Mesenteric adenitis is a consequence of an enteric infection, usually viral, that predominantly affects mesenteric lymph nodes. It is the most frequent diagnosis in children who are found to have a normal appendix at surgery (Hayes 2004). Mes-enteric lymphadenitis is a self-limiting condition requiring only symptomatic treatment. Mesen-teric lymph nodes located at the middle abdomen to the right of the umbilicus, or less frequently at the RLQ, are visualized on US as oval, hypoechoic masses increased in number or size (Fig. 1.75a). In nearly 25% of asymptomatic patients more than five lymph nodes can be observed (Wiersma et al. 2005). Otherwise, a short-axis diameter of 8 mm on CT and 10 mm on US have been proposed as the upper limit of normal lymph node size (Karmazin et al. 2005; Wiersma et al. 2005). Lymphadenopa-
thy due to normal immunization process can be seen in almost 50% of asymptomatic children or in association with a number of abdominal and pelvic disorders. Increased color Doppler flow in tender enlarged lymph nodes reflects_its pathologic nature (Fig. 1.75b). Although exuberant blood flow can be demonstrated in inflamed lymph nodes, this still does not differentiate the cause of the inflammation (HAYdEN 1996). In about half of appendicitis cases, moderately enlarged mesenteric lymph nodes can be seen (PuYlAERt 1990). Rarely, they are prominent, but in such cases a diagnosis of mesenteric lymphadenitis cannot be establish, except when a full identification of a normal appendix is achieved. Therefore, mesenteric adenitis is an exclusion diagnosis that can only be made if normal appendix is identified and other digestive pathologies excluded.
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