3.1. Bleeding risk and regional anatomy

This case illustrates a rare but clinically important vascular complication temporally associated with an ultrasound-guided supraclavicular block. The available evidence suggests that bleeding after supraclavicular block is uncommon. Tsui and colleagues reported vascular puncture rates of 0 to 0.4% in large supraclavicular-block studies and identified no hematomas or published hematoma case reports for this approach in their review¹. Large clinical series have also reported low rates of clinically significant complications after ultrasound-guided supraclavicular block⁸. These data support the safety of the technique at a population level, but they cannot exclude rare, high-consequence events in individual patients.

The supraclavicular fossa is anatomically complex. The subclavian artery is a key landmark, but smaller branches of the thyrocervical system may not be conspicuous on routine grayscale imaging. The transverse cervical and other arterial branches can be at risk during needle advancement^1,3. In addition, anatomic variation in the relationship between the brachial plexus and subclavian artery has been described and ultrasound may reveal variants that materially change the safest needle trajectory⁴. In the present case, no additional pulsatile vessel was visualized during the block, yet a distal thyrocervical branch pseudoaneurysm was later demonstrated. This finding highlights that visualization of the expected major vessels does not prove that all smaller or variant vessels have been excluded from the needle path.

3.2. Patient-specific considerations

The patient had several potential bleeding-risk modifiers, including thrombocytopenia and end-stage renal disease. He was not taking chronic anticoagulation for atrial fibrillation, but the source record does not report whether anticoagulation was used during the preceding dialysis session. Therefore, the relative contribution of platelet dysfunction, thrombocytopenia, uremia, dialysis-related factors and direct arterial trauma cannot be determined. The case also does not establish that the needle directly injured the later-identified branch; the relationship is inferred from the temporal sequence, location of the hematoma and angiographic diagnosis.

Bleeding-risk assessment before peripheral nerve and interfascial plane blocks should be individualized rather than based solely on whether a patient is receiving therapeutic anticoagulation. Expert consensus emphasizes that evidence for bleeding risk is limited and that recommendations should support, rather than replace, clinical judgment¹. In a patient with thrombocytopenia or renal disease, the decision to proceed should incorporate the urgency and benefit of the block, alternative anesthetic strategies, the planned needle path, the ability to compress the site and the feasibility of post-procedure observation.

3.3. Diagnostic implications of delayed symptoms

The initial bedside ultrasound identified the hematoma but did not demonstrate active bleeding or a pseudoaneurysm. Four hours after discharge, the patient returned with new firmness and pain and Computed Tomography Angiography (CTA) then showed a large hematoma with a contrast blush. This sequence is clinically important because pseudoaneurysms may evolve after the initial injury and may be missed when the study is performed early, when the lesion is small or when the relevant branch is difficult to visualize. Ultrasound guidance during the block and an initially reassuring post-procedure examination should therefore not be interpreted as definitive exclusion of delayed arterial injury.

New or progressive swelling, increasing firmness, pain, pulsatility, neurologic symptoms, airway symptoms, hemodynamic change or a fall in hemoglobin should prompt immediate reassessment. When the clinical course is discordant with an initial bedside study, contrast-enhanced Computed Tomography Angiography (CTA) can define the size and extent of the hematoma and identify a contrast blush or pseudoaneurysm. Catheter angiography remains useful when a treatable arterial source is suspected because it can establish the diagnosis and permit selective embolization.

3.4. Management considerations

Management should be individualized according to hemodynamic status, airway and neurologic findings, hematoma behavior and the anatomy of the arterial lesion. Initial measures may include close observation, pressure when anatomically appropriate, serial neurovascular and airway assessment and early involvement of vascular surgery, interventional radiology and other relevant services. The reported patient was initially stable, but delayed clinical progression led to Computed Tomography Angiography (CTA), admission and subsequent angiography.

The distal thyrocervical branch pseudoaneurysm was treated with Onyx and Optoblock coils, followed by percutaneous thrombin injection. Endovascular treatment is commonly used for selected thyrocervical or subclavian branch pseudoaneurysms and branch-vessel hemorrhage, while open or hybrid repair may be appropriate when anatomy, lesion size, collateral circulation or failure of endovascular treatment requires it^9-11. In a retrospective series of subclavian and axillary branch hemorrhage, transcatheter arterial embolization achieved 100% technical success and 85.7% clinical success, although the study population and causes of bleeding were heterogeneous¹¹. These results support early consultation with an endovascular team when imaging identifies a potentially treatable branch-vessel source, but they should not be interpreted as a procedure-specific outcome estimate for supraclavicular block complications.

4. Strengths and Limitations

The principal strength of this report is the clinically detailed sequence from block placement to initial ultrasound, delayed return, Computed Tomography Angiography (CTA), angiographic diagnosis and definitive treatment. The case also documents relevant platelet counts and the absence of early neurologic or respiratory compromise. Limitations include the single-patient design, incomplete information about the exact needle gauge and trajectory, absence of documented dialysis anticoagulation details, lack of a long-term follow-up assessment and inability to prove direct needle injury to the pseudoaneurysm branch. The case should therefore generate vigilance and hypotheses rather than establish incidence or causation.

5. Conclusion

A distal thyrocervical branch pseudoaneurysm can present as a delayed enlarging supraclavicular hematoma after an ultrasound-guided supraclavicular brachial plexus block, even when the initial ultrasound does not show active bleeding or a pseudoaneurysm. Thrombocytopenia and end-stage renal disease may increase concern for bleeding, but the specific contribution of each factor cannot be determined from this case. Progressive swelling or new pain warrants serial clinical assessment and timely escalation to CTA and catheter angiography, with early multidisciplinary management when an arterial source is suspected.

6. Declarations

6.1. Ethics approval

This report describes a single-patient case and was not conducted as human-subjects research. In accordance with University of South Florida IRB guidance, retrospective review of records for publication of a single case report involving three or fewer individuals does not require IRB review or approval.

6.2. Consent for publication

Written informed consent was obtained from the patient for the collection, analysis and publication of the clinical information, including images and photographs. Written informed consent was obtained from the patient for publication of this case report, including all clinical details and images. The patient was informed about the purpose of the report, its intended scientific audience and the measures taken to preserve anonymity.

6.3. Conflict of interest

The authors declare that they have no financial or non-financial conflicts of interest related to this work.

6.4. Funding

The authors received no external financial support for the work reported in this case report.

7. References

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2. Hanumanthaiah D, Vaidiyanathan S, Garstka M, et al. Ultrasound guided supraclavicular block. Med Ultrason. 2013.
3. Govender S, Mohr D, Tshabalala ZN, et al. A review of the anatomy and a step-by-step visual guide to performing an ultrasound-guided supraclavicular brachial plexus block. South Afr J Anaesth Analg. 2019.
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10. El Naamani K, Abbas R, Sioutas GS, et al. A complication of the transradial approach: thyrocervical trunk pseudoaneurysm with hemothorax. BJR Case Rep. 2023.
11. Onishi Y, Shimizu H, Ando S, et al. Transcatheter arterial embolization of the subclavian and axillary artery branches for hemorrhage control. Br J Radiol. 2023;96: 20221132.