1. INTRODUCTION  

Thoracic Outlet Syndrome (TOS) is rare and difficult to diagnose, especially in pediatric patients.   

Challenges in Diagnosis: Symptoms overlap with other conditions, and traditional tests may be inconclusive due to patient cooperation and the dynamic nature of TOS.   

Anterior Scalene Muscle Block (ASMB) as a Diagnostic Tool: A minimally invasive method to confirm neurogenic TOS (nTOS). Its role in pediatrics remains unclear.  

2. PURPOSE  

To emphasize the value of ASMB in diagnosing and guiding treatment in pediatric patients, filling a gap in the existing literature.  

3. CASE DESCRIPTIONS  

* History and Symptoms   

A 12-year-old girl (48.9 kg) presented with right arm weakness, numbness, and intermittent edema for 9 months, along with daily flare-ups and hand discoloration.   

* Examination and Imaging   

Positive EAST (Elevated Arm Stress Test), normal EMG, and chest MRA showing positional subclavian vein compression without thrombosis.   

* Procedure   

Ultrasound-guided Anterior Scalene Muscle Block (ASMB) was performed under minimal sedation using a 22-gauge, 50-mm Sono-TAP needle (PAJUNK®, Germany) with 5 mL of 0.5% ropivacaine (Figure 1A, 1B).   

* Outcomes   

Symptoms improved within 60 minutes (increased strength, reduced tingling), with relief lasting until the evening.   

* Follow-up   

Referred for surgery; underwent first rib excision and brachial plexus neurolysis. Postoperatively, symptoms were completely resolved.   

* History and Symptoms   

A 15-year-old girl (54.8 kg) presented progressive right upper arm pain (8–9/10) over 9 months, along with sharp, radiating pain to fingers, paresthesia, decreased sensation, and trapezius muscle spasms.   

* Imaging   

MR brachial plexus and chest showed right subclavian vein compression in the costoclavicular space during abduction.   

* Procedure   

Ultrasound-guided Anterior Scalene Muscle Block(ASMB) was performed under minimal sedation using a 24-gauge, 40-mm Sono-TAP needle (PAJUNK®, Germany) with 5 mL of 0.5% ropivacaine (Figure 2A, 2B).   

* Outcome   

Immediate pain relief, no numbness with arm movement. Developed transient right-sided Horner’s syndrome and shoulder weakness, both of which resolved quickly.   

* Follow-up   

Referred for surgery; underwent first rib excision one month later. Postoperatively, pain significantly decreased, and arm/hand paresthesia completely resolved.   

4. DISCUSSION   

ASMB can facilitate early diagnosis by providing immediate symptom relief, confirming neurovascular compression, and reducing the need for extensive imaging studies and consultations.   

ASMB guides treatment decisions, including surgery, with temporary and self-limiting side effects. Further studies are needed to refine its role and optimize its use in pediatric care.