Pleural effusion; the abnormal accumulation of fluid within the pleural space represents a frequent clinical problem encountered across pulmonary, general medical, and critical care units [1]. The spectrum of underlying etiologies is broad, spanning congestive heart failure, hepatic hydrothorax, tuberculosis, parapneumonic effusions, empyema, and primary or metastatic thoracic malignancies [2]. Timely, accurate diagnosis and targeted intervention are critical to prevent irreversible pleural thickening, fibrothorax, sepsis, or advanced malignant progression [3].

Historically, the evaluation of pleural effusion relied heavily on physical examination and standard two-view chest radiography (CXR) [4]. However, physical examination lacks sensitivity for detecting small volume effusions (< 300mL) and fails to reliably distinguish pleural fluid from parenchymal consolidation or dense pleural thickening [5]. Plain CXR can only detect effusions when fluid volume exceeds 175 to 200mL on erect views, and it is inherently limited in identifying early fibrin septations, multiloculations, subpulmonic collections, or subtle diaphragmatic nodularity [6]. Furthermore, "blind" or landmark-guided thoracentesis carries a documented pneumothorax rate ranging from 8% to 15%, alongside risks of dry taps, hemothorax, and visceral organ puncture [7].

Over the past two decades, Thoracic Ultrasonography (TUS) has revolutionized the field of respiratory medicine [8]. TUS offers non-invasive, real-time, high-resolution visualization of the chest wall, parietal and visceral pleura, pleural space, lung parenchyma, and diaphragm [9]. Unlike computed tomography (CT), TUS operates without ionising radiation, can be performed dynamically at the bedside, and allows immediate real-time guidance during diagnostic and therapeutic maneuvers [10].

Despite the clear benefits of Point-of-Care Ultrasound (POCUS) utilized by Respiratory Physicians for immediate triage and bedside procedures, specialized Radiodiagnosis evaluation remains vital for complex, atypical, or indeterminate pleural diseases [11]. High-end ultrasound platforms managed by radiologists provide superior tissue characterization, Doppler flow assessment of pleural masses, and precise differentiation of complex chest wall pathologies [12]. A collaborative clinical-radiological framework leverages the immediacy of respiratory care with the diagnostic sophistication of advanced radiology [13].

This study was designed to systematically evaluate the diagnostic yield, sonographic patterns, procedural safety, and clinical outcomes of USG-guided evaluation of pleural effusions in a prospective cohort managed through a collaborative pathway between Respiratory Medicine and Radiodiagnosis.

Study Design and Ethical Considerations This prospective observational cohort study was conducted jointly by the Department of Respiratory Medicine and the Department of Radiodiagnosis at KBN Teaching & General Hospital, attached to KBN University-Faculty of Medical Sciences; a tertiary academic healthcare center, over a 12-month period (July 2025 to June 2026). The study protocol was reviewed and approved by the Institutional Ethics Committee, and written informed consent was secured from all participants or their legally authorized representatives prior to enrollment in accordance with the Declaration of Helsinki. Patient Selection Criteria Inclusion Criteria: • Patients aged ≥18 years presenting with clinically or radiographically documented pleural effusion. • Patients requiring diagnostic thoracentesis, therapeutic drainage, or pleural biopsy. • Provision of signed informed consent. Exclusion Criteria: • Uncorrected severe coagulopathy (International Normalized Ratio [INR] > 1.8 or platelet count < 50,000/µL). • Severe local chest wall skin infections or active burns at potential puncture sites. • Uncooperative or hemodynamically unstable patients unable to maintain basic positioning. Sonographic Evaluation Protocol Patients underwent a sequential two-tier sonographic assessment: 1. Respiratory Medicine POCUS: Performed at the bedside upon admission by trained pulmonologists using a portable, high-definition ultrasound system (Sonosite Edge II) equipped with a 2.0–5.0 MHz low-frequency convex probe for fluid volume estimation and deep tissue penetration, and a 6.0–12.0MHz high-frequency linear probe for detailed pleural membrane inspection. 2. Radiodiagnosis Diagnostic USG: Performed within 12 hours using an advanced radiology ultrasound platform (GE Logiq E10 / Philips EPIQ 7) to confirm findings, conduct detailed color/power Doppler analysis of pleural lesions, and evaluate underlying parenchymal consolidations or diaphragmatic motion. Parameters Evaluated on TUS: • Fluid Volume: Quantified semi-quantitatively and using the Balik formula (V [mL] = 20 X d [mm], where d is the maximum interpleural distance at end-expiration) [14]. • Internal Echogenicity: Categorized into four standard patterns: 1. Anechoic: Completely echo-free fluid space. 2. Complex Non-Septated: Presence of floating cellular debris or echogenic punctate signals without fibrinous strands. 3. Complex Septated: Network of hyperechoic fibrinous strands or lattice-like membranes dividing the fluid into locules. 4. Homogeneously Echogenic: Dense, uniform echogenic particulate suspension (suggestive of empyema or hemothorax). • Pleural Abnormalities: Parietal/visceral pleural thickness measured in millimeters, presence of pleural nodularity, diaphragmatic thickening (> 3 mm), or fixed pleural masses.   Image-Guided Interventions and Pleural Fluid Analysis All invasive procedures were performed under direct real-time ultrasound guidance or immediate pre-procedure mark-and-drive ultrasound guidance depending on effusion complexity. • Thoracentesis: Conducted under local anesthesia (2% Lignocaine) using a 18G to 21G intravenous cannula or thoracentesis set. • Pleural Fluid Processing: Fluid samples were analyzed immediately for physical appearance, total/differential cell count, protein, lactate dehydrogenase (LDH), glucose, adenosine deaminase (ADA), pH, Gram stain, Ziehl-Neelsen stain, bacterial/fungal cultures, Cartridge Based Nucleic Acid Amplification Test (CBNAAT / GeneXpert for Mycobacterium tuberculosis), and cytopathology for malignant cells. • Categorization: Effusions were categorized as transudate or exudate using Light’s Criteria [15]. • Advanced Interventions: In complex, thick, or nodular pleural cases, USG-guided closed pleural biopsy (Tru-Cut 16G/18G needle) or image-guided pigtail catheter (10F–14F) placement was executed collaboratively. Statistical Analysis Data were tabulated using Microsoft Excel and analyzed using SPSS version 28.0 (IBM Corp., Armonk, NY). Continuous variables were summarized as mean ± standard deviation (SD) or median (interquartile range, IQR) based on normality testing. Categorical data were presented as frequencies and percentages. Inter-departmental agreement for sonographic patterns between Respiratory Medicine and Radiodiagnosis was assessed using Cohen's kappa coefficient (Κ). Comparisons of continuous variables across groups were analyzed using Student's t-test or One-Way ANOVA. Categorical correlations (e.g., echogenicity patterns vs. Light’s criteria) were tested using Pearson’s Chi-Square (χ2) test or Fisher’s exact test. Multivariate logistic regression was conducted to determine sonographic predictors of malignant vs. tuberculous exudates. p-values < 0.05 were considered statistically significant.

Patient Baseline Demographics and Clinical Characteristics

A total of 250 patients were evaluated. The mean age was 52.4 ± 14.6 years, with 156 males (62.4%) and 94 females (37.6%). Dyspnea (88.4%) and chest pain (64.8%) were the primary presenting symptoms. Unilateral effusion was present in 218 cases (87.2%; 118 right-sided, 100 left-sided), while bilateral effusions were identified in 32 cases (12.8%).

Final clinical and laboratory diagnoses confirmed Exudative Pleural Effusion in 185 patients (74.0%) and Transudative Pleural Effusion in 65 patients (26.0%). Tuberculosis was the single most common cause of exudates (82/185; 44.3%), followed by Malignancy (54/185; 29.2%) and Parapneumonic/Empyema (38/185; 20.5%). Congestive Heart Failure accounted for the majority of transudates (42/65; 64.6%). Table 1 outlines the complete demographic, clinical, and diagnostic breakdown.

Table 1. Demographic and Clinical Profile of the Study Cohort (N = 250)

Sonographic Echogenicity and Pleural Morphology vs. Light’s Criteria

TUS internal echogenicity patterns demonstrated a statistically significant correlation with the biochemical nature of the pleural fluid (p < 0.001).

As detailed in Table 2, an Anechoic pattern was observed in 110 patients (44.0%), which included 55 of the 65 transudates (84.6%) and 55 exudates (29.7%). Conversely, non-anechoic patterns were virtually exclusive to exudates:

• Complex Non-Septated: Observed in 71 patients (38.4% of exudates vs. 15.4% of transudates).
• Complex Septated: Observed in 52 patients (1% of exudates vs. 0.0% of transudates).
• Homogeneously Echogenic: Observed in 22 patients (9% of exudates vs. 0.0% of transudates).

All 52 complex septated effusions were exudative (32 tuberculous, 14 empyema/complicated parapneumonic, 6 malignant). Parietal pleural thickening (> 3 mm) was detected in 78 exudative cases (42.2%) versus only 2 transudative cases (3.1%; p < 0.001). Nodular pleural thickening was seen exclusively in malignant effusions (n = 28, 51.9% of all malignant cases).

Table 2. Sonographic Features Stratified by Biochemical Classification (Light’s Criteria) (N = 250)

Diagnostic Yield and Interventional Success

Image-guided diagnostic thoracentesis was successful on the first attempt in 242 of 250 patients (96.8%). In 8 patients with minimal or multiloculated fluid (d < 10 mm on static positioning), real-time continuous USG guidance was utilized to secure adequate fluid without dry taps.

For the 185 exudative effusions, fluid biochemistry and cytology established a primary diagnosis in 128 cases (69.2%). In the remaining 57 indeterminate or suspected malignant/tuberculous cases, USG-guided Tru-Cut pleural biopsy or USG-guided catheter drainage was executed:

• USG-Guided Tru-Cut Pleural Biopsy (n=38): Successfully yielded histopathological diagnosis in 35 of 38 cases (1% sensitivity for malignancy/tuberculosis).
• Overall Interventional Diagnostic Yield: Combining fluid cytology, GeneXpert, microbial cultures, and image-guided biopsy achieved an overall diagnostic yield of 2% (172/185) for exudative effusions.

Table 3. Diagnostic Modalities and Yield in Exudative Pleural Effusions (n = 185)

Inter-Departmental Diagnostic Concordance and Procedural Safety

Inter-departmental agreement between Respiratory Medicine clinicians (POCUS) and Radiodiagnosis specialists (advanced USG) was evaluated across all 250 cases.

• Echogenicity Characterization: High agreement (Κ = 0.86, 95% CI: 81–0.91, p < 0.001).
• Detection of Loculations/Septations: Excellent agreement (Κ = 0.91, p < 0.001).
• Pleural Thickness Measurement: Moderate-to-high agreement (r = 0.88, p < 0.001).

Procedural complication rates were extraordinarily low under USG guidance (Table 4). Minor localized pain was reported in 8.4% of cases. Pneumothorax occurred in only 3 patients (1.2%), with only 1 patient requiring chest tube placement (0.4%). Zero instances of accidental intra-abdominal organ (liver/spleen) puncture or severe intercostal artery hemorrhage were encountered.

Table 4. Procedural Complications of USG-Guided Pleural Interventions (N = 250)

Multivariate Analysis: Predictors of Malignancy vs. Tuberculosis

In exudative cases, multivariate logistic regression was performed to determine independent sonographic and clinical predictors that differentiate malignant from tuberculous effusions (Table 5).

Parietal pleural nodularity (OR = 8.45, p < 0.001) and pleural thickness > 5mm (aOR = 3.62, p = 0.004) were independent predictors of malignant effusions. Conversely, complex septations (aOR = 3.12, p = 0.008) and elevated fluid ADA > 40U/L (aOR = 12.4, p < 0.001) strongly predicted tuberculous etiology.

Table 5. Multivariate Logistic Regression for Sonographic Predictors of Malignant Pleural Effusion

*Adjusted for age, sex, smoking status, and total fluid volume.

The clinical management of pleural effusion has evolved rapidly over the past two decades. Thoracic Ultrasonography has transformed from an occasional radiology-consultation tool into an essential bedside diagnostic and procedural standard [16]. This study highlights the clinical efficacy of an integrated collaborative pathway between Respiratory Medicine and Radiodiagnosis. Diagnostic Value of Sonographic Characterization Our findings reinforce that TUS internal echogenicity is intimately linked to pleural fluid pathophysiology [17]. Transudates, characterized by low protein and cellular content, were anechoic in 84.6% of cases. In stark contrast, non-anechoic patterns; complex non-septated, complex septated, and homogeneously echogenic were found almost exclusively in exudative effusions (p < 0.001). The presence of septations or loculations is a hallmark of intense pleural inflammation, driven by pro-inflammatory cytokines, tissue factor expression, and depressed fibrinolytic activity within the pleural cavity [18]. In our study, loculations were detected by TUS in 25.6% of patients, over 80% of whom had normal or non-specific appearances on plain chest radiography. Recognizing early septations in parapneumonic effusions is of paramount clinical importance, as it signals complicated parapneumonic effusion or empyema, prompting early placement of small-bore chest tubes (pigtails) or intrapleural fibrinolytic therapy [19]. Enhancing Interventional Safety and Diagnostic Yield Historically, blind thoracentesis based on physical landmarks carried significant procedural morbidity, with pneumothorax rates exceeding 10% [7]. In our prospective cohort, direct or pre-procedure USG guidance reduced the pneumothorax rate to a minimal 1.2%, with no accidental visceral or organ lacerations. TUS allows the operator to accurately identify the intercostal space with the maximal fluid depth, measure the distance from skin to parietal pleura, track the respiratory excursion of the diaphragm, and avoid the inferior intercostal neurovascular bundle [20]. Furthermore, combining immediate fluid analysis with USG-guided cutting needle (Tru-Cut) biopsy yielded an overall diagnostic success rate of 93.2% for exudative effusions. Image-guided pleural biopsy specifically targets areas of localized pleural thickening or nodularity identified by radiologists, eliminating the low yield and higher risk associated with traditional blind Cope or Abram needles [21]. The Clinical-Radiological Collaborative Model A key highlight of this study is the synergy between Respiratory Medicine and Radiodiagnosis. Point-of-care ultrasound performed by pulmonologists provides immediate bedside triage, rapid identification of fluid presence during acute respiratory distress, and safe execution of emergency thoracentesis [22]. However, radiologists bring advanced expertise in cross-sectional imaging, subtle tissue characterization, spectral Doppler analysis of vascularity, and high-tier image-guided biopsy techniques [23]. Our data demonstrated high inter-departmental concordance (Κ = 0.86) between pulmonologists and radiologists. Establishing joint training protocols, shared imaging archiving (PACS integration), and regular clinical-radiological case reviews bridges the gap between bedside urgency and diagnostic perfection [24]. STUDY LIMITATIONS Several limitations must be acknowledged. First, as a single-center study conducted at a tertiary academic facility, the cohort had a higher prevalence of complex tuberculous and malignant effusions than typical primary care settings. Second, thoracoscopic surgery (Medical Thoracoscopy / VATS) was used as the ultimate gold standard in a small subset (n = 13) of recalcitrant indeterminate cases, while the majority relied on USG-guided biopsy and clinical follow-up. Third, dynamic contrast-enhanced ultrasound (CEUS) was not routinely performed, which may further enhance the differentiation between benign and malignant pleural thickening [25].

Integrated thoracic ultrasonography, managed through structured collaboration between Respiratory Medicine and Radiodiagnosis, significantly improves the clinical care of patients with pleural effusion. Sonographic internal echogenicity reliably differentiates transudates from complex exudative effusions, identifies subpulmonic loculations missed on plain radiography, and predicts underlying tuberculous or malignant etiologies.

Routine adoption of USG guidance during thoracentesis and image-guided pleural biopsy maximizes diagnostic yield (93.2%) while reducing procedural pneumothorax to near-zero levels. Institutionalizing collaborative workflows between chest physicians and radiologists optimizes resource utilization, enhances patient safety, and establishes a modern standard of evidence-based respiratory care.

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