Anomalous origin and aneurysm of the suprascapular artery: the first case observed

Abstract

A 45-year-old woman was referred to our department having suddenly developed, 9 months earlier, a pulsating mass on the right supraclavicular fossa and torticollis. Colour Doppler sonography and computed tomographic angiography showed the presence of an aneurysm (21 mm in diameter) of the suprascapular artery that had an anomalous origin from the subclavian artery. Thoracic outlet syndrome was excluded. After selective arteriography, the aneurysm of the suprascapular artery was successfully treated with ethylene-vinyl alcohol polymer (Onyx, MicroTherapeutics, Irvine, California, USA), a liquid embolic agent. The patient was discharged on the first postoperative day in good condition. Control colour Doppler sonography at 1 year confirmed the complete thrombosis of the aneurysm sac.

BACKGROUND

Aneurysms of the subclavian artery, thyrocervical trunk and its collaterals are extremely rare; they may be the consequence of trauma, central venous cannulation, high performance sport activities (as in baseball players), or result from thoracic outlet syndrome or from atherosclerosis.^1–8 However, no cases of aneurysm of the suprascapular artery with anomalous origin from the subclavian artery are known in the literature. In fact, the suprascapular artery may be a direct branch of the subclavian artery in only 12% of cases whereas, in other cases, its origin may be from thyrocervical trunk (27%), internal thoracic artery (11%) or also from various trunks such as the cervico-scapular trunk (22%), dorso-scapular trunk (4%), and cervico-dorso-scapular trunk (24%).⁹

In this report we describe a unique case of a true aneurysm of the suprascapular artery originating from the subclavian artery, in a patient without any history of trauma. Although the suprascapular artery is a muscular vessel, the presence of an aneurysm constitutes a surgical emergency all the same, especially when the large dimensions of the aneurysm, as was the case for our patient, might cause its rupture.

CASE PRESENTATION

A 45-year-old woman in good clinical condition underwent a colour Doppler sonographic examination for the presence of a nodule in the supraclavicular region, which caused pain when moving her head. An aneurysm (21 mm in diameter) of a collateral vessel (suprascapular artery) of the subclavian artery (fig 1) was detected, and the patient was referred to our department of clinical medicine. It is known that the complex regional anatomy of the posterior cervical triangle and the variable origin of the different cervical and scapular vessels⁹ may facilitate aneurysm formation during cannulation manoeuvres. However, our patient denied experiencing any episode of trauma to the neck and shoulder, and no central venous catheterisation or sporting activity had been performed. On palpation, the 2 cm soft tissue swelling located in the right supraclavicular fossa, just lateral to the insertion of the sternocleidomastoid muscle, was identified as a pulsatile non-tender mass. Physical examination showed normal pressure in both arms and full equal distal pulses. Neurologic examination was also normal, and she had no vertebrobasilar symptoms or pain in the right arm. Laboratory data were normal.

Figure 1.

Colour Doppler sonographic view of the suprascapular artery. In this longitudinal view, the patency of the suprascapular artery past the aneurysm (white arrows) is shown: the flow (below the baseline) draws away from the transducer indicating that it is directed to the muscle.

INVESTIGATIONS

A contrast medium computed tomography (CT) scan confirmed the diagnosis of suprascapular artery aneurysm; however, due to the fact that the suprascapular artery aneurysm was near a trifurcation and that thoracic outlet syndrome was excluded, it was considered advisable to rule out the surgical option. In fact, the patient underwent selective arteriography of the artery. This procedure was performed in the angiography suite under local anaesthesia with a 5 French vertebral catheter that confirmed the presence of an aneurysm of a suprascapular artery arising directly from the third part of the right subclavian artery (fig 2A). On left oblique anterior arteriography, an anomalous origin of the thyrocervical trunk was also found (fig 2B). Intraoperative angiographic dynamic manoeuvres confirmed the absence of a thoracic outlet syndrome.

Figure 2.

Intraoperative selective angiogram of the innominate artery confirming the presence of a large aneurysm (*) of the suprascapular artery (SSA). The SSA arises directly from the subclavian artery at variance with the usual origin from the thyrocervical trunk (panel A). The thyrocervical trunk (TCT) has an anomalous origin from the posterior surface of the subclavian artery (SA) at the level of the internal mammary artery (IMA), as can be seen on a 45° left anterior projection (panel B). aca, ascending cervical artery; CCA, common carotid artery; CCT, costocervical trunk; ita, inferior thyroid artery; tca, transverse cervical artery; VA, vertebral artery; *suprascapular artery aneurysm.

TREATMENT

After superselective catheterisation of the suprascapular artery with a dimethyl sulfoxide-compatible Rebar microcatheter (MicroTherapeutics, Irvine, California, USA), many small side branches arising from the aneurysm were observed. In order to embolise the aneurysm and its smallest collaterals, a total of 0.9 ml of ethylene-vinyl alcohol polymer (Onyx 500, a high viscosity preparation of this liquid embolic agent manufactured by MicroTherapeutics) was injected under fluoroscopic control at a rate of approximately 0.2 ml/min via the microcatheter. Control digital subtraction arteriography was satisfactory (fig 3).

Figure 3.

After superselective catheterisation of the suprascapular artery (SSA) with a 5 French vertebral catheter and a dimethyl sulfoxide-compatible Rebar microcatheter, ethylene-vinyl alcohol polymer (Onyx) is injected slowly via the microcatheter in order to fill up the aneurysm and its side branches. Post-embolisation angiography shows complete suprascapular artery aneurysm exclusion. CCT, costocervical trunk; SA, subclavian artery; VA, vertebral artery.

OUTCOME AND FOLLOW-UP

The postoperative course was uneventful and the patient was discharged on the first postoperative day in good general condition. A mild pain over her shoulder, as well as torticollis, completely disappeared after 2 weeks. Twelve months later the patient is doing well and a control echo colour Doppler has confirmed the complete exclusion of the aneurysm sac.

DISCUSSION

The subclavian artery is the major vessel of the upper thorax that supplies blood to the head and arms. Usual branches of the subclavian artery on both sides of the body are, in sequence, the internal mammary artery, the vertebral artery, the thyrocervical trunk, and the costocervical trunk (fig 4). The suprascapular artery (or transverse scapular artery) is a branch of the thyrocervical trunk in most cases. It usually passes transversely across the neck in front of the scalenus anterior muscle and phrenic nerve, being covered by the sternocleidomastoid muscle. It then crosses the subclavian artery and the brachial plexus, running behind and parallel with the clavicle and subclavius muscle.

Figure 4.

Schematic representation of the most frequent anatomic pattern of the subclavian artery and its collaterals. aca, ascending cervical artery; CCT, costocervical trunk; IMA internal mammary artery; ita, inferior thyroid artery; SA, subclavian artery; SSA, suprascapular artery; tca, transverse cervical artery; TCT, thyrocervical trunk; VA, vertebral artery.

In this report we describe, for the first time, an atraumatic case of aneurysm of the suprascapular artery with anomalous origin from the subclavian artery. This rare anomalous origin (12%)⁹ and the particular location of the aneurysm itself complicated the choice of treatment. In fact, the presence of a trifurcation immediately past the origin of the aneurysm made it difficult, if not impossible, to undertake surgical intervention. Furthermore, clinical and instrumental investigations such as colour Doppler sonography and CT angiography excluded the presence of a thoracic outlet syndrome. In the case of aneurysm of a collateral of the subclavian artery, treatment options include simple observation, surgical intervention, transcatheter embolisation alone or followed by surgery. Therefore, together with interventional radiologists, we decided to perform transcatheter embolisation of the suprascapular artery aneurysm with the high density compound Onyx 500, which is especially indicated for the occlusion of large aneurysms and when their collaterals are numerous and small as in this case. In fact, this liquid embolic agent allowed us to fill both the aneurysm and all the collaterals at one time, with satisfactory intraoperative results (fig 3). To our knowledge, this is the first reported case of true aneurysm of a suprascapular artery successfully treated with Onyx. The pathogenesis of this suprascapular aneurysm remains unclear.

LEARNING POINTS

• The presence of torticollis together with a pulsating mass in the posterior cervical triangle, despite the absence of trauma or cannulation manoeuvres, should arouse suspicion of the presence of an aneurysm.

• Surgical intervention may not be the best strategy, given the complex vascular anatomy of the neck.

• Transcatheter embolisation is safe and highly effective in these situations.