What's New with Intraneural Ganglion Cysts?

BACKGROUND: Intraneural ganglion cysts (IGCs) are rare, mucin-filled lesions that develop within peripheral nerves, most commonly the common peroneal nerve arising from the superior tibiofibular joint. Their pathogenesis has been explained by the unified articular theory. Over the past two decades, new anatomic, imaging, and surgical insights have refined this theory and its clinical application and have been supported by historic perspectives. METHODS: Recent case series, illustrative reports, and systematic reviews from our group and others were analyzed to highlight emerging concepts in the pathoanatomy, imaging, and management of IGCs. Emphasis was placed on common and atypical and rare sites and presentations, advanced imaging techniques, and evolving surgical strategies. RESULTS: Novel findings include crossover patterns and the identification of extreme subparaneurial cysts explaining extensive propagation, recognition of nearly invisible cysts and joint connections on high-resolution magnetic resonance imaging more so than ultrasound, and validation of a phasic mechanism of cyst evolution. Surgical advances include the layered U approach for peroneal IGCs, a joint-only strategy for IGCs, and fluorescein-assisted intraoperative localization. Analysis of the world literature demonstrates a progressive rise in articular branch identification and treatment (5% in the 1990s to 58% in 2021), correlating with a reduced intraneural recurrence rate when the joint connection is addressed. CONCLUSIONS: Current evidence supports the unified articular theory as the definitive explanation for all IGCs. Successful management requires articular branch disconnection and/or treatment of the joint source. Future work should focus on advanced imaging, standardized outcomes, and minimally invasive articular approaches.