How is the Burgos‑Occlusion‑Clot‑Score 2 (BOCS‑2) calculated and used to identify a cardioembolic source in an acute ischemic stroke patient with indeterminate TOAST classification after mechanical thrombectomy?

BOCS-2 Scale: Calculation and Clinical Application

The Burgos-Occlusion-Clot-Score 2 (BOCS-2) is a 4-point scoring system that combines histopathological clot characteristics with angiographic occlusion patterns to identify cardioembolic sources in acute ischemic stroke patients with indeterminate TOAST classification after mechanical thrombectomy, achieving 93.5% sensitivity and 100% specificity for cardioembolism when scores reach 3-4 points 1.

Score Components and Calculation

The BOCS-2 scale integrates two key elements to generate a composite score:

Histopathological Clot Analysis

• Platelet distribution pattern is the critical histological discriminator: clustering patterns indicate cardioembolism, while peripheral patterns suggest large artery atherosclerosis 1.
• Cardioembolic thrombi demonstrate significantly higher proportions of fibrin/platelets, fewer erythrocytes, and more leukocytes compared to non-cardioembolic thrombi 2.
• Platelet-rich clots (>55% platelet content) are strongly associated with large artery atherosclerosis rather than cardioembolism (55.0% versus 21.2%; P=0.005) 3.

Angiographic Occlusion Type (AOT) Classification

• Branching-site occlusions predominantly show clustering platelet patterns and correlate with cardioembolic etiology (p=0.007) 1.
• Truncal-type occlusions predominantly show peripheral platelet patterns and correlate with large artery atherosclerotic disease 1.
• The AOT classification demonstrated stronger statistical correlation with clot histology than TOAST classification alone (p=0.007 versus p=0.02) 1.

Clinical Application Algorithm

Step 1: Obtain Retrieved Thrombus Material

• Collect clot specimens during mechanical thrombectomy from patients with intracranial internal carotid artery or proximal middle cerebral artery occlusions 1.
• Ensure adequate tissue for full histopathologic examination using hematoxylin and eosin staining 1.

Step 2: Perform Histopathological Analysis

• Quantify relative fractions of red blood cells, white blood cells, and fibrin/platelets using machine learning software or manual quantification 1, 2.
• Determine platelet distribution pattern: clustering versus peripheral arrangement 1.
• Calculate percentage of platelet content within the thrombus 3.

Step 3: Document Angiographic Findings

• Record occlusion location during thrombectomy: branching-site versus truncal-type 1.
• Assess recanalization success using modified TICI scale (goal: TICI 2b/3) 4, 5.

Step 4: Calculate BOCS-2 Score

• Assign points based on the combination of platelet distribution pattern and angiographic occlusion type 1.
• Scores of 3-4 points indicate cardioembolic etiology with 93.5% sensitivity and 100% specificity 1.
• Scores of 0-2 points suggest alternative etiologies (large artery atherosclerosis or small vessel disease) 1.

Interpretation for Indeterminate TOAST Cases

High BOCS-2 Score (3-4 Points)

• Reclassify as cardioembolic stroke and initiate appropriate secondary prevention 1.
• Perform comprehensive cardiac evaluation including transesophageal echocardiography to identify atrial sources, patent foramen ovale, or aortic arch atherosclerosis 4.
• Consider anticoagulation therapy after ruling out hemorrhagic transformation 5.

Low BOCS-2 Score (0-2 Points)

• Investigate for large artery atherosclerosis using carotid duplex scanning and cerebral angiography 4.
• Consider antiplatelet therapy rather than anticoagulation 5.
• Evaluate for tandem lesions requiring carotid stenting 5.

Evidence Strength and Limitations

The BOCS-2 scale represents a novel adjunctive diagnostic tool with excellent specificity but is derived from a single-center study of 52 patients 1. The scale addresses a critical clinical gap, as cryptogenic strokes show strong histological overlap with cardioembolic patterns (50% platelet-rich clots in cryptogenic versus 55% in large artery atherosclerosis versus 21.2% in cardioembolism) 3.

Critical Pitfalls to Avoid

• Do not apply BOCS-2 to distal vessel occlusions or posterior circulation strokes, as validation was limited to intracranial ICA and proximal MCA occlusions 1.
• Ensure adequate clot material is retrieved; insufficient tissue precludes reliable histopathological analysis 1.
• Do not use BOCS-2 as the sole determinant of etiology; it should complement comprehensive stroke workup including cardiac imaging, vascular imaging, and clinical assessment 1, 2.
• Recognize that 30% of large vessel occlusions remain cryptogenic despite advanced classification systems, and BOCS-2 may help reclassify a subset of these cases 3.