A Rare Case of Multilocular Thymic Cyst with Follicular Lymphoid Hyperplasia: Radiologic and Histopathologic Features

Abstract

Multilocular thymic cysts are rare and acquired lesions induced by an inflammatory arising within the thymus. We report a rare case of multilocular thymic cyst with follicular lymphoid hyperplasia in a 59-year-old female. Chest CT and MRI revealed a large multilocular cystic mass, which contains thick septa and nodules in the thymus. F-18 FDG PET/CT showed almost no FDG uptake of the multilocular cystic mass but moderate FDG uptake of the solid nodules. Extended total thymectomy was performed. Histopathological findings revealed follicular lymphoid hyperplasia of thymic tissue but no neoplastic lesion. Based on these findings, diagnosis of multilocular thymic cyst with follicular lymphoid hyperplasia was made. This is a rare case that preoperatively was difficult to diagnose.

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Indeterminate Findings on Oncologic PET/CT: What Difference Does PET/MRI Make?

Abstract

Background

Positron emission tomography/computed tomography (PET/CT) with 2-deoxy-2-[¹⁸F]fluoro-D-glucose (FDG) has become the standard of care for the initial staging and subsequent treatment response assessment of many different malignancies. Despite this success, PET/CT is often supplemented by MRI to improve assessment of local tumor invasion and to facilitate detection of lesions in organs with high background FDG uptake. Consequently, PET/MRI has the potential to expand the clinical value of PET examinations by increasing reader certainty and reducing the need for subsequent imaging. This study evaluates the ability of FDG-PET/MRI to clarify findings initially deemed indeterminate on clinical FDG-PET/CT studies.

Methods

A total of 190 oncology patients underwent whole-body PET/CT, immediately followed by PET/MRI utilizing the same FDG administration. Each PET/CT was interpreted by our institution's nuclear medicine service as a standard-of-care clinical examination. Review of these PET/CT reports identified 31 patients (16 %) with indeterminate findings. Two readers evaluated all 31 PET/CT studies, followed by the corresponding PET/MRI studies. A consensus was reached for each case, and changes in interpretation directly resulting from PET/MRI review were recorded. Interpretations were then correlated with follow-up imaging, pathology results, and other diagnostic studies.

Results

In 18 of 31 cases with indeterminate findings on PET/CT, PET/MRI resulted in a more definitive interpretation by facilitating the differentiation of infection/inflammation from malignancy (15/18), the accurate localization of FDG-avid lesions (2/18), and the characterization of incidental non-FDG-avid solid organ lesions (1/18). Explanations for improved reader certainty with PET/MRI included the superior soft tissue contrast of MRI and the ability to assess cellular density with diffusion-weighted imaging. The majority (12/18) of such cases had an appropriate standard of reference; in all 12 cases, the definitive PET/MRI interpretation proved correct. These 12 patients underwent six additional diagnostic studies to clarify the initial indeterminate PET/CT findings. In the remaining 13 of 31 cases with indeterminate findings on both PET/CT and PET/MRI, common reasons for uncertainty included the inability to distinguish reactive from malignant lymphadenopathy (4/13) and local recurrence from treatment effect (2/13).

Conclusions

Indeterminate PET/CT findings can result in equivocal reads and additional diagnostic studies. PET/MRI may reduce the rate of indeterminate findings by facilitating better tumor staging, FDG activity localization, and lesion characterization. In our study, PET/MRI resulted in more definitive imaging interpretations with high accuracy. PET/MRI also showed potential in reducing the number of additional diagnostic studies prompted by PET/CT findings. Our results suggest that whole-body PET/MRI provides certain diagnostic advantages over PET/CT, promotes more definitive imaging interpretations, and may improve the overall clinical utility of PET.

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Instrumentation for Time-of-Flight Positron Emission Tomography

Abstract

Positron emission tomography (PET) is a molecular imaging modality that provides information at the molecular level. This system is composed of radiation detectors to detect incoming coincident annihilation gamma photons emitted from the radiopharmaceutical injected into a patient's body and uses these data to reconstruct images. A major trend in PET instrumentation is the development of time-of-flight positron emission tomography (ToF-PET). In ToF-PET, the time information (the instant the radiation is detected) is incorporated for image reconstruction. Therefore, precise and accurate timing recording is crucial in ToF-PET. ToF-PET leads to better localization of the annihilation event and thus results in overall improvement in the signal-to-noise ratio (SNR) of the reconstructed image. Several factors affect the timing performance of ToF-PET. In this article, the background, early research and recent advances in ToF-PET instrumentation are presented. Emphasis is placed on the various types of scintillators, photodetectors and electronic circuitry for use in ToF-PET, and their impact on timing resolution is discussed.

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Tumor volume is a better predictor of post-operative wound complications compared to tumor size in soft tissue sarcomas of the proximal lower extremity

Abstract

Background

Wide local excision with or without radiation therapy (RT) and chemotherapy is widely accepted as appropriate management for soft tissue sarcomas (STS) of the extremity. Although survival and local control rates are comparable to amputation, post-operative wound complications (WC) following limb salvage can result in significant morbidity for the patient. Certain risk factors such as location, pre-operative RT, and age have been shown to increase the risk of WCs. Somewhat surprisingly, size has not consistently been shown to impact WC rates. The goal of this study is to assess whether tumor volume, as opposed to the traditional measurement of the largest dimension in one plane, correlates with the development of post-operative WCs.

Methods

Between 2000 and 2013, 81 patients with STS of the proximal lower extremity, buttock and pelvis were retrospectively identified from our prospective database. We reviewed the impact of patient, tumor, and treatment variables on postoperative WC. Predictors for WC were evaluated using the Fisher exact test for univariate analysis and logistic regression for multivariate analysis. Tumor volume was determined using the medical image merge (MIM) ^® software program (version 6.5.4, MIM Software, Cleveland, OH). Tumor size (diameter) was determined the historical way of measuring the widest dimension on the sagittal, coronal, and axial planes from the MRI scan at midplane.

Results

The overall WC rate within 6 months of tumor resection was 32 %. WC were more likely to occur with larger tumor volumes (p = 0.015), although not with tumor diameters ≥10 cm (p = 0.55). Neither volume of subcutaneous fat (p = 0.34) or depth of the subcutaneous fat layer (p = 0.82) significantly impacted WC rates. Tumor proximity to skin surface also did not significantly impact WC risk (p = 0.73).

Conclusions

Increase in tumor volume led to a higher risk of post-operative WCs. Assessing tumor volume may allow clinicians to better counsel patients on their risk of post-operative WCs. Tumor volume, as opposed to size alone, should be considered in future sarcoma outcome studies.

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Gene Fusion May Drive Rare Childhood Brain Tumor

Researchers have identified a genetic rearrangement that may drive the development of a rare benign brain tumor in children. The rearrangement, which causes parts of two genes to fuse, may spur the growth of tumors through three distinct biological mechanisms simultaneously, the researchers found.

The study focused on angiocentric gliomas, a rare subtype of low-grade pediatric tumors that was first described less than a decade ago. Fewer than 30 cases have been reported in the scientific literature. Based on their findings, the study authors propose that angiocentric gliomas should be classified as a distinct biologic entity and that the presence of the gene fusion should be used to confirm the diagnosis.

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A phase I trial of panobinostat and epirubicin in solid tumors with a dose expansion in patients with sarcoma

This phase I study evaluated combined panobinostat and epirubicin in patients with advanced solid tumors, establishing a MTD, and demonstrating a correlation between neutropenia, PBMC histone acetylation and clinical benefit. In a sarcoma expansion cohort, more than half of patients, having previously failed anthracycline therapy, benefited, suggesting HDAC inhibition reverses resistance.

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On the tumor risk from dental diagnostic X-ray exposure

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