loculations

Loculation refers to the subdivision of a fluid collection into discrete pockets separated by fibrous or inflammatory septa. Loculations arise when inflammatory or infectious processes cause the formation of connective tissue partitions within a cavity or within organ tissue, leading to multiple small pockets rather than a single, homogeneous collection. The term is used across several specialties and can involve the pleural, peritoneal, or pericardial spaces, as well as solid organs such as the liver or pancreas.

Loculations are most clinically relevant because they complicate drainage and treatment. In the pleural space, loculated effusions are commonly seen with empyema or complicated parapneumonic effusions and are more difficult to drain with a single thoracentesis or chest tube. Intra-abdominal collections, such as liver abscesses or pancreatic fluid collections, may become loculated, requiring targeted drainage of multiple pockets or specialized interventions. Loculations can also occur after surgery or in the setting of ascites, where septations compartmentalize free fluid.

Imaging plays a central role in identifying loculations. Ultrasound can reveal septations within a fluid collection, while computed tomography or magnetic resonance imaging provides more detailed delineation of the septa and can guide drainage planning. Management focuses on source control and complete drainage of all pockets when possible, often using image-guided percutaneous catheter drainage. In loculated pleural infections, adjuncts such as intrapleural fibrinolytics or surgical decortication may be required. Antibiotic therapy is typically guided by the underlying infection and culture results. Follow-up imaging assesses response and the persistence or resolution of loculations.