IS Case 202: Hypothenar hammer syndrome
Imaging Sciences URMC 2008
Publication Date: 2009-05-22
Hypothenar hammer syndrome
Arterial aneurysms are known to occur in the wrist as a result of a single acute trauma or chronic repetitive injury to the ulnar and radial arteries. These two clinical entities are known respectively as the hypothenar hammer syndrome coined by Conn, et al. in 1970  and its counterpart the thenar hammer syndrome coined by Janevski in 1979 . The hypothenar hammer syndrome refers to the clinical syndrome of hand and finger ischemia as a result of repetitive injury to the ulnar artery and superficial palmar arch against the hook of the hamate. This is seen with repetitive hand trauma associated with industrial occupations as well as in athletes. In the thenar hammer syndrome, radial artery aneurysm or thrombosis may also be occupational, but is also frequently related to arterial catheterization for hemodynamic monitoring. Overall, the ulnar artery is most commonly affected, and this may be because the anatomical efficiency of using the hypothenar eminence as a hammer. In the hypothenar hammer syndrome, damage to the ulnar arterial wall leads to aneurysmal dilatation of the ulnar artery in the Guyon canal, usually at the level of the hamate, which compresses the sensory branch of the ulnar nerve. Thrombosis may ensue causing microemboli distally. Thus, the presenting symptoms include digital cold intolerance, ischemic pain, and Raynaud syndrome usually involving the fourth and fifth fingers. Clinically, these aneurysms are often mistaken for soft tissue masses. The two angiographic appearances are a dilated “corkscrew” appearance of the ulnar artery aneurysm with or without distal digital arterial emboli or an abrupt focal ulnar artery occlusion at the hypothenar eminence. The sonographic appearance is a cystic saccular mass arising from the artery with a thickened irregular wall. Sonography is particularly useful to determine the size of the aneurysm when it is not visualized on angiography due to occlusion. Vessel thrombosis is demonstrated by increased echogenicity in the arterial lumen, however care must be taken in distinguishing this from slow flow in a narrowed artery. MRI can be used to delineate the extent of the aneurysm and evaluate for thrombosis. MR angiography can be performed at the same time, with similar findings to DSA, however MRA is limited by its resolution in the digital arteries. CT angiography can be helpful to evaluate for fractures as well as delineate the relationship of the ulnar artery with the hook of the hamate. It can also be used for vascular mapping prior to intervention. The treatment for hypothenar hammer syndrome includes conservative measures such as vasodilators and platelet inhibitors. Thrombolysis, aneurysm resection, and arterial or vein graft interposition can be performed if conservative measures fail.
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