Sinus Lift With Simultaneous Mucous Retention Cyst Drainage for Implant Rehabilitation: Clinical, Tomographic, and Histologic Assessments in a Six-Year Follow-Up Case Report

We aim to report the long-term clinical, tomographic, and histologic outcomes of simultaneous drainage of a maxillary mucous retention cyst (MRC) and lateral sinus floor elevation (SFE), followed by delayed guided implant placement, with a six-year follow-up. A 47-year-old male with an atrophic posterior maxilla (residual bone height (RBH): 1.0 mm) presented with a dome-shaped MRC measuring 22.13 × 15.86 × 27.94 mm (3,266.83 mm³). A lateral window SFE was performed with cyst drainage, careful elevation of the Schneiderian membrane, and grafting using particulate xenograft, covered by a collagen membrane. Cone-beam computed tomography (CBCT) was obtained at one month (T1), eight months (T2), and six years (T3) to assess graft volume and density. At eight months, a guided Ø4.3 × 8.5 mm implant was placed, and a trephine core biopsy was collected for histologic and histomorphometric evaluation. Postoperative healing was uneventful, and the patient remained asymptomatic throughout follow-up. At T1, graft volume was 1,978.61 mm³ (297.24 HU), and the cyst regressed by 6.10% compared with baseline. At T2, graft volume decreased to 1,737.67 mm³ (-12.18% vs. T1), with increased density (690.74 HU), and the MRC was radiographically resolved. Histomorphometric analysis revealed 25.76% new bone, 47.20% residual graft, and 27.04% connective tissue. At T3, graft volume remained 1,508.57 mm³ (-23.76% vs. T1), with a density of 785.91 HU, indicating long-term bone maturation and consolidation. The maxillary sinus remained functional and asymptomatic, with stable peri-implant tissues and no recurrence of the MRC. Simultaneous management of an MRC during lateral SFE allowed safe cyst drainage, predictable graft consolidation, histologic confirmation of new bone formation, and long-term implant success. This single-stage approach represents a pragmatic and effective treatment option in carefully selected cases of atrophic maxilla with cystic sinus lesions.