The posterior-inferior recess of the sinus tympani - radioanatomical investigation for purposes of endoscopic otosurgery in children under five.

BACKGROUND

Sinus tympani (ST) is located in the medial retrotympanum, above the subtympanic sinus, and below the posterior tympanic sinus. The surgical access to the ST may be transmeatal-endoscopic or transmastoid-retrofacial. It depends on the depth and type of ST assessed on axial planes. Recently, a new morphology of ST was found and described using sagittal planes- posterior-inferior recess (PIR). We aimed to explore its presence and morphology in children under five.

METHOD: STs were assessed in tilted-axial planes, according to Marchioni classification, in 150 sets of CT images. Then, STs were checked in near-sagittal planes for the presence of PIR, and the width and depth of the recess were measured.

RESULTS

Tympanic sinus was found in all analyzed scans. The most common type was type B (59,3%), then type C (34,3%) and type A (6.3%). We have found PIR in 109 analyzed tympanic sinuses (36.3%). The average width of the PIR for the studied group was 2.21 ± 0.79 mm (1.15-6.63 mm), and the average depth of PIR was 2.53 ± 1.26 mm (0.85-7.26 mm). PIR was present more often in type C STs than in type B (p < 0,001) and type A (p < 0,001).

CONCLUSION

Posterior-inferior recess of the sinus tympani is a common anatomical variation of the medial retrotympanum in children under five. PIR is the shape of the tympanic sinus that otologists should be aware of when assessing preoperative CT, especially when sinus tympani type A or B is encountered.