What’s the Diagnosis – Case 190
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What’s the Diagnosis – Case 190
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Findings The radiographs demonstrate heterotopic ossification along the course of the interosseous membrane. This is otherwise not germane to the current complaints. The comparison of MRIs demonstrates how technique can make a tremendous difference in being able to render diagnoses especially when it comes to small structures and subtle abnormalities. Notice the difference in slice thickness and overall size of the field of view. These will decrease resolution and limit capacity to make subtle findings. On the MRI, seen is markedly abnormal architecture of the superficial peroneal nerve as it pierces the crural fasica at approximately 10cm superior to the ankle joint. The PSIF sequence is a newer imaging technique with T2 weighting and fat suppression which also helps saturate vascular structures. This sequence allows greater conspicuity of nerve findings. In this case the superficial peroneal nerve becomes focally enlarged, with T2 hyperintense fascicles. The findings are very subtle on the CT exam showing the somewhat limited utility of CT in nerve imaging. The corresponding US comparing the right to left superficial peroneal nerve demonstrates the tremendous utility of US in the imaging of nerves. Seen in this case is the abnormal right sided nerve which is enlarged and hypoechoic as compared to the normal left sided nerve.
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Diagnosis: Superficial Peroneal Nerve (SPN) Entrapment As seen in this case, this process typically occurs where the spn exits the lateral compartment of the leg and traverses the crural fascia to extend into the subcutaneous tissue. This is normally about 10-15cm superior to the ankle joint . This entity most commonly presents with sensory findings. Motor findings involving the peroneus longus and brevis muscle are much less common. The exact cause is often not known but it may relate to prior trauma, muscle herniation, or repetitive motion with flexion and inversion at the foot. Conservative measures are often helpful but in recalcitrant cases, as in this one, surgical intervention with decompression, neurolysis, and fasciotomy may be required.
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References Luc M. Fortier, BA, Michael Markel, BS, Braden G. Thomas, BS, William F. Sherman, MD, MBA, Bennett H. Thomas, BS, Alan D. Kaye, MD, PhD. An Update on Peroneal Nerve Entrapment and Neuropathy. Orthopedic Reviews. Vol. 13, Issue 2, 2021June 18, 2021 EDT. https://doi.org/10.52965/001c.24937 Zare M, Faeghi F, Hosseini A, Ardekani MS, Heidari MH, Zarei E. Comparison Between Three-Dimensional Diffusion-Weighted PSIF Technique and Routine Imaging Sequences in Evaluation of Peripheral Nerves in Healthy People. Basic Clin Neurosci. 2018 Jan-Feb;9(1):65-71. doi: 10.29252/NIRP.BCN.9.1.65. PMID: 29942442; PMCID: PMC6015634. Feger J. Superficial peroneal nerve entrapment. Reference article, Radiopaedia.org, 28 Aug 2021, https://doi.org/10.53347/rID-92632 DOI:https://doi.org/10.53347/rID-92632
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