Unilateral carpal tunnel syndrome caused by an occult palmar lipoma

Carpal tunnel syndrome usually presents bilaterally and space-occupying lesions should be suspected in patients with unilateral symptoms, especially with a long history and when the symptomatic hand shows severe neurophysiologic impairment, while the contralateral hand is neurophysiologically intact. Approximately half of patients with unilateral symptoms have positive electrodiagnostic test results in the asymptomatic, contralateral hand. Space-occupying lesions are known to cause carpal tunnel syndrome and the incidence of space-occupying lesions in unilateral carpal tunnel syndrome is higher than that of bilateral carpal tunnel syndrome. It is easy to detect a mass when it is palpable, but occult lesions may be overlooked easily. Whenever a patient presents with unilateral symptoms and unilateral neurophysiologic impairment, the possibility of a space-occupying lesion compressing the median nerve should be kept in mind in the differential diagnosis. This article presents 2 cases of patients with occult deep palmar lipomas compressing the median nerve and causing unilateral symptoms of carpal tunnel syndrome. We stress the importance of imaging studies in patients with unilateral symptoms that are usually not used in carpal tunnel syndrome. While both patients' symptomatic hands showed severe neurophysiologic impairment, the contralateral hands were totally intact, which is contradictory with a long history. The reported patients were evaluated and magnetic resonance images revealed intra-tunnel lesions. Although lipomas are the most common soft tissue tumor in the body, <5% of the benign tumors of the hand are lipomas. Since the thick palmar fascia is strong, a deep lipoma may not be recognized although nerve compression symptoms may be gross.