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A 31-year-old man with a remote history of blunt abdominal trauma complained of generalized abdominal pain, occasionally associated with post-prandial nausea. He sought medical attention after feeling a “lump” in his abdomen. Radiologic scans revealed a mesenteric mass suspicious for malignancy. The patient underwent a partial small bowel resection, including the mesentery which was eccentrically thickened in one area. The thickening extended to the small bowel serosa but did not extend into the bowel wall, which was grossly normal.
Archive Case and Diagnosis:
This case first appeared as Performance Improvement Program in Surgical Pathology (PIP) 2009, case 14, and is sclerosing mesenteritis.
Criteria for Diagnosis and Comments:
Histologic tissue sections reveal fibrotic bands traversing the mesenteric fat which are composed of plump, proliferating fibroblasts and dense collagen. Interspersed is a diffuse lymphoplasmacytic infiltrate which involves the adipose and fibrous tissue of the mesentery. Many eosinophils and some neutrophils are present, which may represent sequelae of an associated perforation, infection, or recent surgery prior to the current resection. The fibrotic process does not extend into the adjacent bowel, and the muscularis propria appears uninvolved. However, there is involvement of the muscularis and submucosa by the same inflammatory infiltrate seen in the mesentery. These findings are consistent with a diagnosis of sclerosing mesenteritis.
Sclerosing mesenteritis is an idiopathic inflammatory and fibrotic process which has been referred to by a variety of names, including refractile mesenteritis, lipogranuloma of the mesentery, primary liposclerosis of the mesentery, multifocal subperitoneal sclerosis, mesenteric panniculitis, and mesenteric lipodystrophy. The epidemiology of the condition is not well defined, partly due to this inconsistent nomenclature. The overall incidence of sclerosing mesenteritis has been cited at approximately 0.6%. However, autopsy studies have demonstrated a higher incidence, suggesting that a proportion of cases are not diagnosed pre-mortem and may in fact be asymptomatic. The age range at diagnosis spans the 5th and 6th decades, with a median age of 65 years. It has been postulated that the near absence of pediatric cases in the literature is due to a paucity of mesenteric adipose tissue in childhood. While there is some conflict in the literature, the condition is generally believed to be male predominant, with a male:female ratio of roughly 2:1(1,2).
The etiology of sclerosing mesenteritis is not known. Hypotheses regarding pathogenesis include ischemic injury, sequelae of infections, prior abdominal trauma/surgery, autoimmune processes, and paraneoplastic phenomena. Accumulating evidence has shown that adipocytes are active producers of bioactive molecules and cytokines that affect the physiology and pathophysiology of their environment. Adipocytokines produced in the event of mesenteric injury are likely to play a role in the pathogenesis of sclerosing mesenteritis, although the issue of what primary insult leads to dysregulated adipocytokine production has not been settled (3). Regardless, the condition appears to represent a pathologic continuum of injury, inflammation, and ultimately fibrosis.
There is some recent evidence in the literature suggesting that some tumefactive lesions regarded as sclerosing mesenteritis may be a subset of IgG4-related sclerosing disorders (4).
The majority of cases of sclerosing mesenteritis present with vague, non-specific symptoms. The most commonly reported symptoms include abdominal pain, diarrhea, weight loss, nausea/vomiting, and fever. Some patients present with frank bowel obstruction, usually late in the course of disease. Physical examination reveals a palpable abdominal mass in about half of patients. When present, the mass is often ill-defined and is usually located in the left upper quadrant or epigastrium. Laboratory studies are generally unremarkable, although in some cases ESR and CRP may be elevated. While many cases are diagnosed after symptoms emerge, it should be noted that in some reports up to 50% of cases have been discovered incidentally at the time of surgery for unrelated indications (5).
Diagnostic imaging can suggest the diagnosis of sclerosing mesenteritis, but pathologic examination is generally required, and a high degree of clinical suspicion must be present in order to guide the diagnostic process. CT findings often show a soft tissue-density mass in the mesentery which may be either homogeneous or heterogeneous depending on the degree of active inflammation present. Findings considered more specific for sclerosing mesenteritis include the “fat ring sign,” in which fat density is preserved near the mesenteric vessels, and the presence of a “fibrous pseudocapsule,” consisting of a strip of hyperattenuation surrounding the mass. CT guided biopsy or laparoscopic biopsy may be utilized to obtain diagnostic tissue, but some authors suggest that laparotomy with in-situ examination and substantial tissue biopsy may be necessary for confident diagnosis since the differential diagnosis for sclerosing mesenteritis is extremely broad and includes a variety of inflammatory and neoplastic conditions, such as mesenteric edema, mesenteric fibromatosis, inflammatory pseudotumor, inflammatory bowel disease, acute pancreatitis, Weber-Christian disease, Whipple’s disease, gastrointestinal stromal tumor, metastatic carcinoid tumor or signet ring carcinoma, lymphoma, peritoneal carcinomatosis, and liposarcoma.
On gross examination the appearance of sclerosing mesenteritis is variable. The process may diffusely spread through the mesentery, or it may manifest as solitary or multifocal discrete nodules ranging in size from 1.0 cm to over 40.0 cm. Some authors have sub-classified the gross presentation as follows: type I- diffuse mesenteric thickening, type II- single mass, type III- multiple masses, in order of decreasing prevalence. Anatomically, sclerosing mesenteritis most often affects the small bowel mesentery, with a preference for the jejunal mesentery. It may less commonly involve the colonic mesocolon.
Sclerosing mesenteritis is a progressive disease, and some authors have divided it into three phases. Phase 1 (mesenteric lipodystrophy) involves injury to mesenteric adipocytes resulting in fat necrosis and the onset of histiocytic infiltration. At this stage, microscopic examination may reveal a myxoid appearance of resected tissue, and there may be a prominent infiltrate of foamy macrophages. Phase 2 (mesenteric panniculitis) represents the ensuing inflammatory response believed to result from adipocyte injury. Histologic sections show prominent lymphoplasmacytic infiltrates. Phase 3 (mesenteric sclerosis) is the final stage in progression and is represented by sclerosing fibrosis of the mesentery with fibroblast proliferation and dense collagen deposition. Notably, the progression of sclerosing mesenteritis abruptly ends at the bowel wall, and the process does not penetrate the muscularis propria of adjacent bowel, an important characteristic in separating this condition from mesenteric fibromatosis. In general, immunohistochemical stains are of limited utility in the diagnosis. However, immunostains for beta-catenin, smooth muscle actin, and CD117/KIT may be useful in ruling out fibromatosis or gastrointestinal stromal tumor in some cases.
As mentioned above, the pathologic differential diagnosis in cases of sclerosing mesenteritis can be quite wide. Liposarcoma, while more common in the retroperitoneum, may arise in the mesentery and is characterized, as in other locations, by the presence of lipoblasts and cellular atypia of varying degrees as well as by typical vascular and stromal patterns. Mesenteric involvement by Hodgkin lymphoma can be associated with fibrosis and a mixed inflammatory background; however, diagnostic Reed-Sternberg cells will be present. Immunostains for relevant lymphoid markers and B-cell gene rearrangement studies may help reveal the neoplastic elements and differentiate Hodgkin lymphoma from mesenteric sclerosis. Signet ring carcinoma from the GI tract may metastasize to the mesentery, resulting in diffuse or nodular lesions with desmoplastic fibrosis. The identification of infiltrating signet ring cells, perhaps aided by cytokeratin immunostains, will allow this entity to be distinguished. Desmoid-type fibromatosis may also occur intra-abdominally, involving the mesentery. The proliferation of fibroblasts tends to be arranged in sweeping bundles and can closely resemble stage 3 mesenteric sclerosis. However, the adipocyte-related features of stage 1 and 2 mesenteric sclerosis are not seen in mesenteric fibromatosis, as this lesion represents a purely fibroblastic proliferation. Importantly, the respect for the bowel wall exhibited by mesenteric sclerosis is not demonstrated by mesenteric fibromatosis, in which the muscularis propria may be infiltrated by proliferating fibroblasts.
Long term survival of patients with sclerosing mesenteritis is generally excellent, and it is believed that many early-stage cases spontaneously resolve. In general, it is considered a benign condition, which is supported by the finding of previously undiagnosed sclerosing mesenteritis in autopsy cases. Mortality in fatal cases is generally attributable to bowel obstruction in the late stages of fibrotic disease. Consensus dictates that asymptomatic or early phase sclerosing mesenteritis need not be treated, as some cases appear to spontaneously regress, and many of the remaining cases fail to progress. For intermediate or late phase disease, many authors recommend treatment, although there is no recognized standard therapy. Medical regimens that have been used include treatment with corticosteroids, tamoxifen, progesterone, colchicine, cyclophosphamide, or Thalidomide. The efficacy of pharmacotherapy in stabilizing disease is variable. Other than for diagnosis, surgery is generally employed only when fibrosis has resulted in bowel obstruction.