Mesenteric Panniculitis May be a Nonspecific Marker for Malignancy
Abstract & Commentary
Synopsis: Mesenteric panniculitis may be manifested on 0.6% of abdominal CT scans as a mesenteric mass with inhomogeneously mildly increased attenuation, often bordered by a soft-tissue attenuation stripe and typically containing soft-tissue nodules of 5 mm or less surrounded by low attenuation halos.
Source: Daskalogiannaki M, et al. CT evaluation of mesenteric panniculitis: Prevalence and associated diseases. AJR Am J Roentgenol 2000;174:427-431.
Mesenteric panniculitis is an uncommon idiopathic (though possibly autoimmune) chronic inflammatory disorder of the abdominal mesenteric fat. Patients are frequently asymptomatic, but may present with a palpable abdominal mass and/or nonspecific abdominal pain, fevers, weight loss, or bowel symptoms. Laboratory studies are not helpful. With the advent of CT, the process was directly imaged for the first time, and sometimes mistaken for mesenteric neoplasms such as liposarcoma or lymphoma, resulting in unnecessary surgery or biopsy.
To more fully understand and characterize this confusing disorder, Daskalogiannaki and colleagues prospectively evaluated 7620 abdominal CT examinations over a three-year period for the findings of mesenteric panniculitis. The CT criteria for diagnosis were: 1) a solitary, well-defined mass within the mesenteric fat demonstrating inhomogeneous higher attenuation than the fat at the root of the small bowel mesentery; 2) superior mesenteric vessels that were surrounded by this process but otherwise normal in appearance; and 3) normal small bowel loops except for possible displacement.
A mesenteric fatty mass consistent with panniculitis was found in 49 (0.6%) patients. There were 32 women and 17 men, aged 27-84 years with a mean of 62 years. The maximum transverse diameter of the mass ranged from 7 to 15 cm (mean 9.5 cm) and was directed toward the left abdomen (along the typical orientation of the jejunal mesentery) in all but one patient (who had a right-sided location of his proximal jejunum). The fatty mass was frequently (29/49 = 59%) bounded by a high (soft-tissue) attenuation stripe of usually 2 or 3 mm thickness. Adjacent jejunal loops were displaced in 78% of cases. Four-fifths of cases showed well-defined soft-tissue density nodules of 5 mm or less within the mass. Eighty-six percent demonstrated a low attenuation fatty halo around the vessels and/or nodules.
No significant enhancement of the process could be demonstrated in cases that had both noncontrast and contrast-enhanced imaging. In 21 patients who underwent follow-up examinations five months to three years after the initial scan, the masses were stable in 20 and showed slight size increase in one.
Most interesting was the finding of malignancy in 34 (69%) of the 49 patients, about half of which were extra-abdominal in location. The 69% occurrence of malignancy with mesenteric panniculitis was higher than that of the study population as a whole (53%), a statistically significant difference (P < 0.001). Eleven patients had a concurrent benign disease (abdominal aortic aneurysm was most common with 3 cases). In four patients, mesenteric panniculitis was their only finding, and their nonspecific symptoms were attributed to this diagnosis following exploratory laparotomy and biopsy.
Comment by James H. Ellis, MD
Cloudy increased opacity in the fat of the proximal small bowel mesentery (often bordered by a stripe of soft-tissue attenuation and typically containing small nodular densities usually surrounded by low attenuation halos) is an occasional finding on abdominal CT examinations. Daskalogiannaki et al have reviewed a large series of more than 7500 abdominal CT examinations to determine that six in every 1000 (0.6%) will show these findings, which are consistent with the diagnosis of mesenteric panniculitis.
Mesenteric panniculitis is a condition of unknown etiology. A spectrum of disease exists with mesenteric panniculitis representing the fatty-inflammatory end and retractile mesenteric representing the fibrotic end. A variety of synonyms (e.g., sclerosing mesenteritis, mesenteric lipodystrophy) used to describe the disease has led to confusion in terminology.
A histologic diagnosis was available in only four patients in which mesenteric panniculitis was the only abnormality to explain nonspecific symptoms. Thus, the diagnosis must be assumed from the imaging findings in the vast majority of cases. The lack of change in follow-up justifies this approach.
The patients with mesenteric panniculitis had a statistically significantly greater frequency of concurrent neoplasia than did the entire population studied (69% vs 53%). However, many of the malignancies were extra-abdominal, so the association is difficult to understand. The primary malignancies in patients with mesenteric panniculitis were widely distributed among various organs of origin. Daskalogiannaki et al noted that 28 (57%) of the patients with mesenteric panniculitis had undergone one or more prior abdominal surgical procedures. Because comparable data on past surgery were not available for the population as a whole, it remains possible that mesenteric panniculitis might be more closely associated with previous surgery rather than with a concurrent malignancy.
Daskalogiannaki et al noted that an association between mesenteric panniculitis and lymphoma has been suggested in the previous literature. In any experience, the CT scans of patients with non-Hodgkin lymphoma, especially with mesenteric involvement or enlarged nodes at the root of the mesentery, may demonstrate a "dirty" or cloudy-appearing mesentery that may simulate mesenteric panniculitis. Unlike the description offered by Daskalogiannaki et al, the abnormality may improve or disappear with successful treatment or worsen with progression of the disease. Perhaps this appearance is secondary to obstruction to lymphatic flow or to actual lymphomatous involvement of the mesentery. Sometimes the appearance persists even after the lymphoma has completely resolved, perhaps reflecting residual fibrosis or scarring. The point is that one should carefully assess the mesentery for the specific features described by Daskalogiannaki et al and the absence of enlarged mesenteric lymph nodes before ascribing the finding to mesenteric panniculitis and not lymphoma.
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