Potential clinical role of FDG-PET in detecting sarcomatous transformation in von Recklinghausen's disease: a case study and review of the literature

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.

Masses of developmental and genetic origin affecting the paediatric craniofacial skeleton

Although rare, masses and mass-like lesions of developmental and genetic origin may affect the paediatric craniofacial skeleton. They represent a major challenge in clinical practice because they can lead to functional impairment, facial deformation and disfigurement. The most common lesions include fibrous dysplasia, dermoid cysts, vascular malformations and plexiform neurofibromas. Less common lesions include torus mandibularis and torus palatinus, cherubism, nevoid basal cell carcinoma syndrome, meningoencephalocele and nasal sinus tract. This article provides a comprehensive approach for the evaluation of children with masses or mass-like lesions of developmental and genetic origin affecting the craniofacial skeleton. Typical findings are illustrated and the respective roles of computed tomography (CT), cone beam CT (CBCT), magnetic resonance imaging (MRI) with diffusion-weighted imaging (DWI) sequences and ultrasonography (US) are discussed for the pre-therapeutic assessment, complex treatment planning and post-treatment surveillance. Key imaging findings and characteristic clinical manifestations are reviewed. Pitfalls of image interpretation are addressed and how to avoid them. TEACHING POINTS: • Masses of developmental and genetic origin may severely impair the craniofacial skeleton. • Although rare, these lesions have characteristic imaging features. • CT, MRI and ultrasonography play a key role in their work-up. • Recognition of pivotal imaging pearls and diagnostic pitfalls avoids interpretation errors.

[18F]-Fluorodeoxyglucose positron emission tomography in children with neurofibromatosis type 1 and plexiform neurofibromas: correlation with malignant transformation

The objective of this study was to investigate the predictive value of [18F]-fluorodeoxyglucose positron emission tomography (FDG-PET) in detecting malignant transformation of plexiform neurofibromas in children with neurofibromatosis type 1 (NF1). An electronic search of the medical records was performed to determine patients with NF1 who had undergone FDG-PET for plexiform neurofibroma between 2000 and 2011. All clinical, radiologic, pathology information and operative reports were reviewed. Relationship between histologic diagnosis, radiologic features and FDG-PET maximum standardized uptake value (SUV(max)) was evaluated. This study was approved by the Institutional Review Board of our institution. 1,450 individual patients were evaluated in our Multidisciplinary Neurofibromatosis Program, of whom 35 patients underwent FDG-PET for suspected MPNST based on change or progression of clinical symptoms, or MRI findings suggesting increased tumor size. Twenty patients had concurrent pathologic specimens from biopsy/excision of 27 distinct lesions (mean age 14.9 years). Pathologic interpretation of these specimens revealed plexiform and atypical plexiform neurofibromas (n = 8 each), low grade MPNST (n = 2), intermediate grade MPNST (n = 4), high grade MPNST (n = 2), GIST (n = 1) and non-ossifying fibroma (n = 1). SUV(max) of plexiform neurofibromas (including typical and atypical) was significantly different from MPNST (2.49 (SD = 1.50) vs. 7.63 (SD = 2.96), p < 0.001). A cutoff SUV(max) value of 4.0 had high sensitivity and specificity of 1.0 and 0.94 to distinguish between PN and MPNST. FDG-PET can be helpful in predicting malignant transformation in children with plexiform neurofibromas and determining the need for biopsy and/or surgical resection.

The role of [18F]-fluorodeoxyglucose positron emission tomography in predicting plexiform neurofibroma progression

BACKGROUND

The role of FDG-PET for managing patients with plexiform neurofibromas (PN) is unclear. While many PN tumors exhibit periods of rapid growth, others grow slowly or unpredictably and may have periods of relative quiescence. The ability to predict which PN are likely to progress should facilitate a more timely initiation of medical treatments. Since conventional radiographic techniques have limited prognostic value, the use of a functional imaging modality to predict tumor progression is desirable. We hypothesized that PN tumors with high metabolic activity as demonstrated by FDG-PET are more likely to progress in the following year.

METHODS

All patients were clinically stable, but were considered at high-risk for progression based on anatomical location of PN. FDG-PET scans were performed within two weeks of the baseline MRI study. Standardized uptake values (SUV) were calculated for all focally active index lesions and analyzed for correlation with changes in quantitative MRI over the ensuing year.

RESULTS

Fifteen of the 18 enrolled patients showed various degrees of FDG uptake as focal abnormalities, and these abnormalities corresponded to those noted on the MRI scans. Thirteen patients and 19 lesions were evaluable for PN volume change. The SUVmax ranged from 0.9 to 4 (median 1.5). There was a significant difference in the percent increase in PN volume in the following year for lesions that had an SUV > 2 compared to those with lower values (P = 0.016).

CONCLUSIONS

These findings support the hypothesis that FDG-PET imaging predicts PN growth rate, and, therefore, may assist clinician decision making with regard to treatment of PN and enrollment in clinical trials.

The correlation between clinical, nuclear and histologic findings in a patient with Von Recklinghausen's disease

Background

Malignant peripheral nerve sheath tumours (MPNST) are known to develop in patients with Neurofibromatosis type I (NF1) resulting in a decreased overall survival. The association between NF1 and the development of such MPNST has been investigated in detail. The biological behaviour however of multiple disseminated neurofibromas in patients with NF1 and the risk factors for malignant transformation remain unknown. Clinical signs are unreliable and additional imaging techniques are therefore required. Of such, positron emission tomography using [¹⁸F]-2-fluoro-2-deoxy-D-glucose (¹⁸FDG PET) is used to detect malignant changes in neurofibromas.

Case presentation

A case is presented of a patient suffering from NF1 with clinical signs of malignant change and accumulation of ¹⁸FDG in multiple neurofibromas. Histopathological examination of 20 lesions however, did not reveal any malignant features. There was no statistically significant relation between¹⁸FDG accumulation and malignant change, but rather with pain, size and growth.

Conclusion

This case adds to the knowledge of the diverse biological behaviour of neurofibromas in patients with NF1

Value of PET in the Assessment of Patients with Neurofibromatosis Type 1

OBJECTIVE

The objective of our study was to investigate the use of PET in the detection of malignant peripheral nerve sheath tumors (MPNSTs) in patients with neurofibromatosis type 1 (NF1).

MATERIALS AND METHODS

Forty-five patients with NF1 who underwent whole-body PET for suspected MPNST based on clinical symptoms or radiologic examinations were retrospectively evaluated. Ten patients underwent additional carbon-11 (11C) methionine PET because of equivocal 18F-FDG PET findings or because of a discrepancy between the FDG PET and clinical findings. PET images were evaluated for the distribution and uptake pattern, and the standardized uptake values (SUVs) were obtained. Twenty-seven patients underwent biopsy or surgery of the detected lesions and 18 patients were followed up clinically and with repeat imaging studies.

RESULTS

Fifty lesions were identified on FDG PET. There were eight false-positive results and one false-negative on FDG PET. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of FDG PET in detecting MPNSTs in patients with NF1 were 95%, 72%, 71%, 95%, and 82%, respectively. Using 11C methionine PET in combination with FDG PET reduced the number of false-positive results from eight to two, which increased the specificity from 72% to 91%. In five patients, 11C methionine FDG PET contributed additional information about nontarget lesions that influenced treatment planning.

CONCLUSION

FDG PET is a sensitive technique in the detection of MPNSTs in patients with NF1. The addition of 11C methionine PET increases specificity in equivocal cases. PET may improve preoperative tumor staging by detecting metastases or second primary tumors, which often are present in patients with NF1.