Mesenteric tumors are uncommon lesions that are generally considered inclusive of similar lesions of the omentum. Primarily anecdotal references to this class of tumors have been made since the beginning of the 20th century. In 1936, Hart provided the earliest clear description of solid mesenteric tumors. As experience has accumulated in treating these lesions, a more complete picture of the various disease types that manifest as mesenteric masses has emerged.
Mesenteric tumors may be cystic or solid, and they may demonstrate malignant or benign clinical behavior. Although uncommon, they are encountered in all age groups from infancy to the very elderly. These tumors should be considered as an explanation for a palpable abdominal mass, but they are most commonly brought into the differential diagnosis of abdominal pathology once a suggestive radiologic study or an abdominal operation has been performed. An increased awareness of neoplastic and nonneoplastic processes that result in mesenteric masses aids the clinician in recognizing these diseases.
This article discusses mass lesions of the mesentery, including nonprimary tumors with manifestations related to the mesentery. The image below illustrates a lesion that was discovered incidentally.
The mesentery of the gastrointestinal (GI) tract consists of a contiguous, fibrofatty, fanlike structure containing arterial, venous, lymphatic, and neural structures coursing to and from the intestine, along the intestine's entire length.
The small-bowel mesentery and portions of the large-bowel mesentery are mobile within the peritoneal cavity. The mesenteries of the ascending and descending colon become fixed against the retroperitoneum during the normal course of fetal development. The lesser omentum is also technically a mesentery, and any consideration of tumors of these structures is generally inclusive of lesions of the greater omentum as well.
The vast majority of reported mesenteric tumors originate in the small-bowel mesentery or omentum.
Clinical findings and symptoms associated with mesenteric tumors of all types are related to the presence of a mass lesion. Because the mass does not involve the tubular portion of the GI tract per se, obstructive symptoms are generally late findings in malignant mesenteric tumors and large benign tumors.
Without question, pain is the principal manifestation of mesenteric masses in adults and older children. A visceral pattern of pain may be related to mass effect within the peritoneum or to traction on the mesentery. This is generally deep and poorly localized discomfort, frequently described as central within the abdomen.
Benign mesenteric masses
These lesions are almost exclusively found in the mesentery of the small intestine, though cysts of the colonic mesentery have also been described. Most are lymphangiomas, but simple peritoneal cysts and enteric cysts are also found, as well as rare mesenteric mesotheliomas with prominent cystic components.
Primary lipoblastoma of the mesentery has been reported in infants and in children as old as 12 years. This benign tumor of fetal-embryonal fat tissue is generally recognized when an abdominal mass is palpated on physical examination. It is very amenable to surgical excision, though local recurrence has been described. Other benign neoplasms of the mesentery are exceedingly rare, but tumors of neural origin, hamartomas,  and stromal tumors of small size with nonaggressive clinical behavior have been described.
Malignant mesenteric tumors
A relatively few tumor types account for the vast majority of mesenteric malignancies; of these, the small-bowel mesentery is almost exclusively the site of involvement.
Primary malignant mesenchymal or stromal tumors of the mesentery of the bowel (see the image below), as well as of the greater and lesser omentum, are a rare subset of abdominal cancers that resemble either retroperitoneal sarcomas or GI stromal tumors (GISTs) primary to the intestine.  Most of these have been described as leiomyosarcomas. [3, 4] Miettinen et al reported that in a group of 26 cases analyzed by the Armed Forces Institute of Pathology, the incidence of omental and mesenteric tumors was roughly equal. 
Characterization of protein markers of this tumor type has indicated that they are phenotypically very similar to the GIST group and are less often phenotypically related to retroperitoneal leiomyosarcomas. The absence of a detectable primary intestinal tumor signifies a primary mesenteric origin of the lesion.
Patients with mesenteric tumors exhibit signs and symptoms of intestinal obstruction; however, in contrast to primary tumors of the intestine, much bulkier disease may be present before obstructive findings are encountered.
Desmoid tumors of mesentery
Mesenteric desmoid tumors are a relatively infrequent but potentially life-threatening complication of familial adenomatous polyposis (FAP). [6, 7] These tumors are areas of progressive fibroblastic and fibrous proliferation within the mesentery (and, less frequently, the retroperitoneum) that can locally involve vascular structures and can constrict and obstruct the bowel. Although described as histologically benign lesions, their infiltrative pattern of growth can ultimately lead to life-threatening patterns of visceral involvement.
Sporadically occurring desmoid tumors are more numerous than those observed in FAP, though the cumulative risk of the development of these lesions is far greater in patients with FAP. Mesenteric desmoid tumors were originally reported as a component of Gardner syndrome, a phenotypic pattern of FAP that, in addition to intestinal adenomatous polyps, is also associated with bony abnormalities, pigmented ocular fundus lesions, and cutaneous epidermoid cysts and fibromas. That such arbitrary classifications are not necessarily valid is now apparent.
Although a causative relationship in desmoid formation has not been firmly established, various mutations of the APC gene have been identified in these tumors.  Desmoid tumors are more frequently associated with disease-causing mutations distal to codon 1444 of the APC gene.
Primary mesenteric lymphoma, in contrast to primary small-bowel lymphoma, is a disease of the mesenteric lymph nodes that may represent a localized process or a component of a more disseminated pattern of disease. The clinical presentation of mesenteric lymphoma is much like that of other mesenteric tumors, with abdominal pain and palpable mass as the principal findings.
Computed tomography (CT) can characterize the lesion from the standpoint of size and mesenteric location and can raise the probability of the lymphoma diagnosis. The follicular centroblastic-centrocytic histologic type of lymphoma has been shown to predominate at mesenteric sites.  A few cases of mesenteric lymphomas observed in association with immune thrombocytopenia and dermatitis herpetiformis have been reported.
The vast majority of metastatic lesions of the mesentery consist of mesenteric lymph nodes that have become secondarily involved in a neoplastic process of the tubular GI tract. Distinguishing this pattern of tumor growth from primary mesenteric tumors usually presents no difficulty because the GI primary tumor site is usually readily identifiable.
Carcinoid tumors of the small intestine are metastatic to mesenteric lymph nodes at the time of diagnosis in 40-50% of patients, though almost all such tumors that are greater than 2 cm in diameter have associated nodal involvement. Of these, a small subset may have minimal obvious disease within the small intestine and large mesenteric nodal metastases that may account for the vast majority of the tumor burden. In addition, primary mesenteric carcinoids have been described that have been assumed to arise de novo in mesenteric tissues, though the veracity of this assumption is uncertain.
This pattern of disease may be accompanied by extrinsic compression and occlusion of mesenteric arterial blood supply and segmental ischemia or infarction of the intestine. Extensive carcinoid tumor involvement of small-bowel mesentery has been reported in association with a malabsorption syndrome.
Mesenteric lipodystrophy (retractile mesenteritis, mesenteric panniculitis) is a rare condition that can be mistaken for a mesenteric neoplasm on the basis of clinical, radiologic, and gross characteristics. It is a mesenteric thickening or mass that can be nodular in consistency and either focal or diffuse within the small-bowel mesentery. The root of the mesentery and the tissues surrounding the superior mesenteric vessels are invariably involved.
The mass may consist of hypertrophied fatty tissue, dense fibrous tissue, fat necrosis, or combinations of these, along with a nonspecific chronic inflammatory infiltrate. Its presenting symptom is abdominal pain in most patients, though it has been anecdotally reported in association with fever, mesenteric calcifications, and protein-losing enteropathy.
The causative agents are unknown, though an association with lymphoma has been reported. Current data indicate that the condition is nonprogressive and presents no significant danger to the patient.
Treatment is nonsurgical (though the diagnosis is confirmed on operative biopsy) and generally supportive. In patients with more severe symptoms, antimetabolites such as cyclophosphamide have been associated with a decrease in lesion size and with symptom relief. Other reportedly beneficial agents include steroids, colchicine, and tamoxifen.
Infectious etiologies of mesenteric lymph node enlargement include bacterial infection, mycobacterial infection, and histoplasmosis. A large number of these cases have been reported since the onset of the human immunodeficiency virus (HIV) epidemic. Although lymphadenopathy is usually generalized in tuberculosis, mesenteric lymphadenitis has been described as the principal presenting problem.
Castleman disease (giant lymph node hyperplasia) is a rare condition usually observed in the mediastinum. However, cases of isolated mesenteric disease have been reported. These primarily occur in women and can be associated with iron malabsorption and anemia. Sarcoid has been reported as a cause of localized bulky mesenteric lymphadenopathy.
No known etiologic or associated diseases have been reported in cases of primary mesenteric neoplasms. Reactive lymphadenopathy within the mesentery may be a manifestation of systemic, often infectious, disease.
Solid primary tumors of the mesentery are rare. Published reports have consisted of small numbers of cases, which makes it difficult to determine the incidence of specific tumor types. Reasonable estimates of incidence range from 1 case per 200,000-350,000 population. Mesenteric tumors have been described as cystic in 40-60% of cases. 
Numerous anecdotal reports of mesenteric lipomas in adults and children have appeared over the years, suggesting that these probably represent the most frequently encountered symptom-causing solid tumors of primary mesenteric origin.
Malignant primary mesenteric tumors are extremely uncommon, even compared with primary malignancies of the small bowel. Published reports suggest that one third to one half of all mesenteric masses are malignant tumors. The largest case series have been from France and China. [11, 12]
These reports indicate that approximately two thirds of malignant mesenteric tumors are mesenchymatous (most characterized as leiomyosarcoma or liposarcoma), while the remainder are primarily lymphomas.
Cook et al, using Surveillance, Epidemiology and End Results program data, calculated male-to-female incidence rate ratios (IRRs) for various cancers for the period between 1975 and 2004.  According to their results, mesenteric cancer occurred more frequently in females than in males, with the overall male-to-female IRR for cancers of the peritoneum, omentum, and mesentery being 0.18.
The results of surgical treatment of benign cysts and solid tumors of the mesentery are very favorable. This is true of even large benign tumors, though local recurrence has been reported. Death as a consequence of benign masses, with the exception of mesenteric desmoid tumors, can be assumed to be an extremely unlikely event.
Because so few cases have been reported, long-term results of surgical treatment of malignant mesenteric mesenchymal tumors have not been well characterized. In fact, no large series reporting management and outcomes of treatment of this tumor type have been conducted. Published reports suggest that their biologic behavior is similar to that of primary GI mesenchymal malignancies. Reported sites of hematogenously spread metastases include the liver and lungs.
Extrapolating the results of treatment of similarly staged GI stromal malignancies suggests that 5-year survival rates are in the range of 20-50%. No specific postoperative adjuvant or palliative therapies, such as cytotoxic chemotherapy or radiation therapy, have been shown to be of benefit.
Intra-abdominal desmoid tumors are the second most frequent cause of death in FAP patients (after cancer-related deaths).