Digital ischaemia is an uncommon pathology, with an incidence of two cases per 100,000 people per year.1 Diagnosis is mainly based on clinical symptoms: the patient presents a painful digital extremity with signs of ischaemia (blue finger) or even necrosis. Clinical context and medical history are also important to determine the aetiology of digital ischaemia.
The role of imaging modalities is central to the localisation and prediction of the severity of vascular lesions. Intra-arterial digital substraction angiography (DSA) is considered the gold standard for the study of vascular extremities. Furthermore, non-invasive imaging of distal small vessel disease has been developed over recent years; in particular, computed tomographic angiography (CTA) of the upper extremity.
Fewer than 20 significant publications are reported on MEDLINE on this subject and most of them were written before 1990.2
We present here a retrospective study of 32 patients with digital ischaemia who were referred to the ‘hand emergency service’ of Tours University Hospital, France, between August 2006 and August 2009. All 32 patients underwent DSA. In addition, eight patients with suspected hypothenar hammer syndrome underwent CTA, specifically to look for an ulnar artery aneurysm.
Methods
Each patient presenting with a clinical suspicion of hypothenar hammer syndrome underwent both DSA and CTA to analyse the distal extremity of the hand’s vascularisation. CTA was performed with a Brilliance CT 64-channel scanner (Philips Healthcare, Best, The Netherlands) for eight patients with suspected hypothenar hammer syndrome. The patient adopted a prone position, with the forearms and hands close to the gantry centre. The field of view was set at 25cm with a 0.6mm section thickness. Non-ionic, low-osmolality contrast medium (400mg/ml) was injected via an 18-gauge hypodermic needle into the antecubital vein of the non-pathological arm at a rate of 2cc/second, up to a total of 60cc. The reference point for the visual trigger was the brachial artery. Image acquisition was initiated following an appropriate delay after the injection of contrast medium. Image processing was performed using the Philips Brilliance Workspace 3D workstation (Philips Healthcare, Best, The Netherlands), allowing maximum intensity projection and volume rendering reconstructions.
Site of Occlusion and Anatomical Variations
The vascular network of the hand is highly variable. Knowing that anatomical variations exist aids us in the assessment of different clinical patterns and severity of vascular lesions. In accordance with the wealth of variations in the palmar arch, it is possible for the palmar metacarpal arteries and the common palmar digital arteries to have varying sources of vascular supply.3 Communication between the dorsal and palmar systems occurs by way of perforating arteries between the dorsal metacarpal arteries and the deep and superficial palmar arches. The superficial palmar arch is mainly fed by the ulnar artery. This arch is closed in 37% of cases and forms an anastomosis via its superficial radial branch with the radial artery.4 In some cases, the superficial palmar arch is congenitally open. On the radial side of the hand, the common palmar digital arteries originate from the superficial palmar arch. The deep palmar arch is fed primarily by the radial artery. In 95% of cases, it is congenitally closed by an anastomosis with the deep network of the ulnar artery. In <10% of cases, a persistent median artery may be observed.
Aetiologies
Aetiologies are dependent on the site of occlusion and size of pathological vessels: proximal localisations exist – such as lesions of the subclavian artery – as do distal localisations. The wrist is considered the boundary between arteries of medium and small size. The main aetiologies, to be discussed in more detail in the following sections, are:
- embolism;
- atherosclerosis;
- connective-tissue disease as vasculitis;
- drug use; and
- occupational injury (hypothenar hammer syndrome).
Embolism
Embolism is the most common cause of acute arm ischaemia, accounting for 75% of our patients. The proportion of patients with acute arm ischaemia caused by emboli is typically 74–95% in published studies.5–7 Cardiac embolism is the most frequently reported cause of acute arm ischaemia and atrial fibrillation is the usual aetiology. Over the years, the incidence of atrial fibrillation has remained constant, although the cause of atrial fibrillation has changed from valvular heart disease secondary to rheumatic fever to ischaemic heart disease.
The classic imaging findings are either a complete occlusion, producing a filling defect, or an abrupt vessel cut-off in the absence of a proximal atherosclerotic lesion. The filling defect evokes an embolic aetiology and can be seen as obstruction of several proper palmar digital arteries.
Atherosclerosis
There are no accurate epidemiological data on the prevalence of atherosclerotic upper limb lesions. Proximal upper limb arterial stenosis caused by an atherosclerotic plaque can result in thromboembolism or atheroembolism, which may cause large vessel occlusion or, more commonly, acute digital ischaemia.
Connective Tissue Disease as Vasculitis
Vasculitis is a clinicopathological process characterised by inflammation of and damage to blood vessels. Classification depends on the calibre of the diseased vessels: we distinguish pathologies affecting large vessels (such as Takayasu’s disease or giant-cell arteritis) from those affecting medium- or small-sized vessels (such as Buerger’s disease or thromboangiitis obliterans; limited cutaneous systemic sclerosis; CREST syndrome; or lupus).
Takayasu Arteritis
Takayasu arteritis is a rare disease that affects mainly women between 20 and 30 years of age and is characterised by inflammation of large-sized vessels – primarily the aorta and its branches. The pathology of the disease comprises proliferation of the tunica intima; fibrotic contraction of the tunica media and tunica adventitia; and granulomatous vasculitis.
The main clinical sign is the claudication of the extremities. Exceptionally, Takayasu’s disease is accompanied by digital ischaemia. If Takayasu arteritis is suspected, a CTA exam should be performed to study the aortic arch and its branches. Imaging findings, shown in Figure 2, include lumenal narrowing and circumferential thickening of the vessel wall.
Thromboangiitis Obliterans
Thromboangiitis obliterans is a segmental, occlusive, inflammatory process of the arteries and veins, resulting in thrombosis and necessitating recanalisation of the affected vessels. The lesions are localised on small- and medium-sized arteries and veins of the upper and lower extremities. The pathology affects adults aged around 40, by majority men and/or smokers. Exposure to tobacco is essential to the development of the disease. For a young adult smoker, Raynaud’s phenomenon, associated with distal ischaemic arterial lesions and superficial thrombophlebitis should evoke thromboangiitis obliterans. Angiographic findings include severe distal segmental occlusive lesions with normal proximal arteries (no signs of atherosclerosis).
Limited Cutaneous Systemic Sclerosis
Patients presenting with trophic pathologies of the extremities have often already been diagnosed with this autoimmune disease. In this context, imaging is performed to evaluate the severity of vascular lesions and to exclude curable differential diagnoses, such as cardiac embolism. Lumenal imaging, via DSA or CTA, may show distal vascular lesions, such as obstruction of the proper palmar digital arteries.
CREST Syndrome
A subgroup of patients with limited cutaneous systemic sclerosis bears the features of CREST syndrome (calcinosis, Raynaud’s phenomenon, oesophageal dysmotility, sclerodactyly and telangiectasia). The subcutaneous calcifications (see Figure 3) can be of large size, leading to vascular obstruction and, potentially, to systemic sclerotic lesions.
Drug Use
Chemotherapy and the use of toxic substances can lead to severe distal arterial lesions, including digital ischaemic lesions (e.g. cannabis arteritis). Lumenal imaging may show vasospasm of the distal arteries ranging up to the abrupt cessation of the vascularisation.
Hypothenar Hammer Syndrome
Arterial aneurysms of the hand are most often caused by repeated microtrauma (exposure to hand-arm vibration). Hypothenar hammer syndrome is a characteristic form of vascular damage to the terminal portion of the ulnar artery, due to repetitive blunt trauma to the hypothenar region. It is exceptional, predominantly found in men who repeatedly use their hand as substitute for a hammer at work.8 Depending on the frequency and severity of the traumatising event, the resulting vascular lesions may vary from simple arterial spasm, to thrombosis following an intimal lesion, or formation of aneurysms where the tunica media is damaged. This can lead to downstream obstructions caused by micro-emboli. The traumatic impact usually leads to aneurysm formation at the most vulnerable course of the ulnar artery (Guyon’s canal), between the pisiform bone and hamate hook medially and the transverse carpal ligament dorsally. Imaging is necessary to establish the location (see Figure 4), morphology and extent of vessel damage (see Figure 5), as well as to identify collaterals within the dual blood supply of the hand (see Figure 6). The diagnosis is usually confirmed by lumenal imaging showing obstruction of the ulnar artery.
Advanced Imaging Techniques for Studying the Small Vessels of the Hand
DSA remains the diagnostic gold standard for imaging the thin arteries of the fingers. The advantage of transarterial catheter angiography lies in the examination of the vascular periphery and in the diagnosis of vascular emergencies; it is, however, an invasive technique and carries a risk of vasospasm when catheterising small vessels, which restricts their analysis. The availability, rapidity of acquisition, ease of post-image processing analysis and the improvement of spatial resolution have each promoted non-invasive, high-resolution imaging. Non-invasive, high-resolution imaging of small and distal vessels is now possible using contrast-enhanced magnetic resonance angiography and CTA.
For each of the eight cases of suspected thrombosis of an ulnar artery aneurysm in the context of repeated microtrauma, a CTA of the hand was performed. CTA is advantageous as it provides both lumenal and precise soft tissue imaging. In a typical case of hypothenar hammer syndrome, the role of CTA is: firstly, to clearly depict, with a good spatial resolution (0.6mm), the classical abrupt vessel cut-off of the ulnar artery lumen; and secondly, to confirm that vessel pathology is localised opposite the hamate bone. Two other signs are important when imaging the soft tissue of the vessel wall: a localised increase of vessel diameter and a slight, peripheral enhancement around the thrombosed aneurysm, known as the ‘ring sign’. Thanks to 3D reconstructions such as maximum intensity projection and volume rendering, vascular consequences and variations in anatomy and vessel supply can easily be detected. In all cases of hypothenar hammer syndrome, CTA confirmed the existence of a pathological ulnar vessel opposite the hamate. In five cases, a thrombosed aneurysm was found, while in three cases, an irregular vessel wall without aneurysm was detected.
Conclusion
Imaging studies play a central role in the diagnosis, localisation and prediction of the severity of vascular lesions. The role of the radiologist is to answer a single question: is there a curable cause that needs a specific treatment? Proximal atherosclerotic lesions, thrombosed aneurysms and hypothenar hammer syndrome can now easily be detected using a well-constructed CTA protocol. Thanks to the ability to analyse both the vessel’s lumen and wall, hypothenar hammer syndrome can now be described with ease. Recent progress in 3D imaging facilitates the characterisation of the ulnar artery aneurysms, even when thrombosed, which complicate hypothenar hammer syndrome. This point is dominant for therapeutic care.