Mesenteric Adenitis: CT Diagnosis of Primary Versus Secondary Causes, Incidence, and Clinical Significance in Pediatric and Adult Patients

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1 Michael Macari 1 John Hines Emil althazar lec Megibow Received pril 10, 2001; accepted after revision September 21, ll authors: Department of Radiology, bdominal Imaging, NYU Medical Center, Tisch Hospital, 560 First ve., Ste. HW 206, New York, NY ddress correspondence to M. Macari. JR 2002;178: X/02/ merican Roentgen Ray Society Mesenteric denitis: CT Diagnosis of Primary Versus Secondary Causes, Incidence, and Clinical Significance in Pediatric and dult Patients OJECTIVE. Our objective was to determine the clinical significance of mesenteric adenitis when detected on CT. MTERILS ND METHODS. Mesenteric adenitis was considered present if a cluster of three or more lymph nodes measuring 5 mm or greater each was present in the right lower quadrant mesentery. If no other abnormality was detected on CT, then mesenteric adenitis was considered primary. If a specific inflammatory process was detected in addition to the lymphadenopathy, then mesenteric adenitis was considered secondary. Patients with a known neoplasm or HIV infection were excluded. Three separate groups of patients were examined for the presence and cause of mesenteric adenitis. Group 1 consisted of 60 consecutive patients prospectively identified with mesenteric adenitis on CT examinations. Group 2 consisted of 60 consecutive patients undergoing abdominal and pelvic CT for evaluation of blunt or penetrating abdominal trauma. Group 3 consisted of 60 consecutive patients undergoing abdominal and pelvic CT with acute abdominal symptoms. In all patients, the indication for imaging was documented, and the size of the largest lymph node, when present, was measured. In patients with mesenteric adenitis, the CT findings, clinical history, and clinical or surgical follow-up were subsequently evaluated to determine the cause of mesenteric adenitis. RESULTS. In the 60 patients prospectively identified with CT findings of mesenteric adenitis (group 1), 18 (30%) of 60 had primary mesenteric adenitis. The remaining 42 patients (70%) had an associated inflammatory condition that was established on CT as the likely cause of mesenteric adenitis. Mesenteric adenitis was present in none (0%) of the 60 patients in group 2 and in five (8.3%) of 60 patients in group 3. CONCLUSION. The incidence of mesenteric adenitis in patients with and those without abdominal pain is low. When evidence of mesenteric adenitis is present on CT examinations, usually a specific diagnosis can be established as its cause. D etection of mesenteric lymphadenopathy on CT leads to an extensive and challenging differential diagnosis. The evaluation is based on the size, number, location, and attenuation of the lymph nodes; on the associated CT findings; and on the patient s history and clinical presentation. Inflammatory lymph nodes, as present in patients with mesenteric adenitis, are almost always 10 mm or less; homogeneously attenuating; and clustered in the right lower quadrant small-bowel mesentery or ventral to the psoas muscle [1, 2]. Mesenteric adenitis can be divided into two distinct groups: primary and secondary. On imaging, primary mesenteric adenitis has been defined as right-sided mesenteric lymphadenopathy without an identifiable acute inflammatory process or with only mild (<5 mm) wall thickening of the terminal ileum. In most cases of primary mesenteric adenitis, an underlying infectious terminal ileitis is thought to be the cause [2 8]. Secondary mesenteric adenitis is defined as lymphadenopathy associated with a detectable intraabdominal inflammatory process [2, 9 12]. The present study evaluates three groups of patients to address several issues regarding mesenteric adenitis. First, in an effort to determine the incidence of primary versus secondary causes of mesenteric adenitis, over a 7-month period, we evaluated 60 consecutive patients with CT scans that showed mesenteric adenitis. Second, over a 6-week period, we attempted to determine the incidence of mesenteric adenitis on CT scans in 60 symptomatic (abdominal pain) and 60 asymptomatic (trauma) patients. Finally, on the basis of findings for these three groups of patients, we JR:178, pril

2 Macari et al. attempt to address the clinical significance of mesenteric adenitis when visible on CT. Materials and Methods Patients We prospectively evaluated three separate groups of patients. In all three groups, the indication for imaging was based on clinical evaluation. The composition of the groups is detailed below. Patients with HIV infection and patients with known abdominal and pelvic neoplasms were excluded from this study. Only patients who received oral and IV contrast material were included. Mesenteric adenitis was considered present if a cluster of three or more mesenteric lymph nodes each measuring 5 mm or greater was seen in the right lower quadrant. In all cases, patient records were entered into a computer database for subsequent retrieval. ll CT examinations were performed with one of two scanners (HiSpeed dvantage or CTI; General Electric Medical Systems, Milwaukee, WI). Helical CT images were acquired using a slice collimation of either 7 or 5 mm with a reconstruction interval of 6 or 4 mm, respectively; a pitch of 1.5 2; 120 kv; and m. Either 800 ml of barium sulfate (suspension, 2.1% weight volume; Readi-CT 2; E-Z- EM, Westbury, NY) was administered orally, or dilute (2%) water-soluble contrast material (Gastrograffin; ristol-meyers Squibb, Wallingford, CT) was administered orally or via a nasogastric tube in small increments beginning approximately 1 hr before scanning. One hundred fifty milliliters of nonionic IV contrast material (Iopramide [300 mg I/mL]; erlex Laboratories, Wayne, NJ) was administered at a rate of 2 ml/ sec using a power injector (Envision CT Injector; Medrad, Pittsburgh, P) via a 22-gauge catheter that was inserted into an antecubital vein. Group 1. This group was a prospective cohort of 60 consecutive patients evaluated between March and September 2000; in these patients, abdominal and pelvic CT revealed mesenteric adenitis as defined previously. These patients were from two large hospitals and a busy outpatient medical center affiliated with our medical center. In addition to mesenteric adenitis, associated inflammatory conditions in the right lower abdomen (appendicitis, diverticulitis, bowel wall thickening, abscess, and fibrofatty proliferation) were documented when present. This group included 29 males and 31 females (age range, 5 52 years; mean age, 29 years; median age, 25 years). subsequent review of the patients records showed that the clinical indication for abdominal and pelvic imaging as stated in the CT request in this group of patients was suspected appendicitis (n = 44), Crohn s disease (n = 7), nonspecific abdominal pain (n = 6), ulcerative colitis (n = 2), or systemic lupus erythematosis (n = 1). Group 2. This group consisted of a prospective cohort of 60 consecutive patients evaluated between November and December 2000 who were undergoing CT of the abdomen and pelvis after sustaining blunt abdominal trauma. These patients were from a single hospital affiliated with our medical center. CT was performed within 3 hr after presentation to our emergency department. ecause there was no history of antecedent abdominal complaints in any of these patients, they served as a control group to determine the incidence of mesenteric adenitis in asymptomatic patients. The group included 45 men and 15 women (age range, years; mean age, 28 years). Group 3. The final group consisted of a prospective cohort of 60 consecutive patients evaluated between November and December 2000 who were undergoing abdominal and pelvic CT for the evaluation of acute (generalized or localized) abdominal pain. These patients were from the same hospital and were examined during the same period of time as the group 2 patients. In the group 3 patients, the indication for CT was clinically suspected appendicitis (n = 11), small-bowel obstruction (n = 7), diverticulitis (n = 4), pancreatitis (n = 2), or unknown cause of pain (n = 36). Patients with clinically suspected renal calculi who were evaluated with unenhanced CT studies were excluded. Group 3 patients served to approximate the incidence of mesenteric adenitis in adult patients with acute abdominal symptoms. The group included 34 men and 26 women (age range, years; mean age, 33 years). Pediatric patients were excluded from this group because most pediatric patients with symptoms of abdominal pain undergo sonographic evaluation at our institution. Image Interpretation In all three groups, the records of patients with suspected mesenteric adenitis were entered into a database. The CT examinations of the patients were reviewed by two abdominal radiologists in consensus to determine whether mesenteric adenitis was present. Moreover, in all patients with mesenteric adenitis, the size of the largest lymph node measured within the cluster was documented. In differentiating primary from secondary causes of mesenteric adenitis, CT examinations were prospectively evaluated for the presence of conditions that might explain the enlarged lymph nodes. If the examination showed only a cluster of enlarged right lower quadrant mesenteric lymph nodes with the wall of the distal ileum measuring less than 5 mm, a diagnosis of primary mesenteric adenitis was assigned. However, if there was thickening of the terminal ileum (>5 mm) or if another inflammatory condition was detected in the right lower abdomen in addition to findings associated with mesenteric adenopathy, the CT diagnosis was secondary mesenteric adenitis. In all patients, clinical or surgical follow-up (or both) was obtained at the time of discharge or from subsequent review of the medical records. Clinical information was correlated with the imaging findings, which served to determine the final cause of the mesenteric adenitis when present. Results Group 1 In all patients with suspected mesenteric adenitis, the presence of mesenteric adenitis was confirmed by subsequent consensus review by two abdominal radiologists. mong the 60 consecutive patients with right lower quadrant small-bowel mesenteric lymphadenopathy (group 1), 18 (30%) had primary and 42 (70%) had secondary mesenteric adenitis. Primary mesenteric adenitis. The mean age of the 18 patients in this subgroup of patients was 25.2 years, the age range was from 5 to 44 years, and the median age was 21 years. Fourteen of these patients were referred for imaging on the basis of a clinical suspicion of appendicitis, and four had a clinical diagnosis of nonspecific acute abdominal pain. CT revealed enlarged lymph nodes clustered in the right lower quadrant mesentery without a focal in- Fig. 1. Primary mesenteric adenitis in 27-year-old woman with right lower quadrant pain., xial CT scan obtained with IV and oral contrast material at level of upper pelvis shows cluster of lymph nodes (arrow) in right lower quadrant mesentery., xial CT scan obtained at level of terminal ileum (arrow) and cecum shows minimal wall thickening. ppendix was also normal (not shown). Patient improved on antibiotic therapy. 854 JR:178, pril 2002

3 CT of Mesenteric denitis Fig. 2. Primary mesenteric adenitis in 27-year-old woman with right lower quadrant pain. xial CT scan obtained with IV and oral contrast material at level of upper pelvis shows cluster of lymph nodes (arrows) in right lower quadrant mesentery. ppendix and terminal ileum (not shown) were normal. Patient was discharged from emergency department and improved without therapy. flammatory lesion (Figs. 1 and 2). The mean size of the largest lymph node in the right lower quadrant mesentery in patients with primary mesenteric adenitis was 10.8 mm (range, 5 15 mm). In all 18 patients, the appendix was normal, and no other imaging abnormality was identified. In one patient, suspicious terminal ileal thickening of less than 5 mm (Fig. 1) was present. ll patients were discharged after undergoing brief clinical observation or antibiotic therapy. In these 18 patients, the clinical findings of right lower quadrant pain together with the imaging findings showing mesenteric lymph nodes without other CT findings led to a final presumptive diagnosis of primary mesenteric adenitis. On the basis of the initial imaging and clinical findings in these patients, none underwent surgery and none had follow-up imaging within a 12-month interval since the initial CT study. Secondary mesenteric adenitis. The mean age of these 42 patients was 31.3 years, the age Fig. 3. Secondary mesenteric adenitis in 14-year-old girl with right lower quadrant pain and appendicitis., xial CT scan obtained with IV and oral contrast material at level of upper pelvis shows cluster of lymph nodes (arrows) in right lower quadrant mesentery., xial CT scan obtained at level of appendix shows dilated, fluid-filled appendix (arrow) with enhancing wall. Surgery confirmed appendicitis. range was from 8 to 50 years, and the median age was 30 years. The clinical indication for abdominal and pelvic imaging in this group was suspected appendicitis (n = 30), Crohn s disease (n = 7), nonspecific abdominal pain (n = 2), ulcerative colitis (n = 2), or systemic lupus erythematosis (n = 1). In these patients, a specific inflammatory process could be identified on CT; this process was assumed to be the cause of the lymphadenopathy. The underlying cause of the mesenteric adenitis in this group of patients based on CT findings was appendicitis (n = 24), Crohn s disease (n = 8), infectious colitis (n = 6), ulcerative colitis (n = 2), systemic lupus erythematosis (n = 1), and ascending colon diverticulitis (n = 1) (Figs. 3 5). The mean size of the largest lymph node in the right lower quadrant mesentery in patients with secondary mesenteric adenitis was 11.8 mm (range, 5 20 mm). ll patients with CT findings of appendicitis underwent surgery, which confirmed the imaging diagnosis of appendicitis (Fig. 3). Seven of eight patients with CT findings of Crohn s disease had known long-standing disease previously documented on endoscopic biopsy (Fig. 4). The eighth patient with CT findings of Crohn s disease and mesenteric adenitis ultimately underwent endoscopy and biopsy, which yielded findings that confirmed the diagnosis. Of the six patients with infectious colitis, three had documented positive stool cytotoxin results for Clostridium difficile enterotoxin. The remaining three patients were presumed to have infectious colitis with C. difficile on the basis of a clinical response to antibiotic therapy. The two patients with ulcerative colitis and mesenteric adenitis had previous endoscopy documenting ulcerative colitis. The patient with lupus had a known disease and no other clinical or imaging finding to account for Fig. 4. Secondary mesenteric adenitis in 29-year-old man with right lower quadrant pain and Crohn s disease., xial CT scan obtained with IV and oral contrast material at level of upper pelvis shows cluster of lymph nodes (arrow) in right lower quadrant mesentery., xial CT scan obtained at level of previous small-bowel anastomosis shows thickening of small bowel and stranding of mesenteric fat (arrow) consistent with recurrent Crohn s disease. JR:178, pril

4 Macari et al. Fig. 5. Secondary mesenteric adenitis in 34-year-old woman with right lower quadrant pain and ascending colonic diverticulitis., xial CT scan obtained with IV and oral contrast material at level of upper pelvis shows cluster of lymph nodes (long arrows) in right lower quadrant mesentery. Note normal contrast material filled appendix (short arrow)., xial CT scan obtained at level of ascending colon shows inflamed diverticulum (solid arrow) and stranding of fat around ascending colon. Several small lymph nodes (open arrow) are also identified. Patient was treated for right-sided diverticulitis and improved on antibiotic therapy. the mesenteric adenitis, and this patient responded to treatment with steroids. The patient with ascending colon diverticulitis had CT findings of right-sided diverticulitis, which responded to antibiotic therapy and did not require surgery (Fig. 5). No patient underwent lymph node biopsy. Groups 2 and 3 In group 2 patients (those without a history of right lower quadrant pain undergoing abdominal and pelvic CT for trauma), we found no patient (0/60) with CT findings of mesenteric adenitis. In patients with acute abdominal symptoms (group 3), the incidence of mesenteric adenitis was 8.3% (5/60). Two of these cases were primary mesenteric adenitis (Fig. 6) and three cases, secondary mesenteric adenitis. In these three patients, the mesenteric adenitis was as- sociated with appendicitis (n = 2) or with right-sided diverticulitis (n = 1). Mesenteric adenopathy was not present in the remaining 55 patients with acute abdominal symptoms. Discussion Mesenteric adenitis can be divided into two broad categories, primary and secondary. Primary mesenteric adenitis has been defined as right-sided mesenteric lymphadenopathy without an identifiable acute inflammatory process or with mild (<5 mm) wall thickening of the terminal ileum [2 8]. Enlarged mesenteric lymph nodes have been reported to occur in patients with celiac disease, appendicitis, and Crohn s disease [2, 9, 10, 12]. In these cases, mesenteric adenitis can be considered as associated with a specific underlying condition. In most cases of primary mesenteric adenitis, an underlying infectious terminal ileitis is thought to be the cause [2 8]. In patients with primary mesenteric adenitis, the clinical presentation is nonspecific (abdominal pain, fever, and leukocytosis) and leads to a broad clinical and imaging differential diagnosis including appendicitis, infectious enterocolitis, diverticulitis, perforated cecal carcinoma, pelvic inflammatory disease, renal stones and pyelonephritis, and mesenteric adenitis [1, 11, 13]. CT can help differentiate among these entities, thus allowing a more accurate diagnosis to be established [1, 11]. Moreover, the finding of enlarged lymph nodes in the right lower quadrant in the context of the clinical presentation may lead the radiologist to suggest the diagnosis of primary mesenteric adenitis, thus allowing the patient to avoid undergoing surgery. Mesenteric adenitis is a relatively uncommon cause of acute right lower quadrant pain in adults [1, 2, 11, 13, 14]. The reported fre- Fig. 6. Mesenteric adenitis in 25-yearold man with right lower quadrant pain., xial CT scan obtained with IV and oral contrast material at level of upper pelvis shows cluster of lymph nodes (arrows) in right lower quadrant mesentery. Mild thickening of terminal ileum (not shown) was present. Patient was treated with antibiotics but pain increased., Spot radiograph of terminal ileum from small-bowel series performed 2 days after CT shows nodularity to mucosa of the terminal ileum (arrow). Differential diagnosis includes infectious and other causes of terminal ileitis such as Crohn s disease. Colonoscopy and biopsy of terminal ileum revealed severe nonspecific enteritis without granulomas or infectious agent. ntibiotics were discontinued, and patient slowly improved. 856 JR:178, pril 2002

5 CT of Mesenteric denitis quency of primary mesenteric adenitis is variable. Puylaert [8] reported 100 consecutive patients who underwent compression sonography for a clinical diagnosis of appendicitis and found that 14 (14%) had primary mesenteric adenitis with mild terminal ileal thickening. ll 14 patients in this series were adults. Rao et al. [2] found primary mesenteric adenitis to be the second most common cause of right lower quadrant pain after appendicitis, accounting for 7% of the discharge diagnoses in adult and pediatric patients with a clinical suspicion of appendicitis. Kamel et al. [14], studying adult patients with acute right lower quadrant pain, found that only 2% of patients had primary mesenteric adenitis. Some of the discrepancy between these studies in the frequency of primary mesenteric adenitis may be related to the fact that primary mesenteric adenitis is believed to occur more often in children than in adults [15]. In our study of mesenteric adenitis, we found that the incidence of primary mesenteric adenitis was low and that when mesenteric adenitis was present, a specific cause could usually be determined. We found that in adult patients with acute abdominal symptoms (group 3), 8.3% had mesenteric adenitis, of which only two cases (3.3%) were considered primary mesenteric adenitis. Two of these five patients had appendicitis, one had right-sided colonic diverticulitis, and two patients had mesenteric adenitis with no other clinical or imaging abnormality. In group 2, asymptomatic patients sustaining abdominal trauma, none were found to have mesenteric adenitis. Moreover, of the 60 consecutive patients prospectively identified with mesenteric adenitis (group 1), only 18 had a final diagnosis of primary mesenteric adenitis. Most of the group 1 patients, 42 of the 60, were found to have secondary mesenteric adenitis for which an identifiable cause was detected. It is not surprising that secondary mesenteric adenitis was diagnosed with such high frequency in our study. Previous CT reports have documented lymphadenopathy in patients with appendicitis, Crohn s disease, and systemic lupus erythematosis [2, 10, 12]. Rao et al. [2] found that 82% of patients with appendicitis have mesenteric adenitis. When attempting to establish the clinical significance of mesenteric adenitis detected on CT, determining primary versus secondary causes is critical because patient treatment is influenced. It has been reported that in patients with primary mesenteric adenitis, mild thickening of the wall of the terminal ileum may be present. In these cases, the ileal thickening is thought to be caused by an infection that ultimately leads to reactive lymphadenopathy in the mesentery [2, 8]. However, the finding of mild terminal ileal thickening that has been previously reported to occur in patients with primary mesenteric adenitis can be difficult to quantify using CT because of the variability in the degree of distention and of the contrast opacification of the terminal ileum. In cases of mesenteric adenitis with obvious terminal ileal thickening, as occurs in some patients with Crohn s disease and infectious ileitis, the mesenteric adenitis should be considered secondary, and endoscopic biopsies, stool cultures, or small-bowel barium studies should be performed to determine the underlying cause of the adenitis, especially if the patient does not respond to conservative therapy (Fig. 6). In a previously reported study of patients with presumed primary mesenteric adenitis, eight of 18 patients had mild terminal ileal or terminal ileal and cecal thickening [2]. In two of these patients, a diagnosis of Crohn s disease was ultimately made on the basis of endoscopy and biopsy when the patient s condition did not improve. This finding further supports the idea that if a patient with mesenteric adenitis and ileal thickening is not responding to conservative therapy, endoscopy should be considered. y evaluating the incidence of mesenteric adenitis in asymptomatic individuals, we have attempted to address the potential bias of our data by excluding clinically insignificant cases of adenitis. We conclude that the absence of mesenteric adenitis in the group of asymptomatic patients (group 2) has significant implications. It stresses the clinical relevance of mesenteric nodes detected in symptomatic individuals without HIV infection or neoplasm. When enlarged mesenteric nodes are seen, the presence of an associated acute inflammatory process should be inferred, and careful evaluation of the CT examination should be performed to determine whether an underlying cause can be detected. If no underlying cause is detected on CT, then the patient likely has primary mesenteric adenitis associated with a mild infectious ileitis. Treatment should be based on the clinical presentation and symptoms. There are several limitations of our study. Histologic confirmation of lymphadenopathy was not obtained in our patients with mesenteric adenitis. In no patient with primary mesenteric adenitis in either group was an infectious cause established, but stool cultures were not obtained in these patients and they were usually discharged from the emergency department shortly after the CT examination. In distinction, a prior report of patients with primary mesenteric adenitis found that eight of nine stool cultures were positive for Yersinia enterocolitica at the time of diagnosis [8]. However, the combination of clinical and imaging parameters, as well as the patient s response to therapy in each case, established the most likely diagnosis of primary rather than secondary mesenteric adenitis. Second, our study population in all three groups was predominantly made up of adult patients. In groups 2 and 3 in our study, all patients were adults, and in group 1, 44 (73%) of 60 were more than 18 years old. However, our study confirms the results of prior investigators in that when mesenteric adenitis is present on CT, a specific cause can often be detected [2]. Once mesenteric adenitis is identified, it is important to differentiate primary from secondary causes because the management of each is often quite different [2, 14]. Finally, we excluded patients with clinically suspected renal colic because these patients undergo CT of the abdomen and pelvis without oral or IV contrast material. Small mesenteric lymph nodes are likely more difficult to detect if oral and IV contrast material are not administered. It is possible that some of these patients presenting with flank pain may have had mesenteric adenitis. Patients with upper abdominal or retroperitoneal adenopathy as well as patients with HIV or known neoplasm were also excluded. We excluded patients with HIV and known neoplasm because of the high frequency of lymphadenopathy in these patients [16]. In conclusion, there are several clinical implications of this study. First, right lower quadrant mesenteric nodes do not occur in the general, asymptomatic, immunocompetent adult population. Second, an isolated cluster of right lower quadrant mesenteric lymph nodes is an uncommon finding in patients with acute abdominal symptoms, and this finding is often associated with a focal inflammatory process. Third, CT detection of right lower quadrant mesenteric nodes in patients with acute abdominal pain is usually associated with a detectable intraperitoneal inflammatory process in the majority of patients. Failure to identify a concurrent pathologic process leads to a presumptive diagnosis of primary mesenteric adenitis and explains the patient s symptoms. Treatment in these cases should be based on clinical parameters. If a patient does not respond to this therapy, endoscopy or smallbowel barium studies should be considered to determine the cause. JR:178, pril

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