Posterior interosseous nerve entrapment due to bilobed parosteal lipoma

Entrapment of posterior interosseous nerve (PIN) can be due to fracture dislocation of elbow, fibrous arcade of Frohse, neoplasms (lipoma, schwannoma), ganglion cysts and rheumatoid synovitis. Parosteal lipomas are extremely rare. These tumors grow slowly and as they grow, they can compress a nearby nerve producing sensory and motor disturbances. Till date less than 50 cases of PIN entrapment due to parosteal lipoma have been reported in literature. However, to the best of our knowledge, none was bilobed. A 54-year-old female patient presented with progressive weakness of the right-hand extensors including thumb for the last 5 months with no sensory loss. Clinico-radiological findings and electophysiological studies revealed parosteal lipoma causing entrapment of PIN. Surgical excision of the lesion was done through posterior approach. The excised mass was sent for histopathological examination which confirmed the diagnosis of lipoma. Appreciable recovery was first noticed at 3 months and complete recovery was seen at 7 months. No recurrence was seen until 2 years of follow up. Urgent surgical excision is necessary to prevent entrapment of this nerve and facilitate early functional and neurological recovery.