Scientific Session 21 — Musculoskeletal - TumorThursday, May 4, 2017
2512. MRI and PET Characteristics of Malignant Peripheral Nerve Sheath Tumors
Niziolek P*, Sebro R. Hospital of the University of Pennsylvania, Philadelphia, PA
Address correspondence to P. Niziolek (firstname.lastname@example.org)
Objective: Malignant peripheral nerve sheath tumors (MPNST) are rare soft-tissue sarcomas. Major risk factors for these tumors include neurofibromatosis type 1 (NF1) and prior radiation. Various MRI and PET criteria have been proposed to differentiate benign from malignant nerve sheath tumors. We sought to determine if certain MRI and PET characteristics can differentiate benign from malignant nerve sheath tumors in our available database.
Materials and Methods: A retrospective review of MPNST using searches within our radiology report database at our institution was performed. Twenty-four cases of biopsy-proven MPNST were identified that had PET or MRI studies available for evaluation. Thirteen cases of biopsy-proven benign peripheral nerve sheath tumors (PNSTs) with available PET or MRI studies or both were identified for comparison. Recorded lesion characteristics included maximum dimension, location, T2-weighted STIR appearance, gadolinium-enhanced appearance, and maximum standardized uptake value (SUVmax) on pretreatment PET.
Results: Of the 24 MPNST cases, 20 had relevant MRI studies (18 without contrast administration) and eight had PET studies. NF1 was present in nine of the cases. The mean maximum dimension was 8.8 cm with a mean SUVmax of 11; both of these values were statistically different from the benign PNSTs using a t test with p < 0.05. None of the MPNST demonstrated a target sign, seven of 20 demonstrated a tail or string sign, all were heterogeneous on T2-weighted STIR imaging, and one of 18 had a homogeneous appearance on gadolinium-enhanced imaging. Of the 13 benign PNST cases, 11 had relevant MRI (all with contrast enhancement) and seven had PET studies. NF1 was present in four of the cases. The mean maximum dimension was 3.9 cm with a mean SUVmax of 5. Notably, two benign PNSTs had SUVmax of 10 and 9.2; if these two lesions were excluded, the mean SUVmax was 2.9 for benign PNST. Three of 11 cases demonstrated a target sign, three of 11 demonstrated a tail or string sign, all were heterogeneous on T2-weighted STIR imaging, and one of nine had a homogeneous appearance on gadolinium-enhanced imaging.
Conclusion: Lesion size and SUVmax were features that differentiated MPNST from benign PNST; however, two biopsy-proven benign PNST had SUVmax above 9. NF1 was present in 38% of patients with MPNST. Further studies on imaging characteristics to differentiate benign from malignant lesions are warranted, especially in patients with NF1.