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The Prevalence of Incidentally Detected Idiopathic Misty Mesentery on Multidetector Computed Tomography: Can Obesity Be the Triggering Cause?
Canadian Association of Radiologists Journal xx (2016) 1e6 www.carjonline.org
Computed Tomography / Tomodensitometrie
The Prevalence of Incidentally Detected Idiopathic Misty Mesentery on Multidetector Computed Tomography: Can Obesity Be the Triggering Cause? Ebru Unlu, MDa,*, Nazan Okur, MDa, Mehtap Beker Acay, MDa, Emre Kacar, MDa, Serife Ozdinc, MDb, Cinar Balcik, MDa, Ozlem Turksoy Tokgoz, MDc a Department of Radiology, Afyon Kocatepe University Faculty of Medicine, Afyonkarahisar, Turkey Department of Emergency Medicine, Afyon Kocatepe University Faculty of Medicine, Afyonkarahisar, Turkey c Department of Radiology, Antalya Training and Research Hospital, Antalya, Turkey
b
Abstract Purpose: Misty mesentery appearance is commonly reported in daily practice, usually as a secondary finding of various pathological entities, but sometimes it is encountered as an isolated finding that cannot be attributed to any other disease entity. We aimed to assess the prevalence of cases with incidentally detected idiopathic misty mesentery on computed tomography (CT) and to summarize the pathologies leading to this appearance. Methods: Medical records and initial and follow-up CT features of patients with misty mesentery appearance between January 2011 and January 2013 were analysed. The study included cases with no known cause of misty mesentery according to associated CT findings, clinical history, or biochemical manifestations, and excluded patients with diseases known to cause misty mesentery, lymph nodes greater than a short-axis diameter of 5 mm, discrete mesenteric masses, or bowel wall thickening. Results: There were a total of 561 patients in whom misty mesentery appearance was depicted on abdominopelvic CT scans. A total of 80 cases were found to have isolated incidental idiopathic misty mesentery, giving a prevalence of 7%. The common indication for CT examination was abdominal pain. There was a slight female predominance (51.3%). 67.5% of all patients were classified as obese and 17.5% as overweight. Conclusions: The results of the present study show that idiopathic incidental misty mesentery appearance has a significant prevalence. Also, the high body mass index of these patients and the growing evidence of obesity-induced inflammatory changes in adipose tissue are suggestive of an association between obesity and misty mesentery appearance on CT. Resume Objet : Il est assez frequent d’observer un mesentere d’aspect flou dans le cadre de la pratique quotidienne de la radiologie. Bien qu’il s’agisse habituellement d’une constatation secondaire liee a diverses entites pathologiques, il peut s’agir, a l’occasion, d’une constatation isolee non imputable a aucune autre entite morbide. Notre objectif consistait a mesurer la prevalence des observations fortuites de mesentere d’aspect flou idiopathique lors d’une tomodensitometrie (TDM), et a faire un resume des affections qui donnent lieu a de telles constatations. Methodes : Nous avons analyse les dossiers medicaux ainsi que les resultats des tomodensitometries initiaux et de suivi de patients chez qui un mesentere d’aspect flou a ete observe entre janvier 2011 et janvier 2013. L’etude incluait les patients dont les resultats de tomodensitometrie, les antecedents cliniques et les manifestations biochimiques n’ont pas permis de determiner les causes de l’aspect flou. Elle excluait toutefois les patients qui ont presente des affections que l’on savait causer cet aspect flou ou qui ont presente des ganglions lymphatiques dont le diametre de petit axe etait superieur a 5 mm, des masses mesenteriques discretes ou un epaississement des parois intestinales. Resultats : Un mesentere d’aspect flou a ete decele chez 561 patients a l’examen de TDM abdominopelvienne. Quatre-vingts cas d’observation fortuite et isolee de mesentere d’aspect flou idiopathique ont ete releves, ce qui equivaut a une prevalence de 7 %. L’examen de tomodensitometrie s’est avere le plus souvent indique en raison de douleurs abdominales. Une legere predominance feminine a par ailleurs ete relevee (51,3 %). Enfin, 67,5 % des patients ont ete reputes ^etre obeses, alors que 17,5 % ont ete reputes faire de l’embonpoint. * Address for correspondence: Ebru Unlu, MD, Faculty of Medicine, Department of Radiology, Afyon Kocatepe University, Izmir road 7th km, 030400, Afyonkarahisar, Turkey.
E-mail address: [email protected] (E. Unlu).
0846-5371/$ - see front matter Ó 2016 Canadian Association of Radiologists. All rights reserved. http://dx.doi.org/10.1016/j.carj.2015.06.004
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Conclusion : La presente etude revele que la prevalence des observations fortuites de mesentere d’aspect flou idiopathique est significative. L’indice de masse corporelle eleve des patients et les preuves de plus en plus nombreuses que l’obesite modifie les facteurs inflammatoires des tissus adipeux suggerent aussi une correlation entre l’obesite et l’aspect flou du mesentere a l’examen de TDM. Ó 2016 Canadian Association of Radiologists. All rights reserved. Key Words: Misty mesentery; Multidetector computed tomography; Obesity; Prevalence
The term ‘‘misty mesentery’’ is used to describe the pathological increase in mesenteric fat attenuation in computed tomography (CT). This term was introduced by Mindelzun et al [1] as a descriptive imaging finding with an extensive differential diagnosis. It is commonly observed on CT scans performed during daily clinical practice, and when radiologists encounter this imaging finding, they should consider various pathological entities that could lead to this appearance, including infiltration of mesenteric fat and adjacent organs by fluid (ie, oedema, lymph, or blood), fibrous tissue, inflammatory or neoplastic cells [1e3]. Misty mesentery is also considered to be an important CT sign indicating early stages of sclerosing mesenteritis, which is a rare disease characterised by chronic nonspecific inflammation of the adipose tissue of the bowel mesentery (the result of invasion of the mesentery by lipid-laden macrophages) [2,3]. The cause of sclerosing mesenteritis remains unclear and the diagnosis of the disease requires exclusion of neoplastic or other inflammatory causes and may finally require histologic confirmation [2,4e7]. This study was initiated after we had noted that some patients who had undergone abdomen CT for an unrelated reason were incidentally found to have segmental misty mesentery with unknown cause, which could not be associated to other CT findings, patient history, or clinical/ biochemical manifestations. Additionally, none of the patients had discrete mesenteric masses or hyperdense pseudocapsules (peripheral attenuation limiting the mass), which are the diagnostic features for sclerosing mesenteritis [8]. Because the patients did not meet the radiological criteria, they were not diagnosed as sclerosing mesenteritis. More importantly, we have noticed that most of these patients had significantly increased abdominal subcutaneous adipose tissue as a marker of central obesity, and on investigation of patient demographic characteristics, we noted that most of them had high body mass index (BMI). In recent years, it has been well established that obesity is associated with low-grade chronic inflammatory processes characterised by increased levels of circulating inflammatory cytokines, acute phase proteins, as well as adipokines or neuropeptides, in healthy obese subjects [9e12]. All these molecules are produced within adipocytes and also within macrophages and lymphocytes that infiltrate the mesenteric fat [9]. In addition, the inflammatory mediators found in adipose tissue, termed ‘‘adipokines,’’ have been shown to be overexpressed in the mesenteric adipose tissue of subjects with inflammatory bowel disease [13e17].
In the current study, we aimed to assess first the prevalence of idiopathic misty mesentery appearance in CT and second its possible relationship to obesity under the hypothesis that the microinflammatory process triggered by obesity may lead to mesenteric inflammation and consequently misty mesentery on CT. A review of the literature was also undertaken to evaluate the already known causes of misty mesentery and also the link between obesity and inflammation. To the best of our knowledge, this is the first study highlighting the prevalence of idiopathic misty mesentery and the possible link between obesity and this CT finding. Materials and Methods The study protocol was approved by the local Ethical Committee of a Training and Research Hospital. The CT features and medical records of 561 patients in whom misty mesentery appearance was depicted on abdominopelvic CT scans were prospectively collected by an experienced radiologist (N.O.) during the 2-year period from January 2011 to January 2013. Among these, 80 patients having segmental misty mesentery that presented as an incidental finding were included in the present study. The cause of the mesenteric changes in all these patients was unknown, and none of them had any disease that would be known to cause misty mesentery appearance on CT. Also, there were no changes in the misty mesentery appearance and no additional findings were observed during a minimum 1-year period. CT was performed using either an 80-row detector CT (160-slice) scanner (Aquilion Prime, Toshiba Medical Systems, Nasu, Japan) or a 6-slice CT scanner (Brilliance 6; Philips Medical Systems, Amsterdam, the Netherlands). The technique of CT imaging was not standardized because of the variety of different clinical indications. However, to be included in the study, the section thickness had to be a maximum of 5 mm. Twenty-one of the patients underwent nonenhanced CT scans (‘‘renal stone’’ protocol), while the rest of the study population received a diluted lactulose solution of 1000e1500 cc orally and intravenous iodinated nonionic contrast material. Diluted lactulose solution was given in a 1-1.5-hour time period before CT scanning. Intravenous contrast material was administered as a 100 mL bolus infusion at an injection rate of 2-3 mL/second. The analysis population of the present study was patients with idiopathic segmental mild misty mesentery appearance on their CT images. CT criteria for the diagnosis of misty mesentery were as follows: normal mesenteric fat is about
Prevalence of idiopatic misty mesentery on CT / Canadian Association of Radiologists Journal xx (2016) 1e6
the same the density as that of subcutaneous and retroperitoneal fat, ranging between e100 and e160 Hounsfield units (HU) and appears as a homogeneous low attenuation area, whereas segmental misty mesentery was defined as an increased density (typically 40 to 60 HU) compared to subcutaneous and retroperitoneal fat as well as the loss of sharp interfaces between mesenteric vessels. The study excluded patients with diseases known to cause misty mesentery appearance on CT, such as (a) diseases that may be associated with mesenteric oedema: systemic diseases (hypoalbuminemia, heart failure, nephrosis) or cirrhosis, Budd-Chiari syndrome, mesenteric vein thrombosis; (b) diseases that may cause lymphatic obstruction/lymphoedema: constrictive pericarditis, Crohn’s disease, intestinal tuberculosis, intestinal lymphoma, receiving radiotheraphy; (c) diseases that may cause mesenteric inflammation: pancreatitis, cholecystitis, appendicitis, inflammatory bowel disease, diverticulitis, and tuberculous peritonitis; (d) diseases that may cause mesenteric hemorrhage: trauma, anticoagulation therapy, hematological disorders, mesenteric ischaemia; (e) known underlying cancer; (f) patients who never underwent any follow-up abdominal CT; (g) misty mesenteryecontaining lymph nodes greater than a short-axis diameter of 5 mm; (h) discrete masses in the mesentery; and (i) bowel wall thickening. Accordingly, 80 CT exams with misty mesentery appearance were found to be eligible (Figure 1). Two
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radiologists (E.U. and M.B.A.) reviewed the patients’ medical records for clinical histories and presentations, and also evaluated their initial and follow-up CT scans for detection of associated CT findings and exclusion of coexistent diseases that may cause misty mesentery appearance. Axial CT images were evaluated for the site of mesenteric changes, lymphadenopathies, presence or absence of bowel wall changes, dilation of the mesenteric vessels, a fat ring sign (ie, preservation of fat around the mesenteric vessels), and for evaluation of the other abdominal organs. The bowel wall was considered thickened when it exceeded 4 mm and the mesenteric vessels were considered dilated when they exceeded 3 mm in diameter or were increased in number. BMI (kg/m2) was calculated by dividing body weight in kilograms by height in metres squared to assess obesity. A BMI from 18.5e25 kg/m2 was considered normal, from 25e 30 kg/m2 overweight, above 30 kg/m2 obese, and greater than 40 kg/m2 severe or morbid obese [18]. Results Baseline characteristics of patients are presented in Table 1. A total of 561 patients with misty mesentery appearance were collected in a 2-year period from January 2011 to January 2013. After exclusion of patients with coexistent diseases and CT features as study protocols,
Figure 1. Multidetector-row computed tomography (CT) images of the abdomen showing segmental misty mesentery in 2 different patients with high body mass index (BMI). Axial (A) and coronal (B) CT images of an obese patient (BMI ¼ 31.2) show focal haziness of the left upper quadrant mesentery with mild focal increased attenuation of the mesenteric fat. Axial (C) and sagittal (D) CT images of a morbid obese patient (BMI ¼ 40.5) demonstrate multiple lymph nodes all measuring <5 mm in a focal region of misty mesentery.
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Table 1 Baseline characteristics of patients with idiopathic misty mesentery
Discussion
Age, y Gender Female Male Body weight, kg Body mass index, kg/m2 Total Normal weighted Overweight Obese Morbid obese Indications of CT imaging Abdominal pain Abdominal bloating and pain Nausea and abdominal pain Consultant clinics Urology Internal medicine Emergency service General surgery Site of the segmental mesenteric changes Jejunal mesentery Ileal mesentery
Incidental findings are defined as findings that are unrelated to the reason the study is ordered. The improvement in CT image quality and the growing number of imaging techniques performed per patient have led to an increase in the frequency of detecting mesenteric abnormalities, even in asymptomatic patients. Misty mesentery is used to describe the finding of a regional increase in mesenteric fat attenuation associated with small nodes, which is frequently seen in abdominopelvic CT during daily clinical practice. A wide spectrum of pathologies may result in the misty mesentery appearance on CT, however, rarely can the exact cause leading to this appearance be found [1e3]. In an effort to determine the frequency of cases with incidentally detected idiopathic misty mesentery, we have documented a significant number of patients with this finding on CT. The pathologies leading to misty mesentery appearance on CT include diseases that may be associated with mesenteric oedema, lymphoedema, mesenteric inflammation, mesenteric hemorrhage, and neoplasms [2,3]. Misty mesentery is also considered to be an important CT sign of sclerosing mesenteritis. Sclerosing mesenteritis is a rare chronic nonspecific inflammation that affects the adipose tissue of the bowel mesentery and the diagnosis requires exclusion of the wide range of conditions mentioned previously [2e8]. It is subcategorized into 3 stages based on the most predominant histologic tissue type (fat necrosis, inflammation, and/or fibrosis). The first stage, mesenteric lipodystrophy, is characterised by fat necrosis with mesenteric fat replaced by a layer of fat-laden macrophages. The second stage, mesenteric panniculitis, is characterised by non-specific inflammation of the mesenteric fat, which is infiltrated by plasma cells, a small number of white blood cells and fat-laden macrophages. Finally, in the last stage, named retractile mesenteritis, mesenteric fat is replaced by fibrosis and is characterised by an irregular mesenteric mass arising from the root of the bowel mesentery that may be indistinguishable from a malignant mesenteric tumour [2]. This varied terminology has resulted in considerable confusion in many studies, and generally the condition has been categorized into 2 pathological subgroups; it is termed mesenteric panniculitis if inflammation and fat necrosis predominate, whereas the terms fibrosing mesenteritis or retractile mesenteritis have been used if fibrosis and retraction predominate [5e8,18e20]. Although sclerosing mesenteritis has been linked with various diseases (eg, vasculitis, granulomatous disease, malignancies, autoimmune disorders, ischemia, infections, trauma, prior abdominal surgery), the pathophysiology of this condition is unknown [2,6e8]. The exact prevalence of mesenteric panniculitis is unknown, as most of the cases are incidentally detected [2]. In a prospective study, mesenteric panniculitis as an incidental finding was documented at 0.6%. A high rate of 69% of mesenteric panniculitis patients had a coexisting malignancy, 22% had benign disease, and the remaining 9% had no disease explaining this condition [6]. To our knowledge,
47.16 (27e62) 41 (51.2%) 39 (48.8%) 87.04 11.8 (60.6e129.5) 36.8 4.52 12 14 46 12
(21.4e44.3) (15%) (17.5%) (57.5%) (10%)
43 (53.8%) 28 (35%) 9 (11.2%) 27 25 15 13
(33.8%) (31.2%) (18.8%) (16.2%)
59 (75%) 21 (25%)
CT ¼ computed tomography. Values are mean SD ( if range) or mean frequency (if %).
the remaining 80 examinations were eligible for the study, giving a prevalence of 7%. The age range of the patients was 27e62 years (mean age, 47.16 years). Of the 80 cases, 41 (51.3%) were female and 39 (48.8%) were male patients. Of all the scans, 33.8% (n ¼ 27) were performed on urology outpatients, 31.3% (n ¼ 25) on internal medicine outpatients, 18.8% (n ¼ 15) on emergency service patients, and finally 16.3% (n ¼ 13) general surgery outpatients. Indications of initial CT examinations were: investigation of only abdominal pain in 43 cases (53.8%), abdominal bloating and abdominal pain in 28 cases (35%), and nausea and abdominal pain in 9 cases (11.3%). All patients included in the present study had a mild degree of misty mesentery appearance that presented as an incidental finding. Also all the patients had lymph nodes within the misty mesentery that were smaller than a shortaxis diameter of 5 mm. The sites of the segmental mesenteric changes were the jejunal mesentery in 59 patients (75%) and the ileal mesentery in 21 patients (25%). None of the patients had a fatty mass lesion, hyperdense pseudocapsule, fat ring sign, or arterial/venous dilation, which are diagnostic criteria for mesenteric panniculitis. Body weight range was between 60.6e129.5 kg (87.04 11.8 kg) and BMI range was 21.4e44.3 kg/m2 (36.8 4.52 kg/m2). Fifty-four patients (67.5%) were classified as obese (BMI >30 kg/m2) and of those obese patients, 8 (10%) presented with severe/morbid obesity (BMI >40 kg/ m2). Also, 14 of the cases (17.5%) had a BMI within the range of 25e30 kg/m2 and presented as overweight. The remaining 12 patients in the study population (15%) were normal weighted (BMI, 18.5e25 kg/m2).
Prevalence of idiopatic misty mesentery on CT / Canadian Association of Radiologists Journal xx (2016) 1e6
idiopathic misty mesentery appearance has not yet been documented. In the present study, we investigated 561 patients with misty mesentery appearance and demonstrated that 7% (n ¼ 80) had no associated disease that explained this CT finding. The subjects included in our study had mild and segmental increased attenuation in the mesentery associated with small lymph nodes (Figure 1). These findings did not meet the diagnostic criteria of mesenteric panniculitis, as given by Coulier [8], which includes a well-defined mesenteric fatty mass lesion without infiltration of neighboring structures, an increase in mesenteric fat attenuation, lymph nodes within the mass, surrounding hyperdense pseudocapsule and limiting mesenteric fat and hypodense fatty halo surrounding blood vessels and nodes (fat ring sign) (Figure 2). Finally, a minimum of 3 of the 5 typical signs had to be fulfilled for a positive CT diagnosis of mesenteric panniculitis [8]. Accordingly, it is reasonable for us to accept our study population as patients with idiopathic misty mesentery who may be in the early stages of sclerosing mesenteritis, namely a fat necrosis and/or nonspecific inflammation stage, because of the absence of discrete mesenteric masses or hyperdense pseudocapsules. In the present study, all the patients had additional lymph nodes that were <5 mm in diameter. In a study of 37 patients with misty mesentery on CT and a lack of history of malignancy, Corwin et al [21] demonstrated that there was no increased risk for malignancy when the mesenteric lymph nodes had a diameter less than 10 mm in the short axis. Also, Taffel et al [2] stated that lymph nodes less than a short-axis diameter of 5 mm in misty mesentery and no coexistent disease require no further workup. According to these reports, we excluded patients with misty mesentery containing
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mesenteric lymph nodes larger than 5 mm but included patients who were followed up for at least a 1-year period for the possibility of malignancy. The site of the segmental mesenteric changes in our study was similar to that of mesenteric panniculitis, most commonly located on the left, which is the orientation of the jejunal mesentery (jejunal mesentery 75%, ileal mesentery 25%) [2]. In the present study, we found a slight female predominance (51.3%), while mesenteric panniculitis shows a male predominance in most studies [2,6e8]. Also, nonspecific abdominal pain was the common presenting symptom of the study population. Another result of the present study that should be highlighted is that the majority of patients in our study had high BMI; 57.5% of the study population was classified as obese, 10% as morbid obese, and 17.5% as overweight. Finally, only 15% of our study population was normal weighted. According to these results, it is difficult to say that obesity is the primary cause of the mesenteric changes, based on a prevalence study, however, it is suggestive that there may be an association between obesity and misty mesentery appearance on CT. The association of obesity and chronic low-grade inflammation has been evident for several years. Also, in recent years, it is well established that obese people show higher circulating concentrations of pro-inflammatory cytokines such as interleukin 6 and tumour necrosis factor alpha acute phase proteins (C-reactive protein and haptoglobin), as well as adipokines (leptin, adiponectin, and resistin) or neuropeptides (eg, substance P) compared with lean individuals [9e13]. All these proinflammatory factors are produced within adipocytes and also within adipose tissue macrophages and lymphocytes, which infiltrate the mesenteric fat. Therefore, a systemic acute-phase response may be
Figure 2. Multidetector-row computed tomography images of the abdomen showing a well-circumscribed, heterogeneous, fatty mass with increased attenuation consistent with mesenteric panniculitis and characteristic pseudocapsule sign surrounding a focal area of hyperattenuation within the mesentery, limiting heterogeneous mesenteric mass from surrounding normal mesentery (A); preservation of normal fat density in tissues surrounding mesenteric vessels and soft tissue nodules within the area of misty mesentery, thereby creating ‘‘fat halo’’ sign (B).
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triggered with increasing obesity [9e13]. Of particular note, the inflammatory mediators termed ‘‘adipokines,’’ found in adipose tissue, were shown to be overexpressed in the mesenteric fat tissue of subjects with inflammatory bowel disease [14,15]. Although the underlying mechanisms of obesity-induced inflammation are still not fully understood, a mouse study advanced the understanding of obesity-induced inflammation by demonstrating that a marked increase in production of inflammatory adipokines is associated with increased numbers of macrophages in adipose tissue in obese mice, suggesting that overfeeding was the starting signal of this inflammation, and that the metabolic roles of adipocytes change as they enlarge with obesity [13]. Strikingly, this obesity-induced inflamed visceral fat tissue is able to transfer the systemic inflammatory state even when it is transplanted to lean mice as an active endocrine organ [10]. Finally, a correlation has been found between BMI and adipose tissue macrophage number, especially in visceral fat tissue in humans. According to all these studies, and with the fact that visceral fat tissue is especially prone to inflammatory changes, we hypothesize that in obese patients, misty mesentery appearance on CT may be the result of chronic lowgrade inflammation triggered by mesenteric fat deposition. However, prospective studies with larger numbers of obese subjects are needed to strengthen our hypothesis. There are limitations to the present study. First, although our patients had stable lesions during a follow-up of at least 1 year, this did not exclude the existence of some malignancies such as follicular lymphoma, which is known to be a slow-growing lymphoma. Second, the present study was limited by its retrospective nature. However, a prospectively collected, considerable number of patients with misty mesentery appearance and their clinical and radiological follow-up were the strength of this study. Finally, this was a prevalence study and the causal relationship between obesity and misty mesentery appearance could not be confirmed. On the other hand, despite its limitations, this is the first report describing the estimated prevalence of idiopathic misty mesentery appearance on CT and its possible association with obesity. Conclusion We have found a prevalence of idiopathic incidental misty mesentery appearance of 7% among all the patients with this finding, and we also found, previously not reported, a high BMI in most of these patients. Radiologists commonly encounter this imaging finding in daily routine practice, but sometimes cannot determine any associated disease leading to the appearance. Although the underlying cause is unknown, the appearance does not meet the criteria of mesenteric panniculitis and is simply reported as an incidental imaging finding. Therefore, it is suspected that there may be many other conditions causing a misty mesentery appearance on CT that are not yet discovered. Because of the high BMI of our study population and based on growing evidence of obese
visceral adipose tissue as an important source of inflammation, we suggest that obesity itself may be one of the reasons for misty mesentery appearance on CT, leading to mesenteric inflammation. However, further prospective studies with histologic and endocrine correlations are needed to reach clear conclusions and clarify the impact of obesity on this finding.
References [1] Mindelzun RE, Jeffrey RB, Lane MJ, et al. The misty mesentery on CT: differential diagnosis. AJR Am J Roentgenol 1996;167:61e5. [2] Taffel MT, Khati NJ, Hai N, et al. De-Misty-fying the mesentery: an algorithmic approach to neoplastic and non-neoplastic mesenteric abnormalities. Abdom Imaging 2014;39:892e907. [3] Filippone A, Cianci R, Di Fabio F, et al. Misty mesentery: a pictorial review of multidetector-row CT findings. Radiol Med 2011;116:351e65. [4] McLaughlin PD, Filippone A, Maher MM. The ‘‘misty mesentery’’: mesenteric panniculitis and its mimics. AJR Am J Roentgenol 2013; 200:116e23. € Albrecht T, Osterhoff MA, et al. Is mesenteric pan[5] G€ogebakan O, niculitis truely a paraneoplastic phenomenon? A matched pair analysis. Eur J Radiol 2013;82:1853e9. [6] Daskalogiannaki M, Voloudaki A, Prassopoulos P, et al. CT evaluation of mesenteric panniculitis: prevalence and associated diseases. AJR Am J Roentgenol 2000;174:427e31. [7] Horton KM, Lawler LP, Fishman EK. CT findings in sclerosing mesenteritis (panniculitis): spectrum of disease. Radiographics 2003;23:1561e7. [8] Coulier BB. Mesenteric panniculitis. Part 1: MDCTdpictorial review. JBR-BTR 2011;94:229e40. [9] Rodrıguez-Hernandez H, Simental-Mendıa LE, Rodrıguez-Ramırez G, et al. Obesity and ınflammation: epidemiology, risk factors, and markers of inflammation. Int J Endocrinol 2013;2013:678159. [10] Weisberg SP, McCann D, Desai M, et al. Obesity is associated with macrophage accumulation in adipose tissue. J Clin Invest 2003;112: 1796e808. [11] Cottam DR, Mattar SG, Barinas-Mitchell E, et al. The chronic inflammatory hypothesis for the morbidity associated with morbid obesity: implications and effects of weight loss. Obes Surg 2004;14:589e600. [12] Greenberg AS, Obin MS. Obesity and the role of adipose tissue in inflammation and metabolism. Am J Clin Nutr 2006;83:461Se5S. [13] Paik J, Fierce Y, Treuting PM, et al. High-fat diet-ınduced obesity exacerbates ınflammatory bowel disease in genetically susceptible Mdr1a2/2 male mice. J Nutr 2013;143:1240e7. [14] Boutros M, Maron D. Inflammatory bowel disease in the obese patient. Clin Colon Rectal Surg 2011;24:244e52. [15] Bertin B, Desreumaux P, Dubuquoy L. Obesity, visceral fat and Crohn’s disease. Curr Opin Clin Nutr Metab Care 2010;13:574e80. [16] Steed H, Walsh S, Reynolds N. A brief report of the epidemiology of obesity in the inflammatory bowel disease population of Tayside, Scotland. Obes Facts 2009;2:370e2. [17] Mendall MA, Gunasekera AV, John BJ, et al. Is obesity a risk factor for Crohn’s disease? Dig Dis Sci 2011;56:837e44. [18] World Health Organization. BMI classification. Available at: http:// apps.who.int/bmi/index.jsp?introPage¼intro_3.html. Accessed June 12, 2012. [19] van Breda Vriesman AC, Schuttevaer HM, Coerkamp EG, et al. Mesenteric panniculitis: US and CT features. Eur Radiol 2004;14:2242e8. [20] Akram S, Pardi DS, Schaffner JA, et al. Sclerosing mesenteritis: clinical features, treatment, and outcome in ninety-two patients. Clin Gastroenterol Hepatol 2007;5:589e96. quiz 523e4. [21] Corwin MT, Smith AJ, Karam AR, et al. Incidentally detected misty mesentery on CT: risk of malignancy correlates with mesenteric lymph node size. J Comput Assist Tomogr 2012;36:26e9.
Computed Tomography / Tomodensitometrie
The Prevalence of Incidentally Detected Idiopathic Misty Mesentery on Multidetector Computed Tomography: Can Obesity Be the Triggering Cause? Ebru Unlu, MDa,*, Nazan Okur, MDa, Mehtap Beker Acay, MDa, Emre Kacar, MDa, Serife Ozdinc, MDb, Cinar Balcik, MDa, Ozlem Turksoy Tokgoz, MDc a Department of Radiology, Afyon Kocatepe University Faculty of Medicine, Afyonkarahisar, Turkey Department of Emergency Medicine, Afyon Kocatepe University Faculty of Medicine, Afyonkarahisar, Turkey c Department of Radiology, Antalya Training and Research Hospital, Antalya, Turkey
b
Abstract Purpose: Misty mesentery appearance is commonly reported in daily practice, usually as a secondary finding of various pathological entities, but sometimes it is encountered as an isolated finding that cannot be attributed to any other disease entity. We aimed to assess the prevalence of cases with incidentally detected idiopathic misty mesentery on computed tomography (CT) and to summarize the pathologies leading to this appearance. Methods: Medical records and initial and follow-up CT features of patients with misty mesentery appearance between January 2011 and January 2013 were analysed. The study included cases with no known cause of misty mesentery according to associated CT findings, clinical history, or biochemical manifestations, and excluded patients with diseases known to cause misty mesentery, lymph nodes greater than a short-axis diameter of 5 mm, discrete mesenteric masses, or bowel wall thickening. Results: There were a total of 561 patients in whom misty mesentery appearance was depicted on abdominopelvic CT scans. A total of 80 cases were found to have isolated incidental idiopathic misty mesentery, giving a prevalence of 7%. The common indication for CT examination was abdominal pain. There was a slight female predominance (51.3%). 67.5% of all patients were classified as obese and 17.5% as overweight. Conclusions: The results of the present study show that idiopathic incidental misty mesentery appearance has a significant prevalence. Also, the high body mass index of these patients and the growing evidence of obesity-induced inflammatory changes in adipose tissue are suggestive of an association between obesity and misty mesentery appearance on CT. Resume Objet : Il est assez frequent d’observer un mesentere d’aspect flou dans le cadre de la pratique quotidienne de la radiologie. Bien qu’il s’agisse habituellement d’une constatation secondaire liee a diverses entites pathologiques, il peut s’agir, a l’occasion, d’une constatation isolee non imputable a aucune autre entite morbide. Notre objectif consistait a mesurer la prevalence des observations fortuites de mesentere d’aspect flou idiopathique lors d’une tomodensitometrie (TDM), et a faire un resume des affections qui donnent lieu a de telles constatations. Methodes : Nous avons analyse les dossiers medicaux ainsi que les resultats des tomodensitometries initiaux et de suivi de patients chez qui un mesentere d’aspect flou a ete observe entre janvier 2011 et janvier 2013. L’etude incluait les patients dont les resultats de tomodensitometrie, les antecedents cliniques et les manifestations biochimiques n’ont pas permis de determiner les causes de l’aspect flou. Elle excluait toutefois les patients qui ont presente des affections que l’on savait causer cet aspect flou ou qui ont presente des ganglions lymphatiques dont le diametre de petit axe etait superieur a 5 mm, des masses mesenteriques discretes ou un epaississement des parois intestinales. Resultats : Un mesentere d’aspect flou a ete decele chez 561 patients a l’examen de TDM abdominopelvienne. Quatre-vingts cas d’observation fortuite et isolee de mesentere d’aspect flou idiopathique ont ete releves, ce qui equivaut a une prevalence de 7 %. L’examen de tomodensitometrie s’est avere le plus souvent indique en raison de douleurs abdominales. Une legere predominance feminine a par ailleurs ete relevee (51,3 %). Enfin, 67,5 % des patients ont ete reputes ^etre obeses, alors que 17,5 % ont ete reputes faire de l’embonpoint. * Address for correspondence: Ebru Unlu, MD, Faculty of Medicine, Department of Radiology, Afyon Kocatepe University, Izmir road 7th km, 030400, Afyonkarahisar, Turkey.
E-mail address: [email protected] (E. Unlu).
0846-5371/$ - see front matter Ó 2016 Canadian Association of Radiologists. All rights reserved. http://dx.doi.org/10.1016/j.carj.2015.06.004
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Conclusion : La presente etude revele que la prevalence des observations fortuites de mesentere d’aspect flou idiopathique est significative. L’indice de masse corporelle eleve des patients et les preuves de plus en plus nombreuses que l’obesite modifie les facteurs inflammatoires des tissus adipeux suggerent aussi une correlation entre l’obesite et l’aspect flou du mesentere a l’examen de TDM. Ó 2016 Canadian Association of Radiologists. All rights reserved. Key Words: Misty mesentery; Multidetector computed tomography; Obesity; Prevalence
The term ‘‘misty mesentery’’ is used to describe the pathological increase in mesenteric fat attenuation in computed tomography (CT). This term was introduced by Mindelzun et al [1] as a descriptive imaging finding with an extensive differential diagnosis. It is commonly observed on CT scans performed during daily clinical practice, and when radiologists encounter this imaging finding, they should consider various pathological entities that could lead to this appearance, including infiltration of mesenteric fat and adjacent organs by fluid (ie, oedema, lymph, or blood), fibrous tissue, inflammatory or neoplastic cells [1e3]. Misty mesentery is also considered to be an important CT sign indicating early stages of sclerosing mesenteritis, which is a rare disease characterised by chronic nonspecific inflammation of the adipose tissue of the bowel mesentery (the result of invasion of the mesentery by lipid-laden macrophages) [2,3]. The cause of sclerosing mesenteritis remains unclear and the diagnosis of the disease requires exclusion of neoplastic or other inflammatory causes and may finally require histologic confirmation [2,4e7]. This study was initiated after we had noted that some patients who had undergone abdomen CT for an unrelated reason were incidentally found to have segmental misty mesentery with unknown cause, which could not be associated to other CT findings, patient history, or clinical/ biochemical manifestations. Additionally, none of the patients had discrete mesenteric masses or hyperdense pseudocapsules (peripheral attenuation limiting the mass), which are the diagnostic features for sclerosing mesenteritis [8]. Because the patients did not meet the radiological criteria, they were not diagnosed as sclerosing mesenteritis. More importantly, we have noticed that most of these patients had significantly increased abdominal subcutaneous adipose tissue as a marker of central obesity, and on investigation of patient demographic characteristics, we noted that most of them had high body mass index (BMI). In recent years, it has been well established that obesity is associated with low-grade chronic inflammatory processes characterised by increased levels of circulating inflammatory cytokines, acute phase proteins, as well as adipokines or neuropeptides, in healthy obese subjects [9e12]. All these molecules are produced within adipocytes and also within macrophages and lymphocytes that infiltrate the mesenteric fat [9]. In addition, the inflammatory mediators found in adipose tissue, termed ‘‘adipokines,’’ have been shown to be overexpressed in the mesenteric adipose tissue of subjects with inflammatory bowel disease [13e17].
In the current study, we aimed to assess first the prevalence of idiopathic misty mesentery appearance in CT and second its possible relationship to obesity under the hypothesis that the microinflammatory process triggered by obesity may lead to mesenteric inflammation and consequently misty mesentery on CT. A review of the literature was also undertaken to evaluate the already known causes of misty mesentery and also the link between obesity and inflammation. To the best of our knowledge, this is the first study highlighting the prevalence of idiopathic misty mesentery and the possible link between obesity and this CT finding. Materials and Methods The study protocol was approved by the local Ethical Committee of a Training and Research Hospital. The CT features and medical records of 561 patients in whom misty mesentery appearance was depicted on abdominopelvic CT scans were prospectively collected by an experienced radiologist (N.O.) during the 2-year period from January 2011 to January 2013. Among these, 80 patients having segmental misty mesentery that presented as an incidental finding were included in the present study. The cause of the mesenteric changes in all these patients was unknown, and none of them had any disease that would be known to cause misty mesentery appearance on CT. Also, there were no changes in the misty mesentery appearance and no additional findings were observed during a minimum 1-year period. CT was performed using either an 80-row detector CT (160-slice) scanner (Aquilion Prime, Toshiba Medical Systems, Nasu, Japan) or a 6-slice CT scanner (Brilliance 6; Philips Medical Systems, Amsterdam, the Netherlands). The technique of CT imaging was not standardized because of the variety of different clinical indications. However, to be included in the study, the section thickness had to be a maximum of 5 mm. Twenty-one of the patients underwent nonenhanced CT scans (‘‘renal stone’’ protocol), while the rest of the study population received a diluted lactulose solution of 1000e1500 cc orally and intravenous iodinated nonionic contrast material. Diluted lactulose solution was given in a 1-1.5-hour time period before CT scanning. Intravenous contrast material was administered as a 100 mL bolus infusion at an injection rate of 2-3 mL/second. The analysis population of the present study was patients with idiopathic segmental mild misty mesentery appearance on their CT images. CT criteria for the diagnosis of misty mesentery were as follows: normal mesenteric fat is about
Prevalence of idiopatic misty mesentery on CT / Canadian Association of Radiologists Journal xx (2016) 1e6
the same the density as that of subcutaneous and retroperitoneal fat, ranging between e100 and e160 Hounsfield units (HU) and appears as a homogeneous low attenuation area, whereas segmental misty mesentery was defined as an increased density (typically 40 to 60 HU) compared to subcutaneous and retroperitoneal fat as well as the loss of sharp interfaces between mesenteric vessels. The study excluded patients with diseases known to cause misty mesentery appearance on CT, such as (a) diseases that may be associated with mesenteric oedema: systemic diseases (hypoalbuminemia, heart failure, nephrosis) or cirrhosis, Budd-Chiari syndrome, mesenteric vein thrombosis; (b) diseases that may cause lymphatic obstruction/lymphoedema: constrictive pericarditis, Crohn’s disease, intestinal tuberculosis, intestinal lymphoma, receiving radiotheraphy; (c) diseases that may cause mesenteric inflammation: pancreatitis, cholecystitis, appendicitis, inflammatory bowel disease, diverticulitis, and tuberculous peritonitis; (d) diseases that may cause mesenteric hemorrhage: trauma, anticoagulation therapy, hematological disorders, mesenteric ischaemia; (e) known underlying cancer; (f) patients who never underwent any follow-up abdominal CT; (g) misty mesenteryecontaining lymph nodes greater than a short-axis diameter of 5 mm; (h) discrete masses in the mesentery; and (i) bowel wall thickening. Accordingly, 80 CT exams with misty mesentery appearance were found to be eligible (Figure 1). Two
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radiologists (E.U. and M.B.A.) reviewed the patients’ medical records for clinical histories and presentations, and also evaluated their initial and follow-up CT scans for detection of associated CT findings and exclusion of coexistent diseases that may cause misty mesentery appearance. Axial CT images were evaluated for the site of mesenteric changes, lymphadenopathies, presence or absence of bowel wall changes, dilation of the mesenteric vessels, a fat ring sign (ie, preservation of fat around the mesenteric vessels), and for evaluation of the other abdominal organs. The bowel wall was considered thickened when it exceeded 4 mm and the mesenteric vessels were considered dilated when they exceeded 3 mm in diameter or were increased in number. BMI (kg/m2) was calculated by dividing body weight in kilograms by height in metres squared to assess obesity. A BMI from 18.5e25 kg/m2 was considered normal, from 25e 30 kg/m2 overweight, above 30 kg/m2 obese, and greater than 40 kg/m2 severe or morbid obese [18]. Results Baseline characteristics of patients are presented in Table 1. A total of 561 patients with misty mesentery appearance were collected in a 2-year period from January 2011 to January 2013. After exclusion of patients with coexistent diseases and CT features as study protocols,
Figure 1. Multidetector-row computed tomography (CT) images of the abdomen showing segmental misty mesentery in 2 different patients with high body mass index (BMI). Axial (A) and coronal (B) CT images of an obese patient (BMI ¼ 31.2) show focal haziness of the left upper quadrant mesentery with mild focal increased attenuation of the mesenteric fat. Axial (C) and sagittal (D) CT images of a morbid obese patient (BMI ¼ 40.5) demonstrate multiple lymph nodes all measuring <5 mm in a focal region of misty mesentery.
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Table 1 Baseline characteristics of patients with idiopathic misty mesentery
Discussion
Age, y Gender Female Male Body weight, kg Body mass index, kg/m2 Total Normal weighted Overweight Obese Morbid obese Indications of CT imaging Abdominal pain Abdominal bloating and pain Nausea and abdominal pain Consultant clinics Urology Internal medicine Emergency service General surgery Site of the segmental mesenteric changes Jejunal mesentery Ileal mesentery
Incidental findings are defined as findings that are unrelated to the reason the study is ordered. The improvement in CT image quality and the growing number of imaging techniques performed per patient have led to an increase in the frequency of detecting mesenteric abnormalities, even in asymptomatic patients. Misty mesentery is used to describe the finding of a regional increase in mesenteric fat attenuation associated with small nodes, which is frequently seen in abdominopelvic CT during daily clinical practice. A wide spectrum of pathologies may result in the misty mesentery appearance on CT, however, rarely can the exact cause leading to this appearance be found [1e3]. In an effort to determine the frequency of cases with incidentally detected idiopathic misty mesentery, we have documented a significant number of patients with this finding on CT. The pathologies leading to misty mesentery appearance on CT include diseases that may be associated with mesenteric oedema, lymphoedema, mesenteric inflammation, mesenteric hemorrhage, and neoplasms [2,3]. Misty mesentery is also considered to be an important CT sign of sclerosing mesenteritis. Sclerosing mesenteritis is a rare chronic nonspecific inflammation that affects the adipose tissue of the bowel mesentery and the diagnosis requires exclusion of the wide range of conditions mentioned previously [2e8]. It is subcategorized into 3 stages based on the most predominant histologic tissue type (fat necrosis, inflammation, and/or fibrosis). The first stage, mesenteric lipodystrophy, is characterised by fat necrosis with mesenteric fat replaced by a layer of fat-laden macrophages. The second stage, mesenteric panniculitis, is characterised by non-specific inflammation of the mesenteric fat, which is infiltrated by plasma cells, a small number of white blood cells and fat-laden macrophages. Finally, in the last stage, named retractile mesenteritis, mesenteric fat is replaced by fibrosis and is characterised by an irregular mesenteric mass arising from the root of the bowel mesentery that may be indistinguishable from a malignant mesenteric tumour [2]. This varied terminology has resulted in considerable confusion in many studies, and generally the condition has been categorized into 2 pathological subgroups; it is termed mesenteric panniculitis if inflammation and fat necrosis predominate, whereas the terms fibrosing mesenteritis or retractile mesenteritis have been used if fibrosis and retraction predominate [5e8,18e20]. Although sclerosing mesenteritis has been linked with various diseases (eg, vasculitis, granulomatous disease, malignancies, autoimmune disorders, ischemia, infections, trauma, prior abdominal surgery), the pathophysiology of this condition is unknown [2,6e8]. The exact prevalence of mesenteric panniculitis is unknown, as most of the cases are incidentally detected [2]. In a prospective study, mesenteric panniculitis as an incidental finding was documented at 0.6%. A high rate of 69% of mesenteric panniculitis patients had a coexisting malignancy, 22% had benign disease, and the remaining 9% had no disease explaining this condition [6]. To our knowledge,
47.16 (27e62) 41 (51.2%) 39 (48.8%) 87.04 11.8 (60.6e129.5) 36.8 4.52 12 14 46 12
(21.4e44.3) (15%) (17.5%) (57.5%) (10%)
43 (53.8%) 28 (35%) 9 (11.2%) 27 25 15 13
(33.8%) (31.2%) (18.8%) (16.2%)
59 (75%) 21 (25%)
CT ¼ computed tomography. Values are mean SD ( if range) or mean frequency (if %).
the remaining 80 examinations were eligible for the study, giving a prevalence of 7%. The age range of the patients was 27e62 years (mean age, 47.16 years). Of the 80 cases, 41 (51.3%) were female and 39 (48.8%) were male patients. Of all the scans, 33.8% (n ¼ 27) were performed on urology outpatients, 31.3% (n ¼ 25) on internal medicine outpatients, 18.8% (n ¼ 15) on emergency service patients, and finally 16.3% (n ¼ 13) general surgery outpatients. Indications of initial CT examinations were: investigation of only abdominal pain in 43 cases (53.8%), abdominal bloating and abdominal pain in 28 cases (35%), and nausea and abdominal pain in 9 cases (11.3%). All patients included in the present study had a mild degree of misty mesentery appearance that presented as an incidental finding. Also all the patients had lymph nodes within the misty mesentery that were smaller than a shortaxis diameter of 5 mm. The sites of the segmental mesenteric changes were the jejunal mesentery in 59 patients (75%) and the ileal mesentery in 21 patients (25%). None of the patients had a fatty mass lesion, hyperdense pseudocapsule, fat ring sign, or arterial/venous dilation, which are diagnostic criteria for mesenteric panniculitis. Body weight range was between 60.6e129.5 kg (87.04 11.8 kg) and BMI range was 21.4e44.3 kg/m2 (36.8 4.52 kg/m2). Fifty-four patients (67.5%) were classified as obese (BMI >30 kg/m2) and of those obese patients, 8 (10%) presented with severe/morbid obesity (BMI >40 kg/ m2). Also, 14 of the cases (17.5%) had a BMI within the range of 25e30 kg/m2 and presented as overweight. The remaining 12 patients in the study population (15%) were normal weighted (BMI, 18.5e25 kg/m2).
Prevalence of idiopatic misty mesentery on CT / Canadian Association of Radiologists Journal xx (2016) 1e6
idiopathic misty mesentery appearance has not yet been documented. In the present study, we investigated 561 patients with misty mesentery appearance and demonstrated that 7% (n ¼ 80) had no associated disease that explained this CT finding. The subjects included in our study had mild and segmental increased attenuation in the mesentery associated with small lymph nodes (Figure 1). These findings did not meet the diagnostic criteria of mesenteric panniculitis, as given by Coulier [8], which includes a well-defined mesenteric fatty mass lesion without infiltration of neighboring structures, an increase in mesenteric fat attenuation, lymph nodes within the mass, surrounding hyperdense pseudocapsule and limiting mesenteric fat and hypodense fatty halo surrounding blood vessels and nodes (fat ring sign) (Figure 2). Finally, a minimum of 3 of the 5 typical signs had to be fulfilled for a positive CT diagnosis of mesenteric panniculitis [8]. Accordingly, it is reasonable for us to accept our study population as patients with idiopathic misty mesentery who may be in the early stages of sclerosing mesenteritis, namely a fat necrosis and/or nonspecific inflammation stage, because of the absence of discrete mesenteric masses or hyperdense pseudocapsules. In the present study, all the patients had additional lymph nodes that were <5 mm in diameter. In a study of 37 patients with misty mesentery on CT and a lack of history of malignancy, Corwin et al [21] demonstrated that there was no increased risk for malignancy when the mesenteric lymph nodes had a diameter less than 10 mm in the short axis. Also, Taffel et al [2] stated that lymph nodes less than a short-axis diameter of 5 mm in misty mesentery and no coexistent disease require no further workup. According to these reports, we excluded patients with misty mesentery containing
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mesenteric lymph nodes larger than 5 mm but included patients who were followed up for at least a 1-year period for the possibility of malignancy. The site of the segmental mesenteric changes in our study was similar to that of mesenteric panniculitis, most commonly located on the left, which is the orientation of the jejunal mesentery (jejunal mesentery 75%, ileal mesentery 25%) [2]. In the present study, we found a slight female predominance (51.3%), while mesenteric panniculitis shows a male predominance in most studies [2,6e8]. Also, nonspecific abdominal pain was the common presenting symptom of the study population. Another result of the present study that should be highlighted is that the majority of patients in our study had high BMI; 57.5% of the study population was classified as obese, 10% as morbid obese, and 17.5% as overweight. Finally, only 15% of our study population was normal weighted. According to these results, it is difficult to say that obesity is the primary cause of the mesenteric changes, based on a prevalence study, however, it is suggestive that there may be an association between obesity and misty mesentery appearance on CT. The association of obesity and chronic low-grade inflammation has been evident for several years. Also, in recent years, it is well established that obese people show higher circulating concentrations of pro-inflammatory cytokines such as interleukin 6 and tumour necrosis factor alpha acute phase proteins (C-reactive protein and haptoglobin), as well as adipokines (leptin, adiponectin, and resistin) or neuropeptides (eg, substance P) compared with lean individuals [9e13]. All these proinflammatory factors are produced within adipocytes and also within adipose tissue macrophages and lymphocytes, which infiltrate the mesenteric fat. Therefore, a systemic acute-phase response may be
Figure 2. Multidetector-row computed tomography images of the abdomen showing a well-circumscribed, heterogeneous, fatty mass with increased attenuation consistent with mesenteric panniculitis and characteristic pseudocapsule sign surrounding a focal area of hyperattenuation within the mesentery, limiting heterogeneous mesenteric mass from surrounding normal mesentery (A); preservation of normal fat density in tissues surrounding mesenteric vessels and soft tissue nodules within the area of misty mesentery, thereby creating ‘‘fat halo’’ sign (B).
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triggered with increasing obesity [9e13]. Of particular note, the inflammatory mediators termed ‘‘adipokines,’’ found in adipose tissue, were shown to be overexpressed in the mesenteric fat tissue of subjects with inflammatory bowel disease [14,15]. Although the underlying mechanisms of obesity-induced inflammation are still not fully understood, a mouse study advanced the understanding of obesity-induced inflammation by demonstrating that a marked increase in production of inflammatory adipokines is associated with increased numbers of macrophages in adipose tissue in obese mice, suggesting that overfeeding was the starting signal of this inflammation, and that the metabolic roles of adipocytes change as they enlarge with obesity [13]. Strikingly, this obesity-induced inflamed visceral fat tissue is able to transfer the systemic inflammatory state even when it is transplanted to lean mice as an active endocrine organ [10]. Finally, a correlation has been found between BMI and adipose tissue macrophage number, especially in visceral fat tissue in humans. According to all these studies, and with the fact that visceral fat tissue is especially prone to inflammatory changes, we hypothesize that in obese patients, misty mesentery appearance on CT may be the result of chronic lowgrade inflammation triggered by mesenteric fat deposition. However, prospective studies with larger numbers of obese subjects are needed to strengthen our hypothesis. There are limitations to the present study. First, although our patients had stable lesions during a follow-up of at least 1 year, this did not exclude the existence of some malignancies such as follicular lymphoma, which is known to be a slow-growing lymphoma. Second, the present study was limited by its retrospective nature. However, a prospectively collected, considerable number of patients with misty mesentery appearance and their clinical and radiological follow-up were the strength of this study. Finally, this was a prevalence study and the causal relationship between obesity and misty mesentery appearance could not be confirmed. On the other hand, despite its limitations, this is the first report describing the estimated prevalence of idiopathic misty mesentery appearance on CT and its possible association with obesity. Conclusion We have found a prevalence of idiopathic incidental misty mesentery appearance of 7% among all the patients with this finding, and we also found, previously not reported, a high BMI in most of these patients. Radiologists commonly encounter this imaging finding in daily routine practice, but sometimes cannot determine any associated disease leading to the appearance. Although the underlying cause is unknown, the appearance does not meet the criteria of mesenteric panniculitis and is simply reported as an incidental imaging finding. Therefore, it is suspected that there may be many other conditions causing a misty mesentery appearance on CT that are not yet discovered. Because of the high BMI of our study population and based on growing evidence of obese
visceral adipose tissue as an important source of inflammation, we suggest that obesity itself may be one of the reasons for misty mesentery appearance on CT, leading to mesenteric inflammation. However, further prospective studies with histologic and endocrine correlations are needed to reach clear conclusions and clarify the impact of obesity on this finding.
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