The sphenoid sinus one of the posterior group of sinus, considered one of the most difficult sinuses due to its deep location in the skull. The interest in the understanding of the anatomy of the sphenoid sinus increased markedly during the last decades due to the development of endoscopic transsphenoidal approaches to the intracranial structures. The important anatomical relations of the sphenoid sinus make it one of the difficult and challenging structures for the surgeons. In this case report, we present one of the anatomical variations that was found during cadaveric dissection of the head. In this case we found abnormal bony defect in the lateral wall of the sinus, the defect closed just by the lining mucosa of the sinus and the dura from its intracranial side. A point may be of clinical importance to the related nearby structures.