“Stranding” refers to a specific appearance observed on medical imaging, particularly in areas of fat. It describes changes in the normal texture and density of fatty tissues, often indicating an underlying process. This finding serves as a visual clue for healthcare professionals examining scans.
What is Stranding?
On medical imaging like CT scans and MRIs, stranding appears as an abnormal change in fat. Normal fat appears dark gray or black due to its low density, typically around -100 Hounsfield units (HU). When stranding is present, this fat becomes hazy, streaky, or shows linear densities, appearing brighter or more attenuated, with Hounsfield unit values ranging from -20 to +20 HU. This increased attenuation signifies a change in the tissue’s composition.
This characteristic appearance results from the infiltration of fluid, inflammatory cells, or other material into the fatty tissue, causing it to become less uniform and more dense. The linear or hazy patterns reflect the spread of this process along fascial planes or within the fat itself. While commonly seen in the mesentery, omentum, and retroperitoneum, fat stranding can occur in any fatty tissue, including the neck, thorax, and subcutaneous tissues. The severity of stranding can vary, from subtle haziness in mild inflammation to a more pronounced reticular pattern with increased inflammation.
Causes and Associated Conditions
Stranding is most commonly caused by inflammation, where the body’s immune response leads to fluid accumulation (edema) and engorgement of lymphatic vessels within the fat. This inflammatory response can be triggered by various conditions, including infections, ischemia (reduced blood flow), and traumatic injuries.
Specific medical conditions frequently associated with stranding include acute appendicitis, where inflammation of the appendix causes stranding in the adjacent pericecal fat. Similarly, diverticulitis, an inflammation of pouches in the colon, often presents with pericolonic fat stranding. Other examples include pancreatitis, cholecystitis (gallbladder inflammation), and inflammatory bowel diseases like Crohn’s disease, where inflammation extends into the surrounding mesenteric fat, sometimes creating a “misty mesentery” appearance. Less commonly, certain benign and malignant tumors can also induce an inflammatory reaction in adjacent fat, leading to stranding.
How Stranding is Identified and Its Significance
Stranding is primarily identified through cross-sectional medical imaging, with Computed Tomography (CT) scans being the most common modality due to their high sensitivity in detecting subtle changes in fat attenuation. Magnetic Resonance Imaging (MRI) and ultrasound can also reveal inflammatory fat changes; MRI shows stranding as hyperintense streaks on T1- and T2-weighted images. Radiologists interpret these findings by looking for the characteristic hazy or linear densities in fat that deviate from its normal dark appearance.
The clinical significance of stranding lies in its ability to indicate an active pathological process. While stranding itself is a non-specific sign and does not pinpoint a precise diagnosis, its presence directs attention to a particular anatomical region, suggesting inflammation, infection, or other tissue injury. This sign aids in localizing the source of a patient’s symptoms, guiding further diagnostic steps such as additional imaging or laboratory tests, and informing treatment decisions, which might include antibiotics or surgical intervention. The pattern and location of stranding, combined with other clinical information, help physicians narrow down potential causes and assess the severity of a condition.