BACKGROUND: The carotid siphon has a complex structure, which is difficult for two-dimensional imaging observation due to shelter from the basicranial bone. Digital subtraction angiography is conducive to display the course of carotid siphon, but there is a lack of anatomical landmarks. Three-dimensional CT imaging is beneficial to show the structure of carotid siphon and have its measurement, which provides a new and effective means in relevant studies.
OBJECTIVE: To clarify the morphology and calcification distribution of the carotid siphon, thereby providing an objective basis for relevant clinical and basic research.
METHODS: A total of 206 patients, over 50 years old, with no lesions or variation under head and neck CT angiography were selected and divided into non-calcification group (n=70) and calcification group (n=136). The carotid siphon was reconstructed on the imaging workstation to observe the classification (“U”, “V”, “C” and “S” types) and calcification distribution, the bending angles of C4 and C5 segments as well as lumen diameter were measured.
RESULTS AND CONCLUSION: The 70 patients in the non-calcification group were at a mean age of (59.17±10.27) years, and the “U” type accounted for 35.7%, “V” type for 30.7%, “C” type for 27.2%, and “S” type for 6.4%; Among them, 33.3% patients (25/70) had the same type at both sides; the lumen diameter was (4.92±0.63) mm, and the blending angles of C4 and C5 were (87.23±16.66)° and (49.21±16.01)°. In the calcification group, the mean age was (67.39±9.32) years, and there were 41.5% of “U” type, 33.1% of “V” type, 24.3% of “C” type, 1.1% of 24.3%, and among the 136 patients, 43.4% (59/136) showed the same type at both sides; the lumen diameter was (4.90±0.44) mm, and the blending angles of C4 and C5 segments were (84.44±17.20)° and (52.57±14.16)°. There were significant differences in age and “S” type between the two groups (P < 0.05), but no statistical difference in the lumen diameter and blending angles of C4 and C5 (P > 0.05). In the calcification group, the calcification percentage of inwardly and outwardly curved regions was 13.60% and 19.01% for C4, 27.34% and 16.52% for C5, 9.94% and 13.60% for C6. The morphology of the carotid siphon is mostly seen as “U”, “V”, “C” types, and over 50% types are different at both sides. Calcification of the lumen wall is seen most in the inwardly curved region of C5 segment, followed by the outwardly curved region of C4 segment. The incidence of calcification is increased with age, which is lower in the S-type carotid siphon. The lumen diameter and blending angle of the carotid siphon show no correlation with calcifications.