Benign Epithelioid Peripheral Nerve Sheath Tumor BEPNST of

Benign Epithelioid Peripheral Nerve Sheath Tumor (BEPNST) of the Peroneal Nerve : A Case Illustration and Review Craig J Berg, Chris S Karas, EA Chiocca The Ohio State University Medical Center Department of Neurosurgery

Peroneal Nerve Anatomy n Common Peroneal n n n L 4, L 5, S 1, S 2 Supplies biceps femoris, lateral head of gastrocnemius Divides into superficial and deep peroneal nerves

Peroneal Nerve Anatomy

Case n n 39 yo female Sudden onset right leg numbness Acute foot drop Exam n n 4/5 right dorsiflexion and eversion Reproducible paresthesia with palpation of peroneal nerve

Case: Imaging/EMG/Dopplers n n n Lobular/enhancing mass seen on MRI from above lateral femoral condyle to fibular head Doppler negative, pulses intact EMG/NCS n n Absent sural nerve response Chronic peroneal n. injury at fibular head

Case: Imaging n Figure 1 -pre contrast Figure 2 -post-contrast showing enhancing lesion at distal femur

Imaging (continued) n Sagittal Fig 3: postcontrast; Enhancing mass at lateral femoral condyle

Operative Exploration n n Figure 4: Exposure of diseased common peroneal nerve and surrounding structures Note: PN = Peroneal Nerve

Operative Exploration Figure 5: gross discoloration and flattening of common PN.

Surgical Decompression Fig. 6: Intrafascicular dissection with fibroconnective tissue

Surgical Decompression Figure 7: Superior expansion of intrafascicular dissection Transition zone Fascicular infiltration Normal intrafascicular region

Histopathology n n Fig. 8 (Upper) Low-power magnification of our patient’s lesion with diffuse spindle cell proliferation against a myxoid background. (Lower) Low-power magnification of a BEPNST showing epithelioid cells in small cluster Fig. 9 (Upper) S-100 staining from our patient showing no positive cells. (Lower) S-100 staining from a diagnosed lipomatous neurofibroma showing diffusely positive cells.

Differential Diagnosis n BEPNST n n n Epithelioid Neurofibromas Soft tissue Perineuromas Fibrolipomatous Hamartoma Spindle Cell Lipoma Low-grade Spindle Cell Liposarcoma

Differential Diagnosis n Epithelioid Neurofibromas n n n Enhancing on MRI CD 34 positive (non-specific) Usually + S-100 (Our patient was not) Mixture of Schwann cells, fibroblasts, and perineural cells +Café au lait spots on our patient, but MRI of the neuroaxis was negative as was genetic testing.

Differential Diagnosis n Soft tissue Perineuromas n n Unencapsulated, well-circumscribed Exclusively perineural cells (unlike neurofibromas) Some with spindle cell proliferation (as with our patient) CD 34 positive

Differential Diagnosis n Fibrolipomatous Hamartoma n n n Usually gradual onset of symptoms S-100 positive (unlike our patient) Spindle-cell proliferation Lower extremity is UNUSUAL location Perineural invasion UNUSUAL

Differential Diagnosis n Spindle Cell Lipoma n n Mixoid background and spindle cell proliferation (consistent with our patients histopathology) Usually display distinctive Mast Cells

Differential Diagnosis n Low-grade Spindle Cell Liposarcoma n n Pleomorphism (unlike our patient) Positive CD 34, negative S-100 (as with our patient)

Conclusion n n Unusual presentation of slow-growing benign epithelioid peripheral nerve sheath tumor (BEPNST) of the peroneal nerve No clear diagnosis No improvement postoperatively No tumor recurrence 6 months later