A 37 y.o. woman presents with severe pain in the L leg. Hx of varicose veins but no evidenceof dvt on imaging.

what is your differential?

This is a T2 weighted MRI showing a mass behind the knee on the L.

Our pt had  peripheral nerve sheath tumors of  the peroneal nerve. This was diagnosed on the MRI since the tumor could be seen arising from the nerve sheath. These tumors form from Schwann cells which are the glial cells that form the myelin sheath on axons outside the brain.  Peripheral nerves are composed both of a myelin sheath and nodes of Ranvier (places where the myelin is uncovered allowing for rapid generation of impulses.

These tumors are relatively uncommon and 85-90% are benign; not invading the axon. It is the most common type of benign peripheral nerve tumor in adults. They can persent with severe pain.  They can occur in many places in the body and schwannomas of the head and neck occur in 4% of people at autopsy.  The most common is a schwannoma of the vestibular nerve.

Although most schwannomas are benign, there are malignant nerve sheath tumors. The incidence of malignancy is highest in patients with neurofibromatosis type 1.  Previous radiation can make nerves susceptible to malignant transformation as well.The malignant nerve sheath tumors are a type of soft tissue sarcoma and very aggressive. Rest pain can be a sign of malignant tumors.

Schwannomas can arise from the spine as pictured above.

Our patient had severe pain and initially was treated with IV lidocaine 1 mg/hr, oxycodone q 3 hrs (30 mg in 24 hrs), a PCA with hydromorphone .5 q 10 minutes(17 mg /24 hrs), naproxen 250 bid, tylenol 1g q 6 hrs, pregabalin 100 tid, and baclofen 20 tid.  She had a peripheral nerve block for surgery and  post op was on 90 mg of oxycodone in 24 hrs.  She has residual weakness and numbness of the L leg. Path at surgery was consistent with a schwannoma.  Final path is pending

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Ilfeld B, Preciado J, Trescot A. Novel cryoneurolysis device for the treatment of sensory and motor peripheral nerves. Exper Feview of Medical Devices , 2016 Vol 13,(8):713-725.

https://radiologycases.my/2023/02/20/spinal-schwannoma/ Spinal schwannoma, Hassan R.

Sobczuk P, Teterycz P, Czarnecka A, et al. Systemic treatment for advanced and metastatic peripheral nerve sheath tumors—a sarcoma reference center experience. J Clin Med. 2020 Oct;9(10):3157