Proximal sciatic nerve intraneural ganglion
Right (contralateral) sciatica. Left sided lesion detected on MRI Lumbar spine, and subsequently worked up with dedicated MR of the nerve.
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Cystic mass within proximal left sciatic nerve starting medial to sciatic foramen. There is no internal enhancement or significant solid component. It has a tail extending to the posterior hip joint.
Pathogenesis is presumably related to hip joint fluid dissecting into an articular branch, and subsequent centripetal tracking into the parent nerve.
Intraneural ganglion is a rare entity, even rarer in this location. It has been described more commonly in common peroneal nerve around the fibular head.
Without careful individual tailoring of MR techniques, demonstration of the tail tracking to the hip, and evaluation of the internal MR characteristics of the lesion, this can be mistaken as a cystic schwannoma.