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Peritoneal Malignancy in Children: A Pictorial ReviewPeritoneal Malignancy in Children: A Pictorial ReviewConor O. Bogue1, Amanda Murphy2, Oscar M. Navarro1

Department of Diagnostic Imaging1 and Division of Pathology, Pediatric Laboratory Medicine2, The Hospital for Sick Children and University of Toronto, Toronto, Ontario, Canada

IntroductionPeritoneal malignancy is significantly less common in children than in adults, commensurate with the infrequency of neoplasms such as gastrointestinal, ovarian and uterine tumors, that are associated with carcinomatosis in the adult population. When it does occur, it is most commonly metastatic, usually after the neoplasm breaks through the organ capsule or through peritoneal spill at the time of surgery. Primary neoplasms of the peritoneum, such as mesothelioma, are exceptionally rare.

The findings on imaging may include ascites, mesenteric or peritoneal nodules (<3cm) or masses (>3cm), calcification, bowel wall thickening and omental caking (thickening >2mm). A pseudomyxoma-like appearance with scalloping of the solid organs has been described in rhabdomyosarcoma, Wilms and Burkitt lymphoma.

The spread of intraperitoneal malignant cells follows the natural circulation of peritoneal fluid. This is influenced by gravity, negative subdiaphragmatic pressures and the anatomical features of the peritoneum. These mechanisms account for the most common location of tumor seeding being in the pouch of Douglas (>50%). A dominant pelvic mass has been reported in up to 82% of cases of desmoplastic small round cell tumor. Other commonly involved locations are the small bowel mesentery (40%), the sigmoid mesocolon (20%) and the right paracolic gutter (20%).

The purpose of this exhibit is to review those pathologies that may present with peritoneal involvement in children and to illustrate the imaging findings of such entities with different imaging modalities, including ultrasonography, computed tomography and magnetic resonance imaging.

SummaryThe differential diagnosis for peritoneal malignancy in children is broad. Rhabdomyosarcoma, Burkitt lymphoma, Wilms tumor and immature teratoma were the commonest etiologies of peritoneal neoplastic infiltration in our experience. Primary malignancy of the peritoneum is rare in children. The involvement can be demonstrated by ultrasound, CT and MR imaging.

References1. Chung CJ, Bui V, Fordham LA, Hill J, Bulas D. Malignant intraperitoneal neoplasms of childhood. Pediatr Radiol 1998;28:317-321.

2. Hamrick-Turner JE, Chiechi MV, Abbitt PL, Ros PR. Neoplastic and inflammatory processes of the peritoneum, omentum and mesentery RadioGraphics 1992;12:1051-1068.

3. Chung CJ, Fordham L, Little S, Rayder S, Nimkin K, Kleinman PK, Watson C. Intraperitoneal rhabdomyosarcoma in children: incidence and imaging characteristics on CT. AJR 1998;170:1385-1387.

4. Kamona AA, El-Khatib MA, Swaidan MY, Jarar MS, Suleiman AJ, Ali HM, Basharaheel AB, Mansour AH. Pediatric Burkitt’s lymphoma: CT findings. Abdom Imaging. 2007;32:381-386.

5. Slasky BS, Bar-Ziv J, Freeman AI, Peylan-Ramu N. CT appearances of involvement of the peritoneum, mesentery and omentum in Wilms’ tumor. Pediatr Radiol 1997;27:14–17.

RhabdomyosarcomaRhabdomyosarcoma is a soft tissue malignancy of childhood that is thought to arise from primitive mesenchymal cells. It accounts for 5-15% of all solid malignancies in children. At diagnosis, 70% of children are younger than 10 years old. It may present as a focal mass or, rarely, with fever, generalized malaise and bone pain if there is diffuse metastatic disease. Rhabdomyosarcoma may arise from, and metastasize to, nearly all body organs. However, the head and neck (40%) and the genitourinary region (20%) are the commonest primary sites. Diffuse metastatic spread is more often seen with primary tumors in the extremities and with alveolar histology. It may be present in up to 7% of cases at diagnosis or 11% over the course of the disease. Ascites has been reported to be present in most but not all cases with peritoneal spread. Other imaging findings reported include enhancing nodules, masses, omental caking and a pseudomyxoma peritonei-like appearance.

Figure 1. Recurrent rhabdomyosarcoma two years after resection of a bladder primary lesion in a 9 year old male. (a) Axial contrast-enhanced CT image demonstrates omental caking (arrows), ascites (asterisk) and irregular peritoneal thickening (arrowhead). After treatment with chemotherapy the disease relapsed a year later. (b) demonstrates ascites and peritoneal thickening (arrowheads), an omental nodule (arrow) and bilateral hydronephrosis. (c) & (d) The ureteric obstruction is caused by a large ovoid mass extending superiorly from the pelvis (arrowheads)

Burkitt Lymphoma American Burkitt lymphoma is a rapidly growing malignancy of B-lymphocyte origin that occurs in non-endemic form in North America. Sporadic Burkitt lymphoma accounts for 30 to 50% of pediatric lymphomas. In contrast to endemic or African Burkitt lymphoma, the sporadic form is rarely associated with Epstein-Barr virus. Children presenting with sporadic Burkitt lymphoma are often boys between the ages of 5 and 10 years. American Burkitt Lymphoma usually produces bulky extranodal tumors in the abdomen and differs clinically and radiologically from African Burkitt lymphoma, which most often affects the head and neck. The common presenting symptoms include abdominal pain, nausea, vomiting, abdominal distention, gastrointestinal bleeding, weight loss, right lower quadrant mass, and, uncommonly, bowel perforation. Intraabdominal disease can be bulky and enlarge rapidly and has been reported to cause abdominal compartment syndrome. Peritoneal infiltration has been described in up to 24.2% of patients and ascites in 39.3%. When Burkitt lymphoma is the cause of diffuse peritoneal disease, it usually is accompanied by focal gastrointestinal masses and/or significant lymphadenopathy.

Figure 6. 15 year old male with Burkitt lymphoma. (a) Axial CT at diagnosis demonstrates ascites, peritoneal thickening (yellow arrows) and omental infiltration (black arrows). (b) A lower axial CT image demonstrates peritoneal enhancement (arrowheads), omental caking (arrow) and small bowel wall thickening (black arrows). (c) Axial CT at the level of the mesentery demonstrates peritoneal enhancement (black arrows), omental thickening (yellow arrow) and mesenteric lymphadenopathy (arrowheads). (d) Axial CT image through the pelvis demonstrates marked thickening of a small bowel loop (yellow arrows), ascites and peritoneal thickening (black arrows).

Wilms TumorWilms tumor, or nephroblastoma, arises from the metanephros, the mesodermal precursor of the renal parenchyma. Occasionally, it is found to arise in the extrarenal retroperitoneum, presumably within mesonephric remnants. Wilms tumor accounts for 87% of pediatric renal masses and occurs in approximately 1:10,000 children. It accounts for 7% of all childhood cancers. The peak incidence is at 3-4 years with 80% of patients under five years of age. A palpable mass is the commonest presentation; hematuria and pain are less frequent. Arterial hypertension may be present in up to 25%. Metastases are most commonly found in the lungs (85% of cases), liver, and regional lymph nodes. Peritoneal invasion can occur if the tumor breaks through the capsule prior to surgery and/or during surgical manipulation of the tumor. Tumor invasion of the peritoneal cavity results in plaque-like thickening or nodular implants in the omentum (subdiaphragmatic area) or mesentery. The pelvis is a common location of dropped metastases.

Figure 7. Metastatic Wilms tumor in a 5 year old female. (a) Axial CT demonstrates a very large mixed solid-cystic Wilms tumor arising from the right kidney. (b) Axial CT image two years later demonstrates an anterior peritoneal soft tissue mass (white arrows) and fluid attenuation metastatic disease producing a pseudomyxoma-like appearance with scalloping of the liver margins (yellow arrows) and (c) demonstrates a mesenteric soft tissue mass (asterisk), peritoneal masses (arrowheads) and ascites.

Immature Teratoma / Germ Cell Tumor Teratomas are germ cell tumors that are composed of elements from one or more of the embryonic germ layers and contain tissues usually foreign to the anatomic site of origin. Immature teratoma is characterized by containing immature neural tissue and having a greater propensity for recurrence. Except for mature cystic teratoma of the ovary, germ cell tumors are relatively rare. In adults, germ cell tumors account for approximately 30% of primary ovarian tumors. Over 95% of these are mature cystic teratomas. However, in patients younger than 21 years old, about 60% of ovarian tumors are germ cell tumors and one-third of those are malignant. The most common initial presentation is abdominal distention, which is produced by the tumor itself, and ascites. Complications such as rupture or torsion can also occur The testes and ovaries are the most common sites of origin of germ cell tumors but they may also occur at extragonadal sites, such as the anterior mediastinum, the central nervous system and the sacrococcygeal region. Differentiating mature from immature teratoma based on imaging can be difficult, as mature teratomas can have solid elements (called Rokitansky protuberances) and immature teratomas without solid elements have occasionally been seen. Ovarian germ cell tumors are well known to be associated with ascites and intraperitoneal spread.

Figure 8. 13 year old female with peritoneal recurrence of resected ovarian immature teratoma. (a) Axial CT of abdomen demonstrates peritoneal thickening (black arrows), peritoneal masses (yellow arrow) and ascites. (b) A lower CT image demonstrates ascites, irregular peritoneal thickening (yellow arrows) and omental caking (black arrows). (c) CT image of lower abdomen demonstrates ascites with metastatic disease on the parietal (black arrows) and visceral (yellow arrows) peritoneal surfaces.

Desmoplastic Small Round Cell TumorDesmoplastic small round cell tumor has recently been described as a distinctive member of the small round blue cell group of tumors. It is a highly aggressive neoplasm with a mean survival of 2-3 years. It is rare, occurring primarily in adolescents and young adults, and with a male predominance. The clinical presentation may include abdominal distension, a palpable abdominal mass, urinary disorders, fever, weight loss, adenopathy or hepatosplenomegaly. The most common site of origin of the tumor is the peritoneum, followed by the tunica vaginalis of the testis. Peritoneal dissemination is the commonest pattern of metastatic spread. Direct organ invasion, adenopathy and liver metastases may also be seen. The typical radiological appearance is of a dominant abdominal or pelvic mass with peritoneal seeding. Calcification may be seen and contrast enhancement is weak.

Figure 9. Imaging at presentation in a 10 year old male with desmoplastic small round cell tumor. (a) Axial CT image demonstrates a subdiaphragmatic peritoneal mass (arrow) with central calcification. (b) Axial CT image demonstrates a dominant pelvic soft tissue mass (arrow), also with central calcification (arrowhead). (c) Axial CT image six months later demonstrates a peritoneal soft tissue deposit indenting the right lobe of the liver (yellow arrow) and mesenteric lymphadenopathy (black arrows).

Duodenal AdenocarcinomaPrimary duodenal adenocarcinoma is a rare tumor, representing <1% of all gastrointestinal tumors and 25-35% of malignant tumors of the small intestine. The overall 5-year survival is 23-62% but has been reported to be as high as 75% if fully resected. The median age of diagnosis is in the sixth decade of life. In children, intestinal cancers are particularly rare and have been observed to be associated with functional deficiencies of the mismatch repair system causing a cancer-predisposition syndrome such as Lynch syndrome or hereditary non-polyposis colorectal cancer. The clinical presentation may be non-specific and may mimic benign conditions. The most frequent symptoms found are jaundice (11-56%), nausea/vomiting (21-52%), pain (11-59%), weight loss (10-58%) and anemia (23-61%). The most frequent location of duodenal adenocarcinoma is the second portion of the duodenum. Common patterns of spread are pancreatic invasion (22-82%) and lymphadenopathy (26-76%). Little has been written about peritoneal metastatic disease from duodenal adenocarcinoma. The imaging patterns in peritoneal carcinomatosis include fibronodular stranding, nodules, plaques and masses. Mesenteric thickening may produce pleated or stellate patterns on CT.

Figure 10. An 11 year old male with metastatic duodenal adenocarcinoma at presentation. (a) Axial contrast-enhanced fat-suppressed T1-weighted image of the abdomen demonstrates a large mass arising from the distal third part of duodenum (yellow arrows). Note also the liver metastasis (black arrow). (b) Axial CT image through the pelvis in the same patient demonstrates a drop metastasis in the rectovesical space (arrow). (c) Sagittal contrast- enhanced fat-suppressed T1-weighted image of the pelvis demonstrates mild heterogeneous enhancement of the drop metastasis in the rectovesical space. (d) Axial CT image seven months later demonstrates ascites, peritoneal enhancement (white arrow), a peritoneal nodule (yellow arrow) and liver metastastes (arrowheads).

MesotheliomaMesothelioma is a primary malignant tumor of the pleural, peritoneal and pericardial surfaces and of the tunica vaginalis. It is usually diagnosed in the fifth to seventh decades of life and is rare in childhood. In contrast to adult cases, there is no evidence of a causal relationship between mesothelioma in children and asbestos, radiation or isoniazid.

Peritoneal mesothelioma has been reported to occur in children of any age and as young as six weeks. A peritoneal origin is more common in girls, while a pleural origin is more common in boys. Median survival time for adults with peritoneal mesothelioma has historically been less than 12 months, though survivals of 50-60 months have been recently achieved with aggressive multimodality therapy. Long term survival with this regimen has recently been reported in children. Imaging features include thickened peritoneum, nodules, omental masses, ascites and involvement of the mesentery.

Figure 11. 17 year old male with peritoneal mesothelioma. (a) Sagittal ultrasound image of pelvis at presentation demonstrates ascites, nodular peritoneal thickening (white arrows) and a thin walled peritoneal cyst (yellow arrows). (b) Axial and (c) reformatted coronal CT images of the pelvis demonstrates ascites (asterisk), peritoneal thickening and enhancement (arrows). (d) CT of abdomen six months later demonstrates omental infiltration (yellow arrows) and nodular peritoneal thickening (black arrow).

Other Tumors Other extraperitoneal neoplasms reported to metastasize to the peritoneum in children include neuroblastoma and intracranial neoplasms. However, neuroblastoma is associated with ascites less commonly than Wilms tumor, and direct intraperitoneal seeding is rare. The list of intracranial neoplasms reported to have metastasized to the peritoneum via ventriculoperitoneal shunts includes glioblastoma multiforme, gliomas, pinealoblastoma, pineal dysgerminoma, primitive neuroectodermal tumor and medulloblastomas.

Figure 2. Diffuse intraperitoneal rhabdomyosarcoma at presentation in a 3 year old female. (a) Axial CT of the abdomen demonstrates marked omental caking (arrows) and a large volume of ascites (asterisk). (b) Transverse ultrasound image of the left abdomen demonstrates hypoechoic omental caking (arrow), separated from the underlying small bowel (arrowheads) by anechoic ascites (asterisk). (c) Axial CT of the pelvis demonstrates ascites and multiple pelvic peritoneal soft tissue masses (arrowheads). (d) Coronal inversion recovery MR image demonstrates ascites (arrow) and extensive heterogeneous intermediate signal intensity omental caking (arrowheads).

Figure 3. 5 year old female with metastatic bladder rhabdomyosarcoma. A longitudinal ultrasound image of the left side of the abdomen demonstrates ascites, omental caking superiorly (arrow) and a large pelvic mass inferiorly (asterisk).

Figure 4. Axial CT image in a 12 year old boy with end stage metastatic disease from a primary pelvic rhabdomyosarcoma. The abdomen is distended and the peritoneal cavity filled with heterogeneous soft-tissue attenuation metastatic disease, which is compressing the small bowel in the central abdomen.

Figure 5. 13 year old female with peritoneal metastatic disease from a right hand rhabdomyosarcoma. (a) Axial gadolinium-enhanced fat-suppressed T1-weighted image of the hand demonstrates that the primary lesion fills the interosseous space between the third and fourth metacarpals and involves the fourth metacarpal. (b) CT of abdomen at diagnosis demonstrates mild soft tissue thickening of the greater omentum (yellow arrows). Note also the nodules in the paracolic gutters (black arrows).

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This rare neoplasm usually arises in the leaves of the broad ligament or in the fallopian tube. Clinical presentation may include a palpable mass and lower abdominal pain. These tumors can arise anywhere along the trajectory of the wolffian duct, which extends from the hilum of the ovary, along the mesosalpinx and the lateral aspects of the uterus, to the outer third of the vagina. Female adnexal tumors of probable wolffian origin are a distinctive epithelial neoplasm arising from the remnants of the mesonephric duct. Although generally considered a tumor of low malignant potential, these tumors can recur. In a review of the literature, recurrence was documented in 8/71 cases. The sites of recurrence were abdomen, pelvis, liver and lungs.

Figure 13. 17 year old female with a paravaginal wolffian tumor. (a) CT of the pelvis demonstrates a mildly hypodense presacral mass (arrows). (b) Axial fat-suppressed T2-weighted MR image of pelvis nine months later demonstrates two small, round, heterogeneously hyperintense lesions (arrows) in the right hemipelvis. (c) Axial fat-suppressed T2-weighted MR image of the lower abdomen demonstrates a large, round, heterogeneously hyperintense peritoneal mass (arrows). (d) Axial gadolinium-enhanced fat-suppressed T1-weighted image demonstrates only peripheral enhancement of peritoneal mass suggesting that lesion is cystic or necrotic.

Paravaginal Wolffian Tumor

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Dendritic Cell Sarcoma of Pancreas Follicular dendritic cells, interdigitating dendritic cells and Langerhans cells are nonlymphoid, nonphagocytic accessory cells of the lymphoid system. Malignant neoplasms showing dendritic cell differentiation are uncommon. Most reported cases involve lymph nodes. Approximately 30% of cases are located in extranodal sites. These neoplasms usually occur in young or middle aged adults and there is no sex predilection. The clinical presentation is usually that of a solitary mass. Intraperitoneal tumors have resulted in abdominal pain and weight loss. Local recurrence occurs in 36% and distant metastases in 28%. The most common sites of metastases are lung, liver, peritoneum and lymph nodes. Adverse clinical outcome correlates positively with intra-abdominal location, large tumor size (> 6 cm), high mitotic count, coagulative necrosis and cellular atypia.

Figure 12. 16 year old male with pancreatic dendritic cell sarcoma. (a) Axial contrast-enhanced fat-suppressed T1-weighted image of the abdomen demonstrates a large, poorly-enhancing mass (arrows) in the head of the pancreas. (b) CT of abdomen three years later demonstrates a subdiaphragmatic peritoneal deposit (yellow arrows) and a splenic metastasis (black arrow). (c) CT image of the pelvis from the same study demonstrates a hypodense, multilobulated pelvic peritoneal metastatic lesion (arrows).

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