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Findings The radiographs show findings of a prior ACL reconstruction via a hamstring graft. This is otherwise not contributory to this case. The MRI shows marked edema within the extensor digitorum longus muscle. There is a fluid collection (ganglion) that emanates from the proximal tibiofibular joint and extends anteriorly into the extensor digitorum longus muscle. In addition to the prominent focal edema of the muscle there is an overall decreased bulk of the muscle belly of the extensor digitorum longus (EDL).
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Diagnosis: Intraneural Ganglion I will admit the diagnosis in this case has not been proven and the findings are not classic for a peroneal intraneural ganglion. I think this is, however, a good case to discuss the entity and help in distinguishing different ganglia about the proximal tibiofibular joint. Both the deep peroneal nerve and the tibial nerve send an articular branch to the proximal tibiofibiular joint. At times, ganglia extend from the proximal tibiofibular joint along the course of these nerves as intraneural ganglia and at other times ganglia extend from the joint but not along the course of the articular branches as extraneural ganglia. In the references listed, nicely shown is typical architecture for a peroneal intraneural ganglion that extends along the articular branch as a “transverse limb sign” and then also there is a small ganglion within the common peroneal nerve or so called “signet ring sign”. This case does not have those findings but does show the ganglion emanating along the anterior aspect of the joint which is referred to as a tail sign. This represents the connection of the articular branch to the joint. Also the focal process involving the EDL much more so favors an intraneural ganglion of the branch of the deep peroneal nerve to the EDL. An extraneural ganglion would be unlikely to stay limited to just one muscle belly and present with neurogenic findings of a muscle. The issue is that in addressing the intraneural ganglia as compared to extraneural ganglia difference in technique/what is resected may ensue. In both types of ganglia addressing the proximal tibiofibular joint is mandated to help prevent against recurrence.
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References The clock face guide to peroneal intraneural ganglia: critical “times” and sites for accurate diagnosis. Robert J. Spinner, Gauri Luthra, Nicholas M. Desy, Meredith L. Anderson, Kimberly K. Amrami. Skeletal Radiology. December 2008, Volume 37, Issue 12, pp 1091–1099
The clinico-anatomic explanation for tibial intraneural ganglion cysts arising from the superior tibiofibular joint. Robert J. Spinner, Ali Mokhtarzadeh, Terry K. Schiefer, Kartik G. Krishnan, Michel Kliot, Kimberly K. Amrami. Skeletal Radiology. April 2007, Volume 36, Issue 4, pp 281–292
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