Fibromuscular dysplasia (FMD) is a nonatheromatous, noninflammatory arterial disorder of unknown etiology resulting in vessel stenosis and/or aneurysm formation [1]. The renal and cephalocervical arterial beds are classically involved. Involvement of visceral arteries is rare. Mesenteric panniculitis (MP) is an inflammatory process of mesenteric fat, also considered to be of unknown etiology [2]. The small intestinal mesentery is by far the most common site; the colorectal mesentery is less commonly involved [2]. This case describes massive colorectal MP due to FMD of the inferior mesenteric artery (IMA), representing a unique association of two rare entities (Additional file 1).

A 52-year old man came to the emergency department after ten days of steadily worsening crampy pain in the left flank and iliac fossa. His medical history was unremarkable. He had stopped smoking ten years previously (15 pack-years). The temperature was 38.8 C. Physical examination of the lower abdomen elicited some guarding, but the abdomen was otherwise supple with no palpable mass. The leucocyte count was normal. He was admitted to hospital.

An abdominal CT scan showed features compatible with colitis, probably ischemic, extending from the splenic angle to the rectum. The bowel wall was thickened with “infiltration” of the surrounding fat. A 3 cm left renal mass was also noted. Although colonoscopy showed colitis of irregular distribution, perhaps infectious, a biopsy specimen revealed normal colonic mucosa. The patient was discharged with a prescription for an antibiotic.

Four days later he returned to the emergency department with pain similar to that at his first admission. He was admitted to hospital. A CT scan was performed (Fig. 1) which showed a markedly thickened mesentery and a thickened, non-enhancing left colonic wall. The inferior mesenteric artery was irregular, tortuous and stenosed; there was no intravascular thrombosis. Based on these findings, vasculitis was initially considered. Colonoscopy showed marked edema of the mucosa. A biopsy specimen showed ischemic changes.

Three weeks later a diagnostic laparoscopy was performed which found ascites and multiple whitish epiploic appendices, one of which was biopsied with a subsequent microscopic diagnosis of fat necrosis. A loop colostomy was performed.

Six weeks later symptoms of large bowel obstruction developed; a left hemicolectomy with transverse colostomy was therefore performed. During the same intervention a left partial nephrectomy was carried out. The rectal stump was left open with a drain.

Pathologic findings

The renal mass showed microscopic features characteristic of an oncocytoma.

Macroscopic examination of the recto-sigmoid resection specimen (Fig. 2) showed diffuse hemorrhagic necrosis of the mucosa and marked bowel wall thickening with massive mesenteric necrosis. Necrotic fat encased the whole length of the resected bowel.

Microscopic examination (Fig. 3) confirmed marked ischemia and ulceration of the colonic mucosa. The mesentery showed findings typical of fat necrosis. Numerous arteries and arterioles within the necrotic fat were obstructed to varying degrees, often completely, by fibrosis of the intima; the media of these vessels was normal. Atheromata, thrombosis, and inflammation were absent. The changes were considered diagnostic of fibromuscular dysplasia, intimal-type.

The postoperative course was uneventful and the patient was discharged home. Ten months later, he is asymptomatic and he is due to have his colostomy reversed.

Mesenteric panniculitis (MP) is a rare inflammatory disorder leading to “tumorlike” enlargement of the mesentery, the vast majority of cases involving the small bowel [2, 3]. It is characterized by variable degrees of fat necrosis, chronic inflammation and fibrosis. This histologic variability has resulted in other terms which reflect the dominant morphologic finding, including sclerosing mesenteritis and mesenteric lipodystrophy [2]. Numerous clinical associations have been noted and there are many theories regarding etiology [3]. No unifying pathophysiologic mechanism has been elucidated, likely because it is the result of a number of disease processes.

FMD is defined as a “nonatheroscleotic, noninflammatory vascular disease that may result in arterial stenosis, occlusion, aneurysm, or dissection [1]”. The renal and cervicocranial (CC) vascular beds are classically involved [1]. A landmark consensus histologic classification of renal artery FMD was published in 1971, emphasizing the vessel layer involved [4]: 1) intimal fibroplasia (1-2 % of cases), 2) medial, of which there are four subtypes: medial dysplasia with mural aneurysm (60-70 %), medial hyperplasia (5-15 %), perimedial fibroplasia (15-25 %), medial dissection (5-10 %), and 3) periarterial fibroplasia (less than 1 %). Subsequent experience has shown that intimal FMD is more common than was appreciated in 1971, and that there are reliable angiographic correlates to these histologic subtypes [1]. It is noteworthy that the opportunity for microscopic examination of involved vessels in suspected FMD is now exceptional: in a recent review of 447 patients, tissue for pathologic analysis was available in only 3.3 % of cases (from all vascular beds). The diagnosis is now established in essentially all cases by angiographic and noninvasive imaging [1].

The angiographic appearance of medial FMD is classically described as “string-of-beads” (typical FMD) [5] and is secondary to medial thickening causing luminal stenosis, alternating with zones of mural thinning and dilatation (aneurysms), the latter associated with loss of the internal elastic lamina [1, 4, 5]. In certain vascular beds, and, of note, the mesenteric vessels, the string-of-beads change is less frequent. Rather, the angiographic appearance is one of tubular constriction (atypical FMD) [1, 5], which correlates with intimal involvement, such as was present here. Thus, absence of the string-of-beads sign should not reflexively rule out a diagnosis of FMD.

Table 2 also highlights that, although the earliest reports show an overwhelming majority of cases occurring in females, later cases document many more males with visceral FMD, such that men now represent one third of cases. There is also a gender difference regarding associated CC and renal artery involvement: concomitant CC and/or renal artery disease was present in 80 % of females, whereas these vessels were involved individually or together in 32 % of men. Involvement of the IMA is highly unusual; indeed, we describe the first case in which disease is limited to this artery.

Of note, regarding the reported cases of visceral FMD, we must mention an extraordinary publication from 2005 [7] which tallies 30 cases of FMD of the SMA from one Parisian clinic alone, which would thus account for more than one third of all the reported cases retrieved through the PubMed database. As this uniquely vast experience does not sufficiently detail individual patients and includes presentations not described elsewhere (e.g. SMA dissection in eight patients), we have chosen to exclude it from the table.

In conclusion, we describe FMD as the etiology of a case of massive colorectal MP. FMD of visceral arteries may have “atypical” clinical and radiologic features, and, although a rare entity, should be considered when MP is diagnosed.

Written informed consent was obtained from the patient for publication of this case report and any accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.