The retrocochlear recess: radiomorphometric investigation of an anatomical novelty in children under five

To evaluate the presence and measure the depth of newly found air space located posteriorly to the basal turn of the cochlea-retrocochlear recess (RCR).

The area of subtympanic sinus was explored bilaterally using multi-planar reconstruction tools in 280 temporal bone computed tomography scans. We searched for RCR and measured its depth whenever present. We evaluated the presence of subcochlear canaliculus and the position of the jugular fossa bordering the RCR.

The RCR in 192 out of 280 evaluated temporal bones (69%), more commonly in children under 2 years old than aged three to five (p < 0.001). The mean depth of the RCR for the whole studied group measured from posterior pillar of the round window niche was 3.9 ± 1.8 mm, and from promontory - 6.6 ± 1.8 mm. The influence of the jugular fossa on the shape of the RCR was confirmed in 88 out of 192 temporal bones with RCR present (46%), more commonly on the right side (p < 0.001). We found subcochlear canaliculus in only 7.5% of examined bones.

The RCR is a commonly found anatomical space in the vicinity of subtympanic sinus. Its final shape may be affected by the jugular fossa, especially on the right side. The RCR may play role in preoperative evaluation for cholesteatoma surgery or cochlear implantation.