The Petrosquamous Septum in Children-A Misleading Obstacle or Reliable Landmark? A Radioanatomical Study

To evaluate the petrosquamous septum in children under 5 years of age and its usefulness as a surgical landmark using computed tomography (CT); to identify petrosquamous stalactite and its relationship to the ossicular chain and external acoustic meatus is also described.

Retrospective review of CT scans.

Temporal bone radiologic anatomy laboratory.

We examined the presence of the petrosquamous septum in 282 temporal bone CTs. We measured its thickness at the level of the superior semicircular canal, the sinus tympani and the ossicular chain.

The petrosquamous septum was recognized at least at 1 of 6 measurement points in 99.6% of cases, corresponding to 281 temporal bones. The most consistent location was the level of the ossicular chain, where the lateral part of the PS septum was identified in 99% of cases. In 60% of cases, the lateral part was connected to the tegmen. The medial part was found in 73% and over 95% of these were located above the incus, indicating a pathway to the posterior epitympanum. The average thickness of the petrosquamous septum was greatest at the level of the ossicular chain (1.2 ± 0.4 mm) and smallest at the level of the sinus tympani (0.8 ± 0.2 mm).

The petrosquamous septum may serve as a landmark leading to the antrum and epitympanum. Irregularities in the PS septum should be studied preoperatively, as they may lead to misdirection towards the lateral epitympanic wall instead of the incus.