Skeletal muscle metastases on FDG PET/CT imaging.

BACKGROUND: Skeletal muscle metastases (SMM) are a rare occurrence despite the fact that skeletal muscle comprises more than 50% of total body mass. When present, most are asymptomatic and are often found incidentally on imaging. Several studies have reported isolated cases of patients with SMM. The goal of our study was to perform a comprehensive retrospective analysis of the incidence, frequency, and source of SMM in patients with malignancies who underwent whole-body FDG PET/CT imaging for the workup for their malignancy. METHODS: The records of 8492 consecutive patients referred for oncologic imaging at our institution during the period from January 2006 to December 2009 were reviewed. Patients who had SMM on FDG PET imaging were further assessed for collaborating evidence on other imaging modalities, pathology from tissue sampling, and follow-up scans. The incidence of SMM in our setting was calculated, and their association with various primary malignancies was also evaluated. RESULTS: A total of 73 patients with SMM were identified on PET/CT imaging (incidence, 0.86%). Lung cancer was the most frequent source (25 patients [34%]), followed by gastrointestinal tract malignancies (13 patients [18%]), breast cancer (10 patients [14%]), genitourinary malignancies and lymphoma (6 patients [8%] each), melanoma (5 patients [7%]), and other miscellaneous malignancies (3 patients [4%]). Primary source remained unknown in only 5 patients (7%). Most patients with SMM generally had markedly widespread involvement which led to an unusual appearance on FDG PET/CT imaging. However, since most of these patients had stage IV malignant disease by virtue of visceral metastases elsewhere as well, they were generally not upstaged. CONCLUSIONS: Our study confirmed the rare occurrence of SMM. Furthermore, FDG PET/CT can potentially detect unsuspected SMM. Interestingly, in our patient population, lung cancer was found to be the most frequent malignancy metastasizing to the skeletal muscles. Knowledge about the presence and appearance of widespread SMM may aid in appropriate interpretation of FDG PET/CT scans.

18F-FDG PET in pregnancy and fetal radiation dose estimates.

UNLABELLED: The purpose of this study was to estimate the fetal radiation exposure resulting from (18)F-FDG PET procedures performed in pregnant patients with malignancies. METHODS: Five pregnant patients with a biopsy-proven diagnosis of malignancy who underwent (18)F-FDG PET studies were retrospectively reviewed. All patients underwent PET-only studies (and not PET/CT studies) with a reduced (18)F-FDG dose (except for 1 patient who had a negative pregnancy test immediately before the (18)F-FDG PET procedure but was confirmed to be pregnant a few weeks later), including vigorous hydration and diuresis to minimize radiation exposure to the fetus. One patient underwent (18)F-FDG PET twice during her pregnancy (in the second and third trimesters). Fetal radiation dose was independently assessed for each patient, and an analysis was made of fetal radiation doses using the measurements of activity in the fetuses at various stages of pregnancy. RESULTS: Six (18)F-FDG PET studies in 5 pregnant patients were analyzed. The (18)F-FDG PET scans were obtained in early pregnancy (n = 1), the second trimester (n = 2), and the third trimester (n = 3). The fetal dose exposure from (18)F-FDG PET studies was estimated to range from 1.1 to 2.43 mGy for various trimesters in pregnancy (except for the patient in the early stage of pregnancy, in whom activity in the whole uterus was considered, and the fetal dose was estimated to be 9.04 mGy). All patients delivered healthy infants with no visible abnormalities at term. CONCLUSION: The fetal radiation dose from (18)F-FDG PET studies is quite low and significantly below the threshold dose for deterministic effects due to radiation exposure to the fetus. The estimated fetal radiation exposure in our cases was slightly lower than existing estimates on fetal dose exposure, and as more data become available, the current fetal dose estimates may have to be modified accordingly. By addressing an important safety issue dealing with performing medically necessary (18)F-FDG PET in pregnant patients, these data are expected to help in the imaging workup of cancer patients during pregnancy.

FDG PET/CT imaging suggests lymphoma involving prostate may be more resistant to treatment.

FDG PET imaging is generally not useful for prostate cancer. Nevertheless, incidental intense FDG uptake in the prostate warrants further evaluation to assess for prostatic malignancy. We report a case where intense FDG uptake was incidentally noted in an enlarged prostate on FDG PET/CT scan performed for a large left hilar/mediastinal mass (that was also intensely FDG avid along with several additional FDG-avid lesions elsewhere). Biopsy of the prostate and mediastinal lesions revealed large B-cell non-Hodgkin lymphoma at both sites. Serial FDG PET/CT imaging in this patient revealed that the prostatic lymphomatous lesions showed a slower and incomplete response to chemotherapy compared with other sites of lymphomatous involvement (that showed a rapid and complete response to chemotherapy) in the same patient.

Early Detection of Brain Pathology Suggestive of Early AD Using Objective Evaluation of FDG-PET Scans.

The need for early detection of AD becomes critical as disease-modifying agents near the marketplace. Here, we present results from a study focused on improvement in detection of metabolic deficits related to neurodegenerative changes consistent with possible early AD with statistical evaluation of FDG-PET brain images. We followed 31 subjects at high risk or diagnosed with MCI/AD for 3 years. 15 met criteria for diagnosis of MCI, and five met criteria for AD. FDG-PET scans were completed at initiation and termination of the study. PET scans were read clinically and also evaluated objectively using Statistical Parametric Mapping (SPM). Using standard clinical evaluation of the FDG-PET scans, 11 subjects were detected, while 18 were detected using SPM evaluation. These preliminary results indicate that objective analyses may improve detection; however, early detection in at-risk normal subjects remains tentative. Several FDA-approved software packages are available that use objective analyses, thus the capacity exists for wider use of this method for MCI/AD.

Potential value of quantitative analysis of cerebral PET in early cognitive decline.

BACKGROUND: In patients diagnosed with Alzheimer's disease, positron emission tomography brain scans can have characteristic hypometabolic patterns that strongly support this diagnosis, but this pattern is often subtle or absent in early stages. A sensitive and objective method for detection of positron emission tomography abnormalities may have value in early detection of Alzheimer's disease. METHODS: A 2-fluoro-2-deoxy-D-glucose positron emission tomography scans from cognitively impaired patients (n = 43) were compared individually to 28 normal controls using statistical parametric mapping, hypometabolic regions visualized, and clinically correlated. The objective SPM results were compared to the official Nuclear Medicine report based upon subjective interpretation criteria. RESULTS: A total of 22/43 had abnormalities per the Nuclear Medicine physician, while 21/43 appeared normal. The objective analysis detected abnormalities in 41/43 participants, including 19 of 21 that appeared normal. In these 19, 8 had findings consistent with early Alzheimer's disease. CONCLUSION: Objective analysis of positron emission tomography brain scans may extend the ability to detect early brain abnormalities in patients with cognitive decline.

Costosternal chondrodynia simulating recurrent breast cancer unveiled by FDG PET.

FDG-PET imaging, which is routinely used to assess recurrent breast cancer, is nonspecific for malignancies and can detect several inflammatory lesions. Costochondritis following breast reconstructive surgery, presenting with excruciating chest pain or "chondrodynia," is a rare variant of Tietze's syndrome thought to occur due to traction exerted by large breast implants. Diagnosis is usually clinical because no abnormalities are identified on conventional imaging. Two cases have been reported in the literature, but none with FDG-PET. We report a patient with treated breast cancer, presenting with chest pain where FDG-PET to assess for recurrence was consistent with costochondritis and peri-implant inflammation.

Accurate grading of 3 synchronous liposarcomas assessed by PET-CT in a single patient.

Positron emission tomography (PET) with 2-fluoro-deoxyglucose (FDG) has become an established imaging modality that can accurately and noninvasively differentiate malignant neoplasms from benign masses. It is increasingly being used to grade malignant neoplasms as well and has almost replaced other studies like gallium 67-citrate scans for metabolic imaging. We describe an interesting case of 3 synchronous liposarcomas with different radio-opacifications on computed tomography (CT). The more aggressive lesion with more opacity on CT showed intense FDG activity and was found to be a high-grade liposarcoma on pathology. The well-differentiated lesion with more fat content appearing less radio-opaque on CT showed almost no FDG activity and an intermediate grade lesion with intermediate radio-opacity on CT showed mildly increased FDG activity. Dual modality imaging with integrated PET/CT systems have strengthened the confidence of classifying these lesions even before knowing the pathology as depicted in this case.

A Potential Role for F-18 FDG PET/CT in Evaluation and Management of Fibrosing Mediastinitis.

Fibrosing mediastinitis is an uncommon benign disorder, and its pathogenesis and management remain unclear. Conventional imaging techniques (chest radiographs, CT, MRI) may suggest its diagnosis but are frequently nonspecific, and it frequently mimics a malignant process by presenting as a mediastinal mass without calcifications, encasing, and infiltrating adjacent mediastinal structures, and showing an overall aggressive behavior. The value of FDG PET imaging in this entity remains largely unknown with only a few case reports in the literature, and often, biopsy is necessary for definitive diagnosis. We report a case of biopsy proven fibrosing mediastinitis highlighting the utility of PET in the evaluation and management of the disease.

Effect of nicotine and ephedrine on the accumulation of 18F-FDG in brown adipose tissue.

UNLABELLED: This study evaluated the effect of various beta-adrenergic agonists on (18)F-FDG uptake in brown adipose tissue (BAT) in rats using ex vivo biodistribution studies. METHODS: Caffeine (10 mg/kg of body weight, n = 4), ephedrine (5 mg/kg of body weight, n = 4), nicotine (0.8 mg/kg of body weight, n = 9), or a mixture of nicotine and ephedrine (0.8 mg/kg of body weight and 5 mg/kg of body weight, respectively, n = 9) was injected into the peritoneal cavity of female Lewis rats 30 min before intravenous (18)F-FDG injection. One hour after injection of (18)F-FDG, the animals were sacrificed, and BAT, other major organs, and blood were extracted. The biodistribution results were compared with body temperature data. RESULTS: In the rats injected with nicotine or ephedrine, the mean uptake of (18)F-FDG, in percentage injected dose (%ID)/(g of interscapular BAT) x (kg of body weight), was significantly increased (7.9-fold for nicotine and 3.7-fold for ephedrine), compared to the control rats. Nicotine had the strongest effect on (18)F-FDG uptake in BAT. Caffeine increased BAT uptake slightly, but this increase did not reach statistical significance. The combination of nicotine and ephedrine increased the uptake 12.0-fold, compared with control rats; more than either nicotine or ephedrine alone. Uptake of (18)F-FDG in most other major organs did not change significantly. The effect of nicotine was blocked by prior injection of beta-adrenergic antagonists. A transient decrease in body temperature was observed in the nicotine-injected group, and this effect was canceled by prior injection of beta-adrenergic antagonists. No significant change in baseline temperature was seen before or after beta-adrenergic agonist injection. CONCLUSION: Nicotine caused a greater increase in (18)F-FDG uptake in BAT than did other interventions, and the effect was increased when nicotine was combined with ephedrine. The effect of nicotine was completely blocked by prior injection of beta-adrenergic antagonists, indicating that beta-adrenergic agonists increase the metabolism of BAT. These preclinical data suggest that patients should avoid nicotine and ephedrine before undergoing (18)F-FDG PET to minimize (18)F-FDG uptake in BAT.

Reduced presynaptic dopamine activity in fibromyalgia syndrome demonstrated with positron emission tomography: a pilot study.

UNLABELLED: Although the pathophysiology underlying the pain of fibromyalgia syndrome (FMS) remains unknown, a variety of clinical and investigational findings suggests a dysregulation of dopaminergic neurotransmission. We therefore investigated presynaptic dopaminergic function in 6 female FMS patients in comparison to 8 age- and gender-matched controls as assessed by positron emission tomography with 6-[(18)F]fluoro-L-DOPA as a tracer. Semiquantitative analysis revealed reductions in 6-[(18)F]fluoro-L-DOPA uptake in several brain regions, indicating a disruption of presynaptic dopamine activity wherein dopamine plays a putative role in natural analgesia. Although the small sample size makes these findings preliminary, it appears that FMS might be characterized by a disruption of dopaminergic neurotransmission. PERSPECTIVE: An association between FMS and reduced dopamine metabolism within the pain neuromatrix provides important insights into the pathophysiology of this mysterious disorder.

PET imaging today: contribution to the initial staging and prognosis of patients with non-Hodgkin's lymphomas.

Malignant non-Hodgkin lymphomas (NHLs) are commonly staged according to the Ann Arbor staging system developed for Hodgkin's lymphoma. Recently, new staging modalities including metabolic imaging by positron emission tomography (PET) using F-18 fluorodeoxy-glucose (FDG) have been developed. In the present study, we investigated 77 untreated patients with different histologies of NHL both with conventional imaging techniques and FDG-PET. The patients were classified according to the World Health Organization classification and came from 2 major PET imaging centers in Louisiana and Texas. Seventy-six of 77 cases of NHLs were positive by PET imaging. PET imaging resulted, both in high/intermediate grade and indolent NHLs, in a higher stage in more than 20% of cases. In the subtype of high grade NHL diffuse large B cell lymphoma, upstaging by PET appears to be clinically relevant as a marker for a more aggressive tumor. In low grade NHL, stage changes were less pronounced. PET imaging did not reliably detect all cases of bone marrow involvement (especially in indolent lymphomas). However, even in low-grade NHL, clear indications exist for performing PET imaging. The value, the clinical relevance, and new developments in PET imaging for the different types of NHLs are discussed in detail.

Positron emission tomography (PET) positive thyroid incidentaloma: the risk of malignancy observed in a tertiary referral center.

An incidental finding of focal thyroid uptake (thyroid incidentaloma) from an 18F-fluorodeoxyglucose positron emission tomography (PET) positron presents a diagnostic challenge. We evaluated the incidence of thyroid incidentaloma identified by PET scans and the likelihood of malignancy associated with this finding. Records from all patients from January 1, 2000 to November 30, 2003 who had focal thyroid uptake without any history of thyroid disease were culled. Of the 6241 PET scans performed, focal thyroid uptake was observed in 76 patients (1.2%). Only 14 patients (18%) underwent biopsy. Four of 14 patients (28.6%) had papillary thyroid carcinoma, 7 (50%) had hyperplasia, and 1 each had thyroiditis, nodular goiter, and follicular neoplasm. The incidence of PET thyroid incidentalomas was 1.2 per cent and the incidence of malignancy was 28.6 per cent. Given the high likelihood of malignancy, a further diagnostic workup for surgically fit patients is warranted.

Unilateral vocal cord paralysis causes contralateral false-positive positron emission tomography scans of the larynx.

Positron emission tomography (PET) is used in the management of head and neck cancers. It identifies tissue with increased metabolic activity and is not specific for malignancy. A false-positive PET scan of the larynx is associated with vocal cord paralysis. We reviewed PET scan reports of patients with lung cancer from 1998 to 2001 to identify patients with increased 18-fluoro-2-deoxyglucose uptake in the larynx without a known history of head and neck cancer and then correlated this increased uptake with laryngoscopic findings. There were 17 patients who had a positive PET finding in the larynx. Fifteen of those had a false-positive PET scan in the larynx. All had contralateral vocal cord paralysis. Two patients were noted to have head and neck cancer. We conclude that vocal cord paralysis can cause a false-positive PET scan on the contralateral side of the larynx due to overactivity of laryngeal muscles that compensate for the paralyzed cord.

F-18 FDG PET imaging in gastrointestinal stromal tumor.

Gastrointestinal stromal tumor (GIST) is the most frequent mesenchymal malignancy of the gastrointestinal tract. Liver and peritoneum are the most frequent metastatic sites. Surgery is the mainstay of treatment in patients with localized disease. Imatinib mesylate (Gleevec; Novartis Pharmaceuticals, East Hanover, NJ), an inhibitor of tyrosine kinase activity of KIT receptor, has been shown to be an effective treatment in metastatic or unresectable disease. Follow-up of patients treated with Gleevec is controversial. The authors present a case of GIST that showed near-total response with Gleevec on fluorodeoxyglucose positron emission tomography. They suggest positron emission tomography as a useful imaging modality for the monitoring of therapy response in GIST tumors treated with Gleevec.