The tympanic sinus is one of the most important structures of the human temporal
bone. Located in its vicinity are the round window, posterior semicircular
canal and facial nerve. The study was performed on 30 temporal bones taken
from adult cadavers of both sexes. After the tympanic sinus had been identified,
its morphological features were evaluated. The sinus was then measured using
a graticule with an accuracy of 0.05 mm. Also measured were the shortest
distances from the tympanic sinus to the neighbouring structures (the lateral
and posterior semicircular canal, the facial nerve canal and the jugular fossa).
The measurements were performed under a surgical microscope with eye-piece
graduation of 0.05 mm accuracy.
Four main morphological types of fossa of the tympanic sinus and two main
developmental forms, a deep sinus and a shallow sinus, were distinguished. The
existence of a deep sinus was associated with absence of the bridge and the
sinus was shallower when the bridge was prominent. The very deep sinuses
were located close to the facial canal, in some cases penetrating deep in its
vicinity (in some cases even going beyond two thirds of the canal’s circumference),
which poses a real risk of facial nerve damage during surgical removal of
a lesion located in close proximity to the nerve. In most cases the tympanic sinus
is elliptical in shape and its long diameter lies in the vertical plane (mean value:
2.73 × 2.23 mm). The mean distances from the tympanic sinus to the facial
nerve canal, lateral semicircular canal, posterior semicircular canal and jugular
fossa were 1.5 mm, 2.1 mm, 1.59 mm and 5.5 mm respectively. No correlation
was observed between the measurement results and either sex or side