Basilar artery thrombosis

Clinical History

This 35-year-old lady attended A & E complaining of headache and brief loss of consciousness. After an unremarkable clinical assessment she was discharged home. Three hours later she returned with similar symptoms and whilst awaiting review her GSC dropped to 7/15. Intubation was required.

Prompt CT imaging of the head was performed.

Imaging Findings

This 35-year-old lady was imaged with unenhanced CT of the head within 20 minutes of her intubation in A & E. This demonstrated normal appearances of the brain parenchyma, however, the basilar artery was hyperdense, suggesting the presence of acute thrombosis (Fig. 1).

Over the subsequent 12 hours further imaging was undertaken with MR, including diffusion weighted sequences and MR angiography. Acute infarction of the entire pons, secondary to complete occlusion of the basilar artery was demonstrated. High signal change was demonstrated on both the T2 and DWI images (Figs. 2 & 3) with matching low signal change on the ADC map consistent with acute infarction due to diffuse restriction.

MR angiography was performed following embelectomy which shows incomplete demonstration of the basilar artery and absent of the right vertebral artery (Fig. 4).

Discussion

Basilar artery thrombosis is caused by partial or complete obstruction of the basilar artery and may cause brainstem ischaemia or infarction. The basilar artery is the most important artery in the posterior circulation. It is formed at the pontomedullary junction by the confluence of both vertebral arteries. Acute basilar artery occlusion, whether forming primary atheromatous disease or embolism, is a devastating event, almost always resulting in significant morbidity and mortality. Early diagnosis is essential to allow for direct, potentially life or function-saving intervention [1].

CT is typically the first imaging investigation undertaken, with the earliest sign on CT being a hyperdense basilar artery (Fig. 1). In acute stroke patients, the presence of a hyperdense basilar artery on unenhanced CT is a specific but insensitive indicator of acute thrombosis. This may be difficult to detect if the vessels are calcified as in the older patient population. It has a low sensitivity for early ischaemia and usually has the disadvantage of significant artefacts caused by the bony structures surrounding the brain stem and cerebellum. Additional signs of posterior circulation infarction in the brainstem, thalami and cerebellum may be present [2]. The Basilar Artery International Cooperation Study (BASICS) registry team attempted to determine whether the hyperdense basilar artery (HDBA) sign had utility in detecting thrombosis and predicting outcome in patients presenting with signs and symptoms of posterior circulation stroke. The conclusion from the study was that patients presenting with a high pretest probability of posterior circulation stroke based on clinical symptoms, the presence of the hyperdense basilar artery sign on unenhanced CT is a strong predictor of basilar artery thrombosis, and both short- and long-term outcome [3].

Computed tomography angiography (CTA) has been shown to be highly accurate in detecting acute basilar artery occlusion along with MRI with angiographic sequences. It is a true neurointerventional emergency and, which if not treated early, brainstem infarction results in rapid deterioration in conscious level and death. Those that survive typically have a poor outcome. The mortality rate is consistently reported at greater than 70%. Recanalisation may decrease the mortality rate by 50% [1].

Recanalsation of the basilar artery is key to the successful treatment of basilar artery thrombosis and for improving the prognostic outcome. Despite several studies in this field, unresolved issues remain and need further clarification, such as the best method of recanalisation (intra-arterial thrombolysis, mechanical thrombolysis, or combination), the time window for the treatment, and patient selection. In institutions with an advanced neurointerventional service available, intra-arterial pharmacological or mechanical thrombolysis can be considered. Treatment usually involves catheter-directed intra-arterial thrombolysis and intravenous heparin, which carries a significant risk of haemorrhage of up to 15%. Mechanical embolectomy with a clot retrieval device has been used in selected cases. A recent small case series indicated that aspiration thrombectomy performed manually through an intra-arterial catheter can facilitate recanalisation of basilar artery occlusion with acceptable clinical outcomes, when intra-arterial TPA and two passes with mechanical thrombectomy did not ensure complete recanalisation [4].

Differential Diagnosis List

Final Diagnosis

Basilar artery thrombosis with consequential pontine infarction

URL:	https://www.eurorad.org/case/8492
DOI:	10.1594/EURORAD/CASE.8492
ISSN:	1563-4086