18 fdg pet/ct in the diagnosis of malignant peripheral nerve sheath tumours
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18 FDG PET/CT in the diagnosis of Malignant Peripheral Nerve
Sheath Tumours
VS Warbey, RE Ferner, JT Dunn, E Calonje, MJ O’Doherty
St Thomas’ Clinical PET Centre and Department of Clinical Neurosciences
Guy’s, King’s and St Thomas’ School of Medicine
Introduction
MPNST in NF1 – a diagnostic challenge
Overlap of clinical manifestations
MRI identifies site and extent, not reliable in detecting malignant change
Histology is the final arbiter of malignancy
Management requires a Specialist MDM approach
Background
Previous work by our group and others has concluded that 18FDG-PET is helpful in determining malignant change in neurofibromas
Significant difference in SUVmax between benign and malignant lesions with delayed imaging at approximately 200 minutes
SUVmax on delayed imaging < 2.5 2.5 - 3.5 > 3.5
Ferner et al. J Neurol Neurosurg Psychiatry 2000;68:353-357
Bredella et al.AJR 2007;189:928-935
Ferner et al. Ann Oncol 2008; 19(2):390-4
Aims
To evaluate the sensitivity of PET/CT
To clarify the value of early and delayed imaging
To re-validate the current cut-off values for identification of malignant change within neurofibromas using PET/CT
To examine the relationship between SUV and tumour grade
Methods
Patients with symptomatic neurofibromas referred for 18FDG PET/CT were identified from the reports archive
Early and delayed imaging (90 minutes, 4 hours)
SUVmax measured
Classified as malignant: SUVmax rose to > 3.5 on delayed imaging
Histological correlation
Benign
Early Imaging
Late Imaging
Malignant (1)
Early Imaging
Late Imaging
Malignant (2)
Early Imaging
Late Imaging
Results (1)
97 studies were identified from the PET/CT reports archive over a 35-month period from August 2004 to April 2008
Final analysis: 69 studies in 62 patients, 85 neurofibromas Exclusions: No delayed imaging/no focal uptake, alternative
diagnosis, repeat lesion 31 males, 31 females Mean age 31 years, age range 9 – 86
Median imaging times Early 101 minutes (1 hour 41 minutes) Late 252 minutes (4 hours 12 minutes)
Results (2) On the basis of semi-quantitative analysis PET/CT classified:
43 malignant 42 benign
Type of Tumour Negative on 18FDG PET/CT
Positive on 18FDG PET/CT
Neurofibroma 2 6
Atypical 1 9
Low Grade 0 11
High Grade 0 10
Sensitivity 0.97 (95% CI 0.81-0.99)Specificity 0.87 (95% CI 0.74-0.95)
Results (3) - SUVmax Comparsion
Mean SUVmax Benign Lesions on PET
Malignant Lesions on PET
Early 2.0
(CI 1.8-2.3)
7.0
(CI 5.6-8.4)
Late 1.9
(CI 1.7-2.2)
8.1
(CI 6.5-9.6)
Early vs. delayed imaging ([type irrelevant] F 1,83 = 9.98, p=0.0022)Benign vs. malignant ([time irrelevant] F 1,83 = 56.14, p<<0.0001)
Significant interaction effect between time and tumour type (F 1,83 = 14.72, p=0.00017)
SUVmax early vs. delayed imaging for tumours classified as malignant on PET/CT (p=0.0005)
Results (4) - Histology vs SUVmax
Mean SUVmax
Atypical Low Grade High Grade
Early 5.1 7.3 12.0
Late 5.6 7.8 13.7
SUVmax between tumour types ([time irrelevant] F2,27 = 7.91, p=0.002)
SUVmax early vs. delayed imaging (F1,27= 10.58, p=0.003)
Results (5) - Histology vs SUVmax
0
5
10
15
20
25
30
Benign Atypical Low-Grade High-Grade
SU
Vm
ax
Conclusions
Recommend early and delayed PET/CT imaging for accurate lesion characterisation
Continue to recommend a cut-off value SUVmaxD=3.5
Acceptable to maintain a high sensitivity at expense of false positive studies
First study that has demonstrated a correlation between SUVmax and tumour grade
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