Abstract
An aneurysm is an abnormal focal dilatation of a blood vessel that increases its width by more than 50%. They are divided into true and pseudo-aneurysms. Ulnar artery pseudoaneurysm that causes pain, numbness and cold intolerance in the hypothenar region and develops after repetitive trauma has been named hypothenar hammer syndrome. Hypothenar hammer syndrome is a rare clinical entity that occurs more frequently in males and in the dominant hand as a result of repetitive trauma. Patient history and clinical examination are very important in the diagnosis of this disease, which is seen as an occupational disease and is associated with some sports branches. However, it can also occur with a single blunt trauma, in the non-dominant hand and regardless of occupation. Ultrasonography, Doppler, magnetic resonance and angiography help us to visualize an aneurysm. Although activity regulation and various medications are used among the treatments, surgical treatment is at the forefront in the presence of chronic pain and compression symptoms due to the mass. In the presence of signs of vascular insufficiency or a palpable pulsatile mass in the hand, this rare syndrome may be easy to diagnose and manage. But, in atypical cases, such as our case with no symptoms other than nonspecific pain in the hand, the aneurysm causing hypothenar hammer syndrome may mimic a peripheral nerve tumor.

Key words: aneurysm, hypothenar hammer syndrome, nerve tumor