Radioanatomical evaluation of the subtympanic sinus in children under five years old and its clinical implications - high resolution computed tomography study

Abstract

Purpose: This study aimed to evaluate subtympanic sinus (STS) and its vicinity in high-resolution computed tomography (HRCT) scans of children under five years old with non-diseased temporal bones.

Material and method: We divided the whole group into children under 24 months of age (first stage of pneumatisation development) and between 25 and 60 (second stage). We have determined the width of the entrance to STS, depth of the STS, type in relation to facial nerve according to Anschuetz classification, the pneumatisation of posterior and medial air cell tracts, and jugular bulb position. All the HRCTs (280 temporal bones) were analyzed according to the multiplanar reconstruction protocol with symmetrization.

Results: STS's mean width and depth were 2.71 ± 0.60 mm and 3.26 ± 1.11 mm, respectively. The most common STS type was type A (59.3%), followed by type B (30.7%) and type C (10%). The posterior air cell tract (retrofacial cells) was present in 39.3%. The medial air cell tract (hypotympanic cells) was present in 30.7% The jugular bulb position affected the final shape of STS in 17.5%.

Conclusion: The results support the necessity of the classification for the STS. Our study may help with surgical planning regarding endoscopic ear procedures and gives a broader understanding of how pneumatization or jugular bulb might correlate with the final shape of the retrotympanum. The historical remarks track the term's origin for clarity in research and respect for earlier investigators.

Keywords: Endoscopic ear surgery; Middle ear; Retrotympanum; Subtympanic sinus; Temporal bone; Temporal bone computed tomography.

Fig. 1

A Scheme of medial recesses of retrotympanum B Left endoscopic view of medial recesses of retrotympanum with use of 0-degree scope C Detailed left endoscopic view of inferior retrotympanum with use of 0-degree scope slightly clockwise rotated in comparison to image B. Ant – anteriorly, Sup – superiorly, FN - facial nerve, Pro – promontory of cochlea, PTS – posterior tympanic sinus, TS – tympanic sinus, STS – subtympanic sinus, ScC – subcochlear canaliculus, Sm – tendon of stapedius muscle, RWN – round window niche, Ap – anterior pillar, Pp – posterior pillar; photos gathered from the Department’s collection.

Fig. 2

Different types of the subtympanic sinus; STS type A is very shallow and does not reach the anterior border of the facial nerve in transverse sections, type B reaches the circumference of the facial nerve but does not extend beyond its posterior border and type C, defined as very deep, extends beyond the posterior circumference of the facial nerve. All the scans are made in tilted axial plane and show left temporal bones

Fig. 3

a General view of the area of measurements; Co – cochlea, M – manubrium of malleus, In – long crus of incus, FN – facial nerve b Detailed view of the area of subtympanic sinus; Ap – anterior pillar, S – head of stapes, Pp – posterior pillar, asterisk – subtympanic sinus, red area with circle – round window niche c The green area - subtympanic sinus, green line – width of the entrance to the subtympanic sinus, green dotted line – depth of subtympanic sinus; All the scans are made in tilted axial plane and show left temporal bones

Fig. 4

A air cells absent medially to the STS B air cells present medially to the STS C air cells absent posteriorly to the STS D air cells absent posteriorly to the STS E jugular bulb (JB) distant from the bottom of STS F jugular bulb narrowing the STS; asterisk and green area – subtympanic sinus; All the scans are made in tilted axial plane and show left temporal bones