A rare case of lumbar disc herniation mimicking lumbar discal cyst after percutaneous endoscopic lumbar discectomy

We describe a 15-year-old girl who developed lumbar disc herniation (LDH) that mimicked discal cyst on magnetic resonance imaging (MRI) after percutaneous endoscopic lumbar discectomy (PELD). She firstly underwent PELD at another hospital for right leg pain caused by L5-S1 level LDH. Her leg pain temporarily relieved, however, the leg pain recurred soon after the surgery. Postoperative T2-weighted MRI showed that the right S1 nerve root was compressed by a round lesion that had an iso-intense wall and highly intense watery content. At that point, postoperative discal cyst was diagnosed, and she underwent PELD again 3 months after the initial surgery. However, the pain persisted after the second surgery, and she came to our hospital. MRI showed that the lesion had remained the same size as compared to the last surgery. Since two times endoscopic surgery was failed, we performed microscopic posterior decompression and found that the lesion actually contained not a cyst but a wet nucleus pulposus, which was different from what we had expected to find. The pain was alleviated immediately after the surgery. As signal intensity on MRI differs depending on the amount of moisture in the LDH, it should be noted that the LDH sometimes looks like a discal cyst on MRI.