Presentation
Left ankle pain after dropping heavy object on it
Patient Data
There is diffuse soft tissue swelling of the lateral ankle, with focal area of hyperdensity superficial to the fibulotalar interval (best seen on AP view) suggestive of hematoma. No ankle effusion. No acute fracture.
There is a multilobulated heterogenous T1/T2 hyperintense collection superficial to the lateral malleolus and lateral compartment musculature/tendons consistent with hematoma. There is more diffuse thickening and edema of the hypodermal fat about the entire ankle.
There is a longitudinally-oriented partial tear of the peroneus brevis tendon extending from the level of the talofibular ligaments (proximally) to the calcaneo-cuboid joint (distally). The split medial and lateral tendon fibers wrap around the intact peroneus longus tendon, and there is a small amount of fluid signal within the common peroneal tendon sheath. Overlying superior peroneal retinaculum is intact.
The ankle ligaments and remaining tendons are normal. No evidence of fracture.
Distinctly separated hemi-tendons (red arrows) enveloping the intact peroneus longus tendon (teal arrow). Both are surrounded by a small amount of common peroneal tendon fluid.
Case Discussion
Peroneus brevis split tears should not be confused with anatomic variants (i.e. bifid peroneus brevis and peroneus quartus tendons), which may also appear as "extra" tendinous bands within the peroneal tendon sheath. True split tears typically manifest with a "boomerang" appearance of the brevis tendon enveloping the longus tendon, and there is often accompanying fluid within the tendon sheath.
The huge hematoma indicates a traumatic etiology.
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