Spine Anatomy
Section II. Thoracic Spine Overview
The vertebral bodies of the thoracic spine are all generally similar. As rib-bearing vertebrae (usually), there are costovertebral and costotransverse joints. These synovial joints are important clinically, in part, because they are a putative cause of pain in some patients and can demonstrate inflammatory change (similar to facet and other joints) on certain types of images. Compared to the cervical spine, the facet joints are oriented predominantly in the coronal plane. There is typically more prominent dorsal epidural fat compared to the cervical spine.
The similarity and number of thoracic vertebrae introduce the possibility of counting errors. Meticulous counting, ideally cranial to caudal beginning at the upper cervical spine, is imperative. It is important to assess for cervical ribs at C7, variable presence and size of ribs at the thoracolumbar junction, and abnormal number of thoracic vertebrae.
Unlike the cervical spine where several (C1, C2, C7) vertebrae have unique features, the majority of the thoracic vertebrae have similar anatomy with slight differences at the cranial/caudal extents. The costovertebral joints, rib-cage fixation, kyphosis, relatively prominent dorsal epidural fat, prevalence of arachnoid granulations, and tendency of disc herniations to calcify are all clinically-relevant anatomic features.
Compression Fracture & Posterior Element Edema
A patient with a mid-thoracic compression fracture (yellow arrow) and a skin marker over the focal area of pain perception (blue arrow). The posterior element edema is most directly associated with the area of pain, including the interspinous region (white arrow) and facet joints (red arrows); such posterior element edema may be superior or inferior to the level of fracture. Note that this physical correlation does not definitively establish the true pain generators and patterns of pain referral are complex.
Costovertebral Joint Bone Scan Activity
Costovertebral joint activity on 99-Tc-MDP SPECT/CT. Such activity has an unclear association with pain, but often encountered. The costovertebral joints have been proposed as possible pain generators and are generally amenable to percutaneous steroid injection, although there is little data to guide such treatment.
Reference
Verdoorn JT, Lehman VT, Diehn FE, Maus TP. DIR 2015;21:342-347
Localization within the Spinal Canal
One of the most important tasks of a radiologist in assessing spinal pathology is determining location within the spinal canal relative to the spinal cord and dura. Thus, the basic three locations are: 1. extradural; 2. Intradural, Extramedullary; 3. Intramedullary. Axial images, which show a cross-section of the spinal cord and dura, can be particularly helpful
Show giant calcified disc extrusion, meningioma, and intramedullary tumor
Additionally, the internal anatomy of the spinal cord is not exquisitely detailed on imaging, although the central gray and peripheral white matter can be roughly distinguished. The location of pathology within the spinal cord can be an important indicator of likely pathology.
Floating Fat Sign
'Floating fat.' Pediatric patient with pain after a lumbar puncture. Low platelets and imaging was performed to exclude epidural hematoma. CSF is seen infiltrating around the dorsal epidural fat. This can be seen in the thoracic and/or lumbar spine with an iatrogenic leak, such as this case, or also in the setting of spontaneous CSF leaks.
It is always important to review imaging studies for extraspinal pathology, with many important areas to scrutinize on thoracic spine examinations. Extraspinal Causes of thoracic pain include aortic syndromes, pneumonia, pancreatitis, retroperitoneal hemorrhage, scapulothoracic bursitis, and renal/urinary pathology.
Clinically-Unsuspected Aortic Dissection in an Outpatient
70-year-old male with outpatient non-contrast thoracic spine CT for subacute thoracic pain. There was scattered 'degenerative change' throughout the thoracic spine, but the major finding was unsuspected internal displacement of calcification into the aortic lumen, highly suggestive of an aortic dissection. Always evaluate the aorta if it is included on an imaging examination!
