Eur. Radiol. (2001) 11: 2195±2206 DOI 10.1007/s003300100998

Vassilios Raptopoulos Nicholas Gourtsoyiannis

Received: 14 March 2001 Accepted: 4 April 2001 Published online: 28 July 2001  Springer-Verlag 2001 Presented at the 11th Annual Meeting and Postgraduate Course of the European Society of Gastrointestinal and Abdominal Radiology, La Grande Motte, France, 21±24 June 2000

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V. Raptopoulos ( ) Department of Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, 330 Brookline Avenue, Boston, MA 02215, USA E-mail: [email protected] Phone: +1-6 17-6 67 56 96 Fax: +1-6 17-6 67 82 12 N. Gourtsoyiannis Department of Radiology, University Hospital, Medical School of Crete, 7110 Staurakia, Heraklion, Crete, Greece

G AS T R O IN T E S T I N A L

Peritoneal carcinomatosis

Abstract The peritoneum is a mesothelial lining of the abdominal cavity (parietal) and intraperitoneal viscera (visceral). The cavity contains a small amount of fluid, which circulates from cephalad to caudal to cephalad, influenced by negative pressure under the diaphragm during exhalation, gravity, and bowel peristalsis. Peritoneal reflections and mesenteries divide the cavity into various compartments (supramesocolic, inframesocolic, and pelvis). These reflections support the peritoneal organs and provide vascular and nervous connections while within the cavity they influence pathway of intraperitoneal fluid circulation. Capillary force over convex surfaces influence stasis of fluid and promotes peritoneal seeding; thus, there are numerous areas in which peritoneal masses are seen more commonly. These areas include the undersurface of the dia-

Anatomic structures The peritoneum is a mesothelial membrane that lines the inner surface of the abdominal cavity (parietal peritoneum) and extends to cover various solid organs and most of the bowel (visceral peritoneum) [1]. Organs or portions of bowel that are covered almost completely by the peritoneum are categorized as intraperitoneal or simply peritoneal organs or portions of bowel; these include the liver and spleen, the stomach, the first portion of duodenum, all of small intestines, the cecum and the sigmoid colon. In women, the uterus, fallopian tubes,

phragm (negative pressure and capillary force), the omentum (bathed in fluid), the right lower quadrant (oblique course from left superior to right inferior of the small bowel mesentery), the left lower quadrant (transverse course of the sigmoid), and the pelvis (gravity). Peritoneal carcinomatosis may be either primary (mesothelioma) or metastatic. The mode of spread is by direct invasion, lymphatic permeation, peritoneal seeding or hematogenous. The imaging patterns include fibronodular stranding, nodules, plaques, and masses. Mesenteric thickening may produce pleated or stellate patterns. Spiral CT is the most useful modality in diagnosis and follow-up of peritoneal tumors. Keywords Peritoneum ´ Neoplasms ´ Abdomen ´ CT studies

and ovaries are also covered by peritoneum. These structures are connected with the posterior abdomen with various attachments (ligaments, folds, and mesenteries) which, in addition to structural support, provide a conduit for vascular and nerve supply. Anteriorly they are loosely contained by the omentum, a fibrofatty peritoneal reflection. The peritoneal cavity is confined in-between the parietal and visceral peritoneal membranes (Fig. 1). This design allows for various degrees of motion especially of the peritoneal hollow viscera allowing for bowel peristalsis and provides flexibility to accommodate for respiratory motion or changes in

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Fig. 1 Peritoneal cavity and mesentery. Parietal peritoneum (green) lines the abdominal cavity. The visceral peritoneum (yellow) covers the intraperitoneal organs. The root (R) of the mesentery connects the retroperitoneum with the subperitoneal space of the mesentery (M), covered by parietal peritoneum. The ascending (AC) and descending (DC) colon are confined in the retroperitoneum; lateral of each lie peritoneal recesses, the paracolic gutters Fig. 3 Intraperitoneal circulation of fluid (arrows) is governed by gravity and bowel peristalsis toward the pelvis, whereas the negative pressure under the diaphragm during exhalation pulls the fluid upwards. Peritoneal reflections, especially the small bowel mesentery and sigmoid mesocolon, direct the fluid paths

Fig. 2 Divisions of peritoneal cavity. The transverse mesocolon (TrM) divides the peritoneal cavity in the supra- and inframesocolic compartments while the sigmoid mesocolon (SiM) separates the inframesocolic compartment from the pelvis. The small bowel mesentery (SBM) divides the inframesocolic region in right and left. The uterus and broad ligaments (Ut&BL) subdivide the female pelvis in anterior (uterovesical) and posterior (pouch of Douglas) recesses. RSP right subphrenic space; RSH right subhepatic space; FF falciform ligament; HG hepatogastric ligament; HD hepatoduodenal ligament; LS lesser sac; PC phrenicocolic ligament; SP splenorenal ligament; SC splenocolic ligament; LSP left subphrenic space; LSH left subhepatic space; PS perisplenic space; RPCG right paracolic gutter; AC ascending colon; RIMC right inframesocolic space; LIMC left inframesocolic space; DC descending colon; LPCG left paracolic gutter

Fig. 4 Greater omentum (in-between arrows) infiltrated by metastatic ovarian carcinoma, retaining its normal apron-like distribution over the small bowel

bowel caliber. The design also accommodates structural containment of major organs such as the liver and the spleen. The other abdominal organs, parts of bowel, and major central blood vessel (aorta, inferior vena cava) lymphatics and nerves are confined in the retroperitoneum by fibrofatty tissue and retroperitoneal fasciae. Included in the extraperitoneal organs are the pancreas, kidneys, adrenal glands, urinary bladder and prostate. Retroperitoneal intestines are the second, third and

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Fig. 5 Subperitoneum. Retroperitoneal lymphadenopathy (RN) connected with mesenteric lymphadenopathy (MN) in a 46-yearold man with metastatic renal cell cancer, post left nephrectomy

two networks of roughly vertically placed ligaments: on the right, the falciform, hepatogastric, and hepatoduodenal ligaments; and on the left, the phrenicocolic, splenorenal, and splenocolic ligaments. To the right are the right subphrenic, superiorly, and subhepatic inferiorly. The lesser sac is in the middle in-between the two groups of ligaments, and behind the stomach. The left perihepatic, left subphrenic, and perisplenic regions are to the left supramesocolic region [1, 4, 5]. The sigmoid mesocolon has a transverse course and divides the inframesocolic compartment into the abdominal and pelvic regions. The abdominal inframesocolic compartment is subdivided into right and left regions by the small bowel mesentery. These are further subdivided by the mounts from the ascending and descending colon; on the lateral sides of each lay the right and left paracolic gutters (Figs. 1, 2).

Peritoneal cavity and circulation of fluid

Fig. 6 Subperitoneum. Cadaveric cross section of corpse with retroperitoneal masses (straight arrow) extending into the small bowel mesentery (curved arrows)

fourth portions of duodenum, ascending and descending colon, and the rectum. The retroperitoneum is covered anteriorly by the posterior parietal peritoneum. The fibrofatty retroperitoneal extensions in the abdominal cavity covered by peritoneum (ligaments, folds, and mesenteries) are termed subperitoneal compartment connecting the retroperitoneum with the peritoneal structures [2]. In addition to providing vascular, lymphatic, and nerve connections, the subperitoneum acts as both conduit and barrier of spread of disease between the two compartments. Similarly, the peritoneal reflections provide a pathway of spread or barricades to disease extension within the peritoneal cavity.

Peritoneal compartments The peritoneal cavity is divided by the transverse mesocolon into two major compartments: the supramesocolic and inframesocolic (Fig. 2) [1, 3]. The supramesocolic compartment is subdivided into three regions by

The peritoneal cavity is lined by the mesothelial membrane which has a surface of approximately 1.8 m2, approximately that of the skin (Fig. 1). The mesothelium is permeable and in this capacity is used in peritoneal dialysis in patients with chronic illnesses. There is usually a small amount of serous fluid in the peritoneum of approximately 50±100 ml [6]. This fluid does circulate within the peritoneal cavity from cephalad to caudal and back to cephalad directions [3]. The mode of circulation is governed by gravity downward and respiratory motion upward. Negative pressure under the diaphragm during respiratory exhalation pulls peritoneal fluid superiorly. During inhalation, the negative pressure is released and the fluid travels downward by gravity. Bowel peristalsis and peritoneal reflections and mesenteries direct the fluid paths. The circulation of fluid plays a significant role in spread of inflammation and metastatic disease in the peritoneal cavity (Fig. 3).

The omentum The omentum is divided into lesser omentum between the stomach and transverse colon and greater omentum which is ªhangingº from the transverse mesocolon, covering the small bowel in the abdomen and upper pelvis like an apron. It functions as a visceral fixation and exhibits motility to areas of tissue injury in an attempt to shield the abnormality. This motility is not active or amoeboid, however, but influenced by bowel peristalsis, diaphragmatic motion, and body positioning (gravity) [7]. These factors result in movement of the omentum towards areas of irritation, particularly inflammation, but also neoplastic. Floating in the peritoneal cavity, the omentum is bathed in peritoneal fluid

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a

b

Fig. 7 Pathways of spread: a Direct invasion. Adenocarcinoma of the small bowel (straight arrow) with direct invasion of anterior abdominal wall (curved arrow). b Lymphatic permeation. At higher level, lymphatic engorgement (arrow) in the mesentery is noted. This may be either reactive or due to tumorous lymphatic permeation. This type of high detail is now available with spiral and multidetector scanners allowing for fast scanning with thinner collimation

Fig. 8 Pathways of spread: Direct invasion via ligaments. Gallbladder carcinoma (not shown) with stranding extension in the hepatoduodenal ligament (arrow)

and thus a common location of intraperitoneal seeding of neoplastic processes. The omentum is not identifiable as such on imaging studies, such as CT, because it contains primarily fat, blending with the rest of the subperitoneal fat. Soft tissue deposits as in peritoneal carcinomatosis make the structure visible as stranding, nodules or masses (Fig. 4). Following omentectomy, small bowel loops can be seen plastered against the abdominal wall.

The mesenteries Small bowel mesentery is a major fold in the abdomen. It connects in a fan-like manner the small bowel with its root (Fig. 1). The root has an average length of 15 cm and has a course from the upper left to the right lower quadrant [7]. The width of the mesentery, from its root to the bowel junction, is approximately 20 cm, whereas the length of its small bowel border is approximately 7 m. There is marked individual variation in these measurements [8]. This configuration makes the mesentery very flexible to follow respiratory motion and bowel peristalsis. Mesentery's basic function is to hold the small bowel and to connect it with the retroperitoneal blood vessels and lymphatics (subperitoneum). In a sense, it is an extension of the retroperitoneum into the peritoneal cavity. It can thus act as a barrier or conduit of disease, connecting the retroperitoneum with the abdominal cavity (Figs. 5, 6) [9]. It also acts as a barrier of intraperitoneal spread of disease from the right to the left side of the abdomen or funneling pathology to the right lower quadrant via the oblique course of its root. Two other smaller mesenteries, the transverse mesocolon and sigmoid mesocolon, act similarly as relative barriers or conduits of disease located in the upper and lower abdomen, respectively [10].

Pathways of spread The pathways of spread of disease in the peritoneum is common for both inflammatory and neoplastic diseases. These include direct invasion, lymphatic paths, intraperitoneal seeding, and hematogenous spread [3, 11, 12, 13]. Direct invasion of organs may be contiguous from one organ to its periphery (Fig. 7a) or non-contiguous (Fig. 8). Examples of contiguous invasion are development of appendiceal abscess in patients with ruptured appendicitis or direct extension of carcinoma of the

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Fig. 9 Pathways of spread: lymphatic permeation. Adenocarcinoma of the cecum (m) with regional mesenteric lymphadenopathy (arrows)

Fig. 12 Serosal implants: influence of sigmoid mesocolon: left lower quadrant mass (arrow), metastatic gastric carcinoma. Peritoneal seeding influenced by the transverse location of the sigmoid mesocolon

Fig. 10 Pathways of spread: serosal implants. Influence of peritoneal circulation of fluid. Metastatic ovarian carcinoma with serosal implant on the lateral surface of the liver (black arrow) indenting the liver parenchyma (scalloping). Nodular implant in the anterior peritoneum (white arrow). Both are areas with increased capillary forces Fig. 13 Serosal implants: influence of gravity: hypodense drop metastases in the ovaries (arrows) in patient with primary gastric adenocarcinoma. Peritoneal nodule and loculated fluid, seen anteriorly, displace small bowel

Fig. 11 Serosal implants: influence of small bowel mesentery: peritoneal metastatic seeding from colon cancer with mass in right lower quadrant (arrow), a common location of intraperitoneal seeding influenced by the oblique course of the small bowel mesentery

gallbladder in the liver. Non-contiguous spread is governed by the mesentery reflections and ligaments and by lymphatic permeation. Mesentery reflections and ligaments facilitate spread of disease [14]. For example, pancreatitis can extend via the transverse mesocolon to produce local ileus (colon cut-off sign) of the transverse colon. Similarly, gastric or pancreatic cancer can invade the transverse colon via the gastrocolic ligament or transverse mesocolon. Biliary tumors can extend along the gastrohepatic and hepatoduodenal ligaments (Fig. 8), whereas pancreatic tumors can invade the liver via the reverse route. On the left, gastric or pancreatic cancer can extend to the splenic hilum via the gastro-

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Fig. 14 A loculated malignant ascites (a) in patient with primary endometrial carcinoma

Fig. 17 Mesenteric desmoplasia. Metastatic desmoplastic reaction in mesentery (black arrow) with fleck of calcification (white arrow) in patient with malignant carcinoid tumor of the distal small bowel

Fig. 15 Hematogenous spread. Hematogenous metastatic masses, one at visceral peritoneum surrounding bowel (large arrow) and the other in mesentery (small arrow) in patient with malignant melanoma

Fig. 18 Mesenteric neoplasm. Diffuse fibrous histiocytoma of the mesentery (m) infiltrating around the vessels and into the mesenteric folds. These tumors act as locally malignant but rarely metastasize distally

Fig. 16 Primary neoplasm. Liposarcoma of the lesser omentum (white arrows) with highly enhancing mass (black arrow) peripherally

splenic, splenorenal, and phrenicocolic ligaments. Lymphatic permeation is a common pathway of tumors spread (Fig. 7b and 9). Involvement may be continuous from regional to central nodes, or skip nodal groups along the way. Since lymphatic vessels follow the course of the arteries, the root of the mesentery and origin of celiac axis and superior mesenteric artery are common locations of metastatic lymphadenopathy [15]. An example would be sigmoid colon carcinoma extending via lymphatics to lymph nodes in the hepatic hilum. Intraperitoneal seeding is largely directed by the intraperitoneal circulation of peritoneal fluid. The negative pressure under the diaphragm along with increased capillary forces at the dome of the liver make metastatic

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Fig. 19 a Mesenteric neoplasm. Large spindle cell tumor of the mesentery located on the right side on one exam. b On the left on a CT scan done 1 week later. c A CT angiogram helped in surgical planning by identifying feeding mesenteric vessels that help estimate length of bowel to be resected

a

b

c

Table 1 Primary mesenteric tumors Origin

Benign

Malignant

Cystic Developmental

Chylous cyst Serous cyst Lymphatic Lymphangioma Trauma Traumatic cyst Embryonal rests Enteric cyst Dermoid cyst Solid Adipose tissue Lipoma Fibrous tissue Fibroma Nerve elements Neurilenoma Neurofibroma Smooth muscle Leiomyoma Fibromyoma Vascular Hemangioma Mesothelium

Lymphangiosarcoma Malignant teratoma Liposarcoma Fibrosarcoma Malignant schwannoma Leiomyosarcoma Fibromyosarcoma Hemangiopericytoma Malignant Mesothelioma

deposits on the liver surface common (Fig. 10). The oblique course of the small bowel mesentery and transverse course of the sigmoid mesocolon produce relative stasis of fluid. This contributes to the common encounter of peritoneal masses in the upper pelvis, at the level of the iliac crests. The oblique course of the mesentery, from superior left to inferior right, influences deposits in

the right lower quadrant (Fig. 11). Conversely, the transverse course of the sigmoid colon, from middle to left lateral, influences deposits in the left lower quadrant (Fig. 12) [11, 12]. The omentum, bathed in peritoneal fluid, is another common site of seeding (Fig. 4). The parietal peritoneum under the anterior abdominal wall is commonly involved, often at concave surfaces, possibly from pulling of fluid between the omentum and the wall due to capillary force (Fig. 10). Finally, the dependent position of the ovaries and cul-de-sac contribute to the frequent metastatic deposits in these regions by gastric and pancreatic carcinoma, commonly referred to as Krükkenberg tumors (Fig. 13). The amount of ascites varies, and formation of adhesions may restrain fluid from dependent locations such as the pelvis or the lesser sac (Fig. 14). Examples of hematogenous spread include peritoneal metastasis from breast carcinoma or malignant melanoma (Fig. 15). It is not understood why these particular tumors prefer seeding at the peritoneal lining.

Peritoneal tumors Strictly speaking, peritoneal tumors are of mesothelial origin. In practice, however, tumors arising in the sub-

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Fig. 20 Patterns of peritoneal involvement by primary and secondary tumors include masses nodules stranding (St), nodules (Nd), plaques (Pl), and masses (Ma). The mesentery may exhibit a stellate (SM) or pleated (PM) pattern

Fig. 22 MRI scan of patient with peritoneal mesothelioma showing slightly enhancing plaque (arrow) in anterior peritoneum. A second mass in falciform ligament is also present

Fig. 23 Nodular peritoneal deposits. Diffuse peritoneal studding with small nodules in patient with ovarian carcinoma. Such nodules produce significant challenge in all imaging modalities Fig. 21 Nodule imaging. Small metastatic nodule (arrow) seen by US within ascites. In the absence of ascites, these nodules are not visible

peritoneal space involving the mesentery and omentum are usually described under this heading as they indicate a diffuse, non-organ-specific involvement and distribution within the abdominal cavity. Like all tumors, they can be divided in cystic or solid, focal or diffuse. Benign tumors are usually seen in patients younger than 45 years, whereas malignant tumors are more common in patients older than 55 years [7]. The most common primary peritoneal tumor is mesothelioma. Other tumors involving the omentum are liposarcoma (Fig. 16) and hemangiopericytoma [16]. The most common benign tumors of the mesentery are malignant fibrous histiocytoma and spindle cell tumors. Metastatic perito-

neal tumors most often originate from carcinomas of the ovary, stomach, pancreas, and colon. Distant metastases from malignant melanoma, as well as breast and lung carcinoma, are also common.

Mesenteric tumors Two thirds of the mesenteric tumors involve the small bowel mesentery (Table 1) [7]. Symptoms appear late due to mobility and flexibility of the mesentery. Benign mesenteric tumors are more common than malignant. Mesenteric tumors are either fixed or mobile. The mobility of the tumors along with the increased peristalsis may account for occasional torsion of the mesentery. Desmoplastic reaction from carcinoid tumors of the

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Fig. 24 Peritoneal carcinomatosis. Fine peritoneal fibronodular stranding (arrow) in patient with recurrent ovarian carcinoma. Fine detail achieved with newer CT scanners help in making diagnosis sooner

Fig. 25 Peritoneal carcinomatosis. Diffuse involvement. A CT scan in patient with metastatic ovarian cancer with serosal nodules producing scalloping of the spleen and liver (black arrows) and deposits over the falciform ligament (white arrow). Plaque-like involvement of the anterio-lateral peritoneum on the left is noted

small bowel is a common occurrence (Fig. 17). They present as fixed solid masses with a ªstelateº pattern of linear strands [17, 18]. Cysts are common primary tumors of the mesentery [19]. Benign solid tumors are more common than malignant [7, 19]. Diffused fibrous histiocytoma may be potentially locally malignant (Fig. 18) [20]. Benign spindle cell tumors can be mobile and may exert pressure on the small bowel (Fig. 19). CT angiography can be helpful for surgical planning, by localizing feeding vessels and estimating portion of small bowel needed to be resected. Lymphoma usually extends from the retroperitoneum into the mesentery or, less commonly, can be primary arising in the mesentery

Fig. 26 Peritoneal carcinomatosis. Masses. Large peritoneal metastatic masses (M) in a patient with peritoneal mesothelioma. Distinction from metastatic disease is very difficult

(Fig. 6) [21]. Malignant tumors include mesothelioma and mesenchymal tumors arising in the subperitoneum [7, 22]. Secondary tumors are from seeding or distal hematogenous metastasis. Omental tumors are also cystic (omental cysts) of solid [23, 24]. Of the solid tumors, the most common is metastasis (colon, stomach, pancreas, and ovaries) producing omental cake (Fig. 4). Primary solid omental tumors are exceedingly rare [23, 24]; half are benign and half are malignant. Benign tumors include lipoma, leiomyoma, fibroma, and neurofibroma. Malignant omental tumors include leiomyosarcoma and hemangiopericytoma [16]. These tumors tend to spread by direct invasion. They are most frequently noted in the fifth decade.

Role of imaging The role of imaging is to establish the diagnosis and assist with the management of the disease. Helpful hints for the diagnosis are of course the history of previous malignancy. Imaging can identify the primary tumors and can assess the location of the metastatic process (e.g., mesentery and omentum). In addition, the various patterns of peritoneal involvement may be helpful in establishing the diagnosis (Fig. 20). As far as management is concerned, imaging can help in staging of the primary tumors or help in establishing surgical planning. It can also assist in monitoring of treatment. Finally, imaging provides guidance for interventional radiology in performing diagnostic biopsy or therapeutic draining peritoneal fluid collections, to relieve symptoms or treat postoperative complications such as abscess.

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Fig. 27 Mesenteric thickening. A CT scan of a patient with metastatic ovarian carcinoma showing a pleated mesentery pattern (arrows) in patient post omentectomy (white clip in anterior abdomen, middle). Note plastering of bowel loops on anterior abdominal wall

Fig. 29 Extra-abdominal findings. Calcified pleural plaques in patient with peritoneal mesothelioma and diffuse peritoneal thickening

however, by the difficulty in early nodule detection in thin patients without ascites (Fig. 23). This may be the case in many patients with early malignant seeding. In the presence of a reasonable amount of peritoneal fat, however, fine stranding or small nodules can be seen much earlier with the use of spiral thin-collimation scanning (Figs. 6, 24). Fat stranding, although nonspecific, is an important early sign of carcinomatosis and, when present, it should be considered very seriously. CT technique Fig. 28 Mesenteric thickening. Ultrasound showing thick omentum (curved arrow) and pleated mesentery (straight arrows) in patient with peritoneal mesothelioma

Imaging modalities Of the imaging modalities, plain films and fluoroscopy have limited value. Ultrasound is excellent in identifying small peritoneal seeding in the presence of ascites (Fig. 21) [25]. In this respect, MRI appears to be helpful in identifying small peritoneal nodules [26]. These nodules may appear with increase in signal intensity following gadolinium (Fig. 22) [27]; however, MRI is not widely used in peritoneal carcinomatosis. Computed tomography is by far the most popular imaging modality [23, 28]. It provides direct visualization of the primary and secondary tumors. It is a global test, providing information about the tumors as well as its effect on other organs, such as bowel or urinary obstruction. It is a relatively simple exam both for the operator and for the patient and relatively easily interpretable. It is limited,

Incremental or helical cross-sectional CT scanning can be used depending on resources. The use of spiral or multidetector scanners is considerably more comfortable for the patients, while providing thin-collimation images within one or two breath-holds. Oral contrast is extremely useful to differential small- or medium-size nodules or masses from non-opacified bowel. To this purpose, 600±1,200 cc is advisable, as tolerated. However, some patients may not be able to drink contrast, because of bloating or bowel obstruction. High-attenuation oral contrast (barium or iodine base) is preferred to water or negative-attenuation (milk, oil emulsions) contrast media. Intravenous contrast material is also very helpful. Some small nodules may enhance vividly making the diagnosis considerably easier. Scanning at 60-s delay and at excretory renal phase (180 s) is advised to evaluate the peritoneum and the retroperitoneum as well as the renal function. We use thin collimation (2.5±5 mm) and we believe that this improves the ability to detect fine stranding in the fat, which is an early sign of carcinomatosis. Image processing with CT angiography and multiplanar reconstructions has a limited value

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in diffuse disease. They may be useful in surgical planning of focal masses. CT patterns Diffuse peritoneal tumors, including malignant mesothelioma and carcinomatosis, present with numerous CT tumors patterns, which usually represent a continuum of disease spread and tumor burden. These patterns include nodules, fat stranding, plaques, or sheets of soft tissue which progress to omental cake, mesentery thickening, or large discrete masses (Fig. 20). Various amounts of ascites and degrees of lymphadenopathy may be observed. Implantation of small nodules on the peritoneal surfaces result in smooth or nodular thickening and contrast enhancement of the peritoneum (Figs. 24, 25, 26) [29]. On the liver surface, subcapsular deposits indent the parenchyma, described as ªscallopingº (Figs. 10, 25). The presence of calcification, before treatment is instituted, suggests mucin-producing primary tumor such as papillary cystadenocarcinoma of the ovary [30]. Seeding of the mesentery may thicken it and replace its fat with tumorous soft tissue, producing a pleated pattern (Figs. 27, 28) [31, 32]. The patterns of spread of malignancy in the peritoneum can be categorized into three major mechanisms. Direct invasion either contiguous from the tumors or via the peritoneal ligaments. Intraperitoneal seeding which is facilitated by the peritoneal circulation of fluid. These are commonly originate from the ovary, the stomach, and the pancreas. Hematogenous metastases are common from malignant melanoma as well as breast and lung carcinoma.

Malignant mesothelioma comprises 10±20 % of mesothelial tumors. It is associated with prolonged asbestos exposure and is usually, but not always, associated with asbestos-related pleural disease (Fig. 29) [31, 33]. It usually spreads in sheets, and it produces diffused thickening. There is usually small amount of ascites present. It may be difficult to establish a diagnosis with percutaneous biopsy because the tumors are usually pleomorphic. It is advisable to take numerous biopsies from numerous locations [34]. Peritoneal carcinomatosis is malignant seeding of the peritoneum. It most commonly arises from the ovary, the colon, stomach, and pancreas [1, 7, 28]. There is usually ample ascites, often loculated. It manifests as nodules, thickening, or masses. There is involvement of solid organs with metastatic disease as well as lymphadenopathy. Implants on the liver and splenic surfaces are frequently seen. Calcifications are commonly seen on metastases from mucin-producing primary tumors such as colon adenocarcinoma. There is usually enhancement of the tumors seen by CT and MRI. Implantation of the bowel wall is seen and bowel obstruction may be noted. Pseudomyxoma peritonei is rare, usually complication of ruptured appendiceal or ovarian adenocarcinoma. Diffuse peritoneal fluid distributions with separations, scattered nodules, and scalloping of liver and spleen may be seen [35]. The slugging of mucous contents can be seen on US which distinguishes it from simple ascites [31]. In conclusion, peritoneal tumors are rare. Metastatic disease is more common than primary disease. Diffuse disease has poor prognosis. Imaging plays an important role in diagnosis and management.

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