Abstract Sclerosing mesenteritis is an idiopathic inflammatory disease affecting the abdominal cavity. A 10‐year‐old spayed female Pembroke Welsh Corgi was referred to our animal hospital with a 7‐day history of anorexia, vomiting, dyschezia and an abdominal mass. Diagnostic imaging revealed a mid‐abdominal mass with a thickened surrounding mesentery. Histopathological examination of an incisional biopsy specimen, obtained through exploratory laparotomy, indicated pyogenic granulomatous panniculitis. No evident infections or foreign bodies were detected in the abdominal cavity. Based on imaging and histopathological findings, the mass was diagnosed as sclerosing mesenteritis. The dog received prednisolone at an anti‐inflammatory dose, resulting in the complete resolution of the clinical signs and the mass. Prednisolone was tapered over 5 months and then discontinued. The dog remained healthy after treatment. To our knowledge, this is the first documented case of canine sclerosing mesenteritis.

Sclerosing mesenteritis is a rare and often misdiagnosed inflammatory condition of the mesenteric fat with nonspecific symptoms. We report the case of a 41-year-old woman admitted for profuse rectal bleeding, an exceptional resentation of this disease. Endoscopic findings were inconclusive, while CT angiography revealed a retractile, hypodense mass at the mesenteric root encasing the superior mesenteric vessels, with associated varices, mesenteric fat infiltration, and bowel wall thickening. These features were highly suggestive of advanced sclerosing mesenteritis. Surgical exploration confirmed the diagnosis, and a right hemicolectomy was performed with good clinical evolution. Rectal bleeding was attributed to venous compression and collateral mesenteric varices. This case highlights the crucial role of CT in diagnosing sclerosing mesenteritis and guiding treatment, especially in atypical presentations that may mimic malignancy.

Abstract Background Sclerosing mesenteritis (SM) is characterized by chronic fibroinflammatory infiltration of the abdominal mesentery. While commonly affecting the small bowel, we present the first reported case of SM mimicking hilar cholangiocarcinoma by involving the porta hepatis, resulting in chylous ascites, gastric outlet obstruction, and duodenal perforation. Aims To broaden recognition of this rare disease and expand literature on treatment options Methods Case report and literature review Results A 59-year-old man with previous alcoholic pancreatitis presented with one month of progressive abdominal pain and distension. He was found to have large volume chylous ascites and a hilar mass on computed tomography scan. Magnetic resonance cholangiopancreatography confirmed a soft tissue density at the porta hepatis with intra- and extrahepatic duct dilation. Endoscopic ultrasound (EUS) revealed a soft tissue mass and biopsies showed a chronic lymphohistiocytic infiltrate but no malignancy. Positron emission tomography, liver biopsy, and bidirectional endoscopy were unrevealing. Serial large-volume paracenteses were performed for comfort, though portal hypertension was ruled out via transjugular measurements. One month into hospitalization, he developed gastric outlet obstruction from extrinsic mass and required nasojejunal feeding. This was complicated by a contained duodenal perforation managed non-operatively. Palliative dexamethasone was started for presumed cholangiocarcinoma which entirely resolved his symptoms. He was discharged after three months but represented off steroids with recurrent ascites and gastric outlet obstruction. Diagnostic laparoscopy was negative. EUS-guided biopsy again showed the same chronic inflammatory infiltrate. He was diagnosed with SM and started on oral prednisone which resolved his symptoms. He remains in remission as an outpatient on colchicine, tamoxifen, and low-dose prednisone. Conclusions SM is a rare disease characterized by chronic mesenteric inflammation, fibrosis, and fat necrosis. While 10% of cases are incidental findings, complications occur in 24% of patients and include recurrent chylous ascites, small bowel obstruction, and intestinal perforation. Diagnosis is challenging given non-specific findings but can be made on histology and radiology. This benign disease is often mistaken for malignancy, resulting in unnecessary diagnostic tests. To our knowledge, this is only the second reported case of hilar SM, and the first to present with the aforementioned complications. Treatment includes prednisone and tamoxifen, with colchicine, azathioprine, or thalidomide used as steroid-sparing agents. Increased recognition of this entity will help avoid unnecessary diagnostic interventions and inform options for medical therapy. Funding Agencies None

SCLEROSING MESENTERITIS – A CASE REPORT

Sclerosing Mesenteritis: A Concise Clinical Review for Clinicians.

Sclerosing mesenteritis (SM), a fibroinflammatory process of the mesentery, can rarely occur after immune checkpoint inhibitor (ICI) therapy; however, its clinical significance and optimal management are unclear. We aimed to assess the characteristics and disease course of patients who developed SM following ICI therapy at a single tertiary cancer center. We retrospectively identified 12 eligible adult cancer patients between 05/2011 and 05/2022. Patients' clinical data were evaluated and summarized. The median patient age was 71.5years. The most common cancer types were gastrointestinal, hematologic, and skin. Eight patients (67%) received anti-PD-1/L1 monotherapy, 2 (17%) received anti-CTLA-4 monotherapy, and 2 (17%) received combination therapy. SM occurred after a median duration of 8.6months from the first ICI dose. Most patients (75%) were asymptomatic on diagnosis. Three patients (25%) reported abdominal pain, nausea, and fever and received inpatient care and corticosteroid treatment with symptom resolution. No patients experienced SM recurrence after the completion of corticosteroids. Seven patients (58%) experienced resolution of SM on imaging. Seven patients (58%) resumed ICI therapy after the diagnosis of SM. SM represents an immune-related adverse event that may occur after initiation of ICI therapy. The clinical significance and optimal management of SM following ICI therapy remains uncertain. While most cases were asymptomatic and did not require active management or ICI termination, medical intervention was needed in select symptomatic cases. Further large-scale studies are needed to clarify the association of SM with ICI therapy.

Abstract #1385480: Goiter and Abdominal Mass: A Rare Presentation of Riedel’s Thyroiditis

Immunoglobulin G4 (IgG4) related disease is a relatively new disease characterized by inflammation, fibrosis, and eventually sclerosis. It has a tendency to form a mass in the affected organs and may be easily misdiagnosed as malignancy. Sclerosing mesenteritis (SM) is a rare presentation of IgG4-RD.

Introduction: Sclerosing mesenteritis (SM) is an uncommon fibro-inflammatory disease affecting the abdominal mesentery. Although some patients are asymptomatic or have minimal symptoms, SM can present with complications such as bowel obstruction, chylous ascites, and mesenteric ischemia. First-line therapy includes glucocorticoids in combination with tamoxifen in those who are symptomatic. Case Description/Methods: An 82-year-old man with a history of prostate cancer and melanoma in remission and lymphocytic colitis presented with 4-months of poor appetite and 40-pound unintentional weight loss. Computed tomography (CT) abdomen showed an irregular 8.6 cm mesenteric mass with surrounding misty mesentery (Figure, Panel 1). CT-guided biopsy demonstrated fibro-adipose tissue with increased IgG4-positive plasma cells, supporting a diagnosis of IgG4-related SM. Follow-up CT abdomen 6 months later demonstrated enlargement of the mass with new encasement of the jejunal and ileal branches of the superior mesenteric artery and vein. Given impending mesenteric ischemia, he was treated with rituximab, a monoclonal anti-CD20 antibody, with 2 infusions 2 weeks apart without side-effects. He had contraindications to first-line therapy with glucocorticoids given prior suicidal ideation while on budesonide for microscopic colitis. Three months following treatment, his erythrocyte sedimentation rate improved from 52 to 25 (reference range, 3-28 mm/h) and IgG4 level from 851 to 267 (2.4-121 mg/dL). CT abdomen demonstrated a 50% decrease in the volume of the mesenteric mass without significant vascular involvement (Figure, Panel 2) and he had regained 30 pounds. Discussion: Although rituximab has been studied for IgG4-related disease in general, the use of rituximab specifically for IgG4-related SM is not well-known. We report a case of a patient with IgG4-related SM treated effectively with rituximab, suggesting this may be a suitable medication for those who have contraindications or do not respond to current first-line therapy, especially if IgG4-related. Whether this drug would also work in patients with SM not related to IgG4 disease is unknown. Patients treated with rituximab should be closely monitored for infections, as well as allergic and infusion-related reactions.Figure 1.: CT abdomen pelvis of sclerosing mesenteritis before (1) and after (2) rituximab treatment.

Introduction: Intussusception is Intestine telescoping into itself. Commonly benign, self resolving condition seen in children more often. Presentation in adults is rare. It represents 1-5% of all obstructions and intussusceptions. It is commonly associated with a definable lead point in about 70-90% of the cases. There is no exact explanation of the events but luminal location of a mass plus the presence of food in the GI tract contribute to the telescoping event to the distal bowel. Case Description/Methods: A 47-year-old woman with history of anxiety and constipation, presents with 2 weeks of constipation along with recent abdominal pain, nausea, liquid bowel movements, decreased stool caliber, melena, and hematochezia. Denies weight loss. No surgeries or cancer history. No previous endoscopies. CT scan showed a descending colon to sigmoid intussusception with a possible polyp vs diverticulum as the lead point. Intussusception spanning approximately 12.7 cm in length. Patient underwent colonoscopy which revealed a large partially obstructing circumferential, firm, mobile mass in mid sigmoid colon with no bleeding. There was mucosal congestion, superficial areas of erosion but no necrosis or perforation most likely being the site of intussusception appreciated on CT. Diverticula was also found. Partial colectomy was performed. Intraoperatively, tumor involvement at the splenic flexure was noticed. Post operative course was uneventful. The patient was discharged home with no complications. Eventually, biopsy revealed an infarcted intramural lipomatous tumor, 5.5 cm in dimension, completely resected. Peritumoral intra and extramural abscess, and chronic active sclerosing mesenteritis. Diverticulosis without perforation. No evidence of malignancy (Figure 1). Discussion: Colon Intussusception in adults is commonly associated with malignancy or underlying lesions. The incidence of intussusception is about 5% and only 1/4th are symptomatic. The presentation is non-specific and episodic and thus, is difficult to diagnose. It mainly presents with abdominal pain, constipation, bleeding or diarrhea, and severe complications are complete obstruction, perforation, sepsis, ischemia, necrosis, and recurrence. CT imaging is definitive in diagnosis. Surgical intervention is the mainstay management. Prognosis depends on the underlying lesion. The mortality rate is 50% with underlying malignant lesions.Figure 1.: Colonic Mass. Intussescepted bowel.

Introduction: Sclerosing mesenteritis (SM) refers to a spectrum of inflammatory disorders of the bowel mesentery adipose tissue whose pathogenesis is poorly understood, but has been associated with prior abdominal surgery, malignancy, and autoimmune disease. Patients can be asymptomatic or have non-specific abdominal complaints. Diagnosis can be made radiographically, but tissue is required for definitive evaluation. We present a case of severe constipation and abdominal distention due to sclerosing mesenteritis. Case Description/Methods: A 55-year-old male presented with two months of constipation, abdominal pain, and severe distention impairing ability to wear regular-sized clothing. Initial laboratory evaluation was normal, CTAP revealed no obstruction, and colonoscopy was normal. A trial of linaclotide briefly improved symptoms, however he re-presented to an ED with severe pain where CTAP showed an ovoid expansile region of mesenteric haziness within the central abdomen, encircling the mesenteric root vessels, reflecting SM with mass effect on the surrounding bowel (Figure 1A). PET/CT did not show evidence of malignancy. Laparoscopic mesenteric biopsy revealed areas of fat necrosis with associated lipid-laden macrophages; fibrosis was not identified, plasma cells were not prominent, and IgG4 positive cells were absent. Immunostains were negative. Laboratory evaluation was notable for: borderline ANA titer 1:80, positive fibrillarin antibody, and negative Scl-70. Systemic steroids were initiated with some improvement in symptoms, and tamoxifen was later added. Discussion: Sclerosing mesenteritis is a rare inflammatory, fibrotic disease of bowel mesentery fat tissue whose presentation ranges from asymptomatic to severe pain and bowel changes due to obstruction. While its exact pathogenesis is unclear, it may be related to prior surgery, underlying malignancy (eg. lymphoma) or an autoimmune etiology (due to association with conditions such as primary sclerosing cholangitis and retroperitoneal fibrosis). Diagnosis is challenging; CT scan is the most sensitive test, but histological analysis is necessary to evaluate for any underlying etiologies. There is no definitive therapy, but systemic steroids and antifibrotic agents such as tamoxifen have been studied; some patients require surgical resection.Figure 1.: CT-Abdomen and Pelvis: An ovoid expansile region of mesenteric haziness within the central abdomen, encircling the mesenteric root vessels, reflecting sclerosing mesenteritis with mass effect on the surrounding bowel loops.

Sclerosing mesenteritis is a rare condition characterized by chronic inflammation and fibrotic changes of the mesentery. To determine the long-term management and outcomes of patients with sclerosing mesenteritis. Patients with biopsy-proven sclerosing mesenteritis at the Mayo Clinic between January 2006 and December 2016 were identified. Clinical data were collected retrospectively. One hundred and three patients were identified, median age 68.0years (range 35.0-85.3). Most patients were symptomatic (87.4%) at presentation. Patients received no treatment (52.4%), medical therapy (42.7%) or surgery (4.9%) on initial diagnosis. The most common initial regimens were prednisone plus tamoxifen (41.9%), prednisone alone (23.3%), and prednisone plus colchicine (11.6%) with 55.6%, 57.2%, and 60% of patients improving, respectively, p = 0.85 for a difference in response rates. At least half of the patients responded to prednisone plus tamoxifen, prednisone plus colchicine, or prednisone alone at 6.0, 7.2, and 8.4months, respectively. At a median follow-up of 45.6months (95% CI 24.1-69.7), 65.4% of patients were receiving medical therapy. Of those receiving tamoxifen-based, steroid-based, or steroid-sparing regimens, 100%, 87.5%, and 77.8% had improved by their last follow-up appointment respectively, p = 0.15. Prednisone plus colchicine has a similar efficacy to prednisone plus tamoxifen for the initial and long-term treatment of sclerosing mesenteritis. The majority of patients were initiated on medical therapy over the long term with most reporting symptomatic improvement within a year. Death from SM was rare.

Sclerosing mesenteritis is a rare abdominal condition characterized by chronic inflammation and the fibrosis of fat tissue, typically involving the small bowel mesentery. This article presents a case of a 62-year-old patient suffering from sclerosing mesenteritis, whose disease was complicated by perforation of his Meckel’s diverticulum. Proper diagnosis of perforation was delayed due to the presence of ascites which masked signs of peritonitis. The patient was operated on and the perforated diverticulum was resected. The post-operative course was complicated by an episode of intraabdominal bleeding, however, the patient survived. The presented case is probably the first description of a perforation of Meckel’s diverticulum in a patient suffering from sclerosing mesenteritis.

Sclerosing Mesenteritis (SM) is a rare fibroinflammatory disease of unknown etiology in which intestinal obstruction results from encasement of variable lengths of bowel by a dense fibrocollagenous membrane that gives the appearance of a cocoon. To our knowledge no cases of SM have been reported in patients with compensated cirrhosis without ascites. We report a case with SM diagnosed at laparotomy due to rapidly worsening small bowel obstruction, in a patient with compensated alcoholic cirrhosis. A 50-yearsold Caucasian male was evaluated because of cramping abdominal pain and discomfort associated with diarrhea, occasional post-prandial vomiting, fatigue and a significant weight loss. Compensated alcoholic cirrhosis had been diagnosed, two months before current presentation. Physical examination revealed abdominal distention with highpitched metallic sounds and bilateral peripheral pedal edema. Computed tomography of the abdomen demonstrated severe dilated small bowel loops as well as fluid into the peritoneal cavity. Based on the imaging findings, a surgical procedure was carried out. During laparotomy, an extra fibrous layer fully surrounding the small intestine was divided and a side-to-side functional ileo-cecum anastomosis was performed. Histopathological examination revealed fibroconnective tissue proliferation and inflammatory infiltration. Combined with the characteristic surgical findings a diagnosis of SM was made in a patient with compensated alcoholic cirrhosis. The patient recovered uneventfully and at 6-month follow-up he had no symptoms or signs of SM recurrence. The insidious onset of bowel obstruction symptoms in patients with even compensated cirrhosis, should include SM in the differential diagnosis.

INTRODUCTION: Sclerosing mesenteritis (SM) is a rare benign disease of unknown etiology. About 15 % of patients are asymptomatic or have minimal symptoms. It is usually benign in its clinical course, however, SM can mimic certain malignant disorders, such as lymphoma. It poses a diagnostic challenge for clinicians as it can be mistaken for malignancy and vice versa. In our case, the patient diagnosis of lymphoma was obscured by the picture of sclerosing mesenteritis, especially with negative multiple lymph node biopsies. CASE DESCRIPTION/METHODS: A 31 years old Caucasian male with a medical history of PTSD and a history of intussusception of colon requiring large and small bowel resection at age 14 who presented with severe generalized abdominal pain. CT abdomen ruled out any acute abdominal process, though enlarged mesenteric and retroperitoneal lymph nodes worrisome for lymphoma were noted. No history of weight loss, night sweats, or B symptoms. Laboratory investigations demonstrate transaminitis, otherwise, they are relatively unremarkable. CT chest and neck were significant for cervical chain lymphadenopathy. EGD showed gastritis and colonoscopy showed sigmoid colitis. Given his prior laparotomy for intussusception, the patient had retroperitoneal LN biopsy by IR and the pathology was reactive lymph nodes. Excisional cervical LN biopsy revealed the same diagnosis. After an extensive diagnostic work-up including biopsy sampling, which was negative for malignancy, the symptoms and findings were thought to be related to sclerosing mesenteritis. A trial of steroids and tamoxifen did not improve the symptoms. The patient eventually had mesenteric LN resection and pathology revealed follicular lymphoma. DISCUSSION: Sclerosing mesenteritis is rare. In most cases, it is discovered incidentally on abdominal imaging for evaluation of nonspecific abdominal or systemic symptoms. Our case highlights an important clinical finding that lymphoma can masquerade as sclerosing mesenteritis. A presumptive diagnosis of SM can be based on abdominal CT findings of a halo sign or fat ring. However, a histologic evaluation is necessary to rule out other etiologies and confirm SM. Percutaneous biopsies might be non-diagnostic because fine-needle specimens often lack sufficient architectural representation to exclude malignancy. Excisional biopsy by laparoscopy or laparotomy is usually required to obtain tissue. Pathologic confirmation should be obtained in all cases of suspected sclerosing mesenteritis.

Sclerosing mesenteritis (SM) is a rare disease with non-specific clinical manifestations and should be supported by radiological examination and confirmed by histopathological evaluation. Its relationship with cancer especially caecal adenocarcinoma is still unclear. This case report describes a young man who was diagnosed as having SM and poorly-differentiated caecal adenocarcinoma.

Background:Sclerosing Mesenteritis (SM) refers to an entire spectrum of digestive inflammatory disorders. Diagnosis is based on imaging showing an increase of fat attenuation displacing bowel loops and is in most cases non-symptomatic. Several conditions (abdominal trauma/surgery, neoplasia, infectious and inflammatory diseases) are responsible for SM (1). Among neoplasia, Erdheim-Chester disease (ECD) is a rare clonal histiocytosis characterized by long bone involvement, peri-nephric fat infiltration and cardio-vascular involvement associated with compatible histology (2). Biopsy is mandatory to confirm tissue infiltration by histiocytes and detect somatic mutation. Almost 80% of ECDpatients harbor mutation in mitogen activated protein(MAP) kinase pathway especiallyBRAFV600Egene mutation in about 60% of cases(3). No series of patients presenting both pathologies has been reported. Furthermore, no correlation withBRAFmutation status has been described in patient harboring SM and ECD.Objectives:To describe the clinical, radiological and mutational status of patients harboring SM and ECD.Methods:We reviewed the database of patients with histiocytic disorders in Besancon University Hospital. Patient required one abdominal computed tomography showing sclerosing mesenteritis and clinical/histological features of ECD to fulfill the inclusion criteria. All biopsy samples were investigated for mutation ofMAPkinase pathway gene.Results:Four patients suffered from SM and ECD. The median age at the diagnosis of ECD was 68 years old (61-72). All patients described abdominal pain and the mean duration between first symptoms and diagnosis of ECD was 12 months (4-19). The mean CRP level at diagnosis was 40.75 mg/L (5-117). Two patients were found to have myeloid neoplasms (chronic myelomonocytic leukemia (#2) and essential thrombocythemia (#4)) concurrent with ECD diagnosis.Regarding abdominal computed tomography, all patients had a mesenteric mass associated with hyper-attenuated mesenteric fat and a “fat halo sign”. One patient (#2) had ascites and one had splenomegaly (#4) but no patient had enlarged lymph nodes. CT also demonstrated peri-nephric fat infiltration (“hairy kidney”) (4/4), vascular sheathing of aortic branches (3/4), adrenal hypertrophy (1/4) or ureter dilation (1/4). The mean SUVmaxof the mesentery was 7.5 (4.1-10.9) at diagnosis on (18F)- fluorodeoxyglucose-PET. Three patients underwent mesentery fat biopsy and all samples exhibited ECD histology. Regarding mutational status, 75% (3/4) patients hadBRAFV600Emutation.After initiation of therapies for ECD (targeted therapies for ¾ patients), all patients had improvement of digestive symptoms and decreased of SUVmaxon evaluation18FDG-PET during the follow up.Conclusion:ECD should be investigated in patient with symptomatic SM especially if it is associated with peri-nephric fat infiltration. This condition is rare and might be driven by BRAF gene.TABLE 2.Full term pregnancyMultiple gestationPreconception CZP exposureLabor complicationsMaternal infectionsNeonatal infections (< 6 m after birth)Congenital malformationsBreast-feedingNeonates, n/N15/152/155/150/151/150/150/156/15

Sclerosing mesenteritis is a rare non-neoplastic disorder characterized by fat necrosis, chronic inflammation, and fibrosis typically of the small bowel mesentery. Our understanding of this disorder is limited by its rarity as well as inconsistent terminology used across the literature. While prior abdominal surgery or trauma, autoimmunity, infection, ischemia, and malignancy have been suggested to be involved in the pathogenesis of the disorder, it remains poorly understood. The clinical course of sclerosing mesenteritis is generally benign with a large proportion of patients diagnosed incidentally on imaging obtained for other indications. In a subset of patients, symptoms may arise from a mass effect on the bowel, lymphatics, or vasculature resulting in bowel obstruction, chylous ascites, or mesenteric ischemia. Symptomatic patients should be treated with a combination of corticosteroid and tamoxifen as first-line therapy based on retrospective case series and experience in other fibrosing disorders. Surgical intervention may be required in those with persistent obstruction despite conservative treatment, though complete resection of the mass is often not feasible given intimate involvement with the mesenteric vasculature. A careful use of terminology and communication between the radiologist, pathologist, and clinicians in the care of these patients will be essential to future efforts at understanding this disease.

Sclerosing mesenteritis (SM) is a rare benign condition that can have many different presentations, including abdominal pain, gastrointestinal symptoms, weight loss, or fever.1 The pathogenesis of this disease is not well-understood, but it may share a common etiology with other idiopathic primary inflammatory and fibrotic processes, such as mesenteric lipodystrophy (adipocyte necrosis) and mesenteric panniculitis (chronic inflammatory state).1 The reported prevalence is 0.6–2.5%, with a male to female ratio of 2 :1.1–4 The non-specific presentation can make the clinical diagnosis difficult. Abdominal exam can identify a mass in less than 50% of cases, while C-reactive protein (CRP) and erythrocytes sedimentation can be a way to follow its response to treatment.5,6 Abdominal contrasted enhanced computed tomography (CT) scan is the most sensitive imaging modality with two specific signs: “fat ring sign” and “tumor pseudocapsule.”4,7,8 To complete the diagnosis, a pathological examination is often required. This case report highlights how the non-specific presentation of SM can obscure the diagnosis.

Sclerosing mesenteritis is a rare disease entity initially described in 1924 with a prevalence reported to be less than 1%. Sclerosing mesenteritis is a comprehensive term used to describe three almost similar clinical entities including mesenteric panniculitis, retractile mesenteritis, and mesenteric lipodystrophy which only differ by their histology. The etiology of sclerosing mesenteritis is uncertain, but the disease has been associated with trauma, autoimmune disease, surgery, and malignancy. The typical presenting symptom is the abdominal pain, but sclerosing mesenteritis has a broad constellation of presenting symptoms which often makes consideration of the diagnosis unlikely. Treatment for this little-understood disease ranges from surgical intervention for patients presenting with obstructive symptoms to immunosuppressive medical therapy for patients presenting with pain. The purpose of this article is to provide an overview of the literature relevant to the diagnosis, etiology, and management of this condition in hopes of making physicians aware of this unique condition.