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1
Department of Radiology, University Hospital of Heraklion, 711 10 Stavrakia
Heraklion, Crete, Greece.
2
Department of Pathology, University Hospital of Heraklion, Crete,
Greece.
Received April 29, 1999;
accepted after revision June 30, 1999.
Address correspondence to N. Gourtsoyiannis.
Abstract
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SUBJECTS AND METHODS. A total of 7620 consecutive abdominal CT examinations were prospectively evaluated for features common to mesenteric panniculitis such as a well-delineated inhomogeneous hyperattenuated fatty mass at the mesenteric root, envelopment of mesenteric vessels, and no evidence of invasion of the adjacent small-bowel loops that may be displaced.
RESULTS. CT findings of mesenteric panniculitis were seen in 49 patients (0.6%). We found a female predominance. Mesenteric panniculitis coexisted with malignancy in 34 patients and with benign disorders in 11 patients. In the remaining four patients, mesenteric panniculitis, verified on histology, was considered to be responsible for the patients' clinical manifestations; no other abnormality was identified. Soft-tissue nodules (n = 39) and a fatty halo surrounding vessels and nodules (n = 42) were observed in most patients. Follow-up abdominal CT examinations in 29 of the 49 patients showed changes in only one patient.
CONCLUSION. CT findings of mesenteric panniculitis may be seen in patients undergoing abdominal CT for various symptoms.
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Durst et al. [5] describe the condition mostly in middle or late adulthood with a slight male predominance. When symptomatic, patients may present with a palpable abdominal mass and systemic manifestation, including abdominal pain, pyrexia, weight loss, and bowel disturbance of variable duration [5, 6]. Symptoms may be progressive, intermittent, or absent. Laboratory findings, including elevation in erythrocyte sedimentation rate and anemia, are absent or nonspecific. Complete resection of the mass is usually impossible and is generally considered to be of no benefit [5, 7]. Because reports in the literature focus on histologic findings, CT features of this disease have been only sporadically presented [8, 9, 10, 11, 12, 13].
Our objectives were to assess the prevalence of mesenteric panniculitis on the basis of a large series of consecutive abdominal CT examinations, to record possible associated diseases, and to describe the CT features of the disease.
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CT criteria for the diagnosis of mesenteric panniculitis were the following: a solitary well-defined mass composed of inhomogeneous fatty tissue with attenuation values higher than those of the retroperitoneal fat at the root of the small-bowel mesentery, engulfment of superior mesenteric vessels without vascular involvement, and no evidence of invasion of the adjacent small-bowel loops even if displaced [9, 10, 13].
In patients fulfilling all these CT criteria, the presence and type of abdominal or systemic symptoms, their relation to coexisting disease, the medical history, the physical examination findings, and the laboratory data were recorded in detail. CT attenuation values were measured at three different fatty areas of the mass before and after IV contrast administration. Nodular elements within the mass, vessels, or bowel were avoided. CT densities were obtained by circumscribing the region of interest with a cursor and including at least 20 pixels. The mean CT density values of the fatty areas were compared with those of retroperitoneal fat obtained at the same CT section.
CT examinations were evaluated by two abdominal radiologists, and decisions were reached by consensus. Differences in the prevalence of mesenteric panniculitis between patients with and without malignancy were estimated using the chisquare test with the Yates correction. Differences in CT values of fatty areas of mesenteric panniculitis before and after IV contrast administration and differences in CT fat density values between mesenteric panniculitis and retroperitoneum were assessed using the Student's t test. A p value of less than 0.05 was considered statistically significant.
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CT Evaluation
The maximum transverse diameter of mesenteric panniculitis fatty masses
ranged from 7.1 to 15.2 cm (mean ± SD, 9.5 ± 1.4 cm). In 48
patients, the maximum transverse diameter of the mass was directed toward the
left abdomen, where it extended from the mesenteric root to the jejunum
(Fig. 1). In one patient with a
right-sided proximal jejunum and associated vessels, a rightward orientation
was shown (Fig. 2). A
hyperattenuated stripe partly surrounding the mass was depicted in 29 of 49
patients. The thickness of the stripe ranged from 2 to 8 mm and did not exceed
3 mm in most cases (Fig. 3).
The anterior or lateral surface of the mass had a curved appearance in 37
patients, whereas it was lobulated in the remaining 12
(Fig. 3). Displacement of
adjacent jejunal loops was seen in 38 patients.
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Unenhanced and enhanced scans were obtained in 41 of 49 patients. In eight patients, IV contrast material was not administrated because of a medical contraindication or failure to gain IV access. CT attenuation values of the fatty areas of the masses on unenhanced scans ranged from -28 to -85 H (mean ± SD, -54±2 H) and were significantly higher (p < 0.0001) than those of the same patients' retroperitoneal fat, which ranged from -105 to -135 H (mean ± SD, -116 ± 9 H). The difference in CT values of the calculated fatty areas of mesenteric panniculitis before and after IV contrast administration did not reach statistical significance (p = 0.113).
Well-defined nodules of soft-tissue density less than 5 mm in transverse diameter (Fig. 4) were revealed in 39 cases. A hypodense fatty halo with CT densities ranging from -115 to -100 H (mean ± SD, -106 ± 4 H) surrounded vessels and nodules in 42 patients (Figs. 5 and 6A). Congregation of mesenteric vessels was shown in five patients (Fig. 7).
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Associated Diseases
CT findings of mesenteric panniculitis coexisted with malignancy in 34
patients (69.4%). The malignancies included extraabdominal non-Hodgkin's
lymphoma (n = 6), breast carcinoma (n = 5), lung carcinoma
(n = 4), melanoma (n = 3), sigmoid carcinoma (n =
3), rectal carcinoma (n = 2), ovarian carcinoma (n = 2),
endometrial carcinoma (n = 2), prostatic carcinoma (n = 1),
gastroesophageal junction carcinoma (n = 1), hepatoma (n =
1), cervical carcinoma (n = 1), renal carcinoma (n = 1),
pudendal carcinoma (n = 1), and lower extremity angiosarcoma
(n = 1). Of the 7620 patients enrolled in the study, 4017 (52.7%) had
a known malignancy at the time mesenteric panniculitis was diagnosed. The
prevalence of malignancy was different between patients with and without CT
evidence of mesenteric panniculitis (p < 0.001).
Eleven patients had a benign disease: abdominal aortic aneurysm (n = 3), lung sarcoidosis (n = 2), liver cirrhosis (n = 1), liver hemangioma (n = 1), liver echinococcus (n = 1), cholelithiasis (n = 1), collagenous colitis (n = 1), and lupus erythematosus (n = 1). No patient had inflammatory bowel disease, sclerosing cholangitis, or retroperitoneal fibrosis. In eight of the patients with coexisting benign diseases, the presenting symptoms could be attributed to the illness of reference or to the illness revealed by CT scan, whereas in three patientstwo with sarcoidosis and one with liver hemangiomasymptoms were absent.
In the remaining four of the 49 patients, mesenteric panniculitis was the only abnormality identified despite thorough clinical, imaging, and laboratory investigation. These patients presented with nonspecific symptoms, including intermittent abdominal pain (n = 3), weight loss (n = 1), low-grade fever (n = 1), and vomiting (n = 1). The duration of symptoms was 3 weeks to 2 years. Physical examination revealed a mid abdominal mass in two patients and abdominal tenderness in one patient. Abnormal laboratory findings included an increased sedimentation rate of 90 mm/hr in one patient and a decreased hematocrit of 31% in another; in the remaining two patients, laboratory data were within the normal range. All four patients underwent exploratory laparotomy followed by biopsy. On gross inspection, a mass firmly attached to the root of the jejunal mesentery was seen. Areas of discoloration were scattered throughout the involved mesentery and normal fat was intervening the diseased areas. The masses were considered inoperable. Histologic examination of the biopsy specimens revealed infiltration of fat with a large number of lipid-laden macrophages scattered among fat cells or fully replacing them, probably representing a reaction to fat necrosis. A few lymphocytic aggregates and lymphoid follicles dispersed in the lesions were also recognized. Moreover, a variable degree of fibrosis was present in the form of delicate fibrous bands separating lobules of lipid-laden macrophages and fat cells (Fig. 6B and 6C). In all examined patients, the lymphocytic population expressed B and T cell antigens on immunohistochemical analysis. Acute inflammatory exudate and vasculitis were not found. Because the histologic differential diagnosis of the condition included Whipple's disease, special histochemical staining using periodic acidSchiff and periodic acidSchiff diastase were performed and had negative findings.
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Twenty-eight (57%) of the 49 patients had a history of one or more surgical abdominal procedures including appendectomy (n = 11), cholecystectomy (n = 10), sigmoidectomy (n = 3), hysterectomy (n = 2), liver lobectomy (n = 1), and nephrectomy (n = 1). Twenty-two patients had a malignancy and six had a benign disease. A history of ischemic enteritis was reported in one patient.
Follow-Up
Twenty-one patients, 18 with malignancy and three with nonmalignant
diseases, underwent one to six follow-up abdominal CT examinations with an
interval of 5 months to 3 years from the initial CT examination. Stability of
CT findings was depicted in 20 patients. A slight increase in the size of the
fatty mass with mild thickening of the stripe was shown in one patient. None
of the three patients with nonmalignant disease developed malignancy during
the follow-up. Three of four symptomatic patients with biopsy-proven
mesenteric panniculitis were treated with prednisone. Clinical improvement was
observed in two patients. Intermittent episodes of abdominal pain persisted in
the third patient. On follow-up CT 6 months later, no change in the masses was
shown in the treated patients. The fourth patient refused therapy or
follow-up.
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Mesenteric panniculitis is rare [3, 4]. To our knowledge, however, no report documenting its prevalence exists. In the present study, comprising a selected group of patients that underwent CT examination for various indications, the prevalence of mesenteric panniculitis was 0.6%. Most patients with mesenteric panniculitis were female (65.3%) although males and females were almost equally distributed in our study population. This ratio is not in accordance with the 1.8:1.0 male-to-female ratio previously reported in a review of 68 patients [5]. At the time mesenteric panniculitis was diagnosed, the mean age of our patients on CT diagnosis (62 years) was comparable to that reported in the literature [4, 5].
In most of our patients (69.3%) with CT characteristics of mesenteric panniculitis, malignancy, mostly urogenital or gastrointestinal adenocarcinomas or lymphomas, was present. An association of mesenteric panniculitis and malignancy, mainly lymphoma, was previously indicated in the literature [3, 4, 19, 20, 21]. In all our patients, the malignancies were present at the time of CT diagnosis of mesenteric panniculitis. Because previous abdominal CT examinations were unavailable in our series, it is unclear whether mesenteric panniculitis preceded or followed a malignant disease. The pathogenetic mechanism linking mesenteric panniculitis with malignancy is also unknown. Kipfer et al. [4] suggest that mesenteric panniculitis is a nonspecific response to an underlying abdominal malignancy. Data from the present study cannot support this suggestion because in 19 (55.8%) of the 34 patients with mesenteric panniculitis and malignancy, the disease, mostly localized breast or lung carcinoma, was extraabdominal. The possibility of an inborn or acquired condition that renders the patient susceptible to both diseases was also postulated [4]. However, a possible cause common to all patients was not identified in our series. Abdominal surgery or mesenteric thrombosis, conditions that may compromise the vascular supply of the mesentery, were associated with mesenteric panniculitis [22, 23]. In our study, 28 patients experienced abdominal surgery, three had coexisting aortic aneurysm with mural thrombus, and one had a history of ischemic enteritis, disorders that may have triggered the development of a nonspecific inflammatory reaction in the fatty tissue. An autoimmune mechanism was also implicated [1, 24]. Reports suggesting a common autoimmune process that underlies both diseases stress the similarities between mesenteric panniculitis and idiopathic retroperitoneal fibrosis [1, 25]. Although an autoimmune-based theory might provide a possible explanation for the highi percentage of malignancies in our series, our data are not sufficient to substantiate this presumption.
In most of our patients (91.8%), the mesenteric panniculitis was incidentally identified during a CT examination for an unrelated condition. Only four patients presented with clinical manifestations attributed to mesenteric panniculitis. This finding agrees with other studies [3, 4] that describe patients who presented with symptoms usually unrelated to mesenteric disease yet had the disease.
On follow-up CT scans, no evidence of remission or reduction of mesenteric panniculitis was noted in our patients, including those treated with prednisone, although spontaneous remission of the disease process is reported [4]. None of our patients was treated with other means that have been tried without obvious success such as irradiation, antibiotics, emetine, and azathioprine [5]. In addition, no patient in our series showed CT signs of progression in the form of retractile mesenteritis. Progression from panniculitis to fibrosis is rarely documented in the literature [16, 19, 26].
A limitation of this study is the lack of histologic proof of mesenteric panniculitis in most of our patients. Open biopsy was performed in four symptomatic patients with no other disorder identified except mesenteric panniculitis. No patient underwent needle aspiration or other means of histologic confirmation. The incidental asymptomatic nature of the disease in the remaining patients did not justify biopsy. In these patients, the diagnosis was based on the CT appearance and on follow-up CT studies that revealed no additional findings or changes.
Additional CT features were observed in most of our patients: a left-sided orientation of mesenteric panniculitis maximum transverse diameter (97.9%), scattered well-defined soft-tissue nodules less than 5 mm in diameter (79.5%), a hypodense fatty halo surrounding nodules and vessels (85.7%), and a hyperattenuated stripe partly surrounding the mass (59%). These features are not seen in other mesenteric diseases such as lipoma, liposarcoma, lymphoma, or mesenteric carcinomatosis [27], and their presence may lead to a more confident CT diagnosis of mesenteric panniculitis. The overall CT appearance of mesenteric panniculitis was similar in our patients.
The left direction of the disease noted in most of our patients is consistent with the orientation of the jejunal mesentery. This observation is in accordance with macroscopic findings showing that mesenteric panniculitis has a propensity to involve the jejunal mesentery [3, 5]. The fatty halo surrounding nodules and vessels exhibited CT attenuation values suggestive of normal fat. A similar halo representing normal fat interposed between a central lymphoid aggregate or lymph node and a zone of peripherally oriented macrophages has been previously described on histopathology [4, 7]. The fatty tissue of mesenteric panniculitis was hyperattenuated when compared with that of the retroperitoneal fat. Infiltration, mainly with lipid-laden macrophages revealed on biopsy specimens, might be responsible for the high-attenuation values of fat seen on CT scans.
In our study, CT evidence of mesenteric panniculitis was seen more commonly in abdominal CT examinations than expected on the basis of the sporadic cases previously described. The disease was usually asymptomatic and frequently associated with abdominal or distal malignancy. CT features, including the envelopment of the superior mesenteric vessels by a well-delineated fatty mass, the displacement of adjacent bowel loops, well-defined soft-tissue nodules less than 5 mm, a fatty halo, and a hyperattenuated stripe, may enable differentiation of mesenteric panniculitis from other potentially confusing conditions.
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