[Schwannoma of the common peroneal nerve. A differential diagnosis versus rare popliteal cyst].

The presented case concerns a patient with neuralgia of the common peroneal nerve and progressive neurological deficit caused by interfascicular growth of schwannoma. The ultrasound diagnostics identified the lesion as a popliteal cyst. Magnetic resonance imaging revealed features of atypical cyst location. Due to the clinical course, it was decided to decompress the nerve trunk. An interfascicular tumor was identified intraoperatively. Particular nerve bundles were separated microsurgically and the tumor of schwannoma morphology was removed. The postoperative course brought resolution of neuralgia and improvement of peroneal nerve function. In the case in question attention was focused on the differential diagnostics of processes located in the popliteal fossa. Imaging examination indicated an atypical cyst location rather than a morphologically solid tumor. The clinical course is essential for determining the nature of the lesion. Decompressing the common peroneal nerve in microsurgical technique allows the prevention of further neurological symptoms in the postoperative course.