Stimulation Contractility Gradient of a Neuromuscular Choristoma Within the Sciatic Nerve: 2-Dimensional Operative...

Neuromuscular choristoma (NMC) is a rare congenital nerve lesion that is classified by the presence of heterotopic muscle fibers intercalated within nerve fascicles.1 The presence of NMC typically causes progressive neuropathy and bony/soft tissue undergrowth, often leading to a shortened atrophic limb.2,3 The typical appearance of NMC on magnetic resonance imaging is an enlarged fusiform nerve that exhibits minimal gadolinium enhancement.4 While there is increasing documentation of pathognomonic clinical and radiographic features for various diffuse fusiform peripheral nerve lesions, nerve biopsy is still occasionally required for some patients given the rarity of these diseases and progressive neuropathic features.The intraoperative appearance of NMC and its unique electrical stimulation properties are quite interesting. Intrafascicular replacement of nerve by skeletal muscle gives the nerve a red beefy color and causes the fascicles to contract with electrical stimulation.5 In this video, we demonstrate the intraoperative appearance and contractile properties of NMC in a 60-yr-old woman with progressive sciatic neuropathy. Histologic and immunohistochemical studies identified a gradient of intralesional mature skeletal muscle within the NMC, with substantially fewer desmin-positive skeletal muscle fibers in the distal aspect. A gradient of contractility with intraoperative stimulation seemed to correlate with this pathology. These findings suggest that the lesional extent of NMC may not be clinically or grossly evident, reflecting a varying distribution of skeletal muscle within the affected nerve.The Mayo Clinic Institutional Review Board Office for Human Research Protection does not require approval for single participant case studies. The subject involved in this study was not identifiable and the general surgical consent form included permission for intraoperative photos and video.