Case Summary
A 42-year-old, right-hand dominant male presented with several months of progressive right upper extremity motor weakness. The patient first noticed weakness and then the complete loss of extension of the long finger and ring finger, followed by the loss of extension of the small finger, and eventually weakness of the thumb and index finger extension. The patient’s wrist extension was intact, and there were no palpable masses or inciting traumatic events. Electromyography (EMG) and nerve conduction studies (NCS) were ordered and demonstrated posterior interosseous nerve (PIN) involvement. Magnetic resonance imaging (MRI) of the right forearm showed a well-circumscribed mass over the radial head. The patient was taken to the operating room for excision of the mass. Intraoperatively a 44 mm x 27 mm x 16 mm lipoma located deep against the PIN, causing obvious clinical PIN narrowing, was excised. All branches of the radial nerve were spared, and a complete decompression of the PIN was performed. The patient had progressive and continued recovery of finger extension postoperatively.