Presentation
Spontaneous pain in the left popliteal fossa after a few days of daily running. The pain began insidiously and radiated into the anterior and posterior distal third of the thigh during combined flexion-rotation knee with tenderness to pressure, accompanied by a cramping sensation along the rear of the calf, especially on the lateral side.
Patient Data
T1-weighted and fat-suppressed T1-weighted MRI images showing a lesion to the superior popliteal fossa, involving the posterior tibial nerve. The lesion with regular margins is hypointense on T1-weighted sequences while fat-suppressed T1-weighted axial and sagittal sequences after contrast, showing marked contrast uptake with a few a little periheral areas not displaying contrast uptake. The entering and exiting nerve can be seen.
Surgery
Medial incision lateral to the posterior tibial artery. Identified the posterior tibial nerve and a swelling was noted along its course at the level of the knee joint. Under microscopic guidance, the nerve sheath was incised and a soft, ovoid mass (diameter 1.5 cm x 1 cm) was noted with few fibers attached medially to the nerve sheath. Careful dissection of the mass was performed and it was completely excised. The nerve bundles were identified and left intact.
Histological report
Presence of hypocellular (Antoni A) areas with hypercellular (Antoni B) areas combined with the presence of Verocay bodies, compatible with the diagnosis of benign schwannoma.
Case Discussion
Neuropathic compression pain in the popliteal fossa may be secondary to several etiologies. The most common causes of local neurovascular compression are Baker's cysts, adventitial cysts of the popliteal artery, thrombophlebitis, synovial sarcomas, popliteal artery aneurysms, and nerve entrapments.
Case courtesy of Dr.ssa Laura Braccaioli
Radiographer: TSRM Fabio Imola
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