Ultrasound imaging of the thoracic spine can be challenging due to peculiarities in its anatomy. The osseous framework of the thoracic spine makes up for a narrow acoustic window with limited ultrasound visibility of the spinal canal and neuraxial structures. 1,2 Ultrasound visibility of the thoracic spine also varies depending on the plane 1 of the ultrasound imaging and which part of the thoracic spine is being imaged. 1 Ultrasound visibility progressively decreases as one moves up the thoracic spine. 1 Currently data are limited on the use of ultrasound to guide or assist thoracic epidural injections. 3,4 This chapter briefly outlines the anatomy, the technique of ultrasound imaging, and sonoanatomy of the thoracic spine relevant for thoracic epidural injection.
BASIC ANATOMY OF THE THORACIC SPINE
The thoracic spine is made up of a column of 12 vertebrae (Fig. 7–1) that makes up the midsection of the vertebral column. The thoracic vertebrae are identified by the presence of articular facets on the lateral surface of the vertebral bodies for articulation with the head of the ribs (Figs. 7–1 to 7–4). There are also facets on the transverse processes of all, except the 11th and 12th vertebrae, for articulation with the tubercle of the ribs (Fig. 7–1). The thoracic vertebrae are intermediate in size between the cervical and lumbar vertebrae, with the lower thoracic vertebrae being a lot larger than the upper thoracic vertebrae (Fig. 7–4) and the upper thoracic vertebrae (T1–T2) being similar in size to the cervical vertebrae (Fig. 7–2). The thoracic spine has a primary curvature, which is concave anteriorly, but also has a lateral curvature that is slightly concave to the left, most likely from greater use of the right upper extremity and pressure from the aorta.
Thoracic spine (lateral view). VB, vertebral body.
Second thoracic vertebra (superior, anterior, and lateral view). TP, transverse process; VB, vertebral body; SC, spinal canal; SAP, superior articular process; IAP, inferior articular process; IVN, inferior vertebral notch.
Sixth thoracic vertebra (superior, anterior, and lateral view). TP, transverse process; SVN, superior vertebral notch; SC, spinal canal; SAP, superior articular process; IAP, inferior articular process.
Twelfth thoracic vertebra (superior, anterior, and lateral view). TP, transverse process; SC, spinal canal; SAP, superior articular process; IAP, inferior articular process; SVN, superior vertebral notch; VB, vertebral body.
Typical Thoracic Vertebrae
The 2nd to 8th thoracic vertebrae are considered typical thoracic vertebrae (Figs. 7–2 and 7–3), ...