Various complications after microendoscopic discectomy (MED) are well known, but postoperative discal cyst is a unique and relatively unknown complication. Here, we report on two teenage patients who presented with postoperative discal cyst after MED for herniated nucleus pulposus (HNP), which resolved after conservative treatment. The patients were diagnosed with HNP at L4-5 and L5-S1 based on MRI and then treated by MED. Postoperative discal cyst was diagnosed on MRI after recurrence of symptoms. Both patients were managed conservatively. T2-weighted MRI demonstrated hyperintense collections adjacent to the operated intervertebral disc level, which were communicating with the corresponding disc annulus. Because the clinical symptoms were relatively mild, the patients were managed conservatively; both made a complete clinical recovery with radiological evidence of improvement. Postoperative discal cyst is a relatively unknown complication after MED for HNP. Surgeons should be aware of this postoperative complication when operating on young individuals with HNP.

Background. Discal cyst has been identified as a rare cause of low back pain and radiating leg pain. The pathogenesis and management of this condition are still debated. The largest number of reported cases had undergone microsurgery while very few cases have been treated with percutaneous endoscopic discectomy (PED). Methods. An 18-year-old boy complained of low back pain radiating to right leg after a minor road traffic accident. Diagnosis of a discal cyst at L4-L5 level was made based on magnetic resonance imaging (MRI). Despite conservative management for 6 months, the low back pain and radiating leg pain persisted so surgical treatment by PED was performed under local anesthesia. As the patient was a very active baseball player, his physician recommended a minimally invasive procedure to avoid damage to the back muscles. Results. The patient's low back pain and leg pain disappeared immediately after surgery and he made a rapid recovery. He resumed mild exercise and sports practice 4 weeks after surgery. Complete regression of the cystic lesion was demonstrated on the 2-month postoperative MRI. Conclusion. A minimal invasive procedure like PED can be an effective surgical treatment for discal cyst, especially in active individuals who play sports.

High-intensity zone (HIZ) was originally described as a high-intensity signal on T2-weighted magnetic resonance (MR) images, located in the posterior annulus fibrosus, clearly separated from the nucleus pulposus. Among symptomatic patients with low back pain, HIZ is present in 28-59% of cases. In morphologically abnormal discs, high sensitivity and specificity of 81% and 79%, respectively, were reported for HIZs and concordant pain during discography. In contrast, another report indicated low rates. Although most papers reported high sensitivity and specificity for this relationship, it remains controversial. Regarding the pathology of HIZs, inflammatory granulation tissues are found at sites showing HIZs. Such inflammatory tissues produce pro-inflammatory cytokines and mediators, which sensitize the nociceptors within the disc and cause pain. An effective treatment for this condition is yet to be established. Recently, minimally invasive surgery using percutaneous endoscopic discectomy (PED) under local anesthesia was introduced. After removal of the degenerated disc material, the HIZ is identified with the endoscope and then coagulated and modulated with a bipolar radio pulse. This technique is called thermal annuloplasty. In conclusion, HIZs is an important sign of painful intervertebral disc disruption, if identified precisely based on factors such as location and intensity.

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