Even small aneurysms can bleed: a ruptured small idiopathic aneurysm of the internal thoracic artery

Abstract

Internal thoracic artery (ITA) aneurysms are rare, but a rupture is potentially fatal. Most cases of ITA aneurysms are iatrogenic, caused by, for instance, previous sternotomy or pacemaker implantation. Other known aetiologies are vasculopathies, either of inflammatory origin or as part of connective tissue disorders like Marfan's syndrome, Ehler-Dahnlos syndrome or neurofibromatosis Type 1. Idiopathic ITA aneurysms are exceedingly scarce. The present case illustrates an unusual scenario, which posed diagnostic challenges, where spontaneous rupture of an idiopathic or possibly very late post-traumatic aneurysm of the left ITA led to a life-threatening bleeding, successfully treated by endovascular coiling with standby preparation for conversion to open surgery. This case demonstrates the importance of the careful interpretation of radiological findings and the significance of multidisciplinary collaboration between radiologist and clinician.

INTRODUCTION

The internal thoracic artery (ITA) is a relatively large artery with an average blood flow of 60 ml/min [1], which under different conditions can increase to as much as 175 ml/min [2, 3]. Accordingly, injury to the ITA can cause severe or even fatal bleeding.

Aneurysm development in the ITA is very unusual, with only around 40 cases being reported in the last 40 years [4]. Since atherosclerosis rarely affects the ITA, this aetiology cannot explain aneurysmal disease in this location. Instead, a clear majority of ITA aneurysms are iatrogenic, caused by, for instance, sternotomy or pacemaker implantation. The leading causes behind the remaining, non-iatrogenic cases are thought to be either inflammatory vasculitis or connective tissue disease related to, for instance, Loeys-Dietz syndrome, Marfan's syndrome, Ehler-Danlos syndrome, neurofibromatosis Type 1 or fibromuscular dysplasia, summarized by Okura et al. [4]. A third possible cause of ITA aneurysms is trauma [5]. Idiopathic cases are, on the other hand, extremely rare and have, to our knowledge, only been reported once [4].

CASE REPORT

A 57-year old man treated for hypertension and hyperlipidaemia by a combination of metoprolol, enalapril, hydrochlorothiazide, felodipine and simvastatin presented in the emergency room with left-sided shoulder pain. He admitted to poor compliancy with respect to anti-hypertensive treatment. Twenty-one years previously, he had suffered a high-energy motor vehicle accident (90 km/h) with isolated bilateral fractures of the scapulae, treated conservatively. There was no family history of aneurysms or sudden death, even though there was a hereditary burden of ischaemic heart disease on the paternal side.

The patient was stable upon admission (Table 1 shows the vital statistics), and as the most prominent symptom was shoulder pain, he was examined by an orthopaedic surgeon, treated with a tablet diclofenac 50 mg and was about to be discharged under the diagnosis of frozen shoulder. Just before the patient left the emergency room, he again experienced sudden left-sided shoulder pain radiating towards the side of the chest. He concomitantly lost blood pressure to 80/50 mmHg and was urgently taken to undergo computed tomography (CT) scan under suspicion of aortic dissection, which revealed a large left-sided pleural effusion and haemomediastinum. There was no sign of pathology in the thoracic aorta. However, the left ITA (LITA) was tortuous and slightly widened in its proximal-mid section, which led to the suspicion of a small aneurysm, but without any ongoing contrast extravasation (Fig. 1A). It was decided to perform an urgent angiographic examination of the LITA and aorta to rule out any sign of rupture, even though the patient's condition stabilized. Blood group testing was performed in case of a need for transfusion.

Table 1.

Vital parameters upon admission.

Blood pressure	180/120 mmHg
Heart rate	85/min
Peripheral oxygen saturation	97%
Respiratory frequency	16/min
Haematocrit	45%
Haemoglobin	15.8 mg/dl
Leucocyte count	7.2 × 109/l

Figure 1.

Radiological examinations. Reconstructed sagittal (A) section from the initial CT scan revealing the aneurysm of the left internal thoracic artery, LITA (black arrow) as well as the haemomediastinum and haemothorax (white arrows). A thickening of the sternum can also be seen (white arrow head). The patient improved instantaneously after coiling, performed distally and proximally of the aneurysm (B). The black arrow points to where the aneurysm was (B).

The patient was taken to the hybrid operation room. A central venous catheter and an arterial line were inserted. The patient again experienced pain in the shoulder and chest, and blood pressure dropped to 70/45 mmHg, upon which blood transfusion was started. Because of rapid deterioration, the patient was intubated with a double-lumen tracheal tube to enable one-lung ventilation and conversion to open surgery via thoracotomy. A cardiothoracic operation team was assembled.

Puncture of the femoral artery and selective catheterization of the left subclavian artery and LITA were performed. Angiography demonstrated a small LITA aneurysm without any signs of extravasation. However, the patient was still highly instable and needed constant transfusion to maintain a blood pressure of 70/45 mmHg.

When catheterizing the aneurysm with a microcatheter (Renegate™ STC18, Boston Scientific), it easily slipped outside the wall of the aneurysm and contrast injection showed no flow, confirming a position of the catheter just outside the vessel wall. It was decided to occlude the LITA with detachable coils (Interlock DC, Boston Scientific) placed distally and proximally to the small aneurysm (Fig. 1B). The blood pressure and haemodynamics improved immediately, and the procedure could be terminated under stable conditions. No examination of the aorta was deemed necessary. A chest tube was placed and 700 ml of blood rapidly drained. Five units of packed red blood cells, five units of fresh-frozen plasma and 1 l Ringer's acetate were transfused at the maximum rate during the procedure.

The patient was taken to the intensive care unit and extubated the next day. Due to severe hypertension, nitroglycerin (1 mg/ml) was started. On the second postoperative day, the patient was taken to the cardiothoracic ward for continued monitoring and anti-hypertensive treatment. A chest X-ray on the third postoperative day revealed that the mediastinum was still significantly widened and there were bilateral pleural effusions, more prominent on the left side. Ultrasonography of the heart demonstrated normal heart function and the absence of fluid in the pericardial space. Control CT scan on postoperative day 5 showed regression of the mediastinal fluid, a moderate amount of left-sided, and a small amount of right-sided, pleural effusion. This was assessed to be satisfactory and the patient was discharged home the next day. Subsequent follow-up was largely uneventful.

DISCUSSION

Idiopathic ITA aneurysms are exceedingly scarce, and have, to our knowledge, only been reported once [4]. The aetiology of the aneurysm in the present case cannot be absolutely defined—we have characterized it as idiopathic, but it could possibly be considered very late post-traumatic. It is probable that the poorly managed hypertension contributed to the rupture. In the current patient, the trauma occurred 21 years ago, whereas in a reported case of post-traumatic ITA aneurysm it occurred only a few months after the accident [5]. Also, the aneurysm in the present case was small, which argues against the trauma as a primary cause, as this would have meant an extremely slow growth. However, we cannot deny with certainty that the trauma could have been a contributing factor, particularly as there is a possible area of callus in the sternum, in front of the LITA.

The objective of this report was to share the diagnostic uncertainty the case presented; there was severe mediastinal bleeding without obvious cause, and no extravasation was seen on the CT scan. The only aberrant finding was the slightly anomalous LITA, and based on this, a decision for urgent intervention was taken. However, extravasation was also absent on the initial angiogram, raising uncertainty regarding whether this was the right track. The diagnosis became apparent first after direct catheterization of the small aneurysm, demonstrating contrast extravasation. This report therefore adds to the limited body of knowledge regarding ITA aneurysms and also illustrates a classic pitfall; the patient showed a multiphasic disease course, and was about to be discharged when pronounced deterioration occurred. The lack of extravasation and the multiphase disease course are likely explained by unstable thrombus formation around the rupture.

Conflict of interest: none declared.