Characteristics of MPNSTs with non-Hypermetabolic FDG PET-CT Imaging
Courtney Pendleton, MD1, Cecilia Fung, BA1, Robert J. Spinner, MD2 and Stephen M Broski, MD1, (1)Mayo Clinic, Rochester, MN, (2)Department of Physical Medicine and Rehabilitation, Mayo Clinic, Rochester, MN
Introduction:
Patient history, clinical examination and radiologic features play a large role in evaluating whether a peripheral nerve sheath tumor is benign or malignant (MPNST).
PET imaging determines whether a lesion is hypermetabolic, thus more likely to be an MPNST. This can determine the utility of percutaneous biopsy, and more effectively target image-guided biopsy.
A percentage of patients with pathology proven MPNST have PET scans that do not demonstrate a hypermetabolic lesion.
Methods:
Our institution's records were reviewed from 1990-2019, and all patients with pathology-proven MPNST were selected. Patients with fluorodeoxyglucose-positron emission tomography computed tomography (FDG PET-CT) were retrospectively reviewed by a single radiologist, and the SUVmax was calculated.
All scans were retrospectively classified as markedly heterogeneous, mildly heterogeneous, and homogeneous.
Patients with only PET-MRI were excluded, as SUVmax between MRI and CT is not equivalent, and the cutoff value (<4.3) was determined using FDG PET-CT. Patients where an SUVmax could not be calculated were excluded.
Patients with a SUVmax <4.3 were considered to have a 'negative" FDG PET-CT.
Results:
76 patients met inclusion criteria. Of these, 72 had "positive" FDG PET-CT imaging; 4 had "negative" FDG PET-CT imaging.
PET "Positive"
The average age at diagnosis was 44.8 years (range: 16.3 - 81.3; SD 18). Twenty-eight patients were female (38.9%).
The average SUVmax was 10.9 (range: 4.7 - 35.1; SD 5.4). Forty-four tumors demonstrated marked heterogeneity (61.1%); twenty-one showed mild heterogeneity (29.2%), and 7 were homogeneous (9.7%).
PET "Negative"
The average age at diagnosis was 47.3 years (range: 36.1 - 59.0; SD 10.1). Two patients were female (50%).
The average SUVmax was 3.3 (range: 2.2 - 3.9; SD 0.78). No tumors demonstrated marked heterogeneity (0%); two showed mild heterogeneity (50%), and 2 were homogeneous (50%).
Comparison of PET "Positive" and PET "Negative"
There was no significant difference in the average age of diagnosis or patient distribution by sex.
As expected, based on the SUVmax cutoff of <4.3 for PET "negative" MPNST, the average SUVmax differed significantly between the two groups (3.3 v 10.9, p = 0.0065).
Patients with PET "positive" MPNST were significantly more likely to demonstrate marked heterogeneity (0% v. 61.1%, p = 0.0167). Patients with PET "negative" MPNST were significantly more likely to demonstrate homogeneity (50% v. 9.7%, p = 0.0159).
Conclusion:
Patients with an SUVmax < 4.3 and a homogeneous tumor should raise suspicion for an MPNST, particularly if their history and clinical examination are concerning.
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