The term “loculated” is frequently encountered in medical imaging, describing a complex state of fluid accumulation. It signifies that a collection of fluid (pus, blood, or serum) is not free-flowing, but compartmentalized into multiple smaller pockets or cavities. Understanding this state influences the medical approach to diagnosis and treatment.
Understanding the Core Definition
The concept of a loculated collection stems from the Latin root word loculus, meaning “a small place” or “chamber.” When a fluid collection is described as loculated, the large cavity has been divided into multiple smaller loculi. These internal divisions are caused by the formation of fibrous membranes, known as septa, which act as barriers within the fluid space.
This partitioning process typically occurs as a reaction to underlying inflammation or infection, particularly in long-standing fluid accumulations. The inflammatory response leads to the deposition of fibrin strands, a protein involved in blood clotting, which mature into tough, non-dissolving barriers. As these septa solidify, the fluid collection loses its ability to move freely and conform to gravity, becoming trapped in isolated compartments.
Where the Term Loculated Appears
Loculation is most commonly observed in areas of the body where fluid accumulates in potential spaces, particularly around the lungs and within the abdomen. The most frequent clinical example is a loculated pleural effusion, which is an abnormal buildup of fluid surrounding the lungs. This often occurs in the setting of infection, such as empyema, where the pus-like fluid thickens and the pleural membranes become inflamed and scarred.
In the abdomen, the term is applied to collections like loculated ascites or abscesses. Ascites is the accumulation of fluid in the peritoneal cavity, and loculation can occur when this fluid is confined by existing adhesions, malignancy, or severe infection. Abscesses in organs like the liver or ovaries can also become multiloculated, meaning the core of the infection is split into several distinct pus-filled pockets.
Why Loculation Impacts Treatment
The presence of septa makes loculated collections significantly more challenging to treat compared to free-flowing fluid. Standard drainage techniques, such as placing a single needle or catheter, often fail because the catheter only accesses one of the many isolated pockets, leaving the rest of the fluid trapped. To address this, physicians rely on imaging guidance, like ultrasound or CT scans, to precisely map the individual locules and place multiple drainage catheters.
A specialized, less invasive approach involves the use of fibrinolytic agents, such as tissue plasminogen activator (tPA), instilled directly into the cavity. These agents work by dissolving the fibrin septa, effectively turning the loculated collection back into a single, drainable space.
When these methods fail, or if the fluid is too thick and organized, surgery is often necessary. Minimally invasive video-assisted thoracic surgery (VATS) or open surgery may be required to manually break up the adhesions and remove the fibrous peel, allowing the affected structure, such as the lung, to fully re-expand.