A novel microvascular arterio-neural pathway for intraneural ganglion cyst formation secondary to cystic adventitial disease: illustrative case.

backgroundCystic adventitial disease (CAD) and intraneural ganglion cysts (IGCs) are rare mucinous lesions typically linked to an articular origin via macroscopic conduits. While secondary propagation between vascular and neural systems may occur through shared fascial sheaths, a direct microvascular route has not been previously described. OBSERVATIONS: A 60-year-old man presented with progressive left tibial neuropathy. High-resolution 7T MRI and surgery revealed a large popliteal CAD lesion connecting to the knee joint via the middle genicular artery, alongside a secondary tibial IGC lacking an independent articular nerve connection. Findings demonstrated that high-pressure CAD mucin tracked along a small connecting vascular branch, creating a novel microvascular arterio-neural pathway to infiltrate the tibial nerve. Targeted articular branch disconnection and cyst decompression yielded significant clinical improvement, with no recurrence on 7-month follow-up 7T MRI. LESSONS: This case expands the unifying articular theory, demonstrating that synovial fluid propagation can exploit a microvascular arterio-neural pathway rather than strictly macroscopic fascial planes. High-resolution 7T MRI is essential for visualizing these subtle connections. Successful management requires meticulous identification and disconnection of the primary joint connection to prevent recurrence. https://thejns.org/doi/10.3171/CASE26411.