Regressing intraneural nodular fasciitis of the femoral nerve.

Intraneural nodular fasciitis is an extremely rare phenomenon with thirteen prior published reports, only one of which involved the femoral nerve. Our case involves intraneural nodular fasciitis of the femoral nerve discovered on imaging after a patient reported months of debilitating symptoms initially attributed to labral pathology from femoroacetabular impingement. MRI of the right hip demonstrated an avidly enhancing intraneural mass with partially infiltrative, spiculated margins. Given that these features have only been described in one prior case of intraneural nodular fasciitis with the majority of cases demonstrating well-defined margins, the mass was concerning for malignancy. As with most prior published cases, complete resection of this lesion was not possible due to nerve involvement; however, symptomatic observation remained possible as progression or recurrence of this entity is uncommon. Over multiple follow-up MRIs, the mass progressively decreased in size. Here, we present a case of infiltrating intraneural nodular fasciitis of the femoral nerve with findings of regression, the first to be objectively documented on MRI in the literature.