Mesenteric panniculitis (MP) is a rare, inflammatory condition affecting the fatty tissue within the mesentery, a continuous fold of tissue that supports the intestines in the abdomen. While its name may sound complex, the condition is generally benign and often discovered incidentally during imaging for other issues. MP involves chronic, non-specific inflammation that causes fat cells in the mesentery to degrade and be replaced by inflammatory cells and scar tissue.
Defining Mesenteric Panniculitis
The mesentery is an organ structure in the abdomen, composed of a double fold of the peritoneum, which attaches the small and large intestines to the back abdominal wall. This tissue provides a pathway for blood vessels, nerves, and lymphatic channels that supply the intestines, and it contains a significant amount of fat tissue. The term “panniculitis” specifically refers to the inflammation of fat tissue, meaning mesenteric panniculitis describes inflammation within the mesentery’s fat layer.
The pathology of MP is understood to progress through a spectrum of three stages. The initial phase is known as mesenteric lipodystrophy, where immune cells called foamy macrophages begin to replace the normal fat cells, but inflammation remains minimal. This stage is often asymptomatic and may resolve on its own.
The second stage is true mesenteric panniculitis, which involves a greater infiltration of inflammatory cells, including plasma cells and polymorphonuclear leukocytes, leading to more pronounced inflammation. The final stage is retractile mesenteritis, which is characterized by the accumulation of collagen and extensive fibrosis, or scarring, within the mesentery. This fibrotic tissue can contract and retract, leading to potential complications.
Identifying the Symptoms
A significant proportion of individuals with MP remain entirely asymptomatic, meaning the condition is often found accidentally when imaging the abdomen for unrelated reasons. When symptoms do manifest, they tend to be non-specific, which can make a direct diagnosis challenging. The symptoms are typically related to the inflammation and subsequent pressure the affected tissue puts on nearby structures.
The most frequently reported complaint is chronic abdominal pain, which can range from vague to more severe. This pain is sometimes accompanied by other gastrointestinal issues, such as persistent diarrhea or constipation, as well as general abdominal bloating and distention. In some cases, the inflamed mesentery forms a palpable abdominal mass that a doctor may be able to feel during a physical examination.
Patients may also experience systemic symptoms, including nausea, vomiting, a general feeling of malaise, and unintentional weight loss, often due to a loss of appetite or early satiety. Symptoms can wax and wane over time, but their non-specific nature necessitates a thorough medical evaluation to rule out other conditions.
Determining the Cause and Risk Factors
The precise cause of MP remains unknown, and in many cases, it is classified as idiopathic, meaning it arises spontaneously. Theories suggest that MP may be a non-specific response to various stimuli or potentially an autoimmune process where the body’s immune system mistakenly attacks the mesentery’s fat tissue. The presence of inflammatory markers in blood tests and the link to other autoimmune conditions supports this hypothesis.
Several factors and conditions have been associated with a higher incidence of MP. Prior abdominal trauma or surgery, such as an appendectomy or hernia repair, is frequently noted in patient histories, suggesting that local injury may initiate the inflammatory cascade. The condition is also sometimes found in conjunction with various abdominal malignancies, including lymphoma, colon cancer, and kidney cancer, although a direct causal link is not always established.
Other systemic conditions, such as retroperitoneal fibrosis, Riedel thyroiditis, and sclerosing cholangitis, have been linked to MP. Infections, both bacterial and viral, and vascular issues like mesenteric arteriopathy, are also considered potential triggers for the inflammatory process.
The Diagnostic Process
Diagnosing MP can be challenging because of its rarity and the lack of unique symptoms, often requiring a process of elimination. The initial workup typically begins with a physical examination and blood tests, which may reveal general signs of inflammation, such as an elevated erythrocyte sedimentation rate or C-reactive protein level. These lab results are not specific to MP and only indicate inflammation is present.
Computed Tomography (CT) scans are the primary and most effective method for identifying the condition, as the imaging provides clear visualization of the mesentery’s structure. Radiologists look for characteristic signs, including the “misty mesentery,” which describes the hazy, increased density of the fat tissue compared to normal abdominal fat. Other specific CT findings include the “fat halo sign,” a ring of preserved fat surrounding the encapsulated mesenteric vessels, and a thin, hyper-attenuating “pseudocapsule” around the mass.
Imaging confirms the presence of MP and assists in the differential diagnosis, distinguishing it from conditions with similar appearances, particularly abdominal lymphoma or carcinoid tumors. In cases where the imaging findings are ambiguous, or when malignancy cannot be conclusively ruled out, a tissue biopsy may be performed to obtain a definitive histological diagnosis.
Management and Long-Term Outlook
The management strategy for MP is tailored to the presence and severity of the patient’s symptoms. For individuals who are asymptomatic, the recommended approach is often “watchful waiting,” where the condition is simply monitored with follow-up imaging to ensure it does not progress. Since the condition is generally benign, many cases will resolve spontaneously without any intervention.
For patients experiencing significant pain, weight loss, or other bothersome symptoms, medical treatment is initiated primarily to reduce inflammation. Corticosteroids, such as prednisone, are frequently the first line of treatment due to their powerful anti-inflammatory effects. Non-steroidal anti-inflammatory drugs (NSAIDs) may also be used to manage pain and mild inflammation.
If corticosteroids are ineffective, or for long-term management, a physician may prescribe immunomodulatory agents, such as azathioprine, colchicine, or tamoxifen. These medications suppress the immune system’s overactive response and control the chronic inflammation. Surgical intervention is reserved for the rare instances where complications arise, such as a complete bowel obstruction caused by the mass effect of the inflamed and fibrotic tissue. The prognosis for most patients is favorable, as MP is typically non-progressive and does not generally pose a long-term threat to life.