of PET/CT into the conventional work-up of esophageal cancer requires a multidisciplinary approach that combines the information from PET/CT with results of clinical assessment, diagnostic CT, endoscopic gastroduodenoscopy, and endoscopic ultrasonography. PET/CT has limited utility in T staging of esophageal cancer and relatively limited utility in detection of dissemination to locoregional lymph nodes. However, PET/CT allows detection of metastatic disease that may not be identifiable with other methods. PET/CT is not sufficiently reliable in the individual patient for determination of treatment response in the primary tumor. Interpretation of PET/CT results is optimized by understanding the diagnostic limitations and pitfalls that may be encountered, together with knowledge of the natural history of esophageal cancer and the staging and treatment options available.

Focal Hepatic Activity During Ventilation-Perfusion Scintigraphy Due to Systemic-Portal Shunt Due to Superior Vena Cava Obstruction From Histoplasmosis-Induced Fibrosing Mediastinitis

A 59-year-old woman with a history of fibrosing mediastinitis secondary to histoplasmosis diagnosed on mediastinoscopy presented with dyspnea. A ventilation-perfusion scan demonstrated decreased perfusion to the entire right lung. In addition, the perfusion images demonstrated focal abnormal activity in part of the liver. On computed tomography of the chest, there was significant soft tissue opacification in the mediastinum occluding the right pulmonary artery, with passage of the injected contrast via collateral vessels to the liver. The main collateral pathway was via the right internal thoracic vein and the umbilical vein. Pulmonary angiography confirmed complete occlusion of the right pulmonary artery.

Fibrosing mediastinitis as a rare sequel of iatrogenic rupture of bronchogenic cyst--a case report

Fibrosing mediastinitis is a chronic disease process with a spectrum of etiology. We report a 51-year-old female who underwent incision and drainage procedure in the neck for deep neck and mediastinal abscess. Five years later she developed fibrosing mediastinitis. This lesion infiltrated from neck base into the upper mediastinum with tracheal compression and vessel encasement. She had resection of the lesion which proved to be a ruptured bronchogenic cyst with chronic inflammation. This rare case illustrates the importance of including inflammatory bronchogenic cyst in the etiology of deep neck abscess formation. And we further find a ruptured bronchogenic cyst with chronic inflammation as an etiology of fibrosing mediastinitis.