Intradural disc herniation is rare. In a colon cancer patient who suffered from low back pain for several years, MRI examination showed evidence of vacuum phenomenon and ring enhancement at the level of L3-4. Intradural herniation of an intervertebral disc was confirmed surgically. Pathological evidence of intradiscal gas is rarely reported in the literature, however, an association between intradural disc herniation and pneumocysts was demonstrated in this case. The implications of our sequential radiological and pathological findings for the pathogenesis of intradural pneumocysts are discussed.