Background:
The location of the sigmoid sinus within the mastoid cavity is quite variable. An anteriorly- displaced vertical segment of the sigmoid sinus constitutes an uncommon but dangerous anatomical variation that surgeons rarely encounter during surgery. In this variation, the sigmoid sinus lays underneath a very thin bony flap, which makes it easily damaged. Thus, an abrupt fatal bleeding might occur. Despite the many hypotheses about its origin (Chronic otitis media, hypopneumatization, etc.), the pathogenesis of this variation is still not completely understood.
Case presentation:
We present a case where the vertical segment of the left sigmoid sinus was encountered just underneath a one- millimeter bony flap in the posterior wall of the external auditory canal during an attempted myringoplasty.
Conclusion:
Anatomical variations of the sigmoid sinus are not uncommon, and the otolaryngologist should be aware of such variations to prevent unpleasant, intra- operative surprises.