Delayed cerebrospinal fluid leak (CSFL) occurring 21 days post-lumbar unilateral biportal endoscopic surgery: A case report.

RATIONALE: While minimally invasive endoscopic surgery has emerged as the primary approach for managing lumbar degeneration, cerebrospinal fluid leakage (CSFL) remains a common complication in traditional open spinal procedures. However, the literature documenting CSFL occurrence in minimally invasive endoscopic interventions is scarce, with delayed-onset cases (beyond 20 days postoperatively) representing an exceptionally rare clinical entity. PATIENT CONCERNS: We describe the case of a 60-year-old man who underwent unilateral transforaminal endoscopic spine surgery. On the 21st postoperative day, a cystic mass developed at the surgical site. DIAGNOSES: Delayed postoperative CSFL was diagnosed. INTERVENTIONS: The patient underwent a sequence of interventions: initial pressure bandaging and skin suturing, followed by lumbar cistern drainage and open dural repair surgery (which failed), and ultimately a successful 14-day course of continuous lumbar drainage. Post-drainage, he received core lumbar muscle training for rehabilitation. OUTCOMES: The continuous lumbar drainage ultimately resolved the CSFL after 14 days, with drainage volume peaks noted on days 7 and 10. At recovery, the patient resumed daily activities; however, he retained a residual reduction in right ankle dorsiflexion muscle strength (grade 3/5). LESSONS: Managing delayed CSFL is complex. While continuous lumbar drainage can be an effective definitive treatment, it may require an extended duration. This case underscores the importance of vigilant postoperative monitoring for delayed complications.