What causes enlargement and dilatation of the anterior humeral circumflex artery?

Causes of Enlargement and Dilatation of the Anterior Humeral Circumflex Artery

The most common causes of enlargement and dilatation of the anterior humeral circumflex artery include trauma, aneurysm formation, arteritis/vasculitis, and degenerative vascular diseases.

Pathophysiological Mechanisms

The anterior humeral circumflex artery (AHCA) plays a critical role in the vascular supply to the humeral head, though it provides less overall blood supply (36%) compared to the posterior humeral circumflex artery (64%) 1. Enlargement and dilatation of this vessel can occur through several mechanisms:

1. Traumatic Causes

• Direct trauma to the shoulder region
• Repetitive microtrauma in overhead athletes, particularly pitchers 2
• Fractures of the proximal humerus disrupting the vascular architecture
• Chronic compression or impingement of the vessel

2. Aneurysmal Disease

• True aneurysms - degenerative weakening of all arterial wall layers
• False aneurysms (pseudoaneurysms) - typically post-traumatic
• Embolizing aneurysms - can lead to distal occlusion 3

3. Inflammatory Conditions

• Vasculitis affecting medium-sized vessels:
  • Giant cell arteritis/Takayasu's arteritis 4
  • Polyarteritis nodosa
  • Behçet's syndrome
  • Wegener's granulomatosis

4. Degenerative Vascular Diseases

• Arteriomegaly - generalized arterial enlargement 4
• Fibromuscular dysplasia affecting non-coronary arterial beds 4
• Erdheim's cystic medial necrosis 4
• Connective tissue disorders:
  • Marfan syndrome
  • Ehlers-Danlos syndrome

5. Anatomical Variations

• Abnormal origin patterns of the circumflex humeral arteries 5
• Compensatory enlargement due to occlusion of other vessels

Clinical Significance

Enlargement of the AHCA is clinically significant because:

1. The AHCA provides the anterolateral ascending branch that forms the arcuate artery, which is crucial for humeral head perfusion 6

2. Aneurysms of the AHCA can lead to:

   • Thromboembolic complications with distal ischemia 3
   • Potential compression of adjacent neurovascular structures
   • Risk of rupture in certain cases

3. In cases of proximal humeral fractures, the AHCA is disrupted in approximately 80% of cases, though osteonecrosis is less common than expected due to collateral circulation from the posterior humeral circumflex artery 1

Diagnostic Approach

For suspected AHCA enlargement or dilatation:

• Ultrasound imaging is typically the first-line diagnostic tool
• CT angiography or MR angiography for detailed assessment
• Conventional angiography may be used for definitive diagnosis and potential intervention

Management Considerations

Treatment depends on the underlying cause:

• For traumatic aneurysms: Surgical resection with potential vascular reconstruction
• For inflammatory causes: Treatment of the underlying vasculitis
• For degenerative causes: Monitoring and intervention based on size and symptoms

Pitfalls and Caveats

1. The anterior humeral circumflex artery is smaller and provides less blood supply to the humeral head than previously thought, with the posterior humeral circumflex artery providing 64% of the blood supply 1

2. Aneurysms of the circumflex humeral arteries may be underdiagnosed, particularly in overhead athletes 2

3. When surgical intervention is necessary for AHCA aneurysms, saphenous vein grafts are preferred over prosthetic materials 3

4. Anatomical variations in the origin and course of the AHCA are common and should be considered during surgical procedures in the axillary region 5