Evolution of neuromuscular choristoma into neuromuscular choristoma-associated desmoid-type fibromatosis: evidence from serial MRI

Summary

Objective: Neuromuscular choristoma (NMC) is a rare developmental lesion that may give rise to desmoid-type fibromatosis (DTF) within the same nerve territory (NMC-DTF). While MRI features of NMC are well established, the natural history of progression to NMC-DTF has not been systematically described. This study aimed to define radiological groups from NMC to NMC-DTF using serial MRI and a literature review. Methods: Following IRB approval, the authors retrospectively analyzed 28 patients with NMC from their institutional database. Diagnosis was based on pathology or classic clinicoradiological features. Sequential MR images were reviewed to evaluate nerve enlargement, enhancement patterns, low T1/T2 foci, and NMC-DTF formation. Cases were classified into 3 radiological groups: 1) classic NMC with typical MRI features (group I), 2) NMC plus, with atypical features (foci of low T1/T2 signal intensity and/or at least moderate postcontrast enhancement; group II), and 3) NMC-DTF with a mass outside of the epineurium (group III). Data were correlated with pathology results and prior reports from the literature. Results: Of the 28 patients, 24 underwent serial MRI. Eleven patients presented with group I features, 4 with group II, and 9 with group III. Among group I patients with follow-up imaging, 4 (36.4%) progressed to group III over a mean of 6.2 years and 1 (9.1%) to group II. All 4 group II patients (100%) developed NMC-DTF within a mean of 3.0 years. All group III patients demonstrated NMC-DTF extending beyond the epineurium. No prior cases in the literature documented radiological progression from NMC to NMC-DTF on serial MR images. Conclusions: The authors propose a framework for NMC progression based on radiological features, identifying group II as being high risk and a potential transitional phase for the formation of DTF. Structured surveillance with serial MRI is essential to prevent iatrogenic triggers and improve management strategies in patients with NMC.