Utility of ultrasound in the diagnosis and management of a radial nerve perineurioma in a pediatric patient.

Background: Intraneural perineuriomas are tumors originating from the perineurial cells surrounding nerve sheath fascicles. Intraneural perineuriomas represent about 1% of peripheral nerve tumors and are often misdiagnosed due to their rarity. In this case, we report a pediatric patient with a radial nerve perineurioma, in which ultrasound played a key role in diagnosis. Case Description: We present the case of a 4-year-old male with over 6 months of progressive left upper extremity weakness found to have chronic left radial neuropathy distal to the triceps branch of the radial nerve on electromyography/nerve conduction study. Ultrasound showed a well-defined fusiform hypoechoic mass of approximately 1.5 × 0.5 × 0.8 cm, with the radial nerve noted to enter and exit the mass. Magnetic resonance imaging (MRI) did not encompass the pathology. The mass was excised with small margins, and pathology was consistent with perineurioma. The resultant 3 cm gap was repaired through nerve grafting. Surveillance MRI showed no recurrence of the perineurioma over time. Conclusion: Ultrasound served as a necessary adjunct in the workup of upper extremity weakness despite negative MRI findings. This imaging modality should be considered if there is high clinical suspicion of a peripheral nerve lesion.