Original Abstract
In malignant pleural effusion (MPE), malignant cells may settle in a gravity-dependent gradient due to the weight of cells. We aimed to compare diagnostic yield of cytology between aspirates from lower, upper and 5th intercostal spaces in suspected malignant moderate to massive effusion under transthoracic ultrasound guidance (TUS). This single-center, analytical, cross-sectional study was conducted over 6 months. 62 subjects with suspected MPE having moderate to massive effusion on TUS were asked to either sit or recline on bed at 45 - 90inclination for 2 hours. Under TUS guidance, diagnostic thoracentesis was done from lowermost space (2 intercostal spaces [ICS] above the level of diaphragm), uppermost space (1-2 ICS below highest level) and triangle of safety. Diagnostic yields for malignancy on cytology were compared between three sites. 36 subject's cytology returned positive for malignancy. The median lowest and highest ICS of aspiration was 7th and 4th ICS respectively. Lower space aspirate showed higher positivity (88.9%) compared to upper space (58.3%; Mcnemar critical value 3.84, p=0.013). It showed poor agreement (k=-0.085 p=.473) to upper space and moderate level (k=0.321, p=0.025) with mid axillary line aspirate (72%, n=26). Lung malignancies showed better lower space aspirate positivity than extra-pulmonary (p=0.018). Pleural nodule, central/ peripheral lung mass and cancer sub-type did not affect the diagnostic yield. No complications were noted in any subject. Diagnostic thoracentesis from lower ICS may provide higher cytological yield in suspected MPE, however, this must be done only under TUS guidance to prevent complications.