The study group includes patients in whom the investigation of pleural effusion begins directly with pleural biopsy by Local Anesthesia Thoracoscopy (LAT) under conscious sedation. In these patients, imaging with chest CT and/or thoracic ultrasound has been performed and lymphocytic exudate is confirmed in fluid aspiration.

The Control Group includes patients admitted with undiagnosed pleural lymphocytic exudate, who undergo Standard of Care (SOC) diagnostic strategies according to BTS guideline including among others, 3 samples for cytological examination (40-60 ml each), chest tube drainage, microbiological and immunological studies. If the diagnosis is not established and there is still indication for pleural biopsy patients are referred either for surgical biopsy or LAT.

The patient is placed in a lateral decubitus, with the affected hemithorax upwards. Ensuring a venous line and full monitoring of vital functions. Mild sedation is given and a dose of Ceftriaxone is given 30 minutes before. Local anesthesia is injected in layers, starting from the skin and working up to the intercostal muscles, intercostal nerve, and periosteum of the rib.

Development of pneumothorax is done using a 16-gauge Boutin needle. 15 spontaneous breaths are sufficient to create a pneumothorax, and entry of rigid thoracoscope into the hemithorax through a 11-13 mm Trocar. Multiple biopsies from the parietal pleura are taken and pleurodesis is made according to operator judgment. A chest drain 20-22 G is placed and sutured.

A chest X-ray is performed 2-8 hours later after the patient is transferred to the ward. Chest drain is removed after 24h if fluid production is <250ml and lung re-expansion.

Time to diagnosis is defined as the period between the first thoracentesis ,showing a lymphocytic exudate, of a newly discovered pleural effusion in a patient without prior signs of pleural disease to the time of multi-disciplinary team final diagnosis involving a pathology report of biopsy samples.

The time from the patient's admission in the hospital with diagnosis of unexplained lymphocytic pleural effusion until discharge with or without final diagnosis.

A Visual Analogue Scale (VAS) measures the intensity of pain the patient feels after the intervention (Medical Thoracoscopy vs Surgical Biopsy). A horizontal line ranging from 0 to 10, (0=No pain, 10=Extreme pain), is used. The patient is examined every day, until his discharge and is asked to mark on the line his respective level of discomfort/pain.