What area is recommended for an MRI to diagnose thoracic outlet syndrome, the neck or the brachial plexus?

MRI of the Brachial Plexus is Recommended for Diagnosing Thoracic Outlet Syndrome

A dedicated MRI of the brachial plexus is the recommended imaging modality for diagnosing thoracic outlet syndrome, not a neck MRI. 1, 2

Rationale for Brachial Plexus MRI

MRI is the mainstay of plexus imaging for thoracic outlet syndrome for several key reasons:

• It provides superior definition of intraneural anatomy and can localize pathologic lesions when electrophysiologic and physical findings are nonspecific 1
• It allows evaluation of the brachial plexus, muscular attachments, and sites of compression in the thoracic outlet 1
• It can demonstrate causative lesions of neurogenic TOS, including cervical ribs, congenital fibromuscular anomalies, and muscular hypertrophy 1
• It can identify brachial plexus compression in the costoclavicular, interscalene, and pectoralis minor spaces 2

Specific MRI Protocol for Thoracic Outlet Syndrome

The imaging protocol should include:

• High-resolution T1-weighted and T2-weighted sequences in sagittal and axial planes 1
• Evaluation in both neutral and arms-abducted positions to demonstrate dynamic compression 1
• Turbo spin-echo T2-weighted or STIR sequences to evaluate for alternative diagnoses 1
• Orthogonal views through the oblique planes of the plexus 1

Why Not a Neck MRI?

A standard neck MRI is insufficient because:

• Imaging acquisition for the brachial plexus differs significantly from sequences used in a standard neck MRI 1
• A dedicated brachial plexus MRI includes specific positioning and sequences to evaluate the entire course of the plexus through the thoracic outlet 1
• Standard neck MRIs may miss fibrous bands and other subtle anatomical anomalies that compress the brachial plexus 3

Diagnostic Value of Brachial Plexus MRI

Brachial plexus MRI has demonstrated high diagnostic value:

• It can visualize fibrous bands compressing the brachial plexus with high positive predictive value 3
• It can detect increased T2W signal within compressed plexus portions (C8 spinal nerve, inferior trunk, or medial cord), confirming diagnosis 3
• It has shown 79% sensitivity and 87.5% specificity in identifying brachial plexus deviation in symptomatic patients 4

Additional Imaging Considerations

While brachial plexus MRI is the primary recommendation:

• Chest radiography should be performed first to identify osseous abnormalities 2
• Ultrasound duplex Doppler may be used as a second-line imaging modality to evaluate vascular compression 2
• CT with IV contrast may be considered if vascular complications are suspected 2

Common Pitfalls to Avoid

• Ordering a standard neck MRI instead of a dedicated brachial plexus MRI protocol
• Failing to include dynamic positioning (neutral and arms-abducted)
• Not communicating the specific clinical suspicion of thoracic outlet syndrome to the radiologist
• Relying solely on imaging without correlating with clinical symptoms and electrophysiological studies

In conclusion, when thoracic outlet syndrome is suspected, a dedicated MRI of the brachial plexus with appropriate positioning and sequences is essential for accurate diagnosis and should be ordered rather than a standard neck MRI.