Endoscopic ultrasound-guided fine needle aspiration/biopsy (EUS-FNAB) plays a key role in diagnosing mediastinal lesions. The choice of needle gauge may impact diagnostic yield, especially for tissue-intensive diagnoses such as lymphoma. This study aimed to assess the diagnostic performance, safety, and procedural efficiency of 19/20-gauge (G) versus 22G needles in EUS-FNAB for mediastinal masses.

A retrospective analysis of a prospectively maintained EUS registry was performed at a single tertiary referral centre (University Hospital Southampton NHS Foundation Trust) for all patients who underwent endoscopic ultrasound-guided fine needle aspiration or biopsy (EUS-FNAB) of solid mediastinal lesions between January 2020 and January 2025.

Patients were categorised according to the needle calibre used: 19/20-gauge (G) (large-bore group) and 22G (standard-bore group). Exclusion criteria included cystic or predominantly necrotic lesions, procedures performed for non-diagnostic therapeutic indications, or incomplete data.

Data collected included: demographics and indication for EUS-FNAB , needle type and number of passes, procedural duration (scope insertion to withdrawal), cytological and histological outcomes, sample adequacy (graded as satisfactory or unsatisfactory based on cellularity and presence of core tissue), adverse events within 7 days (bleeding, perforation, infection, or cardiorespiratory instability).

Primary outcomes were diagnostic sensitivity, specificity, and overall accuracy of EUS-FNAB for establishing a definitive diagnosis, verified against surgical histopathology or clinical follow-up ≥6 months.Secondary outcomes included sample adequacy, number of needle passes, procedural time, and safety.

A total of 136 patients were included: 40 in the 19/20G group and 96 in the 22G group. Baseline demographics, lesion characteristics, and procedural indications were comparable between groups (p > 0.05).

Diagnostic performance:the diagnostic sensitivity for malignancy was significantly higher with the 19/20G needles compared to 22G (94.1% vs 90.0%, p = 0.04).Overall diagnostic accuracy was also superior in the 19/20G group (95.0% vs 88.5%, p = 0.03).Sample adequacy for histological evaluation was achieved in 97.5% of 19/20G cases compared with 89.6% in the 22G group (p = 0.02).

Procedural metrics: The mean number of needle passes required to obtain an adequate specimen was 2.0 ± 0.1 with 19/20G versus 3.2 ± 0.2 with 22G (p < 0.01).Mean procedural duration was significantly shorter with 19/20G needles (18.3 ± 2.1 min vs 23.5 ± 2.4 min, p = 0.01).

Diagnostic subgroup analysis: In lesions where lymphoma was suspected (n = 24), the diagnostic yield was markedly higher with 19/20G needles (93.8% vs 80.0%, p = 0.02). In non-lymphomatous malignancies or benign granulomatous disease, diagnostic accuracy between groups was not significantly different (p > 0.05).On multivariable logistic regression, needle gauge (19/20G) remained an independent predictor of diagnostic accuracy (adjusted OR 2.47, 95% CI 1.12–6.10, p = 0.03), while lesion size and location were not significant.

Safety : No major complications occurred in either group. Minor self-limiting bleeding at the puncture site occurred in two patients (one per group), with no delayed haemorrhage or infection observed (p = 0.82).

EUS-FNAB with 19/20G needles is safe and offers superior diagnostic yield and procedural efficiency compared to 22G needles in the evaluation of mediastinal masses. Larger bore needles should be considered, particularly when lymphoma or diagnoses requiring core tissue architecture are suspected.