Anterior knee schwannoma
Schwannomas are rare, benign, often solitary, slow growing nerve sheath tumors. They are most often located in the brachial plexus (39%), followed by a slight predominance in the upper limits (30%) compared with their appearance in the lower extremities (24%).

This 53-year-old male presented to our office with complaints of an enlarging right knee mass causing intermittent, vague pain for the past couple months. He denied trauma to right knee, numbness, tingling and weakness. He reported vague knee pain with knee flexion and to palpation. Patient had a 2 × 2 cm firm, tender, mobile mass on right anterior knee. A neurological examination revealed intact motor and sensation.

Macroscopically, the tumor appeared encapsulated, rubbery and pink-tan in color. Microscopic examination reveals that tumor composed of biphasic spindle hypercellular Antoni A areas and hypocellular Antoni B areas. Higher magnification reveals that spindle tumor cells are narrow, elongate, wavy with tapered ends interspersed with collagen fibers. Immunohistochemical staining revealed that most tumor cells reacted strongly for S-100 protein. Combined with immunohistochemical profile, these histological features are diagnostic of benign schwannoma.

Source: Journal of Surgical Case Reports

Read more: https://academic.oup.com/jscr/article/2019/9/rjz236/5565024
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