Transverse US of the tarsal tunnel with marked swelling noted

(Arrow) is at cortical surface of medial malleolus.
(Small arrowhead) is posterior tibialis tendon.
(Large arrowhead) points to tibial nerve.
(Dashed arrow) is on flexor hallucis.
Darker (hypoechoic) spaces represent fluid diffusely throughout the tarsal tunnel. (Short arrow) points to cortex of talus.
(Thick arrow) sits on the flexor digitorum tendon.