Diagnosis

Sclerosing mesenteritis

PATHOLOGIC FINDINGS

The analysis of the frozen section was consistent with fibrosis, metaplastic bone, and chronic inflammation. Following the results of the frozen section analysis, an 82-cm small bowel segment with attached mesentery was resected. On pathology, a firm, partially calcified mass was present at the mesenteric root with irregular calcifications and dense fibrosis. Multiple nodules were seen and revealed a pattern of end-stage fatty necrosis. Surrounding the areas of nodularity, fibroblastic proliferation was seen extending into adjacent adipose tissue and surrounding large mesenteric vessels and nerves. Minimal inflammation was present. With these findings, a pathologic diagnosis of sclerosing mesenteritis was made. The patient was ultimately discharged from the hospital without further complications.

Findings

A computed tomogram (CT) of the abdomen and pelvis was performed. A lobulated inhomogenous soft tissue mass with a fibrotic retractile appearance was present in the small bowel mesentery, studded with coarse calcifications and surrounded by mesenteric stranding (Figure 1). The initial diagnostic impression was that this lesion represented a carcinoid tumor.

During expoloratory laparotomy, a hard yellow-red mass was identified at the root of the small bowel mesentery.

Discussion

Sclerosing mesenteritis is a rare, poorly understood benign entity that encompasses a spectrum of mesenteric inflammation and fibrosis. The peak incidence is in the sixth or seventh decade, and it is slightly more common in males. The reported age range of patients, however, is 7 to 87 years.¹ The clinical presentation may include abdominal pain, nausea, vomiting, and weight loss. Nonspecific laboratory findings may include elevated leukocytes and increased erythrocyte sedimentation rate. Multiple names have been used for this entity, including mesenteric panniculitis, retractile or liposclerotic mesenteritis, mesenteric Weber-Christian disease, and xanthogranulomatous mesenteritis. The term sclerosing mesenteritis is thought to best cover the spectrum of presenting features for this entity. The diagnosis is made depending on the extent to which inflammatory or fibrotic components predominate. The acute or subacute phase of the disease is termed panniculitis, where fatty degeneration and inflammation is the predominant feature.^2,3 The chronic form, termed retractile mesenteritis, is considered when fibrosis is the dominant feature.^2,3 This entity is believed to be idiopathic; however, various causes of this entity have been postulated, including ischemic or autoimmune processes.^2-4

Myriad CT presentations have been described for sclerosing mesenteritis. The typical description includes the presence of a heterogeneous mesenteric mass of soft tissue attenuation, with fibrotic or cystic components.³ It is characterized by fatty necrosis, fibrosis with retraction, and, occasionally, calcification of the mesentery.² There may be fibrofatty thickening of the mesentery with inflammatory changes ranging from fatty necrosis to mesenteric fibrosis, retraction and calcification.² Calcification, as seen in the case presented here, is a component that is less frequently seen and may occur secondary to fat necrosis.

Based on CT findings, the differential diagnosis for sclerosing mesenteritis, besides carcinoid tumor, includes carcinomatosis, mesenteric lymphoma, and desmoid tumor.² Differentiation must also be made from Crohn's disease, where fibrofatty changes (which are characterized by ulcerations along the mesenteric border) are present, extending into the leaves of mesentery with fatty infiltration, thickening, and retraction. Other entities that must be differentiated from sclerosing mesenteritis are inflammatory pseudotumor and lipogenic liposarcoma.³

Lymph node enlargement and involvement of the bowel wall may occur. The fat-ring sign in cases of panniculitis has been described to aid in differentiating sclerosing mesenteritis from other entities.³ A peripheral, low-density halo surrounds the mesenteric vessels, whereas the fat farther away from the vessels affected by the inflammatory process will be of higher attenuation. The fat-ring sign, however, is a nonspecific indicator that may be seen in a number of different entities, such as radiation-treated non-Hodgkin's lymphoma, and is not specific for sclerosing mesenteritis.⁵ In our case, a subtle fat-ring sign was identified upon retrospective analysis of the CT.

Another finding that may be observed in sclerosing mesenteritis is the presence of a pseudocapsule surrounding the affected mesentery, seen as a soft tissue density band. This pseudocapsule is identfied at the border of normal and abnormal mesentery.³ In cases of retractile mesenteritis, a greater soft tissue component is evident in the mesenteric mass, which indicates the presence of fibrosis. In suggesting the diagnosis of sclerosing mesenteritis, the absence of factors (such as metastasis, multiple tumor sites, or elevated levels of 5hydroxyindoleacetic acid in urine, as seen in carcinoid), may aid in narrowing the differential diagnosis.

The sonographic appearance of sclerosing mesenteritis has been reported as a heterogeneous mass with predominance of both hypoechoic and hyperechoic features.¹ Small bowel series may show separation of loops, kinking of small bowel, and fold thickening.² The colon may occasionally be involved with evidence of narrowing and thumb printing. Magnetic resonance findings are described in the literature as areas of intermediate signal on T1-weighted sequences and very low signal on T2-weighted sequences.²

Histopathologically, lipid-laden macrophages, known as lipophages, are seen.⁴ Also present are fibrous tissue, plasma cells, and eosinophils. The lesion affects the mesentery and submucosal fat of the small bowel but spares the mucosa. Progressive involvement with this process can lead to the obstruction of mesenteric lymphatics and mesenteric vessels. This may result in submucosal edema and luminal narrowing. The presence of multiple cystic masses within the mesentery, which represent lymphatic cysts, has also been observed.¹

In most cases, the disease has a self-limited course with complete resolution. In such cases no intervention is necessary. However, it is very difficult to diagnose this entity preoperatively. Complicated cases with bowel obstruction may be treated surgically with resection. Mesenteric panniculitis is usually self-limited, but may recur. Retractile mesenteritis may resolve spontaneously; however, an aggressive variant may be treated with corticosteroid and chemotherapeutic agents, such as cyclophosphamide and azathioprine.

CONCLUSION

Recognizing the imaging characteristics of a mesenteric lesion is particularly important, not only to raise the possibility of sclerosing mesenteritis as a part of the differential diagnosis, but also to determine the extent of disease and to guide surgical intervention and subsequent management efforts.

1. Johnson LA, Longacre TA, Wharton KA Jr, Jeffrey RB. Multiple mesenteric lymphatic cysts: An unusual feature of mesenteric panniculitis (sclerosing mesenteritis). J Comput Assist Tomogr.1997;21: 103-105.
2. Kronthal AJ, Kang YS, Fishman EK, et al. MR imaging in sclerosing mesenteritis. AJR Am J Roentgenol. 1991;156:517-519.
3. Sabate JM, Torrubia S, Maideu J, et al. Sclerosing mesenteritis: Imaging findings in 17 patients. AJR Am J Roentgenol.1999;172:625-629. Comment in: AJR Am J Roentgenol. 2000;174:259-260.
4. Mindelzun RE, Jeffrey RB Jr, Lane MJ, Silverman PM. The misty mesentery on CT: Differential diagnosis. AJR Am J Roentgenol. 1996;167:61-65.
5. Valls C. Fat-ring sign in sclerosing mesenteritis.AJR Am J Roentgenol.2000;174:259-260.