Peritoneal thickening with fat stranding: peritoneal metastasis and beyond.

Transcription

1 Peritoneal thickening with fat stranding: peritoneal metastasis and beyond. Poster No.: C-0880 Congress: ECR 2016 Type: Educational Exhibit Authors: E. Diez, N. Arevalo, E. Barcina García, E. Roa, J. Gredilla Molinero ; Madrid/ES, madrid, ma/es Keywords: Inflammation, Neoplasia, Diagnostic procedure, CT, Abdomen DOI: /ecr2016/C-0880 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 48

2 Learning objectives * To expose the normal peritoneal anatomy to procure a proper understanding of imaging findings. * To describe the wide spectrum of diseases that affect the peritoneum. * To illustrate the principal radiological findings of these entities with CT as the main radiological technique making emphasis on pitfalls and differential diagnosis. Background Peritoneal metastases are relatively common in tumors of the abdomen and usually imply a poor prognosis, but there is also a wide variety of diseases, which entail a better prognosis, that can mimic peritoneal metastases. Diseases of the peritoneum are common but there is an important overlap in their imaging findings, so precise diagnosis based on imaging alone is often difficult to achieve and the main goal of radiologic evaluation is to differentiate between benign and malignant diseases, which is essential for an adequate patient management. In this educational exhibit we review the anatomy of the peritoneal cavity and present a pictorial review of different neoplastic and non-neoplastic conditions that affect the peritoneum, illustrate their principal radiological findings using CT as the main imaging technique and make emphasis on pitfalls and differential diagnosis of these entities. Findings and procedure details PERITONEUM AND PERITONEAL CAVITY PERITONEUM The peritoneum is a thin, serous membrane that lines the internal surface of the abdomen and pelvis wall (parietal peritoneum) and also covers and is reflected over most of Page 2 of 48

3 the abdominal viscera (visceral peritoneum); both layers are continuous and enclose a potential space, the peritoneal cavity which contains a small amount of lubricating fluid. Both parietal and visceral peritoneum consist of a single layer of squamous epithelial cells, called mesothelium, and a thin layer of connective tissue, the former being the free surface of the peritoneum permitting viscera to glide easily against the abdominal wall and against one another. Abdominal viscera can be divided anatomically by their relationship with the peritoneum. There are two main groups: intraperitoneal organs, which are completely covered by visceral peritoneum (examples include stomach, liver and spleen) and retroperitoneal organs, which lie outside the peritoneal cavity because they are partially covered by peritoneum (examples include pancreas, kidneys, ascending and descending colon). PERITONEAL REFLECTIONS Visceral peritoneum covers and is reflected over most of the abdominal viscera to form some peritoneal ligaments, the mesentery and the omentum. Peritoneal reflections carry blood vessels, nerves and lymphatics from the retroperitoneum to the intraperitoneal organs. Page 3 of 48

4 Fig. 1: Sagittal diagram of abdomen showing peritoneal reflections. Yellow line = parietal peritoneum, Blue line = visceral peritoneum, L= liver, S = stomach, T= transverse colon, B= small bowel loops. References: Hospital Infanta Leonor - Madrid/ES Mesentery. A mesentery is a double layer of peritoneum that attaches an intraperitoneal organ to the posterior abdominal wall. It provides a pathway for nerves, blood vessels and lymphatics from the body wall to the viscera. Mesentery of the jejunum and the ileum is simply called "mesentery", and mesentery related to other organs is named according to the viscera it is connected to (examples include transverse and sigmoid mesocolon). Omentum. The omentum is a double layer of visceral peritoneum that extends from the stomach and duodenal bulb to other abdominal organs. The greater omentum consists of four layers of peritoneum. It connects the stomach and proximal part of the duodenum to the transverse colon, leaving a fold that covers the colon and the small bowel loops. The lesser omentum attaches from the lesser curvature of the stomach and the proximal part of duodenum to the liver. It consists of two contiguous components: the hepatogastric and the hepatoduodenal ligament. Peritoneal ligaments. A peritoneal ligament is a double fold of peritoneum that connects viscera to other viscera or to the abdominal wall. The falciform Page 4 of 48

5 ligament and the triangular ligament are the peritoneal ligaments of the liver, whereas the gastrosplenic ligament and the splenorrenal ligament are the peritoneal ligaments of the spleen. Fig. 2: Axial diagram of the upper abdominal cavity showing peritoneal ligaments. Yellow line = parietal peritoneum, Blue line = visceral peritoneum, L=liver, St=stomach, S=spleen, Striped area= retroperitoneum. References: Hospital Infanta Leonor - Madrid/ES PERITONEAL SPACES All these peritoneal ligaments and their attachments separate the peritoneal cavity into different peritoneal spaces, which provides a pathway for the extension of intraabdominal diseases. Transverse mesocolon divides the peritoneal cavity into the supramesocolic and inframesocolic compartments. There are two paracolic spaces located lateral to the peritoneal reflections of the right and left sides of the colon. Pelvis is also part of the peritoneal cavity. Page 5 of 48

6 SUPRAMESOCOLIC COMPARTMENT There are two supramesocolic spaces: the left and the right supramesocolic spaces, which usually communicate freely. The right supramesocolic space includes the right subphrenic space, the subhepatic space and the lesser sac. The right subphrenic space is separated from the left subphrenic space by the falciform ligament. The subhepatic area is divided into anterior and posterior subhepatic spaces, both communicating freely anatomically. The lesser sac lies behind the lesser omentum, the stomach, the duodenal bulb and the gastrocolic ligament, and anterior to the pancreas. It s bounded on the left by the gastrosplenic and splenorrenal ligaments and on the right by the caudate lobe of the liver and the Foramen of Winslow, through which the lesser sac communicates with the right subhepatic space. The left supramesocolic space includes the left subphrenic and perisplenic spaces. These spaces usually communicate freely. A stricture of particular significance in the left supramesocolic space is the phrenicocolic ligament, which is a relative impediment to the spread of pathologic conditions from the perisplenic space to the left paracolic space. Page 6 of 48

7 Fig. 3: Diagram showing peritoneal reflections and intraperitoneal compartments. References: Hospital Infanta Leonor - Madrid/ES INFRAMESOCOLIC COMPARTMENT The obliquely oriented root of the mesentery divides the inframesocolic compartment into two spaces: the right and the left infracolic spaces. The smaller right infracolic space is bounded inferiorly by the junction of the mesentery with the cecum, whereas the larger left infracolic space communicates freely with the pelvis. Both right and left infracolic spaces are separated from the paracolic spaces by the ascending or the descending colon. The right paracolic space is larger and communicates freely with the right subphrenic space, whereas the left paracolic space is narrow and is interrupted from continuity with the left subphrenic space by the phrenicocolic ligament. PELVIC SPACE Page 7 of 48

8 Pelvis is the most gravity-dependent part of the peritoneal cavity and is continuous with both paracolic spaces. The peritoneum in the pelvis is continuous in the male pelvis, whereas in women is discontinuous at the ostia of the oviducts, through which fluid can spread from the extraperitoneal space to the peritoneal cavity It's divided into paravesical spaces, rectovesical pouch and rectouterine pouch (in females). PERITONEAL FLUID CIRCULATION The normal peritoneal cavity contains a small amount of lubricating fluid that is continuously circulating through the peritoneal spaces due to movement of the diaphragm and peristalsis of bowel loops. Non-encapsulated fluid tends to collect in the pelvic recesses. Next it flows up the paracolic spaces. The ascent through the left paracolic space is slow due to its narrowness and the presence of the phrenicocolic ligament, so fluid mainly ascends through the right paracolic space to the right subhepatic and right subphrenic spaces. Direct passage of fluid from the right subphrenic space to the left subphrenic space is prevented by the presence of the falciform ligament. Page 8 of 48

9 Fig. 4: Diagram of the pathways of flow of intraperitoneal fluid (yellow arrows) and the predominant sites for arrested peritoneal fluid (*). References: Hospital Infanta Leonor - Madrid/ES There are watershed regions in the peritoneal cavity which are areas where fluid pools favouring the deposition of malignant cells and growth of neoplastic lesions. These watershed regions are the right paracolic and subhepatic space, the ileocolic junction, the root of the sigmoid mesentery and the pouch of Douglas. It's important to check these areas for detecting tumoral implants. PERITONEAL CARCINOMATOSIS Peritoneal carcinomatosis is a metastatic manifestation of many organ-based malignancies, mainly carcinomas of the gastrointestinal tract and ovaries. It s the most common malignancy of peritoneal cavity, even in the absence of a known primary neoplasm. Page 9 of 48

10 CT findings that suggest the diagnosis of peritoneal carcinomatosis include ascites and peritoneum, greater omentum and mesentery involvement. Ascites: The presence of intraperitoneal fluid, either free or loculated, is present in up to 70% of cases. It can be produced by obstruction of the subphrenic lymphatic vessels, which leads to difficulty in absorption of peritoneal fluid, or by excessive production or peritoneal fluid caused by the secretion of a vascular permeability factor by the tumoral cells. Fig. 5: Ascites in peritoneal carcinomatosis. 1. Free intraperitoneal fluid. Axial CT scan in a 52 years old male with colorectal cancer shows free intraperitoneal ascites (A), there is also nodular infiltration of the greater omentum (*). 2. Axial CT scan shows loculated ascites (LA) with thin septa and peritoneal enhancing (white arrows) in a male with stage 4 colon cancer with colectomy and ileostomy on the right side. References: Hospital Infanta Leonor - Madrid/ES Page 10 of 48

11 Peritoneal features: Invasion of the peritoneum is seen on CT as a nodular or diffuse thickening of this serous membrane, which enhances after IV contrast material administration. There can also be tumor implants, the 4 main locations where they locate are the right paracolic space, the ileocolic junction, the root of the sigmoid mesentery and the pouch of Douglas. Calcification within peritoneal implants suggests peritoneal metastases from ovarian cancer. Fig. 6: Diffuse peritoneal thickening in peritoneal carcinomatosis. Axial contrastenhanced CT scan shows diffuse thickening and enhancement of the peritoneum (arrows) with massive ascites (A) that medialize small bowel loops. References: Hospital Infanta Leonor - Madrid/ES Page 11 of 48

12 Fig. 7: Frequent locations for peritoneal implants. 1. implant in the right paracolic space (D=descending colon), 2. implant near the ileocolic junction (C=cecum, T=terminal ileum), 3. implant in the root of the sigmoid mesentery (S=sigmoid colon), 4. implant in the rectovesical pouch (R=rectum, B=bladder) References: Hospital Infanta Leonor - Madrid/ES Greater omentum features: Involvement of greater omentum on CT is shown as omental fat stranding in early stages, either alone or with small nodules within the fat. In latter stages, a solid mass replaces the omental fat, giving the typical appearance of an "omental cake". Page 12 of 48

13 Fig. 9: Greater omentum involvement in peritoneal carcinomatosis. 1 Axial contrastenhanced CT scan shows an early form of greater omentum involvement with fat stranding and small nodules within the omental fat (arrows). There is also massive ascites (A). 2 Axial contrast-enhanced CT scan and 3 sagittal reformatted image show a later form of greater omentum infiltration with omental fat substituted by a solid mass (*) giving the typical appearance of an "omental cake". There is also free intraperitoneal fluid (A). References: Hospital Infanta Leonor - Madrid/ES Mesentery features: Infiltration of mesentery is seen on CT as mesenteric fat stranding with one or more mesenteric nodules or masses, which can be confluent. An indirect sign is the fixation of the stomach or a bowel segment. Page 13 of 48

14 Fig. 10: Mesentery infiltration in peritoneal carcinomatosis. Axial contrast-enhanced CT scan in a patient with peritoneal carcinomatosis shows fat stranding (arrows) and pathologic lymph nodes (*) within the mesentery. References: Hospital Infanta Leonor - Madrid/ES TC MIMICS OF PERITONEAL CARCINOMATOSIS There are many neoplastic and non-neoplastic processes that may mimic peritoneal carcinomatosis in CT imaging. Findings in these processes may be similar to those in peritoneal carcinomatosis, but there are some findings that suggest other diagnosis. These CT mimics of peritoneal carcinomatosis include: Page 14 of 48

15 Fig. 11: CT mimics of peritoneal carcinomatosis References: Hospital Infanta Leonor - Madrid/ES Pseudomixoma peritonei Pseudomixoma retroperitonei refers to intraperitoneal accumulation of a large amount of mucinous ascites secondary to rupture of a mucinous tumor. The most common cause is the rupture of a mucinous tumor of the appendix. CT signs include ascites and infiltration of the peritoneum and greater omentum. But there are many signs that suggest pseudomixoma peritonei as the main diagnosis: Ascites typically loculated causing scalloping of visceral surfaces Fig. 13 on page 36 Calcifications may be present, usually curvilinear There are not solid peritoneal masses. Identification of a mucocele of the appendix Fig. 12 on page 35 Page 15 of 48

16 Fig. 14: Pseudomixoma peritonei of appendicular origin. 1 and 2 axial contrastenhanced CT scans show both free (*) and multiloculated (L) intraperitoneal effusion with scalloping of the liver and spleen. There are also peritoneal enhancement (arrow) and nodules within the greater omentum (n). References: Hospital Infanta Leonor - Madrid/ES Peritoneal Mesotelioma Mesothelioma is an uncommon primary tumor that originates from the serous membranes of the pleura, pericardium, or peritoneum. Peritoneal involvement is related in up to 25% of cases. CT findings may be similar to those seen in peritoneal carcinomatosis with infiltration of greater omentum, thickening of peritoneum, ascites and mesenteric nodules. There are other associated signs that suggest peritoneal mesothelioma as the etiology of peritoneal involvement: Clinical evidence of occupational asbestos exposure Calcification of peritoneal masses may be found Presence of pleural or pericardial abnormalities (calcified plaques). Page 16 of 48

17 Lack of evidence of primary or secondary malignancy, and absence of lymphadenopathy within the abdomen. Fig. 15: Peritoneal mesothelioma. 1 and 2 axial contrast-enhanced CT scans show abundant ascites (A) with micronodular invasion of the greater omentum (*). Pericardial effusion (P) and pleural effusion (pl) with calcified pleural plaque (arrow) were also found. Antecedent of occupational exposure to asbestos was confirmed. References: Hospital Infanta Leonor - Madrid/ES Peritoneal Lymphomatosis Lymphomatous peritoneal infiltration usually occurs in high grade lymphomas, Burkitt lymphomas and lymphomas in AIDS patients. It s shown on CT scan as invasion of greater omentum and mesentery, diffuse peritoneal thickening, and typically non-loculated ascites. Other signs that guide the diagnosis of peritoneal lymphomatosis are: Page 17 of 48

18 Pathologic mesenteric and retroperitoneal lymphadenopathy, typically confluent encasing mesenteric blood vessel without infiltrating them (sandwich sign). Fig. 16 on page 39 Splenomegaly may be present. Involvement of stomach or terminal ileum, with wall thickening and fat stranding. Fig. 17: Peritoneal lymphomatosis. 1 and 2 axial contrast-enhanced CT scans from the same patient show slight splenomegaly (S) with mesenteric fat stranding, mesenteric lymphadenopathy (M) and peritoneal enhancement (arrow) associating preaortic and retroperitoneal (R) lymphadenopathy. 3 and 4 axial contrast-enhanced from other patient show multiple pathologic lymph nodes within the mesentery (*) with slight mesenteric fat stranding. There is a tumor on the gastrointestinal tract (jejunum) (J) and a small amount of fluid in the pelvis (not shown). References: Hospital Infanta Leonor - Madrid/ES Gastrointestinal Stromal Tumor: Page 18 of 48

19 Gastrointestinal stromal tumors (GIST) refer to tumors arising from the mesenchyme of the gastrointestinal tract. They typically express the c-kit protein, which is highly specific of GISTs. The majority of GISTs are sporadic; however they occasionally occur in the setting of a Carney triad or neurofibromatosis type 1. GISTs mostly arise from the stomach (up to 70%), and it's rarely seen arising from the peritoneum (mesentery, greater omentum) which is called extra-gastrointestinal GIST, the latter form usually with a large mass at the time of diagnosis. There are a certain number of signs that point to GIST: GIST of the mesentery usually manifests as a large mass typically hyper vascular at the periphery with central areas of hemorrhage or necrosis. Calcification is uncommon. Peritoneal deposits may be seen in aggressive tumors, mimicking peritoneal carcinomatosis, but lymphadenopathy is not usually seen. Page 19 of 48

20 Fig. 18: Gastrointestinal stromal tumor (GIST) arising from the mesentery. 1. Axial contrast-enhanced CT scan shows a large mass (M) with central necrosis and peripheral enhancement. 2.Axial contrast-enhanced CT scan 1 year after surgical resection of the mass shows relapse of the disease with multiple mesenteric nodules (*) and peritoneal enhancement (arrows). References: Hospital Infanta Leonor - Madrid/ES Mesenteric desmoid tumor Desmoid tumor is an uncommon benign neoplasm with high tendency to local invasion and recurrence but without metastasis. It may occur sporadically or associated either with familiar adenomatous polyposis or Gardner Syndrome. Mesenteric desmoid tumor is seen on CT scan as a large mesenteric mass within the mesentery displacing surrounding structures and vasculature, usually well circumscribed but in some cases it may show ill-defined margins. Late enhancement after IV contrast administration is characteristic due to their large fibrous component. Page 20 of 48

21 Fig. 19: Mesenteric desmoid tumor. Axial contrast-enhanced CT scan shows a large mesenteric mass (*) with ill-defined margins displacing surrounding bowel loops and blood vessels (arrows). There is also a small amount of free intraperitoneal fluid (arrowhead). References: Hospital Infanta Leonor - Madrid/ES Mesenteric carcinoid tumor Carcinoid is a neuroendocrine tumor, commonly found in the small bowel. Primary mesenteric carcinoid tumor is rare, although secondary mesenteric involvement is common. On the CT scan: The primary tumor may not be seen, but the metastatic mesenteric lymphadenopathy and desmoplastic reaction are usually more notorious. Calcification may be seen. Peritoneal tuberculosis The abdomen is the most common site of extra-pulmonary tuberculosis, with peritoneal disease being the most common form within the abdomen, which is frequently associated with other forms of gastrointestinal tuberculosis. Peritoneal tuberculosis is divided into three forms with important overlap of their imaging findings: wet type (the most frequent, accounting for 90%), fibrotic-fixed type, and dry type (the less common form). CT findings seen in peritoneal tuberculosis include: Smooth and regular thickening and enhancement of the peritoneum Enlarged mesenteric or retroperitoneal lymphatic nodules, which may show hypodense center. Calcifications within peritoneum or lymph nodules Ascites Page 21 of 48

22 Fig. 21: Peritoneal tuberculosis. Axial contrast-enhanced CT scan shows free intraperitoneal fluid (*) with linear peritoneal enhancement (arrow) and multiple small lymph nodes (n) within the mesentery fat. References: Hospital Infanta Leonor - Madrid/ES Although there is an overlap in their imaging findings, there are more specific imaging features seen in each form of peritoneal tuberculosis: Wet type: abundant high attenuation ascites (HU 20-45). High attenuation is due to high protein and cellular content. Fibrotic type: omental 'cake-like' mass with loculated ascites Dry type: mesenteric lymphadenopathy and fibrous adhesions in the peritoneum. Sclerosing mesenteritis. Sclerosing mesenteritis (also known as chronic fibrosing mesenteritis, retractile mesenteritis, mesenteric lipodistrophy and mesenteric paniculitis) is a rare disease of unknown etiology characterized by fibrolipomatous thickening of the small bowel mesentery, chronic inflammation, and finally mesenteric fibrosis. Page 22 of 48

23 Histologically there are considered to be two stages of the disease; the acute stage is known as "mesenteric panniculitis" in which inflammation and fat necrosis predominate over fibrosis, and the chronic stage known as "retractile mesenteritis" with more fibrosis than inflammation and fat necrosis. The latter is considered to be a more invasive form of mesenteric panniculitis. CT imaging findings consist of: at early stages it s seen as a well demarcated soft-tissue mesenteric mass with slightly higher density than fat, and blood vessels traversing the lesion surrounded by a hypo attenuating rim of normal fat. At advanced stages a soft tissue fibrous mass with a stellate contour is developed within the mesentery, which may retract or narrow adjacent bowel loops. Fig. 22: Mesenteric paniculitis and retractile mesenteritis. 1. Axial contrast-enhanced CT scan shows a soft-tissue mesenteric mass (*) with slightly higher density than fat and blood vessels traversing the lesion surrounded by a hypo attenuating rim in a patient with mesenteric paniculitis (arrow). 2. Axial contrast-enhanced CT scan from other patient shows a soft tissue mass (m) with stellate contour within the mesentery, Page 23 of 48

24 there is also mesenteric fat stranding and small lymph nodes, in a patient with retractile mesenteritis. References: Hospital Infanta Leonor - Madrid/ES Diffuse peritoneal Leiomyomatosis. Diffuse peritoneal Leiomyomatosis is an uncommon condition characterized by the development of multiple smooth muscle-like nodules in the peritoneal cavity. The origin of the process remains unknown; but it's associated with increased serum levels of gonadal steroids. It's mainly located in the peritoneum and greater omentum. The absence of ascites or secondary deposits and an adequate clinical context suggest the diagnosis of diffuse peritoneal leiomyomatosis. Fig. 23: Peritoneal Leiomyomatosis. Axial contrast-enhanced CT scan in a 34-years old female shows greater omentum involvement with multiple nodules (*) within the omental fat. References: Hospital Infanta Leonor - Madrid/ES Page 24 of 48

25 Images for this section: Fig. 1: Sagittal diagram of abdomen showing peritoneal reflections. Yellow line = parietal peritoneum, Blue line = visceral peritoneum, L= liver, S = stomach, T= transverse colon, B= small bowel loops. Hospital Infanta Leonor - Madrid/ES Page 25 of 48

26 Fig. 2: Axial diagram of the upper abdominal cavity showing peritoneal ligaments. Yellow line = parietal peritoneum, Blue line = visceral peritoneum, L=liver, St=stomach, S=spleen, Striped area= retroperitoneum. Hospital Infanta Leonor - Madrid/ES Page 26 of 48

27 Fig. 3: Diagram showing peritoneal reflections and intraperitoneal compartments. Hospital Infanta Leonor - Madrid/ES Page 27 of 48

28 Fig. 4: Diagram of the pathways of flow of intraperitoneal fluid (yellow arrows) and the predominant sites for arrested peritoneal fluid (*). Hospital Infanta Leonor - Madrid/ES Page 28 of 48

29 Fig. 5: Ascites in peritoneal carcinomatosis. 1. Free intraperitoneal fluid. Axial CT scan in a 52 years old male with colorectal cancer shows free intraperitoneal ascites (A), there is also nodular infiltration of the greater omentum (*). 2. Axial CT scan shows loculated ascites (LA) with thin septa and peritoneal enhancing (white arrows) in a male with stage 4 colon cancer with colectomy and ileostomy on the right side. Hospital Infanta Leonor - Madrid/ES Page 29 of 48

30 Fig. 6: Diffuse peritoneal thickening in peritoneal carcinomatosis. Axial contrastenhanced CT scan shows diffuse thickening and enhancement of the peritoneum (arrows) with massive ascites (A) that medialize small bowel loops. Hospital Infanta Leonor - Madrid/ES Page 30 of 48

31 Fig. 7: Frequent locations for peritoneal implants. 1. implant in the right paracolic space (D=descending colon), 2. implant near the ileocolic junction (C=cecum, T=terminal ileum), 3. implant in the root of the sigmoid mesentery (S=sigmoid colon), 4. implant in the rectovesical pouch (R=rectum, B=bladder) Hospital Infanta Leonor - Madrid/ES Page 31 of 48

32 Fig. 8: Calcified peritoneal implants in peritoneal metastasis from ovarian carcinoma. 1,2 3 and 4 axial contrast-enhanced CT scans show multiple calcified peritoneal implants (arrows) and free intraperitoneal ascites (*). Hospital Infanta Leonor - Madrid/ES Page 32 of 48

33 Fig. 9: Greater omentum involvement in peritoneal carcinomatosis. 1 Axial contrastenhanced CT scan shows an early form of greater omentum involvement with fat stranding and small nodules within the omental fat (arrows). There is also massive ascites (A). 2 Axial contrast-enhanced CT scan and 3 sagittal reformatted image show a later form of greater omentum infiltration with omental fat substituted by a solid mass (*) giving the typical appearance of an "omental cake". There is also free intraperitoneal fluid (A). Hospital Infanta Leonor - Madrid/ES Page 33 of 48

34 Fig. 10: Mesentery infiltration in peritoneal carcinomatosis. Axial contrast-enhanced CT scan in a patient with peritoneal carcinomatosis shows fat stranding (arrows) and pathologic lymph nodes (*) within the mesentery. Hospital Infanta Leonor - Madrid/ES Page 34 of 48

35 Fig. 11: CT mimics of peritoneal carcinomatosis Hospital Infanta Leonor - Madrid/ES Page 35 of 48

36 Fig. 12: Pseudomixoma peritonei of appendicular origin. 1 and 2 axial contrast-enhanced CT scans a mucinous tumor of the appendix (M) with curvilinear calcification within the appendix wall (arrow), and adjacent intraperitoneal fluid (*). Hospital Infanta Leonor - Madrid/ES Page 36 of 48

37 Fig. 13: This picture shows typical hepatic and splenic scalloping secondary to extrinsic compression by mucinous masses (red lines) in a patient with pseudomixoma peritonei. Hospital Infanta Leonor - Madrid/ES Page 37 of 48

38 Fig. 14: Pseudomixoma peritonei of appendicular origin. 1 and 2 axial contrast-enhanced CT scans show both free (*) and multiloculated (L) intraperitoneal effusion with scalloping of the liver and spleen. There are also peritoneal enhancement (arrow) and nodules within the greater omentum (n). Hospital Infanta Leonor - Madrid/ES Page 38 of 48

39 Fig. 15: Peritoneal mesothelioma. 1 and 2 axial contrast-enhanced CT scans show abundant ascites (A) with micronodular invasion of the greater omentum (*). Pericardial effusion (P) and pleural effusion (pl) with calcified pleural plaque (arrow) were also found. Antecedent of occupational exposure to asbestos was confirmed. Hospital Infanta Leonor - Madrid/ES Page 39 of 48

40 Fig. 16: This picture shows the typical sandwich sign in a patient with lymphoma with confluent mesentery lymph nodes (m) encasing the mesenteric vasculature (v) without compressing it. Hospital Infanta Leonor - Madrid/ES Page 40 of 48

41 Fig. 17: Peritoneal lymphomatosis. 1 and 2 axial contrast-enhanced CT scans from the same patient show slight splenomegaly (S) with mesenteric fat stranding, mesenteric lymphadenopathy (M) and peritoneal enhancement (arrow) associating preaortic and retroperitoneal (R) lymphadenopathy. 3 and 4 axial contrast-enhanced from other patient show multiple pathologic lymph nodes within the mesentery (*) with slight mesenteric fat stranding. There is a tumor on the gastrointestinal tract (jejunum) (J) and a small amount of fluid in the pelvis (not shown). Hospital Infanta Leonor - Madrid/ES Page 41 of 48

42 Fig. 18: Gastrointestinal stromal tumor (GIST) arising from the mesentery. 1. Axial contrast-enhanced CT scan shows a large mass (M) with central necrosis and peripheral enhancement. 2.Axial contrast-enhanced CT scan 1 year after surgical resection of the mass shows relapse of the disease with multiple mesenteric nodules (*) and peritoneal enhancement (arrows). Hospital Infanta Leonor - Madrid/ES Page 42 of 48

43 Fig. 19: Mesenteric desmoid tumor. Axial contrast-enhanced CT scan shows a large mesenteric mass (*) with ill-defined margins displacing surrounding bowel loops and blood vessels (arrows). There is also a small amount of free intraperitoneal fluid (arrowhead). Hospital Infanta Leonor - Madrid/ES Page 43 of 48

44 Fig. 20: Carcinoid tumor. Axial contrast-enhanced CT scans show multiple mesenteric masses (m) with desmoplastic reaction (arrow) and mesenteric fat stranding. Note there is mural thickening of a jejunum loop (*) representing the primary tumor. Hospital Infanta Leonor - Madrid/ES Page 44 of 48

45 Fig. 21: Peritoneal tuberculosis. Axial contrast-enhanced CT scan shows free intraperitoneal fluid (*) with linear peritoneal enhancement (arrow) and multiple small lymph nodes (n) within the mesentery fat. Hospital Infanta Leonor - Madrid/ES Page 45 of 48

46 Fig. 22: Mesenteric paniculitis and retractile mesenteritis. 1. Axial contrast-enhanced CT scan shows a soft-tissue mesenteric mass (*) with slightly higher density than fat and blood vessels traversing the lesion surrounded by a hypo attenuating rim in a patient with mesenteric paniculitis (arrow). 2. Axial contrast-enhanced CT scan from other patient shows a soft tissue mass (m) with stellate contour within the mesentery, there is also mesenteric fat stranding and small lymph nodes, in a patient with retractile mesenteritis. Hospital Infanta Leonor - Madrid/ES Page 46 of 48

47 Fig. 23: Peritoneal Leiomyomatosis. Axial contrast-enhanced CT scan in a 34-years old female shows greater omentum involvement with multiple nodules (*) within the omental fat. Hospital Infanta Leonor - Madrid/ES Page 47 of 48

48 Conclusion Peritoneal diseases are common and may be difficult to diagnose due to the overlap in their imaging appearance. The principal goal of radiologic imaging evaluation is to distinguish between benign and malignant conditions, so knowledge of the different diseases affecting the peritoneum allows the radiologist to provide a proper differential diagnosis and suggest pertinent patient management. Personal information References Diop AD, Fontarensky M, Montoriol PF, Da Ines D. CT imaging of peritoneal carcinomatosis and its mimics. Diagn Interv Imaging 2014;95: Levy AD, Arnaiz J, Shaw, JC, Sobin LH. Primary Peritoneal Tumors: Imaging Features with Pathologic Correlation. Radiographics. 2008;28: Meyer MA. Dynamic Radiology of the Abdomen: Normal and Pathologic Anatomy. New York: Springer-Verlag, Smiti S, Rajagopal KV. CT mimics or peritoneal carcinomatosis. Indian J Radiol Imaging.2010; 20(1): Tirkes T, Sandrasegaran K, Patel AA, Hollar MA, Tejada JG, Tann M, Akisik FM, Lappas JC. Peritoneal and Retroperitoneal Anatomy and Its Relevance for Cross-Sectional imaging. Radiographics 2012;32(2): Page 48 of 48