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Complications of Thoracic Discography

Fabricio Assis MD, FIPP¹, Joao Henrique Araujo MD², and Francisco Morato Dias Abreu MD¹

¹ Singular – Pain Management Center, Campinas, SP, Brazil
² Centro de Dor Criciúma, Criciúma, SC, Brazil

Introduction/History

About 5% of patients who suffer from chronic pain have thoracic pain. Often, on presentation, these cases are challenging to diagnose and treat, and can have a similar impact on disability. It is mandatory to exclude red flags; in the thoracic region, cardiovascular conditions must be considered.

Specific information about thoracic spinal pain and discs is scant. The prevalence of thoracic discogenic pain (DP) is unknown.

In the absence of obvious pathology such as deformity, infection, tumors or instability, it is often difficult to pinpoint a specific anatomic structure as the cause for the patient’s pain. In the past, the thoracic intervertebral disc (IVD) was mostly unacknowledged as a source of pain; however, it is now known that thoracic discs may account for up to 11% of all disc lesions.

Discography is a diagnostic tool and is considered the gold standard for the diagnosis of DP. It was first described in 1948 by Hirsh and Lindblom as a method of obtaining an image of a herniated disc. However, they were also able to identify reproduction of the patient’s pain while injecting contrast, in short, by applying pressure. These observations led to the use of discography in attempts to identify symptomatic discs prior to cervical and lumbar spine fusion surgeries [1]. Most of the initial excitement about discography waned after reports of very high false-positive rates, from 30 to 100% [2], but more recent studies have shown that the use and monitoring of controlled pressure during provocative discography can ensure reasonable false-positive rates [3].

Chronic thoracic pain algorithms suggest that it is usually best to perform diagnostic medial branch blocks before considering discography. This recommendation is probably due to the higher incidence of facet joint pain and the limited evidence for thoracic discography.

Anatomy of the Intervertebral Disc

Thoracic IVDs have been shown to cause chronic back pain, and although thoracic DP has been described before, it has not been thoroughly studied as yet. Understanding spine and disc anatomy is fundamentally important for proper assessment and treatment.

IVDs connect adjacent vertebrae by their vertebral bodies; thus, they play an important role in maintaining vertebral spine stability and mobility. The thoracic spine possesses important features such as the presence of the ribs and their respective joints, physiologic curvature, and mobility. IVDs fit into this elaborate architecture and are often related to pain conditions and may therefore be targeted in diagnostic and therapeutic procedures [4].

Some specific parts of the IVD and their accompanying features warrant special attention, among them:

The Nucleus Pulposus

It is a central, gelatinous, somewhat posterior portion of the IVD that represents approximately 40% of the volume of the IVD. The nucleus pulposus is made up of collagen fibers, elastin fibers, and a highly hydrated aggrecan gel. Collagen fibers are randomly distributed and elastin fibers radially organized [5].

The Annulus Fibrosus

The annulus fibrosus forms the outer layers of the IVD, representing 60% of its volume. It consists of concentric lamellae with parallel, mostly type I, collagen fibers, and elastic fibers between each lamella [6].

The Vertebral End Plates

The end plate (EP) is seen as the layer of tissue that connects the IVD to the vertebral body and can be considered part of either the former or the latter. Although the IVD may receive nutrients by diffusion from the outer layers of the AF, it seems that most of this supply comes from the bone marrow in the vertebral body through the EP [7].

Innervation and Vascularization

The IVD is virtually devoid of blood vessels and only the outermost layer of the AF receives direct blood supply. Blood vessels in the vertebral body supply the EP and the NP, while the inner layers of the AF depend on osmosis to receive nutrition and eliminate metabolic waste [4].

Innervation of the IVD is complex and there is evidence that it is not predominantly segmental via the closest dorsal root ganglion (DRG). Its afferent pathway leaves from the ventral and dorsal plexuses that are interconnected and receives contributions from small branches of the sympathetic trunk, rami communicantes, perivascular nerve plexuses of segmental arteries and the sinuvertebral branches [8].

Typically, IVD innervation accompanies the blood vessels and is therefore restricted to the outer layers of the AF. But research shows that, in patients with chronic low back pain, innervation can extend to the innermost layers of the AF and even to the NP, in 46% and 22% of patients, respectively. These nerve fibers express substance P and probably play an important role in the pathogenesis of chronic low back pain [9].

Understanding the anatomic features of IVDs can foster a better understanding of the pathophysiologic mechanisms of DP. It was only in the 1930s that IVD innervation was first identified. Since then, there has been a growing amount of data showing that IVDs are a potential source of nociception.

Indications

Discography is a diagnostic tool for evaluation of DP. Conventional imaging studies cannot determine if a degenerated IVD is painful but are useful in identifying some worrisome conditions such as infection, fracture, and tumors. Physical exam is fundamental and should include neurologic assessment.

Although IVD degeneration has some correlation with age, neither is directly correlated to discography results or prognosis. On the other hand, annular disruption and positive discography correlate to prognosis; therefore, the test can be used to rule out or plan an interventional procedure [10].

The test should be considered if the following four criteria have been met:

Pain symptoms are chronic (over 3 months)
Conservative therapy has failed
Non-invasive studies were unable to clarify the origin of the pain condition
There is no contraindication for the procedure.

Contraindications

Contraindications are similar to those applied to other spinal interventional procedures, including [11]:

Untreated psychological disorders
Patient refusal
Coagulopathy and use of anti-coagulants
Thrombocytopenia and use of anti-platelet drugs
Allergy to both iodinated and non-iodinated contrast media.

Precautions

Recommended:

Prior experience: Only pain physicians with prior experience in lumbar and cervical procedures should perform these procedures
High level of skill: The physician should be well-trained in thoracic injections on the whole, especially in thoracic discography, as they can be demanding, technically intensive, and unforgiving procedures
Informed consent: Secure patient consent before performing the procedure
Thorough study of anatomy: Before thoracic discography, do complete physical exam and review complementary imaging tests
Allergy check: Ask patient about any allergies or skin diseases
Equipment preparation: Equipment and medications should be prepared in advance
Patient monitoring: Monitor vital signs non-invasively
Oxygen administration: Administer by nasal cannula
Sterile procedure: Follow sterile techniques throughout intervention
Cefazolin (within 60 min before incision) 1–2 g or Vancomycin (within 2 hours before incision), 20 mg/kg single dose or Clindamycin (within 60 min before incision): 600–900 mg
Chlorhexidine-alcohol–based skin preparation.

Technique

Before the Procedure

Informed consent is mandatory, and it is especially important to ensure the patient grasps the concept of the diagnostic nature of the procedure. The procedure should be performed in a surgical theater and sterile technique should be followed as if it were an open surgical procedure. Assistance of an anesthesiologist is recommended.

Patient is placed in prone position with a pad under the thorax, arms positioned alongside the head. Asepsis and antisepsis with chlorhexidine solutions and placement of sterile surgical drapes is mandatory. The physician and all assistants must wear full surgical garb.

Tunnel Vision Technique

Selected IVD must be identified and placed in the center of the fluoroscopic image by counting down from the 1st or the 12th thoracic vertebra. If there is a known or suspected anatomic variation, fluoroscopic imaging must be compared to the MRI study.

Next, C-arm is tilted for optimal visualization of the IVD – aligning the inferior end plate of the superior vertebrae (Figure 27.1). Following this step, lateral oblique can be done to either side. The radiographic reference is to place the superior articular process (SAP) in the middle of the vertebral body. We aim to open up a tiny space between the SAP and the head of the rib (Figure 27.2).

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