Traumatic brachial plexopathy

The Scar Solution Natural Scar Removal

Scar Solution Book By Sean Lowry

Get Instant Access

Overview

Traumatic brachial plexopathy, which accounts for approximately 50% of cases, can be caused by compression, stretching, or, in its most extreme form, disruption of nerves or avulsion of nerve roots, with or without fractures involving the cervical spine or clavicle [4]. If fracture is suspected, a radiograph (clavicle) or noncontrast CT with multiplanar reformatting (cervical spine) should be the initial study [4]. MRI is the study of choice for cases in which fractures of the clavicles or ribs may be causing extrinsic compression on the brachial plexus, typically the upper trunk

(Fig. 1), but suspected nerve root avulsion requires a different imaging algorithm.

The main cause of cervical and upper thoracic nerve root avulsion is a traction-induced injury, primarily from motorcycle accidents in adults [5] and shoulder dystocia in neonates. The prompt and accurate diagnosis of traumatic nerve root avulsions is essential to determine which patients might benefit from neurosurgical reconstruction. The prognosis and treatment options depend on differentiating preganglionic injuries from nerve

Upper Trunk Brachial Plexopathy
Fig. 1. Coronal T1 (A) and fat-suppressed FSE T2 (B) images of the right brachial plexus showing mass effect on the upper trunk from a displaced clavicle fracture (arrow). The upper trunk is enlarged and edematous.

root avulsion versus more distal postganglionic lesions from other causes [6].

Clinical examinations and electromyography (EMG) are occasionally inaccurate at determining the level or levels of the damaged roots because of normal anatomic variations within the brachial plexus [7-9]. The gold-standard test for determining nerve root avulsion remains the exploratory laminectomy, during which the surgeon directly evaluates the integrity of the dorsal and ventral nerve roots [10]. Because of the morbidity and mortality risks involved with such a procedure, few patients with suspected nerve root avulsions choose to undergo it.

Surgeons therefore have turned to neuroradio-logic imaging procedures to determine the presence of nerve root avulsions. Traditional imaging modalities, such as radiography, MRI, and CT, have had mixed success in visualizing nerve roots; whereas these modalities are quite good at detecting the pseudomeningoceles associated with avulsions, reliably visualizing the nerve roots has been a persistent problem. Recent improvements in CT and MRI technology have made the reliable visualization of the roots possible on a routine clinical basis. These various imaging techniques are described in the following sections.

Plain-film myelography

With the advent of safe contrast agents for intrathecal injection, it became possible to detect nerve root avulsions using plain-film myelo-graphic techniques. Several classic studies served as the foundation for noninvasive detection of cervical nerve root avulsion [11-13]. These plain-film techniques have become less important, however, because new CT methods provide better resolution and more accurate categorization of nerve root status. Therefore, these plain-film techniques will not be discussed further.

CT myelography

Early CT equipment, although revolutionary, suffered from many limitations, including large slice thicknesses. As a result, routine CT myelog-raphy was typically performed with a standard slice thickness of 5 mm, because that was the best the scanners could achieve at the time (eg, see references [14,15]). One study even concluded that plain-film myelography was more sensitive for detecting avulsions than CT myelography in the absence of pseudomeningocele [16]. These CT myelogram protocols still remain in common use

Myelogram With Pseudomeningocele

Fig. 2. Standard-resolution CT myƩlographie images (5 mm thick). Note that only the right exiting roots are visualized at this level (arrows); the left exiting roots are not seen. Also, because of the thickness of the slice, the dorsal roots for the adjacent level are also seen (arrowheads) but cannot be followed out to the neural foramina.

Fig. 2. Standard-resolution CT myƩlographie images (5 mm thick). Note that only the right exiting roots are visualized at this level (arrows); the left exiting roots are not seen. Also, because of the thickness of the slice, the dorsal roots for the adjacent level are also seen (arrowheads) but cannot be followed out to the neural foramina.

today. Although nerve roots are occasionally visualized using such thick slices, more often they are obscured because of partial volume artifacts, which render the roots undetectable. Fig. 2 shows a typical CT myelogram using a thickness of 5 mm; the roots are barely visible.

Because most cervical rootlets are approximately 1 mm thick, ideally they should be imaged with a 0.5-mm slice thickness to ensure adequate sampling (Nyquist limit, a basic rule of imaging physics). As the CT technology progresses, this theoretic possibility is becoming a reality. Currently available multidetector CT scanners can routinely scan with 1.25-mm slice thicknesses, and advanced 64-detector CT scanners will soon be available that can routinely scan slices as thin as 0.5 mm. Fig. 3 shows examples of partial and complete nerve root avulsions obtained using these thin-slice techniques. Two reconstruction algorithms are shown: a "hard-bone kernel'' is used to preserve edge details at the expense of additional noise, whereas a "soft standard kernel'' is used to reduce image noise at the expense of edge details. In the current authors' experience, hard kernels are more effective at detecting avulsions, because they accentuate the edges of the nerve roots relative to the adjacent myelogram dye.

Avulsion Cervical Nerve Root Mri

Fig. 3. High-resolution CT myelographic images (1.25 mm thick) of complete and partial nerve root avulsions. (A) Normal left dorsal and ventral roots (arrows) but complete avulsion of the right dorsal and ventral nerve roots (arrowhead) are shown. (B) Partial avulsion of the left ventral root (arrowhead). Note the thinning of the left ventral root relative to the right. The left dorsal root is completely avulsed. Note that (A) was reconstructed using soft kernels and (B) was reconstructed using a hard kernel. Image A therefore appears more blurry but less noisy than image B.

Fig. 3. High-resolution CT myelographic images (1.25 mm thick) of complete and partial nerve root avulsions. (A) Normal left dorsal and ventral roots (arrows) but complete avulsion of the right dorsal and ventral nerve roots (arrowhead) are shown. (B) Partial avulsion of the left ventral root (arrowhead). Note the thinning of the left ventral root relative to the right. The left dorsal root is completely avulsed. Note that (A) was reconstructed using soft kernels and (B) was reconstructed using a hard kernel. Image A therefore appears more blurry but less noisy than image B.

Realistically, no imaging technique is without artifacts. Occasionally, vessels in the thecal sac mimic nerve roots; a serpiginous vessel could easily be interpreted as a nerve root on static images. Likewise, scar tissue can occasionally mimic a nerve root, because the path of the scar tissue

may be parallel to the nerve roots. Fig. 4 shows some of these pitfalls. In the authors' experience, by using the workstation to scroll through the image stack, in most cases we are able to visually trace the origin of the root from the cord and track it through the cerebrospinal fluid (CSF) into the neural foramen. Thus, even with high-quality source images, there can be difficulties confirming the presence of an avulsion.

Three-dimensional reconstructions may be helpful. Fig. 5 shows examples of complete nerve root avulsions as shown on coronal reconstructions performed using a postprocessing workstation. A curved-reformatting technique is used to "straighten" the cervical spine, allowing all the nerve roots to be visualized in a single slice. These reconstructions are labor-intensive, and require approximately 20 to 30 minutes for an experienced CT technologist to complete. Good reconstructions can be obtained; often, however, beam-hardening artifacts from the shoulders obscure details at the C7 and T1 levels, making interpretation difficult. Therefore, axial images are currently preferred for making determinations of nerve root avulsion.

MRI "myelography"

Magnetic resonance myelographic techniques are simply T2-weighted MRI sequences that accentuate the contrast between the spinal cord and roots and the adjacent CSF. These include regular spin-echo and fast spin-echo (FSE) techniques, and have various names depending on the particular MRI equipment vendor. Occasionally, gradient echo techniques are used, but these are less helpful because of reduced signal-to-noise ratios (SNRs) and lower native resolution.

Traditional MRI examinations also have suffered from partial volume artifacts; relatively thick slices are necessary to obtain acceptable SNRs at the expense of detecting the avulsions themselves. Furthermore, MRI also suffers from other artifacts, including patient motion (eg, swallowing, tremor, respiratory, cardiac) and CSF pulsation artifacts, which can also degrade image quality [17]. Fig. 6 shows some of these typical artifacts.

Several MRI studies have used axial 5-mm-thick slices, with variable success at detecting avulsions [18-24]. Others have tried oblique acquisitions in an attempt to minimize the effects of these artifacts. For example, Doi et al [25] used a thin-slice overlapping coronal oblique imaging

Fig. 4. High-resolution CT myelographic images (A, 1.25 mm thick; B, 0.675 mm thick, in a 5-month-old patient). (A) A linear density is shown lying on the posterolateral wall of the right neural foramen (arrows), presumably the right dorsal root. This ''root'' could not definitely be traced back to the cord, however, and therefore it probably represented scar tissue. The interpretation was further complicated by a small vessel (arrowhead), which touched the cord in a more rostral location, mimicking the origin of the right posterior root. (B) Several small vessels (arrowheads) are shown along the dorsal and ventral surface of the cord; these can occasionally be confused with nerve roots (arrows). The left dorsal and ventral roots are completely avulsed, although a root remnant is noted within the small left pseudomeningocele (curved arrowhead).

Root Avulsion Myelo

Fig. 5. Coronal reconstructions of high-resolution CT myelographic data sets. The cervical spine has been electronically "straightened" using a reformatting technique, such that all the dorsal and ventral roots are in a single plane. (A) All of the dorsal roots areshown in a single image (arrows). Note that the right C7 dorsal root is absent (arrowhead). (B) The ventral roots are shown in a single image (arrows). In this case, the right C6 and C7 roots (arrowheads) are absent. A small density is present in the expected location of the C6 root; this was believed to be scar tissue.

Fig. 5. Coronal reconstructions of high-resolution CT myelographic data sets. The cervical spine has been electronically "straightened" using a reformatting technique, such that all the dorsal and ventral roots are in a single plane. (A) All of the dorsal roots areshown in a single image (arrows). Note that the right C7 dorsal root is absent (arrowhead). (B) The ventral roots are shown in a single image (arrows). In this case, the right C6 and C7 roots (arrowheads) are absent. A small density is present in the expected location of the C6 root; this was believed to be scar tissue.

technique to better delineate the nerve roots. Although successful, the examination time was very long (25 min). In general, the thinner the MRI slice, the better the accuracy for detecting avulsions.

A relatively new MRI technique has recently become available called true fast imaging with steady-state precession (true-FISP), a variation of an older steady-state technique known as constructive interference in steady state (CISS). For an excellent outline of the history of true-FISP, see Gasparotti et al [6]. This technique generates good T2-weighted contrast with extremely thin slices while maintaining good SNR. The resulting

1- to 2-mm-thick slices are potentially quite useful for noninvasively evaluating nerve root avulsions [26]. Fig. 7 shows some images acquired with these techniques. As for all imaging techniques, however, these sequences are prone to artifact, with prominent "wrapping" artifacts contaminating the images at the edges of the image volume (eg, top and bottom slices for axial images). This is an active area of sequence development, and improvements should be commercially available within the next few years.

Was this article helpful?

0 0
How To Reduce Acne Scarring

How To Reduce Acne Scarring

Acne is a name that is famous in its own right, but for all of the wrong reasons. Most teenagers know, and dread, the very word, as it so prevalently wrecks havoc on their faces throughout their adolescent years.

Get My Free Ebook


Post a comment