The sinus tympani is located on the medial wall of the tympanum between the subiculum and the ponticulus. It extends in a posterior direction, medial to the pyramidal eminence, stapedius muscle, and facial nerve and lateral to the posterior semicircular canal. The sinus is subject to great variability in the size and in posterior extent. The entrance of the infrapyramidal portion is likewise subject to striking variation in respect to size and shape.
The otologic surgeon must be aware of the variability of the sinus and reconciled to his inability to clean the sinus thoroughly in some patients. The limitation thus set by structure may necessitate a modification of an operative procedure planned in advance of surgical exploration.