Diagnostic approaches and clinical challenges of imaging in peripheral nerve tumors: data from the multicenter...

Peripheral nerve tumors (PNTs) are diagnostically challenging due to their heterogeneous histology, variable size, diverse anatomical locations, and imprecise signs of malignancy. Imaging is crucial for detection, characterization, and surgical planning. This study systematically assessed imaging data to identify diagnostic patterns and their limitations across different techniques, as well as to generate a focused, standardized imaging recommendation.

A retrospective analysis was conducted on 396 patients with histopathologically confirmed tumors associated with peripheral nerves from five centers participating in the prospective Peripheral Nerve Tumor Registry in Germany and Austria. Preoperative imaging data including MRI, high-resolution ultrasound (HRU), CT, and PET-CT were evaluated with a focus on tumor size, contrast enhancement (CE), T2 signal characteristics, cystic components, and patterns of tissue infiltration and correlated with clinical and histopathologic data. MRI protocols were assessed for consistency.

MRI was the primary modality in 94.7% of patients (n = 375), although protocols varied: 7% lacked contrast-enhanced sequences, 22% lacked T2-weighted sequences, and 95% lacked apparent diffusion coefficient maps. Tumors were classified as benign (group 1, n = 321 [81.1%]), malignant (group 2, n = 24 [6.1%]), or rare (group 3, n = 51 [12.9%]). Median tumor sizes were 28.0 (IQR 22.0, range 4-130) mm, 59.5 (IQR 53.0, range 22-96) mm, and 52.0 (IQR 64.0, range 7-190) mm for groups 1-3, respectively. Benign tumors were significantly smaller than malignant and rare tumors (each p < 0.001). CE was present in 97.5%, mainly showing an inhomogeneous pattern in malignant and rare tumors. An inhomogeneous T2 signal (n = 214) and cystic components (n = 99) were more frequent in malignant (79%) and rare (43%) tumors. Perilesional edema (n = 13) and tissue infiltration (n = 26) were found in 84.6% of malignant and rare tumors. Receiver operating characteristic (ROC) analysis identified a tumor size cutoff of 44.5 mm, indicating malignancy (area under the ROC curve = 0.83, sensitivity 78.8%, specificity 75.0%). FDG (18-fluorodeoxyglucose)-PET revealed overlapping maximum standardized uptake values (6.1-33.7) across all groups.

MRI offers critical morphological detail, supports differentiation between tumor subtypes, and guides surgical planning. Therefore, it is the imaging of choice in PNTs, whereas PET-CT and HRU may help to close diagnostic gaps left by MRI. Establishing standardized imaging protocols is essential to improve diagnostic accuracy and support consistent, high-quality patient care.