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Mesenteric Nodes on a CT

Here is an article about mesenteric nodes showing on a CT scan. GIST does not frequently spread to the lymph nodes.

http://www.ajronline.org/cgi/content/full/184/1/41

We have shown that mesenteric lymph nodes greater than 3 mm in short-axis diameter are found in approximately 39% of healthy adults. When present, mesenteric lymph nodes are usually multiple, with nearly half of these patients having five or more nodes detected. Given that radiologists now see these nodes so frequently, we must first explain the reason that we see them and then discuss whether these nodes are normal or abnormal.

The most obvious reason that we see these nodes in current clinical practice is the use of MDCT scanners. The thin collimation possible with MDCT allows improved spatial resolution for detecting and discriminating between small objects. Therefore, less volume averaging occurs between the small lymph nodes and other structures within the mesentery, particularly the small bowel and vessels. Among the other factors responsible for the more frequent visualization of mesenteric lymph nodes is routine use of PACS computer workstations for reviewing CT studies by scrolling through images. By scrolling, one may more clearly distinguish lymph nodes from vessels, because vessels can be traced as tubular structures extending over many images. Lymph nodes stand out against the mesenteric fat as tiny, often rounded, soft-tissue densities that appear and disappear over one or two images. Faster scanning times and techniques such as bolus tracking for administering IV contrast material also help to better opacify the mesenteric vessels, allowing easier detection of lymph nodes.

Most reports defining the size criteria for normal lymph nodes were written in the era before MDCT and PACS [1-7]. Many of these reports made no reference to lymph nodes at the mesenteric root or to nodes scattered throughout the mesentery. Indeed, one of the earlier reports of CT of the normal mesentery stated that normal lymph nodes were not routinely identified in the mesentery [8]. Therefore, unlike many areas of radiology, no standardized reference point has been determined for the size of normal mesenteric nodes.

More recent reports using MDCT have described the presence of lymph nodes within the mesentery seen with coexistent inflammatory, infectious, or malignant processes [9-11]. The size of these nodes has been reported to range from 5 to 20 mm. It is clear that smaller lymph nodes are detectable using MDCT.

Tumors involving lymph nodes as small as 5 mm in the short-axis diameter have been detected on MDCT in patients with proven malignancy. This is alarming, given that many studies defining the size criteria for normal abdominal lymph nodes have suggested that normal nodes may be as large as 9 mm in the upper and 11 mm in the lower paraaortic regions [5]. Because cross-sectional imaging is now performed with increasing frequency, mesenteric lymph nodes that are smaller than these cutoff points are routinely identified.

Having detected mesenteric lymph nodes, we must decide what to do with them. Some radiologists suggest obtaining a follow-up MDCT scan to ensure that these nodes are not the earliest manifestation of lymphoma or metastatic disease from an occult primary neoplasm. Even if these lymph nodes are thought to result from an infectious or inflammatory process, obtaining a follow-up MDCT scan is sometimes suggested to ensure full resolution. No appropriate time interval has been recommended for this follow-up MDCT scan. Some have suggested obtaining a follow-up scan several weeks after the initial examination in patients in whom infection or inflammation is believed to be the cause of the finding. This approach will not allay fears of underlying malignancy should these nodes persist on the subsequent scan. Others have suggested longer follow-up intervals, but no consensus is available. Although we did not obtain any formal follow-up data to determine whether the MDCT scans of our study population were truly normal, we did search the hospital database records in all cases. In no patient was there evidence, either by hospital visit or on radiologic imaging, to suggest the interval development of disease at 1-year follow-up. The possibility always exists that patients went to other institutions for further medical care. We acknowledge that this is a limitation of our study; however, we believe that it is reasonable to take this trauma population as representative of the healthy population.

We have found that lymph nodes up to 4.6 mm in the maximum short-axis diameter and 3.6 mm in the mean size are frequently found in the mesentery of the healthy population. These nodes are a normal finding and require no follow-up imaging. This approach results in fewer unnecessary MDCT scans and allows patients to avoid unnecessary radiation exposure.