Is focal hyperintense signal within the ulnar nerve at the cubital tunnel in the presence of anconeus epitrochlearis indicative of underlying cubital tunnel syndrome requiring decompression and transposition of the ulnar nerve?

Management of Ulnar Neuropathy with Anconeus Epitrochlearis and MRI Hyperintense Signal

Focal hyperintense signal within the ulnar nerve at the cubital tunnel in the presence of anconeus epitrochlearis is strongly indicative of underlying cubital tunnel syndrome requiring surgical decompression and transposition of the ulnar nerve. 1

Diagnostic Significance of MRI Findings

The presence of focal hyperintense signal on T2-weighted MRI neurography represents a significant finding in ulnar nerve entrapment:

• MRI is considered the reference standard for imaging ulnar nerve entrapment, with T2-weighted hyperintensity indicating nerve inflammation and edema 1
• When this finding occurs in conjunction with an anconeus epitrochlearis muscle, it creates a specific anatomical scenario that typically requires surgical intervention
• The hyperintense signal indicates active nerve compression and inflammation, suggesting that conservative measures alone may be insufficient

Role of Anconeus Epitrochlearis in Cubital Tunnel Syndrome

The anconeus epitrochlearis is an anomalous muscle that has a complex relationship with cubital tunnel syndrome:

• Present in approximately 8.5% of patients with cubital tunnel syndrome 2
• While generally the muscle may actually be protective against developing cubital tunnel syndrome in many individuals 3, when it does cause symptoms:
  • It typically presents in younger patients
  • Symptoms tend to develop more rapidly
  • Symptoms are often activity-related
  • A palpable mass may be present in the cubital tunnel area 2

Surgical Management Approach

When MRI shows hyperintense signal in the ulnar nerve with an anconeus epitrochlearis muscle present, surgical intervention is indicated:

1. Surgical technique options:

   • Myotomy (excision) of the anconeus epitrochlearis muscle combined with:
     • Submuscular transposition of the ulnar nerve (preferred for cases with significant compression)
     • In situ decompression of the ulnar nerve (for milder cases) 4

2. Rationale for transposition:

   • Transposition is particularly indicated when there is:
     • Evidence of nerve subluxation
     • Significant compression with MRI signal changes
     • Failure of conservative management 5

3. Surgical outcomes:

   • Studies show excellent outcomes with myotomy of the anconeus epitrochlearis combined with ulnar nerve transposition 4, 2
   • One study reported that all but one patient had clinical resolution or improvement following surgery, with the single failure occurring in a patient who received only myotomy and in situ decompression without transposition 4

Important Considerations

• Intraoperative assessment is crucial to determine the contribution of the anconeus epitrochlearis to nerve compression by observing the change in vector and tension of muscle fibers over the ulnar nerve during passive elbow movement 4
• Submuscular transposition provides a healthy vascular bed for the nerve and soft tissue protection, which is particularly beneficial in cases with significant compression 5
• Endoscopic techniques for anterior subcutaneous transposition may offer minimally invasive alternatives with potentially faster recovery 6

Potential Pitfalls

• Simple decompression without addressing the anconeus epitrochlearis may lead to persistent symptoms 4
• Insufficient mobilization during transposition can lead to kinking of the nerve, requiring revision surgery 5
• Failure to extend decompression at least 5-6 cm distal to the medial epicondyle may result in incomplete relief 5

The presence of both MRI hyperintense signal and anconeus epitrochlearis represents a specific anatomical scenario that typically responds best to surgical decompression with transposition rather than conservative measures alone.