CT And MR Imaging Features of a Non- of the Mesentery

Sevdenur Çizginer1, Servet Tatlı1, Eric L. Snyder2, Joel E. Goldberg3, Stuart G. Silverman1

Brigham and Women’s Hospital, Harvard Medical School,Division of Abdominal Imaging and Intervention, Department of Radiology1, Departments of Pathology2 and General Surgery3, Boston, MA

Wide range of congenital and acquired that arise from various tissue linings of the are grouped as mesenteric cysts. A non-pancreatic pseudocyst of the mesentery is an uncommon, acquired pathologic entity, developing secondary to trauma or infection. Awareness of the imaging features of non- pancreatic pseudocyst may help radiologists to differentiate them other abdominal neoplastic processes and may prevent unnecessary . We report CT and MR imaging features of a non-pancreatic pseudocyst of the mesentery. Key words: Pseudocyst, mesentery, CT, MR

Eur J Gen Med 2009; 6(1):49-51

INTRODUCTION Five months later, the patient was admitted A non-pancreatic pseudocyst of the to the emergency room again for a sudden mesentery is an uncommon, acquired onset of left upper quadrant pain and . pathologic entity, developing secondary to He denied fever. His biochemical laboratory trauma or infection (1-3). These mesenteric values were within normal limits. On physical cysts are unrelated to and the wall examination, he exhibited involuntary of a pseudocyst is composed of fibrous tissue guarding, rebound, and tenderness over the rather than epithelial lining that are seen in epigastrium and left upper quadrant. Bowel true cysts (2, 3). It may be difficult to make sounds were normal. CT scan of the abdomen an accurate preoperative diagnosis of a non- demonstrated interval increase size of the left pancreatic pseudocyst from other mesenteric upper quadrant fatty mass measuring 6.4×4.5 cysts or (1). We report CT and cm. There was a new nodular soft tissue MR imaging features of a non-pancreatic rim surrounding the mass and fat stranding pseudocyst of the mesentery. in the adjacent mesentery and omentum. A soft tissue density in the dependent portion CASE and two punctuate calcification abutting its A 59-year-old man presented to the medial aspect is also noted. MR imaging emergency room with two-day history of was obtained for further evaluation with a , nausea and . His protocol including axial FSE T2–weighted past medical history was significant for partial images, axial in-phase and out-of-phase T1- gastrectomy and gastrojejunostomy due to weighted, and axial dynamic fat suppressed peptic ulcer perforation twelve years ago and T1-weighted gradient-echo images following colonic resection ten years ago. CT scan intravenous administration of 20 cc of of the abdomen showed a 5.0×3.8 cm, well- gadolinium. On T2- weighted images, the marginated, rounded mass in the left upper internal content of the mass showed bright quadrant, within the small bowel mesentery. signal intensity with dependent dark signal The mass showed homogenous fat attenuation intensity material. On dual echo T1-weighted and contained no soft tissue component images, the internal content of the mass (Figure 1). The adjacent small bowels and showed leveling. While the non-dependent mesenteric vessels were compressed. Based portion was being bright on in-phase images on these CT findings, the mass was interpreted and demonstrating significant signal drop on as a lipoma. out-of-phase images, indicating presence of fat, the dependent portion showed no signal Correspondence: Servet Tatli, MD drop. Post gadolinium images confirmed, Department of Radiology, Brigham and Women’s Hospital, Harvard Medical School, 75 Francis Street, a 3 mm thick enhancing rim (Figure 2). Boston, MA 02115 Interval development of enhancing rim raised Phone: 617-732-6304, Fax: 617-732-6317 concern for development of a liposarcoma or E-mail: [email protected] 50 Çizginer et al.

Figure 1. Contrast-enhanced axial CT Figure 2. Dynamic fat suppressed T1- image demonstrates a 5.0 × 3.8 cm, weighted image following intravenous well-marginated mass within the small gadolinium shows enhancement of the bowel mesentery (arrow). The mass wall of the cystic mass (arrow). showed homogenous fat attenuation and was interpreted as a lipoma.

a superimposed inflammatory process and the abdomen are grouped as mesenteric cysts. patient underwent for elective exploratory Therefore, the term of “mesenteric ” refers laparotomy two months after. At surgery, to topographic site rather than histological a firm cystic mass was encountered in the diagnosis. Mesenteric cysts can originate mesentery of the proximal jejunum. The mass from lymphatic (lymphangiomas), mesothelial together with a segment of small bowel and its (mesothelial cyst), gastrointestinal (enteric mesentery was resected and sent to pathology duplication cyst and enteric cyst) cells, or can laboratory for evaluation. be secondary to trauma, surgery or infection The gross specimen showed a 6.5×4.0 (pseudocyst) (2). cm cystic mass, which was filled with Pseudocysts develop secondary to trauma homogeneously white, milky fluid. The or infection and thought to be the sequelae mass was adherent to the mesenteric side of of a mesenteric or omental hematoma or an the small bowel without of bowel abscess that did not resorb completely (3). wall. Histologic evaluation of the cyst These cysts are unrelated to pancreatitis; showed the material in the cyst cavity was therefore, the cystic fluid contains no high acellular, necrotic, and lipid-like. The cyst levels of amylase or lipase. Therefore, to wall was lined by fibrous tissue, with no prevent confusion with much more common evidence of an endothelial lining and showed pancreatic pseudocyst, mesenteric pseudocysts chronic inflammation with lipid clefts and are called as nonpancreatic pseudocyst. They calcification, which are indicative of prior may be found incidentally on an rupture. There were adjacent disorganized patient; abdominal pain, nausea, and vomiting muscular arteries and veins that exhibited are the most frequently reported symptoms intimal , organizing thrombus and (4). A palpable mass is often the only finding recanalization. Therefore, the final diagnosis on physical examination (4). On gross was rendered as a non-pancreatic pseudocyst pathological examination, nonpancreatic of the mesentery that had undergone focal pseudocysts appear as unilocular, thick- rupture. walled cystic mass in the mesentery or omentum with serous, hemorrhagic, purulent DISCUSSION or occasionally chylous content (3-6). The Mesenteric cysts are rare intrabdominal wall of a nonpancreatic pseudocyst contains masses with an incidence of approximately no endothelial lining on histopathologic 1/100,000 hospital admission in adults (1). examination and is composed of fibrous Wide range of congenital and acquired cysts tissue that may present calcifications and that arise from various tissue linings of the inflammatory changes (3-6). CT and MR findings of mesenteric pseudocyst 51

On sonography, nonpancreatic cysts cysts from other origins by the presence of frequently demonstrate intracystic echogenic mesothelial cell lining in their inner surface debris (4). Thick-walled cystic mass that may (2, 3). These cysts are typically unilocular, contain fluid-fluid level is typical CT imaging contain serous material, and more commonly findings of a nonpancreatic pseudocyst. located in the mesentery or omentum (3). While the non-dependent portion of the cyst Mesothelial cysts have no discernable wall or shows fat density, the dependent portion internal septations. demonstrates water density. These two In our case, the patient’s age and imaging components are easily mixable by patient’s appearance with unilocular cyst with thick motion, and it required approximately 30 wall makes congenital lymphangiomas minutes for the fluid-fluid level to form (4). unlikely, and the lack of endothelial lining is This is the reason why the cyst of our patient not consistent with a neoplastic process such showed homogeneous fatty content on CT as lymphangioma, mesothelial cyst or a cyst scan whereas demonstrated a fluid-fluid level of enteric origin. In the light of presence of on MRI due to longer scan time, allowing fibrous wall in histological evaluation, the fluid-fluid level to form. MRI can reliably cyst likely represents an acquired pseudocyst demonstrate the fatty content of a cyst by that developed secondary to a prior surgery. using either frequency selective fat saturation When symptomatic, surgical excision or chemical shift (in-phase and out-of phase) of a nonpancreatic pseudocyst is usually imaging (6). Although, frequency selective recommended (4). If the adjacent bowel is fat suppression technique effectively reduces closely involved, than an excision of the cyst macroscopic fat signal, so a larger amount with a segmental resection of the bowel may of fat is required for its effect, such as in be necessary (4). lipomas and liposarcomas, chemical shift In conclusion, a nonpancreatic pseudocyst imaging allows identifying small amount of is seen in patients with prior history of (microscopic) fat within a mass. abdominal infection, surgery or trauma and Chylous content of a cyst is not unique has distinct imaging features, characterized to nonpancreatic pseudocyst. Rarely, by a thick-walled solitary cyst with chylous lymphangiomas and enteric duplication cyst content. Awareness of these imaging features can also have a fatty content. Lymphangiomas may help radiologists to differentiate them are rare benign tumors that composed of a from other abdominal neoplastic processes proliferation of dilated lymphatic spaces and may prevent unnecessary surgery. lined by flat endothelial cells, and typically occur in the head and neck of children REFERENCES (2, 3). Lymphangiomas can also occur 1. Vanek VW, Phillips AK. Retroperitoneal, in the abdomen; most commonly in the mesenteric, and omental cysts. Arch Surg retroperitenium or mesentery (1). On imaging, 1984;119(7):838-42 they are typically seen as multiloculated, less 2. Ros PR, Olmsted WW, Moser RP Jr, Dachman AH, Hjermstad BH, Sobin LH. Mesenteric and frequently unilocular, non-enhancing, thin- omental cysts: histologic classification with walled cystic structures and show variable imaging correlation. Radiology 1987;164(2): attenuation value, ranging from clear fluid 327-32 to fat. When it located in the small bowel 3. Stoupis C, Ros PR, Abbitt PL, Burton SS, mesentery, the cystic space may be filled with Gauger J. Bubbles in the belly: imaging chyle (6). Enteric duplication cysts are ectopic of cystic mesenteric or omental masses. enteric tissue and contain all enteric layers in Radiographics 1994;14(4):729-37 their wall, including mucosa, muscularis and 4. Fujita N, Noda Y, Kobayashi G, et al. Chylous nervous plexus. They are usually attached to cyst of the mesentery: US and CT diagnosis. Abdom Imaging 1995;20(3):259-61 a normal bowel and present as a thick-walled, 5. Yang DM, Jung DH, Kim H, et al. unilocular cyst with serous content, which Retroperitoneal cystic masses: CT, clinical, may be rarely chylous (3). The wall of enteric and pathologic findings and literature review. duplication cyst may enhance with contrast. Radiographics 2004;24(5):1353-65 Unlike enteric duplication cyst, an enteric 6. Pereira JM, Sirlin CB, Pinto PS, Casola G. CT cyst is lined by enteric mucosa only and and MR imaging of extrahepatic fatty masses appears as a thin-walled, unilocular cyst with of the abdomen and pelvis: techniques, serous content (3). diagnosis, differential diagnosis, and pitfalls. Mesothelial cysts result from incomplete Radiographics 2005;25(1):69-85 fusion of peritoneal layers and are pathologically differentiated from the