Ultrasound of the Gastrointestinal Tract

Mesenteric Lymphadenopathy (p 11)

Giovanni Maconi, Elisa Radice, and Gabriele Bianchi Porro
2.1 Introduction

Wíth the increasing use of abdominal and bowel ultrasound in the screening and follow-up of bowel diseases, enlargement of the regional mesenteric lymph nodes have become a fairly common clinical finding, particularly in children and young adults. Therefore, since lymphadenopathy may often be an incidental finding in patients being examined for various reasons, the sonographer (and the physician) must decide whether it is a normal finding or a sign of a patient’s condition requiring further study. Indeed, mesenteric lymphadenopathy may be a manifestation of various disorders (Table 2.1).

2.2 Normal Mesenteric Lymph Nodes

Regional mesenteric lymph nodes are usually detected as the result of a symptom-directed diagnostic work-up, by a variety of imaging techniques, including ultrasound and colour Doppler ultrasonography, computed tomography (CT) and magnetic resonance imaging (MRI).

When they are found, the main goal of the diagnostic technique is to suggest whether it is a normal finding or the sign of a past or ongoing abdominal disease, and in this context, to differentiate its benign from malignant nature. The ultrasonographic criteria of the enlargement of mesenteric lymph nodes has been variably defined as the detection of nodes larger than 4 mm in the short axis (Sivit et al. 1993) and larger than 10 mm in the long axis (Watanabe et al. 1997).

This sonographic definition is in agreement with that of a study based on CT studies in an adult population where mesenteric lymphadenitis has been defined as three or more lymph nodes, each 5 mm or greater 5 mm in the short axis (Macari et al. 2002).

However, this size might not be a reliable normal cut-off value in children where it is much more controversial. A recent study showed that using a threshold of short-axis 5 mm for enlarged mesenteric lymph nodes might yield an unacceptably high percentage (54%) of false-positive results and that a better defi - nition of enlarged mesenteric lymph node would be a short axis of >,8 mm, which yielded only a 5% falsepositive rate (Karmazyn et al. 2005).

Therefore, the sonographic detection of oval, elongated, U-shaped lymph nodes with a short-axis diameter up to 4 mm in adults and 8 mm in children, should be considered a normal finding and should not be misdiagnosed as an early manifestation of a lympho-proliferative disorder.

The size of the nodes alone does not always re. ect underlying disease. The number and distribution of lymph nodes is also important. Normal mesenteric lymph nodes may be routinely identified at the mesenteric root and throughout the mesentery, in particular in right iliaca fossa in children (Karmazyn et al. 2005) and at the mesenteric root in adults (Lucey et al. 2005) (Fig. 2.1).

Size, site and number of lymphadenopathy detected by abdominal ultrasound may therefore help in suggesting their nature, or at least in differentiating among their main causes, which may be neoplastic, infectious or inflammatory.