Diagnosis

Tarsal Tunnel Syndrome

Case Discussion

The tarsal tunnel is a fibro osseous complex at the posteromedial aspect of the ankle, extending distally to the plantar foot. It is bordered by the flexor retinaculum and the medial walls of the calcaneus, talus, and tibia. It contains the tibialis posterior tendon, the flexor digitorum longus tendon, the posterior tibial neurovascular bundle, and the flexor hallucis longus tendon.

Tarsal tunnel syndrome is a common cause of recalcitrant heel pain. It is secondary to entrapment and compression of the posterior tibial nerve (or its branches) beneath the flexor retinaculum. Clinical symptoms include burning pain and paresthesia made worse with weight bearing, sensory impairment, and potentially motor deficits. Patients predisposed to tarsal tunnel syndrome include those with pes planus foot type, venous varicosities, abductor hallucis hypertrophy, and neurofibromas, although most cases are idiopathic. Post-surgical or post-traumatic fibrosis and flexor tendon tenosynovitis may also cause tarsal tunnel syndrome.  

If tarsal tunnel syndrome is secondary to a fibrous lesion, it will appear as low signal intensity on both T1- and T2-weighted images. If the cause is a fluid containing lesion (varicosities, ganglion, etc.) it will appear as intermediate signal intensity on T1-weighted images and high signal intensity on T2-weighted images.

Secondary or ancillary findings supporting tarsal tunnel syndrome include myoedema involving the intrinsic muscles of the foot in the acute/subacute stages and atrophy with fatty replacement in the later stage.   

A related condition that selectively affects the Lateral Plantar Nerve and results in Lateral Foot Muscle Myoedema and Atrophy is Baxter’s Neuropathy.

Key Images

Tarsal tunnel syndrome in a 50-year-old woman with a history of left plantar fasciotomy and nerve repair, now complaining of sharp pain in the same foot.

A. Axial T2 image of the left foot shows a slightly thickened and edematous tibial nerve (red arrow) surrounded by hypointense scarring/cicatrisation (yellow arrow) throughout the tarsal canal.
B. Axial T1 image shows a distorted and compressed/effaced tibial nerve (red arrow) and adjacent nodular fibrous tissue (yellow arrow).
C. Axial PD SPIR image shows abnormal high signal throughout the medial head of quadratus plantae muscle (yellow arrow), consistent with impingement-related denervation myoedema. 
D. Axial PD SPIR image shows abnormal high signal throughout the quadratus plantae muscle (yellow arrow), consistent with impingement-related denervation myoedema.
E. Axial T2 TSE image shows high signal edema and co-existing fatty atrophy (yellow arrow), consistent with chronic and active impingement. 

References

  1. El-Zawawi MS, Ebied OM, Abdou Sileema ER. Role of magnetic resonance imaging in the diagnosis of ankle impingement. Menoufia Medical Journal 2017; 30(1):99-103
  2. Erickson SJ, Quinn SF, Kneeland JB, Smith JW, Johnson JE, Carrera GF, Shereff MJ, Hyde JS, Jesmanowicz A. MR imaging of the tarsal tunnel and related spaces: Normal and abnormal findings with anatomic correlation. American Journal of Roentgenology 1990; 155:323-328