Magnetic resonance imaging appearance of targeted muscle reinnervation and regenerative peripheral nerve interfaces...

Patients with extremity sarcomas may require amputation when limb salvage surgery is not possible. Targeted muscle reinnervation (TMR) and regenerative peripheral nerve interface (RPNI) are procedures that can reduce neuroma formation, though neuromas can still occur. This study aims to describe the MRI characteristics of TMR/RPNI, examine changes in neuromas over time, and differentiate these from sarcoma recurrence on MRI.

All patients at our institution between 2013 and 2024 who underwent upper or lower extremity amputation due to sarcoma, underwent TMR/RPNI, and had follow-up MRI imaging were included. Two radiologists evaluated the incidence and appearance (size, signal characteristics, enhancement pattern, morphology) of neuromas and their evolution. Statistical analysis employed the chi-squared test and McNemar's test.

Sixty-two TMRs and 46 RPNIs were performed in 26 patients (7 upper, 19 lower extremity amputations). Seven patients had TMR-only, 7 had RPNI-only, and 12 had both, with an average follow-up of 517 days (range 91-1705 days). MRI identified nodular, T2 hyperintense, enhancing foci averaging 0.8 cm in diameter (range 0.3-2.0 cm) at 44% of nerve surgery sites and in 73% of patients at initial follow-up. These foci, presumed to represent neuromas, decreased over time (p < 0.001) with a significant reduction in nodule size for TMR-only patients (p = 0.007). Two recurrences showed increasing irregular nodule size.

TMR and RPNI procedures show T2 hyperintense nodules on the first follow-up MRI, which decrease in incidence over time. TMR significantly reduces neuroma size. Increases in nodule size should prompt concern for recurrence.