Maxillary sinus wall fenestration at the lateral wall or floor of the sinus can result from many potential factors, such as the repair of oro-antral communication, Caldwell-Luc antrostomy, tooth extraction after an endodontic or periodontal infection that eroded the sinus wall, and the combination of sinus pneumatization and alveolar ridge resorption after teeth removal. When sinus wall fenestration is observed on radiographs, it usually indicates adhesion between the sinus membrane and buccal flap, which makes the reentry surgery for subsequent sinus augmentation challenging. To minimize surgical complications in these challenging scenarios, this paper presents a split-flap surgical technique for the management of soft tissue adhesion between the sinus membrane and alveolar mucosa when attempting a lateral window sinus augmentation.