Curious case of Misty Mesentery Poster No.: C-1385 Congress: ECR 2015 Type: Authors: Keywords: DOI: Educational Exhibit T. Simelane 1, H. Khosa 2, N. Ramesh 2 ; 1 Dublin/IE, 2 Portlaoise/IE Abdomen, Anatomy, Small bowel, CT, Education, Diagnostic procedure, Inflammation, Neoplasia 10.1594/ecr2015/C-1385 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. www.myesr.org Page 1 of 12
Learning objectives Mesenteric fat has a same density as the fat in the subcutaneous tissue {- 100 to -160 HU}. Infiltration of the increases the density to {- 40 to -60 HU } with loss of the sharp interface with the vascular structures - a hazy appearance that is often referred to as a "Misty Mesentery" Background The mesentery is a double fold of the peritoneum. True mesenteries {the small bowel, the transverse mesocolon and the sigmoid} all connect to the posterior peritoneal wall. Some mesenteries do not connect to the posterior peritoneal wall-- The greater omentum: connects the stomach to the colon The lesser omentum: connects the stomach to the liver The mesoappendix: connects the appendix to the ileum The small bowel mesentery is a broad fan-shaped fold of peritoneum connecting the loops of jejunum and ileum to the posterior abdominal wall Its connection with the posterior abdominal wall, its root, measures about 15 cm and extends obliquely from the duodenojejunal flexure on the left of the second lumbar vertebra to the right lower quadrant anterior to the upper part of the right sacroiliac joint. Mesenteric fat has a same density as the fat in the subcutaneous tissue {- 100 to -160 HU}. Infiltration of the increases the density to {- 40 to -60 HU } with loss of the sharp interface with the vascular structures - a hazy appearance that is often referred to as a "Misty Mesentery" This pathological increase in mesenteric fat attenuation is non-specific and may be secondary to infiltration of the mesenteric fat with inflammatory cells, malignant cells, fibrosis or fluid { blood, oedema, lymph} It is ususally an incidental finding, however, underlying disease may need to be excluded, idiopathic is often labelled as mesenteric panniculitis Page 2 of 12
Findings and procedure details It can occur due to infiltration of the mesenteric fat with inflammatory cells, fluid (oedema, lymph, blood), malignant cells and fibrosis In the normal mesentery, the blood vessels are clearly visualised due to low attenuation of the mesenteric fat In case of misty mesentery, the vessels lose their sharp interfaces and may be partially / completely effaced; Typical features include a left-sided distribution, a 'fat halo' sign, nodules and a pseudotumorous hyperdense stripe. Mildly enlarged lymph nodes are seen, calcification may rarely be seen. It is associated with malignancy, surgery, infection, autoimmune conditions and trauma Thrombosis of the superior mesenteric vein may be associated with increase in fat density, probably due to oedema Conditions causing misty mesentery appearance on CT scan: Oedema - heart failure, hypoalbuminemia, portal hypertension, inferior vena cava obstruction Inflammation - pancreatitis, appendicitis, inflammatory bowel disease, diverticulitis Haemorrhage / trauma Neoplasms - lymphoma, pancreatic carcinoma, colonic carcinoma, breast carcinoma, GIST, carcinoid Idiopathic - mesenteric panniculitis Lymphoedema due to obstruction of lymphatics A 'Misty mesentery' is a non-specific finding on CT scans and a cause for this should be sought. CT changes consistent with mesenteric panniculitis include positive findings; a left-sided distribution, 'fat-halo' sign, pseudotumorous hyperattenuation stripe, nodules and the absence of features suggesting haemorrhage, neoplasia, lymphoedema. Mildly enlarged lymph nodes are seen, calcification may rarely be seen. It may be surrounded by a hypoattenuated fatty "halo sign" and a surrounding hyperattenuating pseudocapsule It has been suggested that there are two pathological subgroups: Mesenteric Panniculitis, representing the very large major subgroup where inflammation and fat necrosis predominate and Retractile /Scelrosing Mesenteritis {rare}, where fibrosis and Page 3 of 12
retraction predominate, with mass lesion and areas of calcification, it may coexist with malignancies including lymphoma, breast, lung & colonic cancer, melanoma. Findings could be identical changes seen in carcinoid tumour. Mesesentric panniculitis is an inflammatory infiltration of the mesentery with variable mesenteric inflammation. The prevalence of mesenteric panniculitis on CT scans is around 0.6%, usually seen in patients over 50 years of age{though two of our patients were 40 years old}, slight male predominance. It is usually self-limiting, however, follow up studies are usually recommended. The radiological diagnosis of mesenteric panniculitis is based on classical CT signs: the presence of a well-defined "mass effect" on neighbouring structures constituted by mesenteric fat tissue of inhomogeneous higher attenuation than adjacent retroperitoneal or mesocolonic fat and containing small soft tissue nodes (sign}.. The differential diagnosis includes all disorders that can affect the mesentery. The most common ones are lymphoma, well-differentiated liposarcoma, peritoneal carcinomatosis, carcinoid tumor, retroperitoneal fibrosis, lipoma, mesenteric desmoid tumor, mesenteric inflammatory pseudotumor, mesenteric fibromatosis and mesenteric edema. Images for this section: Page 4 of 12
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Conclusion The appearance of Misty Mesentery could be an incidental finding on CT, however an underlying cause should always be excluded. The prevalence of mesenteric panniculitis on CT scans is around 0.6%. Typical features include a left-sided distribution, a 'fat halo' sign, nodules and a pseudotumorous hyperattenuation stripe{ pseudocapsule} Personal information T Simelane, Consultant Radiologist H Khosa Consultant Radiologist Midland Regional Hospital, Portlaoise, Ireland N Ramesh Consultant Radiologist Midland Regional Hospital, Portlaoise, Ireland References 1. The misty mesentery: mesenteric panniculitis and it mimics P McLaughlin, A Filippone, M Maher, AJR, Feb 2013, Vol 200, No. 2, W116-W123 2. Misty mesentery: pictorial review of multidetector row CT findings. A Filippone, A Cianci, ML Storto, Radiol Med 2011, 116.351-365 Page 11 of 12
3. Incidentally detected misty mesentery on CT: Risk of malignancy correlates with mesenteric lymph node size MT Corwin, AJ Smith. RG Sheirman, J Comp Assist Tomogr, 2012, Jan-Feb: 36 {1}:26-9: doi: 10.1097/RCT.0b013e3182436c4d 4. CT findings in mesenteric panniculitis : Case 8685 Eurorad: URL: www.eurorad/ case.php?id=8685 Page 12 of 12