Anatomy of the Thoracic Outlet (Anatomic Inlet)
Statement C is false: The body of the seventh cervical vertebra forms the posterior boundary of the thoracic outlet.
The thoracic outlet (anatomic inlet) is a critical anatomical space through which important neurovascular structures pass between the thorax and upper extremity. Understanding its correct anatomical boundaries is essential for diagnosing and managing thoracic outlet syndrome.
Correct Anatomical Boundaries of the Thoracic Outlet
- The manubrium sterni forms the anterior border of the thoracic outlet 1
- The first ribs form the lateral boundaries of the thoracic outlet 2
- The first thoracic vertebra (T1), not the seventh cervical vertebra (C7), forms the posterior boundary of the thoracic outlet 2
- The subclavian vessels and lower trunk of the brachial plexus pass through the thoracic outlet over the first rib 3
- The esophagus and trachea pass through the thoracic outlet 1
Understanding the Thoracic Outlet Spaces
The thoracic outlet contains three distinct anatomical spaces where neurovascular compression can occur:
- The interscalene triangle (between anterior and middle scalene muscles) 4
- The costoclavicular space (between clavicle and first rib) 4
- The subcoracoid or pectoralis minor space (beneath the pectoralis minor muscle) 2
Clinical Relevance of Thoracic Outlet Anatomy
Understanding the correct anatomy of the thoracic outlet is crucial for:
- Proper diagnosis of thoracic outlet syndrome (TOS) variants 3
- Accurate interpretation of imaging studies used to evaluate TOS 5
- Successful surgical approaches for thoracic outlet decompression 6
Common Anatomical Variations
Several anatomical variations can predispose to thoracic outlet syndrome:
- Presence of cervical ribs 4
- Fibromuscular bands 3
- Variations in scalene muscle insertions 3
- Hypertrophy of scalene or pectoralis minor muscles 4
Diagnostic Imaging of the Thoracic Outlet
Various imaging modalities can evaluate thoracic outlet anatomy:
- MRI/MRA can visualize neurovascular structures in both neutral and stressed positions 5
- CT/CTA can identify bony abnormalities and vascular compression 5
- Ultrasound with dynamic maneuvers can demonstrate vascular compression in real-time 4
The false statement is C because the first thoracic vertebra (T1), not the seventh cervical vertebra (C7), forms the posterior boundary of the thoracic outlet.