The document discusses the anatomy of the sinus tympani, a cavity located in the posterior region of the tympanic cavity. It describes how the sinus tympani was first named and discussed in 1820. It defines the two portions of the retrotympanum based on the position of the facial nerve. It outlines different shapes that the sinus tympani can take, including classical, confluent, partitioned, and restricted, and different types - A, B, and C - based on its extension in relation to the facial nerve. The shapes and types of the sinus tympani can influence the surgical approach used for cholesteatoma surgery.

1. Prof. Dr. Bikash Lal Shrestha
Department of ENT-HNS
Dhulikhel Hospital
Kathmandu University Hospital
Nepal

2.  The sinus tympani was first named by Meckel' in
1820 who considered only that portion which is
anterior to the pyramidal eminence and did not elude
to the important posterior extension medial to the
pyramidal eminence and facial nerve.
 Steinbrugge in 1889 point out that the sinus could
pass medial to the canal of the facial nerve.

3.  The retro tympanum is the posterior
area of the tympanic cavity : Divided
into two portions with respect to the
position of the facial nerve
1. Medial portion known as sinus
tympani .
2. Lateral portion known as facial
sinus/recess.

4. Sinus tympani
(Medial Portion)
Sinus tympani
Facial recess /sinus
(Lateral Portion)
Vertical segment of
facial nerve

5.  Sinus tympani (ST), lies medial to the pyramidal
eminence, the stapedial muscle and the facial
nerve and lateral to the posterior semicircular
canal and the vestibule.

6.  The Sinus tympani, composed of two different
sectors: the inferior retrotympanum (represented
by the sinus subtympanicus {ss}) and the superior
retrotympanum (represented by the sinus
tympani {st} and the posterior sinus {ps})
Superior retrotympanum
Inferior retrotympanuim

7.  Classical shape: When the sinus tympani is
located between the ponticulus and subiculum
lying medial to the facial nerve and to the
pyramidal process.

8.  Confluent shape: When an incomplete ponticulus
is present and the sinus tympani is confluent to
the posterior sinus.
Incomplete ponticulus

9.  Partitioned shape: When a ridge of bone
extending from the third portion of the facial
nerve to the promontory area is present,
separating the sinus tympani into two portions
(superior and inferior).
Ridge of bone
Promontory
VII Nerve

10.  Restricted shape: When a high jugular bulb is
present thus reducing the inferior extension of
the sinus tympani.

11.  Sinus tympani Type A, a limited sinus tympani
without medial and posterior extension with
respect to the third (vertical) portion of facial
nerve.

12.  Sinus tympani Type B, Sinus tympani with medial
extension without posterior extension with
respect to the third portion of facial nerve.

13.  Sinus tympani Type C, Sinus tympani with medial
and posterior extension with respect to the third
portion of the facial nerve.

14.  Sinus tympani shape and depth can influence
surgical approach in cholesteatoma surgery.
 In the case of a shallower sinus tympani, an
endoscopic exploration is chosen.
 While in a deeper sinus tympani, a retrofacial
approach is usually preferred.

15.  Donaldson JA, Anson BJ, Warphea RL et al (1970) The surgical anatomy of the sinus tympani. Arch Otolaryngol 91:219–227
 Nogueira JF, Mattioli F, Presutti L, Marchioni D (2013) Endoscopic anatomy of the retrotympanum. Otolaryngol Clin NorthAm 46(2):179–188
 Proctor B (1969) Surgical anatomy of the posterior tympanum. Ann Otol Rhinol Laryngol 78(5):1026–1040
 Marchioni D, Mattioli F, Alicandri-Ciufelli M, Presutti L (2009) Transcanal endoscopic approach to the sinus timpani: a clinical report. Otol
Neurotol 30(6):758–765
 Marchioni D, Alicandri-Ciufelli M, Piccinini A, Genovese E, Presutti L (2010) Inferior retrotympanum anatomy revisited: an endoscopic
anatomic study. Laryngoscope 120(9):1880–1886
 Marchioni D, Valerini S, Mattioli F, Alicandri-Ciufelli M, Presutti L. Radiological assessment of the sinus tympani: temporal bone HRCT
analyses and surgically related findings. Surg Radiol Anat. 2015;37(4):385-392.

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