What is the diagnosis and treatment for heel pain with a 6 mm ganglion cyst in the sinus tarsi?

MRI Interpretation: Sinus Tarsi Syndrome

The MRI findings reveal sinus tarsi syndrome, characterized by a 6 mm ganglion cyst and infiltrating fluid within the tarsal sinus, with fatty replacement and scarring. This condition is likely causing the patient's heel pain and should be treated with conservative measures initially, followed by more invasive interventions if symptoms persist.

Understanding Sinus Tarsi Syndrome (STS)

Sinus tarsi syndrome is characterized by pain in the lateral aspect of the foot, specifically in the tarsal sinus area. The MRI findings in this case show:

• 6 mm fluid signal lesion (ganglion cyst) in the tarsal sinus
• Infiltrating fluid within the tarsal sinus
• Fatty replacement and scarring

These findings are consistent with sinus tarsi syndrome, which is often misdiagnosed as a chronic ankle sprain 1. The tarsal sinus is a cone-shaped cavity located between the talus and calcaneus, and inflammation in this area can cause significant pain and functional limitations.

Clinical Correlation

The MRI report specifically mentions to "correlate clinically for sinus tarsi syndrome," which is appropriate given:

• The patient's complaint of heel pain
• Pain at the site of Achilles insertion
• Normal Achilles tendon on MRI (ruling out Achilles tendinopathy)
• Presence of pathological changes in the tarsal sinus

Treatment Algorithm

First-Line Treatment (Conservative Management)

1. Rest and activity modification to reduce stress on the affected area
2. Anti-inflammatory medications (NSAIDs) to reduce pain and inflammation
3. Physical therapy focusing on:
   • Strengthening of peroneal muscles
   • Proprioceptive training
   • Range of motion exercises
4. Orthotic devices to correct foot biomechanics and provide support
5. Corticosteroid injection into the tarsal sinus - shown to provide significant functional improvement for at least 6 months 2

Second-Line Treatment (If Conservative Management Fails)

1. Advanced injection therapies:
   • Platelet-rich plasma (PRP) injections
   • Ozone injections (both have shown similar long-term outcomes to corticosteroids) 2

Third-Line Treatment (For Refractory Cases)

1. Subtalar arthroscopy - both diagnostic and therapeutic
2. Sinus tarsectomy - reserved for patients who do not respond to conservative treatment 1

Monitoring and Follow-up

• Re-evaluate after 4-6 weeks of conservative treatment
• If symptoms persist, consider corticosteroid injection
• Follow-up imaging is typically not necessary unless symptoms worsen or fail to improve with appropriate treatment

Important Considerations

• Sinus tarsi syndrome is often post-traumatic, though the patient's history doesn't mention specific trauma 3
• The condition can cause a feeling of instability, particularly when walking on uneven surfaces 1
• The American College of Radiology notes that MRI is appropriate for evaluating chronic foot pain after initial radiographs are nondiagnostic 4
• Recent research suggests that "sinus tarsi syndrome" may be a catch-all phrase for various pathologies affecting this region, and more specific diagnosis should be sought when possible 5

Prognosis

With appropriate treatment, approximately two-thirds of patients respond well to conservative management 3. For those requiring surgical intervention, about 90% experience cure or significant improvement 3.