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1 Department of Radiology, University of North Carolina School of Medicine, Campus Box 7510, Chapel Hill, NC 27599-7510.
Received June 13, 2005;
accepted after revision August 18, 2005.
SAM and CME available online at
www.arrs.org.
Abstract
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The educational objectives of this continuing medical education activity are to describe the normal anatomy of the brachial plexus, to name the most common symptoms associated with a brachial plexopathy, to describe the most common imaging findings resulting from trauma to the brachial plexus, to describe the imaging manifestations of common neoplasias affecting the brachial plexus, and to also describe the imaging findings and symptoms related to irradiation-induced brachial plexopathies.
Conclusion
In this article, I have illustrated and described the normal anatomy of the brachial plexus; the most common symptoms related to brachial plexopathy; and imaging findings related to trauma, tumors, and irradiation affecting the brachial plexus.
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Description of the Images
T2-weighted MR images depict pseudomeningoceles, which appear as a tear in
the meningeal sheath that surrounds the nerve roots with extravasation of CSF
in the neighboring tissues. Because pseudomeningoceles are filled with fluid,
they are easily identifiable on T2-weighted MR images (Figs.
1,
2A, and
2B).
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| QUESTION 1 Regarding the utility of different imaging techniques to evaluate traumatic injuries of the brachial plexus, which of the following is true?
QUESTION 2 The brachial plexus is formed by which of the following?
QUESTION 3 Which of the following statements regarding the symptoms of a brachial plexopathy is true?
QUESTION 4 Regarding the goals of treatment of the brachial plexus, which of the following statements is false?
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Solution to Question 1
A recent study evaluated 35 patients with a total of 175 traumatic brachial
plexus avulsions [1]. All
patients were evaluated with CT and MRI after undergoing myelography, and both
techniques were found to have a sensitivity of approximately 93% for the
detection of these injuries. When evaluated prospectively, both imaging
methods performed equally (thus, Options A and B are not true and
Option C is true). This is true only for traumatic avulsions, of which
more than 80% will develop pseudomeningoceles. These pseudomeningoceles
represent a tear in the meningeal sheath that surrounds the nerve roots and
extravasation of CSF into the neighboring tissues. Because they are filled
with fluid, they are easily identifiable on T2-weighted MR images (Figs.
1,
2A, and
2B). They also fill with
contrast material on myelography, a fact that facilitates their identification
on postmyelography CT [2].
In infants, the use of MRI is recommended because postmyelography CT is a minimally invasive procedure and adequate information is generally provided by noninvasive MRI. MR myelography is helpful in depicting pseudomeningoceles in a fashion similar to conventional myelography, but it is a supplemental method because most of the lesions are identifiable on MRI (thus, Option D is not true). In addition, MRI may show edema of the brachial plexus in stretching injuries (Fig. 3).
In another recent study, neurosurgeons were asked which method they prefer and use to evaluate the avulsed brachial plexus before surgery [3]. Eighty percent prefer postmyelography CT, 20% prefer MRI, and 41% use both methods, whereas the remaining participants expressed no preference. In addition, all agree that chest radiographs are indispensable in evaluating for diaphragmatic paralysis, which generally implies an irreparable lesion of the brachial plexus (Option E is not true).
Solution to Question 2
The anterior spinal rootlets are motor, whereas the posterior rootlets are
sensory; both arise from the spinal cord
[4]. After the level of the
dorsal root ganglia (which are in the neural foramina), the anterior and
posterior rootlets merge and immediately split into anterior and posterior
rami, both of which contain a mixture of motor and sensory elements. Thus, the
anterior rami are located just beyond the neural foramina and will continue to
form trunks of the brachial plexus. The posterior rami do not form the
brachial plexus and innervate the paraspinal muscles.
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The levels of the nerve roots from which the brachial plexus is formed may vary slightly [4-6]. In some patients, the brachial plexus is formed by the anterior rootlets of C4 through C7 (termed a "prefixed" brachial plexus), while in others it is formed by the anterior rootlets of C6 through T2 (termed a "postfixed" brachial plexus). The brachial plexus is never formed by all the cervical nerve roots (Option D is not correct). The slight variations regarding the formation of the brachial plexus may slightly affect the patient's physical examination, but these variations are of little importance in the imaging evaluation of the brachial plexus [7].
Solution to Question 3
As a general rule, most brachial plexopathies present with vague and
nonspecific symptoms (Option A is not correct)
[8]. For this reason, lesions
affecting the brachial plexus may remain undiagnosed in many patients for long
periods of time. There are, however, some general rules regarding symptoms due
to a brachial plexus lesion that can be helpful when assessing patients with
brachial plexopathies. Purely or mostly motor symptoms are generally seen in
young patients (Option B is correct). These symptoms are commonly due
to stretching injuries or avulsions. Associated findings may help to localize
the site of injury (Table 1).
Stretching, also called "neuropraxia," injuries are commonly seen
in neonates, particularly after breech deliveries with shoulder dystocia
[8,
9]. Stretching injuries are
also common after vehicular crashes, particularly motorcycle crashes, which
are also common in young male patients.
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Complete flaccid paralysis of an upper extremity is seen after avulsion of a brachial plexus [10]. Although 80-90% of patients with neuropraxia injuries will recover some function, the loss of function is permanent in patients with avulsions. In adults, primary and secondary tumors are the most common cause of a brachial plexopathy [11]. These tumors infiltrate the brachial plexus and commonly extend into the spinal column and neural foramina, resulting in both sensory and motor symptoms (Option C is not correct). Indeed, in older patients, a brachial plexopathy is most often mixed (sensory and motor).
Prior radiation therapy, particularly for breast or lung cancer, is a common cause of brachial plexopathy. In most of these patients, the symptoms are usually sensory (thus Option D is not correct). The motor innervation provided by the brachial plexus is described in Table 2.
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Solution to Question 4
Successful treatment of brachial plexus injuries entails a multifaceted
approach that includes physical rehabilitation and, when indicated, surgical
intervention (Option A is true, and thus not the correct answer)
[12]. The cornerstone of all
brachial plexus injuries is physical rehabilitation. Although this type of
therapy may have a significant impact in treating stretching injuries,
particularly those in infants, its results are more limited in adults and in
patients in whom the brachial plexus has been avulsed.
For supraganglionic nerve avulsions, there is generally no treatment, but early experience with microanastomoses of the roots and of the roots to the spinal cord is promising [13]. In most patients, some nerve regeneration will occur. Although this nerve regeneration leads to useful muscle function in only one third of patients, it leads to control of pain in most patients (Option B is true).
Juxtaforaminal and more distal avulsions may be treated with microsurgical grafting and anastomoses [14]. Grafting and anastomoses may be done using the phrenic, spinal accessory, and medial pectoral nerves and the sensory and motor branches of the intercostal nerves and even the contralateral brachial plexus. Injuries to the C5 and C6 nerve roots are the most common and result in abnormalities of glenohumeral abduction, exorotation, and biceps function. Thus, restoration of biceps and shoulder function is important in the treatment of brachial plexus injuries (Options C and D are true) [15]. Prolonged immobilization of the affected arm and shoulder needs to be avoided because it may result in a frozen extremity (thus, Option E is false and is the correct answer).
Injuries to the C7, C8, and T1 nerve roots are relatively less common and affect the function of the lower arm and hand. Hematomas can compress the brachial plexus, and some hematomas may be amenable to surgical drainage. Similarly, aneurysms and pseudoaneurysms of the subclavian artery may result in a compressive plexopathy and may need to be treated predominantly with stenting without or with embolization to preserve the artery's native lumen.
Conclusion
The accurate anatomic identification of the site of injury to the brachial
plexus relies mostly on MRI. It is important to know the clinical symptoms of
brachial plexus injury because they may help to pinpoint the area of damage.
In most infants and young children, a brachial plexopathy is due to trauma and
most of the symptoms are motor ones; however, in adults, the most common
lesions are related to underlying tumors and to their treatment. In these
patients, the brachial plexopathies tend to be both motor and sensory (mixed
type). Patients with an avulsion at the root entry zone (seen mostly as
pseudomeningoceles) have a grave prognosis, and surgery is not feasible in
most of these patients. Lesions distal to the roots may be amenable to
grafting and anastomoses. Restoration of the function of the shoulder and
elbow and control of phantom pain are the most important goals of
treatment.
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Solution to Question 1
"Pancoast's tumor" is a term used to describe a bronchogenic
neoplasia that arises in the apical pleuropulmonary groove (the superior
sulcus); most are non-small cell cancers (squamous cell carcinomas,
adenocarcinomas, or large cell carcinomas)
[16]. They generally progress
by direct extension and invasion of the brachial plexus, intercostal nerves,
stellate ganglion, neighboring ribs, and vertebrae. Involvement of the
brachial plexus and of the adjacent vertebrae is seen in fairly advanced cases
(thus, Options A and B are not correct)
[17]. Supraclavicular
lymphadenopathy denotes an N3 stage (according to the TNM classification) and
also represents an advanced stage of the disease (Option C is not
correct).
Perhaps the earliest sign of extrathoracic and brachial plexus involvement is invasion of the interscalene fat pad by the tumor (Option D is correct). This fat pad normally lies between the an-terior and the middle posterior scalene muscles just cephalad to the lung apex. The trunks of the brachial plexus are found in this fat pad. On coronal T1-weighted MR images, the interscalene fat pads have a triangular appearance and should always be present, bright in signal intensity, and bilaterally symmetric (Fig. 6). Obliteration of this normal bright fat signal by a mass arising in a lung apex generally implies invasion of the brachial plexus, and surgical resection may no longer be feasible [17].
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| QUESTION 1 The earliest sign of brachial plexus involvement by a Pancoast's tumor (superior sulcus tumor) is which of the following?
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Tumors that involve the brachial plexus include primary tumors that arise from the brachial plexus (nerve and nerve sheath tumors that may be benign or sarcomatous) [18] (Fig. 7). Secondary tumors are most common in adults and include Pancoast's tumors, metastases (generally from breast carcinoma), lymphoma, leukemia, and multiple myeloma (from adjacent bone involvement) (Fig. 8). Lipomas and other tumors may arise outside the brachial plexus and may compress the brachial plexus (Figs. 9A, and 9B). Nontumoral masses, such as aneurysms and pseudoaneurysms, may also result in compressive brachial plexopathies (Figs. 10A, and 10B). The method of choice in the evaluation of suspected brachial plexus tumors is MRI [19].
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Conclusion
A variety of masses may affect the brachial plexus primarily or
secondarily. The most common primary tumors are schwannomas. Neurofibromas and
sarcomas are rare unless the patient has underlying neurofibromatosis 1. Of
the lung tumors, the superior sulcus ones (Pancoast's type) tend to involve
the brachial plexus early; this indicates a grave prognosis and in many
patients makes the tumor not resectable. Metastases (mostly from breast
carcinoma) may invade or compress (or both) the brachial plexus. Occasionally,
some masses result in a plexopathy just by compression of the nerves.
Large tumors commonly result in a compressive neuropathy. Lipomas tend to be soft and need to attain a large size before producing symptoms. Aneurysms and pseudoaneurysms of the subclavian artery may compress the brachial plexus and also produce symptoms. It is critical to show involvement or lack of involvement of the brachial plexus in all patients with tumors in this vicinity because involvement of the nerves generally places the patients in a nonsurgical category.
| QUESTION 1 Which one of the following statements is false regarding this patient's disease?
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Solution to Question 1
Inflammatory processes affect the brachial plexus relatively commonly. One
of the most common inflammatory processes occurs after irradiation, generally
with doses of 6,000 cGy or more
[20]. Unlike carcinomas that
tend to present as focal masses, postradiation plexopathies show loss of
clarity and distortion of the brachial plexus (particularly its branches,
cords, and divisions with sparing of the trunks and roots), high T2 signal
intensity, and mild contrast enhancement. Thus, the findings shown in
Figure 11 are unlikely to be
due to the patient's primary carcinoma and are most likely the sequela of
treatment (Option A is true). Metastases to the brachial plexus nearly
always present as discreet masses and not as diffuse thickening (Option
B is false and, thus, is the correct answer).
Postirradiation brachial plexopathies may be acute and present within 6 months after initiation of irradiation or be delayed and manifest 6 months after termination of treatment. The former type of plexopathy is believed to be due to vascular ischemia and tends to be permanent, whereas the latter is generally a transient and often reversible process (Option C is true). As a general rule, most irradiation-induced brachial plexopathies manifest 5-30 months after treatment (peak period, 10-20 months).
The differential diagnosis for the findings described for the case presented here includes viral neuritis, allergic (generally drug-induced) neuritis, and infections (Option D is true) [21, 22]. Viral plexitis is more commonly found in men between the ages of 30 and 70 years and resolves 6-12 weeks after presentation without sequelae (Fig. 12). The brachial plexus may also be involved in heredofamilial plexitis, such as hypertrophic neuropathies (the most common probably being Charcot-Marie-Tooth disease) [23]. In these processes, the brachial plexus will appear diffusely thick and hyperintense on T2-weighted images (Fig. 13). Chronic inflammatory demyelinating is another of the relatively common hypertrophic polyneuropathies that may present identical imaging findings. Diffusion nerve thickening in children may be due to Dejerine-Sottas disease.
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Conclusion
Inflammatory brachial plexopathies are relatively uncommon, and, when
found, most are secondary to the effects of prior therapeutic irradiation.
Postirradiation plexopathy may be acute and irreversible or chronic and
reversible. Both have similar imaging findings: diffuse thickening and high T2
signal intensity. These findings may be at times difficult to separate from
diffuse tumor infiltration, particularly when contrast enhancement is present.
Viral plexopathies tend to be a diagnosis of exclusion and generally present
acutely and resolve spontaneously after treatment with just antiinflammatory
drugs. If the nerves of the brachial plexuses are diffusely thickened, the
differential diagnosis needs to include the hypertrophic polyneuropathies.
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