CERVICOTHORACIC JUNCTION: BRACHIAL PLEXUS BENIGN AND MALIGNANT TUMORS
- The origin of a brachial plexopathy is often not understood from the physical examination and clinical circumstances and may acutely threaten one or more other important and sometimes vital functions.
- Imaging can most often provide a very likely diagnosis.
- Imaging is critical to proper medical decision making beyond the diagnosis.
- Imaging-guided biopsy may be useful in more difficult diagnostic cases.
The general approach to mass lesions of the cervicothoracic junction (CTJ) is presented in Chapter 163 and should be reviewed at this time if necessary. This chapter presents examples of the benign and malignant tumors that occur in the brachial plexus in both pediatric and adult patients. These tumors may present as a plexopathy and/or as a mass that might potentially produce a plexopathy.
ANATOMIC CONSIDERATIONS IN DIFFERENTIAL DIAGNOSIS
The anatomy of the brachial plexus and its relationship to the CTJ is presented initially in Chapter 149. This anatomy is also presented in a focused review in Chapter 163 as a foundation for the diagnostic approach to masses of the CTJ region that involve the brachial plexus. Those sources of anatomy information should be reviewed at this time, if necessary. The zones of the plexus at risk for compression are discussed in Chapter 165.1,2
Techniques and Relevant Aspects and Pros and Cons
The detailed factors related to producing optimal imaging strategies and protocols for this region of anatomy are discussed in detail in Chapters 149 and 163. In summary, ultrasound is of limited use in brachial plexus masses except when the plexopathy is accompanied by signs and symptoms due to possible vascular occlusion that might be monitored with Doppler techniques. Magnetic resonance imaging (MRI) is the primary diagnostic tool in most instances of plexopathy when there is not an acute vascular component to the presentation.
The ideal MRI pulse sequence choices for a brachial plexus study would be those done with homogenous fat suppression across the range of the required T1 and T2 weighting necessary for a definitive study. Unfortunately, this remains a goal even when optimal receiver coil design is available because of the inhomogeneity of the B0 magnetic field related to coil loading challenges in this odd-shaped anatomic region. Newer parallel imaging water/fat separation techniques show some promise for improvement over frequency-selective fat suppression, but widespread application and validation of this approach for brachial plexus evaluation is not currently available. So, while fat-suppressed images are often “recommended” for brachial plexus evaluation, they are often unacceptably degraded and considerably prolong the scanning session, often with limited additional yield of diagnostic information.
Axial acquisitions remain the mainstay for basic analysis. Those images must include both sides if subtle pathologic changes must be detected. Moreover, acquisitions must include the entire axillary sheath whenever causative pathology might involve the distal brachial plexus. Coronal images are useful. Sagittal images are overrated for their utility and the first thing that can be eliminated in these protocols that are often far too complex. Studies must frequently include acquisitions with closely coupled receivers, such as dedicated shoulder coils, for the best images. These more localized techniques eliminate the ability to compare both sides comprehensively unless multiplexed in a manner that allows both sides to be studied with the highest possible detail.
In summary, excellent-quality, definitive brachial plexus imaging is not simple to accomplish efficiently when the goal of the study is to exclude pathology with a high degree of confidence.
DIAGNOSTIC APPROACH TO BRACHIAL PLEXUS MASSES
General Manifestations and Findings
Computed Tomography and Magnetic Resonance Imaging
The imaging appearance of the mass in question will vary with its specific etiology. Solid masses are the most common, and these will vary greatly in enhancement pattern and degree of vascularity and may have regressive changes due to hemorrhage and/or necrosis. Calcification may be present and harder to recognize on MRI than on computed tomography (CT). Some of these masses have well-defined margins, and some will have irregular or infiltrative margins that suggest a malignant or inflammatory (Chapter 166) etiology or some sort of reactive change.
In general, brachial plexus masses will fall into one of two morphologic categories:
- A well-circumscribed mass (Fig. 167.1)
- An infiltrative process with margins that extend beyond the margins of individual roots, trunks, and cords of the plexus (Figs. 167.2 and 167.3)