Background and Objectives Ultrasonography of the lumbar spine provides information to facilitate the placement of neuraxial anesthesia. Likewise, thoracic spine ultrasound (US) might conceivably improve the quality and safety of thoracic epidural anesthesia. The objective of this study was to advance our understanding in this area by providing a detailed description of the sonoanatomy of the thoracic spine.

Methods This was a prospective, observational, cohort study in 61 adult volunteers. We performed US scanning of all thoracic interspaces in the right paramedian sagittal oblique (PSO) and transverse median (TM) planes. The images were classified as conclusive and inconclusive, depending on the visibility of ligamentum flavum–dura mater complex (Lf-Dm). The primary outcome was the presence of conclusive images. The secondary outcomes were measurements of various distances between sonoanatomic elements. Data are presented as mean (SD), unless otherwise specified.

Results Overall, the incidence of conclusive images was higher in the PSO than in the TM plane (74.5% [15.4%] versus 37.5% [39.7%], P < 0.001). In the lower thoracic levels, 98% of images were conclusive in both planes, but the number of conclusive images decreased progressively in the upper thoracic levels, more so in the TM than in the PSO plane. The mean depth to Lf-Dm was similar when measured in both PSO (4.0 [0.7] cm) and TM planes (4.1 [0.7] cm).

Conclusions Ultrasound imaging of the thoracic spine in the PSO plane provides better views of the Lf-Dm compared with the TM plane. A upper incidence of inconclusive sonograms should be expected in the upper thoracic segments, which can be attributed to the narrower acoustic windows at these levels.