Varying degrees of FDG uptake in multiple benign neurofibromas on PET/CT

Imaging Features of Neurofibromatosis Type 1 in the Abdomen and Pelvis

OBJECTIVE. Loss of the neurofibromatosis type 1 (NF1) tumor suppressor protein causes uninhibited activation of the RAS oncogene, which leads to tumorigenesis in patients with NF1. This case-based review discusses imaging manifestations of NF1 in the abdomen and pelvis, highlighting key genetic associations and management to elucidate features different from the general population. CONCLUSION. The spectrum of pathologic findings includes gastrointestinal tumors such as gastrointestinal stromal tumors, genitourinary lesions including urogenital neurofibromas, vascular entities such as renal artery stenosis, and less common associations like lymphoma.

Evaluation of the most commonly used (semi-)quantitative parameters of 18F-FDG PET/CT to detect malignant transformation of neurofibromas in neurofibromatosis type 1

In patients with neurofibromatosis type 1, transformation of neurofibromas into a malignant peripheral nerve sheath tumor (MPNST) is a severe complication of the disease. Fluorine-18-fluorodeoxyglucose PET/computed tomography (PET/CT) is a viable option for detecting malignant tumors in neurofibromatosis type 1 patients. The aim of this review was to assess the diagnostic performance of the most frequently used parameters of PET/CT in detecting MPNST. An extensive computer search was performed using the Cochrane Library, Pubmed, and Medline/Embase databases. Two reviewers independently extracted data of relevant studies and assessed the methodological quality (QUADAS-2). The diagnostic performance of PET/CT parameters in individual studies was determined by calculating a diagnostic odds ratio (DOR) using the absolute numbers of true-positive, true-negative, false-positive, and false-negative test results. A total of eight studies were included, of which three evaluated the standardized uptake value as a diagnostic parameter, two assessed the tumor-to-liver (T/L) ratio, and three articles described both parameters. The cut-off values for maximum standardized uptake value (SUVmax) ranged from 3.2 to 4.5; for the T/L ratio, the cut-off values were between 1.0 and 4.3. The sensitivity and specificity ranged from 90 to 100% and from 80 to 100%, respectively (SUVmax). T/L ratios were associated with 92-100% sensitivity and 72-94% specificity. The corresponding DORs ranged from 57 to 145 (SUVmax) and 35 to 655 (T/L ratio). Both the SUV and the T/L ratio are associated with high sensitivity combined with acceptable specificity in detecting MPNST. There is a tendency toward higher DORs using the T/L ratio, but the number of studies is limited.

(18)F-FDG PET/CT in an unusual case of cardiac plexiform neurofibromatosis

Cardiac involvement is rare in neurofibromatosis 1 (NF 1). Very few cases of cardiac masses in this entity have been documented in the world literature. We present the F-FDG PET/CT findings in a rare case of cardiac plexiform neurofibromatosis.

Solitary fibrous tumor of the infratemporal fossa

Solitary fibrous tumors represent fewer than 2% of all soft tissue tumors, and only about 12-15% of them occur in the head and neck. We report a case of a 38-year-old male who presented with a six-month history of increasing right cheek swelling. Computed tomography of the paranasal sinuses with contrast demonstrated a well-circumscribed avidly enhancing mass in the right retroantral fat. On magnetic resonance imaging the lesion was homogenously slightly hyperintense to muscle on T1 weighted and T2 weighted images and enhanced avidly with contrast. Surgical resection was performed and pathology was consistent with solitary fibrous tumor. There have been very few reported cases of solitary fibrous tumors in the infratemporal fossa and none described as originating in the retroantral fat.

Pelvic mass in von Recklinghausen's neurofibromatosis: diagnostic issues: a case report

Background

Leiomyomas are benign smooth muscle cell tumours. They are the most common uterine neoplasms, although they may also occur elsewhere, such as in the gastrointestinal and urinary tracts. Leiomyomas are uncommon in von Recklinghausen's neurofibromatosis (NF1). However, the literature suggests that the association of NF1 and leiomyomas or leiomyosarcoma is not entirely coincidental.

Case Report

We report here the unusual case of a 47-year-old woman with NF1 who presented menorrhagias and a hard, tender pelvic mass composed of uterine leiomyomas. Positron emission tomography/computed tomography disclosed an area of increased 18-fluorodeoxyglucose (FDG) uptake in the upper right part of the mass that raised the suspicion of malignancy. Magnetic resonance imaging revealed numerous intramural leiomyomas ranging from 1 to 6 cm, including a 6-cm submucosal leiomyoma that had abundant cellularity, matching FDG uptake. Abdominal hysterectomy was performed and microscopic examination confirmed the diagnosis of multiple benign smooth muscle tumours (uterine leiomyomatosis).

Conclusion

Our case illustrates several diagnostic issues that arose while exploring this pelvic mass. Moreover, the association of uterine leiomyoma and NF1 may not be fortuitous.

[Potential sources of diagnostic pitfall and variants in FDG-PET/CT]

Oncological FDG PET show variants and findings that may lead to a diagnostic error and that may be clarified by the morfofunctional imaging from PET/CT. In this article we show the experience acquired since a Siemens PET/CT Biograph LSO Pico3D was applied in our centre. We describe some representative examples of FDG distribution patterns which may lead to erroneous interpretations of the clinical studies when they refer to specific clinical situations. The examples included are classified into two main groups according to the cause: Technical and biological, and the latter into physiological and non-physiological (pathophysiological). Patterns are described within the biological group showing changes of the FDG biodistribution that may reduce the uptake in tumoural lesions, the physiological variants that may be interpreted as pathology, the effects of previous treatment and uptakes related to benign diseases.

CONCLUSION

We consider that knowledge of these variants and findings to be crucial in order to obtain optimal performance of PET/CT and to overcome the PET limitations.

Whole-tumor perfusion CT parameters and glucose metabolism measurements in head and neck squamous cell carcinomas: a pilot study using combined positron-emission tomography/CT imaging

BACKGROUND AND PURPOSE

Previous (separately performed) perfusion CT (PCT) and PET studies have been inconclusive regarding the correlation of functional tumor characteristics. The purpose of this study was to perform dual assessment of head and neck squamous cell carcinomas (SCCAs) to examine the relationship between perfusion measurements derived from PCT and glucose standardized uptake values (SUV).

MATERIALS AND METHODS

We prospectively evaluated 15 primary and recurrent SCCAs using combined positron-emission tomography (PET) and CT of the head and neck. SUV(mean), SUV(max), blood flow (BF), blood volume (BV), mean transit time (MTT), and permeability (PS) values were calculated with use of manually drawn regions of interest (ROIs) over the lesions and the healthy muscle tissue. Parametric comparison test, correlation coefficients, and regression analysis were performed.

RESULTS

The mean (+/- SD) SUV(mean), SUV(max), BF, BV, MTT, and PS values in the tumor tissue were 6.26 (+/- 1.48), 15.25 (+/- 3.81), 91.50 (+/- 24.69), 5.08 (+/- 1.17), 7.51 (+/- 2.24), and 23.08 (+/- 8.77), respectively. All PET/CT and PCT parameters of muscle versus tumor tissue were statistically different (.0001 < P < .001). There were significant correlations between BF and SUV(max) as well as SUV(mean) (r = 0.57; P = .02 and r = 0.63; P = .011, respectively) in the tumors. Significant correlation was also found between PS and SUV(mean) (r = 0.53; P = .04) in the tumors. Regression analysis showed: SUV(max) = 0.09 x BF + 7.2 (R(2) = 0.33; P = .02), SUV(mean) = 0.05 x BF + 2.22 (R(2) = 0.45; P = .011), and SUV(mean) = 0.05 x PS + 5.36 (R(2) = 0.35; P = .04). The tumor to nontumor (muscle) SUV(mean) and SUV(max) ratio was 9.45 (+/- 3.55) and 17.58 (+/- 4.32), respectively. BF-ratio SUV(mean) and BF-ratio SUV(max) showed significant correlations (r = 0.64; P = .01 and r = 0.53; P = .04, respectively). Regression analysis showed ratio SUV(mean) = 0.14 x BF-3.48 (R(2) = 0.42; P = .01) and ratio SUV(max) = 0.14 x BF + 4.51 (R(2) = 0.29; P = .04).

CONCLUSION

Tissue perfusion-metabolic coupling is evident in head and neck SCCAs and may provide additional diagnostic information in patients undergoing PET/CT studies.

Positron emission tomography/computed tomography (PET/CT) in children

Although PET imaging has been available for more than two decades, its use has greatly increased lately due to the advent of PET/CT, readily available sources of commercially supplied FDG, and mobile scanners. These features have enabled PET scanning to expand beyond select major university medical centers, with on-site cyclotron facilities to smaller institutions including free- standing children's hospitals. In these settings, imaging is generally limited to FDG, which suffices for most applications, with the majority of studies performed for tumor imaging. FDGI is being used for evaluation of many tumors in children, with its use in lymphoma being the most established. In lymphoma, it has proven quite useful in determining whether active tumor is present in residual masses following treatment, which may otherwise contain only residual fibrous tissue. For brain tumors, FDGI has some relation to tumor grade, although its more important role is distinguishing recurrent or residual tumor from the effects of treatment, particularly radiation necrosis. For neurological evaluation, interictal FDGI is helpful in localizing potential seizure foci for subsequent subdural EEG monitoring. Because of the relatively long uptake time of FDG, true ictal studies cannot be performed with FDG, and these remain within the domain of SPECT imaging of tracers such as Tc-99m HMPAO. Examinations utilizing radiopharmaceuticals other than FDG are significantly more limited in their availability and are limited to PET centers with on-site cyclotrons. However, these additional agents open the door to many additional studies, including more specific tumor-imaging agents of certain tumors such as neuroblastoma. Another neurotransmitter, F-18-fluoro-L-dopa, is of benefit outside of the central nervous system for evaluating infantile hyperinsulism. The use of PET/CT in children is increasing quickly, particularly FDGI imaging of tumors. It is expected that over the next few years, its role will become increasingly better defined.