Current Procedural Terminology (CPT) code 32100 represents a major surgical procedure involving an open thoracotomy with direct exploration of the pleural cavity and thoracic organs. A thoracotomy is a highly invasive surgical incision into the chest wall, providing direct, unhindered access to the pleural space, lungs, esophagus, trachea, and the heart. This specific procedural code is utilized exclusively when the primary intent and the final extent of the surgical operation is diagnostic exploration, rather than a definitive therapeutic intervention or an anatomical resection such as a lobectomy or pneumonectomy. During this operation, the patient is almost universally placed in a lateral decubitus position under general anesthesia, usually with selective single-lung ventilation facilitated by a double-lumen endotracheal tube to deflate the operative lung. The cardiothoracic surgeon makes an extensive incision, most commonly a posterolateral, anterolateral, or axillary thoracotomy, depending on the suspected pathology and the thoracic region requiring maximum visualization. The superficial soft tissues and deep musculature, including the latissimus dorsi and serratus anterior muscles, are carefully divided or spared depending on the exact surgical technique. The targeted intercostal muscles are then separated, and a robust mechanical rib spreader is inserted to firmly retract the ribs, thereby exposing the thoracic cavity. Once completely inside the pleural space, the surgeon conducts a systematic, meticulous, and comprehensive manual and visual examination of the visceral and parietal pleura, the pulmonary parenchyma, all identifiable mediastinal structures, and the diaphragm. This level of extensive open exploration is frequently indicated for patients presenting with severe, undiagnosed blunt or penetrating chest trauma, uncontrolled or occult intrathoracic hemorrhage, suspected complex mediastinal or pulmonary masses, or persistent, unexplained pleural effusions where minimally invasive techniques like Video-Assisted Thoracoscopic Surgery (VATS) are heavily contraindicated, technically impossible, or have already proven insufficient. If a discrete source of minor bleeding is identified, surgical hemostasis is immediately achieved. However, it is a critical coding rule that if the diagnostic exploration mandates a more complex, definitive surgical repair or major resection during the very same session, the appropriate code for that specific therapeutic procedure must be reported entirely in place of 32100. Following the complete inspection and execution of all necessary diagnostic steps, large-bore chest tubes are typically placed to adequately drain residual air and serosanguinous fluid, and the chest wall is meticulously reconstructed and closed in multiple anatomical layers.