Neuromuscular choristoma-associated desmoid-type fibromatosis: Establishing a nerve territory concept

Introduction: Desmoid-type fibromatosis (DTF) frequently arises in patients with neuromuscular choristoma (NMC). We hypothesize that NMC-associated DTF occurs in soft tissues innervated by the NMC-affected nerve, and arises from CTNNB1-mutated (myo) fibroblasts within or directly adjacent to the NMC. Materials and methods: A retrospective review of patients treated at our institution was performed for patients with biopsy-confirmed diagnosis of NMC-DTF. Clinical presentation, physical examination, electrodiagnostic findings and radiological features (MR and FDG PET/CT images for each NMC-DTF) and pathologic re-review of available materials were analyzed. A literature review was also performed. Results: Eight patients from our institution met the inclusion criteria. All patients presented with neuropathic symptoms and soft tissue or bone changes in the nerve territory innervated by the NMC. All MR images (N=8 cases) showed the characteristic features of NMC, and also showed direct contact between unifocal (N=5) or multifocal (N=3) DTF(s) and the NMC-affected nerve NMC. FDG PET/CT (N=2 cases) showed diffuse, increased FDG uptake along the entire affected nerve segment, contiguous with the FDG-avid DTF. In all cases, the DTFs arose in the soft tissues of the NMC-affected nerve’s territory. No patient developed DTF at any other anatomic site. Conclusions: These data demonstrate that NMC-DTF arises solely within the NMC-affected nerve territory, and has direct contact with the NMC itself. Based on all these findings and the multifocality of NMC in several cases, we recommend imaging and surveillance of the entire NMC-affected nerve (from spine to distal extremity) to identify clinically-occult DTF in patients with NMC.