Radiological relations of sigmoid sinus with oto-neuro-surgical landmarks with its surgical risk-stratification indicating classification.

Abstract

Objective: Detailed pre-operative HRCT scan-based measurement of the distance between surgical landmarks with lateral or sigmoid sinus (SS) and classification of its relations with surgical landmarks.

Study design: Observational Study.

Setting: Tertiary care center.

Patients: Patient volunteers above 18 years of age undergoing scans for various reasons.

Interventions: Axial Sections of HRCT of 260 temporal bones obtained from patient volunteers were studied with the help of RadiAnt DICOM Viewer (version 2023.1).

Main outcome measures: Closest distance of the SS from the posterior wall of the external auditory canal wall (CW), the vertical portion of the facial nerve (VPFN), the short process of incus (SPI), lateral (LC), and posterior semi-circular canal (PC), was measured. The SS relation with the mastoid was classified as type 1-4 depending upon the shortest distance of the sinus from the posterior canal wall millimeters.

Results: The mean distance of the SS from surgical landmarks was 14.6 ± 2.7 mm for SPI, 11.1 ± 3.1 for CW, 11.4 ± 2.9 for VPFN, 10.1 ± 2.8 for PC, and 11.9 ± 2.7 LC. All measured distances were significantly more on the left side (p < 0.05, Z test), except the difference in distance from LC. The greatest range of variation (5.2 to 21.8 mm) was seen in the distance between SS and VPFN. The most common type of relationship between SS and CW was type 3, present in 64% of subjects, while the least common group was type 1, with nearly 1% of subjects.

Conclusion: The assessment of distances and relations of various surgical landmarks with SS, with the proposed novel classification based on SS-CW distance, can be essential for preoperative planning and risk mitigation.

Level of evidence: 3: