Radiological Findings-

MRI of the left brachial plexus (Fig. 1, 2, 3, 4) shows a well-defined heterogeneously T1 hyperintense lesion in the left axillary region. It is hyperintense on T2 with flow voids. It measures approximately 3.5 x 6 x 4.3 cm. The axillary artery is attenuated in calibre and courses anterior to the lesion - abutting its wall. There is compression of the cords of the brachial plexus at the level of the lesion. The roots and trunks of the brachial plexus are normal. 

Fig 1, 2, 3, 4: MRI brachial plexus: A well-defined left axillary pseudoaneurysm (3.5 × 6 × 4.3 cm), T1 heterogeneously hyperintense and T2 hyperintense with internal flow voids, compressing the brachial plexus cords; roots and trunks appear normal.

Left upper limb colour Doppler (Fig. 5, 6, 7)  reveals a large, heterogeneously hypoechoic, focal outpouching arising from the posterior wall of the left axillary artery. It has a wide neck measuring approximately 1.4 cm. It demonstrates the characteristic “yin-yang” sign. There is partially thrombosis with approximately 20% of the sac volume being occupied by the thrombus. The left axillary artery shows normal colour flow, triphasic waveform and velocity. 

Fig 5, 6, 7: Colour Doppler showing a large (1.4 cm neck) heterogeneously hypoechoic pseudoaneurysm from the posterior wall of the left axillary artery with classic ‘yin-yang’ sign and ~20% mural thrombus.

Contrast enhanced CT scan of the left upper limb (Fig. 8) reveals a large pseudoaneurysm arising from the left axillary artery. The aneurysm engulfs the axillary artery inferiorly, anteriorly and posteriorly. The wall of the pseudoaneurysm compresses the proximal axillary artery and causes luminal narrowing over a length of approximately 2 cm. There is an irregular peripheral thrombus along the wall of the pseudoaneurysm. 

Fig 8: CECT of the left upper limb showing a large pseudoaneurysm encasing the axillary artery with ~2 cm proximal narrowing and irregular peripheral mural thrombus.

Fig 9 (left): Photograph  showing a red ulcer on the lateral aspect of the tongue.

Fig 10 (right): Photograph showing skin discoloration associated with chronic lower limb deep vein thrombosis.

Contrast enhanced CT scan of brain reveals partial lumen occluding thrombosis of superior sagittal sinus. (Fig. 12, 13).

Fig 11, 12: Contrast-enhanced CT scan of the brain showing thrombosis of the superior sagittal sinus.

Radiological diagnosis:

Left axillary pseudoaneurysm compressing the divisions and cords of the left brachial plexus. 

Laboratory investigations- HLA B51 positive.

ICBD Score:

• Oral ulcers (2 points)

• Genital ulcers (2 points)

• Neurological: CVST history (1 point)

• Vascular: bilateral DVT, axillary artery pseudoaneurysm (1 point)

Total = 6 points - Strongly diagnostic for Behçet’s disease. 

Final diagnosis:

Vascular Behçet’s with left axillary pseudoaneurysm compressing the left brachial plexus. 

Management: 

A joint opinion from the cardiovascular and thoracic surgery department and Vascular interventional radiology team was obtained. Resection of the pseudoaneurysm with end-to-end anastomosis of the axillary artery was advised to relieve the mass effect and prevent rupture. In view of the underlying vasculo-Behçet’s disease, the patient has been started on corticosteroids to control active vasculitis and reduce perioperative inflammation. Careful preoperative planning is underway to minimize the risk of vascular compromise while balancing anticoagulation needs given the history of cerebral venous sinus thrombosis and deep vein thrombosis. Long-term management for this patient will include immunosuppressive therapy and regular rheumatology and vascular follow-up.

Timeline

Discussion:

Behçet’s disease (BD) is a chronic, relapsing, multisystem inflammatory disorder characterized by vasculitis affecting arteries and veins of any size. Vascular involvement—collectively referred to as vasculo-Behçet—is reported in 7–38% of cases and represents a major cause of morbidity and mortality [1]. While venous manifestations such as deep vein thrombosis and cerebral venous sinus thrombosis are more common, arterial lesions, though less frequent, tend to be more severe due to their tendency to rupture. Among arterial lesions, pseudoaneurysms predominate over true aneurysms in BD, a pattern attributed to the destructive nature of the underlying pan-vasculitis [2]. 

In BD, immune-mediated injury involves all vessel wall layers, with pronounced neutrophilic infiltration of the media leading to fragmentation of elastic fibers and collagen. This structural weakening predisposes the artery to focal rupture. Blood escaping through the disrupted intima and media is contained by the adventitia or surrounding soft tissue, forming a pseudoaneurysm [3]. The axillary artery is an unusual location for pseudoaneurysm development in BD, but it may be predisposed due to its medium-to-large caliber, relative superficiality, and mechanical stress from upper limb mobility.

Compression neuropathy occurs when the pseudoaneurysm expands within the confined axillary space, exerting direct pressure on the brachial plexus. This can present with pain, sensory deficits, and motor weakness, potentially mimicking primary neurological disorders and delaying diagnosis. In our patient, the pseudoaneurysm was detected incidentally during MRI evaluation for suspected brachial plexus pathology, underscoring the importance of considering vascular causes in atypical neurological presentations.

Management of arterial pseudoaneurysms in BD requires a dual approach: control of underlying inflammation and repair of the vascular lesion [4]. High-dose corticosteroids, immunosuppressive agents such as cyclophosphamide, and biologic agents (e.g., anti-TNF therapies) are essential to suppress active vasculitis and reduce recurrence risk [5]. Surgical or endovascular repair is often necessary to prevent rupture or relieve compressive symptoms. Endovascular options, such as covered stent placement, are increasingly favored in acute settings due to lower procedural trauma and reduced risk of new anastomotic pseudoaneurysm formation, although anatomical feasibility remains a determining factor [6, 7, 8]. Regardless of intervention type, recurrence rates remain high if disease activity is not controlled. 

Axillary artery pseudoaneurysm with brachial plexus compression in BD is exceedingly rare, with few cases reported in literature. The present case is further notable for the coexistence of multiple vascular manifestations—including prior cerebral venous sinus thrombosis and bilateral lower limb DVT—reflecting aggressive vasculo-Behçet. Early recognition, multimodal imaging, and coordinated medical-surgical management are critical for favorable outcomes. 

This case emphasizes that in patients with BD, especially those with a history of vascular involvement, unusual neurological presentations should prompt evaluation for vascular lesions, as timely diagnosis and intervention can prevent irreversible neurological damage and life-threatening complications.

Key Learning Points

Pseudoaneurysm formation in Behçet’s disease results from inflammatory destruction of the arterial media and elastic lamina, leading to focal rupture contained by adventitia or surrounding tissue.

Upper-limb arterial involvement in vasculo-Behçet’s is rare; axillary artery pseudoaneurysms are exceptional and seldom reported.

Mass effect on adjacent neurovascular structures, such as the brachial plexus, can cause symptoms that mimic primary neurological disorders, potentially delaying diagnosis.

Multimodal imaging—including MRI, CT angiography, and Doppler ultrasound—plays a pivotal role in differentiating compressive neuropathy from primary nerve pathology.

Aggressive disease control with immunosuppressive therapy is essential prior to or alongside surgical or endovascular repair to reduce the risk of recurrence.

High recurrence and rupture risk demand close follow-up with serial imaging in patients with arterial lesions in Behçet’s disease.

References:

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