Background The intercostal artery is thought to be shielded in the groove of the superior rib; however, the course and variability of the intercostal artery, and factors which may influence these, have not been described in vivo. Describing these variables in vivo has potentially important implications for avoiding complications during common pleural procedures.
Methods Maximum intensity projection (MIP) reformats in the coronal plane were produced from CT pulmonary angiograms, to identify the posterolateral course of the contrast opacified intercostal artery. A novel semi-automated computer segmentation algorithm was used to identify and measure distances between the lower border of the superior rib, the upper border of the inferior rib and the position of the intercostal artery when exposed in the intercostal space, and manually verified by a radiologist. Position and variability of the artery were described and then analysed for association with clinical factors using a random effects regression model.
Results 298 arteries were analysed from 48 patients (mean age 60 years). The mean lateral distance from the spine over which the artery was exposed within the intercostal space (‘unsafe artery length’) was 39 mm with wide variability (SD=10 mm, 10th to 90th centile 28 mm to 51 mm, Abstract P64 Figure 1A). At 3 cm lateral distance from the spine 16.6% of arteries were shielded by the superior rib, compared to 96.6% at 6 cm. Unsafe artery length was not associated with age, sex, rib space or side. Using regression modelling, variability of arterial position (as SD and coefficient of variation) was significantly associated with age (coeff 0.91, p<0.001) and rib space number (coeff −2.60, p<0.001) (Abstract P64 Figure 1B). Variability of arterial position was strongly negatively correlated with lateral distance from the spine (Pearson's −0.77, p<0.001).
Conclusions The intercostal artery is exposed within the intercostal space in the first 6 cm lateral to the spine; variability of its vertical position is greater in older patients and more cephalad rib spaces. This implies that pleural interventions within 6 cm lateral to the spine should be conducted with caution and that the risk of intercostal artery laceration is potentially higher in older patients and more cephalad rib spaces.