Recognition of peroneal intraneural ganglia in an historical cohort with “negative” MRIs

Background: The objective of this study was to review an historical cohort of patients with peroneal neuropathy and magnetic resonance imaging (MRI) read as negative for mass or cyst to determine if occult peroneal intraneural ganglion cysts can be identified on subsequent imaging review and to use this as an estimation of how under-recognized this pathologic entity is. Method: The patient cohort utilized in this study was a previously published control cohort of 11 patients with peroneal neuropathy and MRI read as negative for mass or cyst. Clinical history, neurologic examination, and MRI studies of the knee were reviewed for each of the included patients. The primary outcome of interest was the presence of peroneal intraneural ganglion cyst on MRI. Results: Overall, 7 of 11 (64%) patients in this historical “normal” cohort had evidence of a peroneal intraneural ganglion cyst on subsequent review of imaging. Deep peroneal-predominant weakness, knee pain, and tibialis anterior-predominant denervation/atrophy were seen more commonly in patients in whom an intraneural cyst was identified. Conclusions: This retrospective cohort study provides evidence that peroneal intraneural ganglion cysts are an historically under-recognized cause of peroneal neuropathy, with 64% of this historical “negative” cohort having evidence of a cyst on subsequent imaging review. Larger studies are needed to determine the treatment ramifications of identifying small cysts and to determine the clinical features suggestive of an intraneural ganglion cyst.