The instabile and hurting foot…  


A 32-year-old man gets referred to your lab by an orthopedic colleague with the referral diagnosis being “neuropathy?”.

The man tells you about pain in the right foot he experiences mostly while walking. Because of this, the orthopedic sent him to MRI of the right foot. The MRI describes several degenerative changes in the lateral metatarsal bones and joints as well as atrophy of the intrinsic plantar muscles of the foot.

Upon inspection you notice a tumor at the medial ankle. It is round, firm and elastic in palpation, not causing any pain. The patient says that it has been there nearly his whole life and also his brother and father have the same swelling in this area. Upon palpation of the tumor, the patient reports tingling of the sole.

Motor nerve conduction studies of the tibial nerve were already available: 

Image 1: Standard motor NCS of the right tibial nerve (stimulation at ankle and popliteal fossa, recording from M. abductor hallucis brevis) 

Image 2: Transtarsal latency of the right tibial nerve (stimulation below and above medial malleolus, recording from M. abductor hallucis longus, upper limit normal 2.4 ms at our lab) 


The conclusion of the NCS was posterior tarsal tunnel syndrome.

You now grab your ultrasound probe and see the following:

Video: You are following the lateral plantar nerve from proximally to distally. White arrow: lateral plantar nerve

Image 3: Measurements of the tumor in three dimensions and vascularization.

Now what is your diagnosis?


Looking forward to your feedback.


Best regards and keep scanning!


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