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Original Report |
1 Department of Radiology, The Children's Hospital of Philadelphia, 34th and
Civic Center Blvd., Philadelphia, PA 19104.
2 Division of Oncology, The Children's Hospital of Philadelphia, University of
Pennsylvania School of Medicine, Philadelphia, PA.
3 Department of Pathology, The Children's Hospital of Philadelphia, University
of Pennsylvania School of Medicine, Philadelphia, PA.
Received February 13, 2004;
accepted after revision September 15, 2004.
Address correspondence to R. Bellah.
Abstract
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CONCLUSION. Characteristic CT features of DSRCT include bulky intraabdominal soft-tissue masses that involve omental and serosal surfaces, without a distinct organ of origin; solid, dominant, heterogeneous pelvic masses in the retrovesical or rectouterine spaces; and concurrent metastases, common at the time of diagnosis, particularly those involving lymph nodes and liver.
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Abdominopelvic CT findings and follow-up are summarized in Table 1. All patients had multiple omental, serosal, or mesenteric masses (Figs. 1A, 1B, and 1C). Nine patients (81.8%) had dominant masses in the retrovesical or rectouterine spaces, with dimensions that varied from 6 to 25 cm (mean, 14.3 cm) (Figs. 1A, 1B, and 1C). Isolated dominant masses in the upper and mid abdomen were seen in only two patients (18.2%) (Figs. 2A, 2B, and 2C). Ten patients (91%) presented with masses larger than 10 cm. All dominant tumors displayed heterogeneous enhancement after IV contrast administration. Scattered amorphous or punctuate tumor calcification was seen in six patients (54.5%) (Fig. 2A). Six patients (54.5%) had associated lymphadenopathy, either in the retroperitoneum or in the mesentery. Small amounts of ascites were present in seven patients (63.6%). Liver metastases were found in six patients (54.5%). These metastases appeared as hypoattenuating nodules with variable sizes (ranging from 0.8 to 12.7 cm) and number (solitary to multiple). Pelvic tumor involvement caused partial urinary tract obstruction in five patients (45.5%) and variable bowel dilatation due to partial bowel obstruction in two patients (18.2%).
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Among eight patients who underwent chest CT at the time of initial presentation, four (50%) showed lymph node enlargement measuring 1.0-4.0 cm in the shortest axis. The lymph node groups most commonly involved were the internal mammary and paracardiac lymph nodes, seen in three patients (37.5%). Mediastinal nodal groups that were less commonly involved included right paratracheal, subcarinal, prevascular (two patients), aortopulmonary window, left paratracheal, right hilar, and retrocrural (one patient). Pleural effusion was seen in two patients (25%). Pericardial effusion and thickening were seen in one patient. Eight of 11 patients died from the disease. Three patients are alive; one is in treatment without a favorable response, one is in treatment for relapsed disease (32 months after diagnosis), and one is free of disease (9 years after diagnosis). Abdominopelvic or chest CT findings had no significant correlation with the outcome of patients.
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Gerald and Rosai [9] first described DSRCT in 1989. In 1991, Gerald et al. [7] proposed DSCRT as a distinct entity when specific histologic, immunohistochemical, and karyotypic features of the tumor were realized. Before that time, DSCRT might have been classified as an atypical variety of small round cell tumors or as an unusual form of malignant mesothelioma, adenocarcinoma, carcinoid tumor, or germ cell tumor. The most striking histologic feature of DSCRT is the desmoplastic stroma that envelops the tumor cells. This stroma is generally densely collagenous or fibromyxoid and encases well-defined nests of primitive undifferentiated cells (Fig. 2C). Focal areas of nonenhancement or low attenuation noted on contrast-enhanced abdominopelvic CT possibly represent fibrous components of these tumors, in addition to necrosis. These tumors are strikingly polyphenotypic when analyzed with immunohistochemistry. They often display reactivity for mesenchymal, epithelial, and neural markers, a feature that is useful in distinguishing them from PNETs, lymphomas, rhabdomyosarcoma, and other pediatric tumors with a small round blue cell appearance. From the standpoint of karyotype, DSRCT shows a characteristic balanced translocation involving chromosomes 11 and 22, similar to PNET and Ewing's sarcomas. In the case of DSRCT, the translocation creates a unique fusion chimeric transcript involving the WT1 (Wilms' tumor) and EWS (Ewing's sarcoma) genes.
The histopathogenesis of DSRCT remains unknown. Because most DSRCT arise in the peritoneal cavity without a primary visceral site of origin, most investigators believe that the tumor originates from the mesothelium (or from submesothelial or subserosal mesenchyme), which is most extensive in the peritoneum [7]. DSCRT has also been described at other sites, including the paratesticular region, pleural region, lung, ovary, sinus cavity, central nervous system, and stomach. All patients in our series presented with masses in the peritoneal cavity.
Most patients with DSRCT come to clinical attention because of vague gastrointestinal or genitourinary discomfort secondary to extrinsic compression by the tumor. Because patients often initially present with abdominal pain or large, palpable abdominal masses, CT is most often used for initial diagnosis. Because, at the time of initial diagnosis, disseminated tumor with multiple abdominopelvic masses and metastases (liver or lymph node) often exists, CT is also most often used for staging and follow-up. Similar to others [1-3, 5, 6], we found the most common abdominopelvic findings to be multiple, low-attenuation soft-tissue masses in the omentum or mesentery or along abdominopelvic peritoneal surfaces, without a distinct organ of origin. Tumor calcification, liver metastases, abdominal lymphadenopathy, ascites, urinary tract obstruction, and bowel obstruction also have been documented in previous studies [1-3, 5, 6]. A striking feature of our study, not emphasized in previous reports, was the presence of a dominant mass in the retrovesical or rectouterine space (seen in 82% of our patients). We speculate that the dynamics of the natural flow of peritoneal fluid, and the dependent location of the pouch of Douglas, account for the prevalence of malignant implants in this location. It is also not surprising that tumor deposits were frequently noted in other known sites of peritoneal fluid pooling, such as the paracolic, perihepatic, and infracolic spaces.
We noted a correlation between the presence of a retrovesical mass, lymphadenopathy, and ascites. All patients who had ascites and lymphadenopathy also had masses in the retrovesical or rectouterine spaces; two patients with no ascites and lymphadenopathy had no masses in the retrovesical spaces. Liver metastases also correlated strongly with the presence of a retrovesical mass. In five (83.4%) of six patients with liver metastases, dominant retrovesical masses were present. Although one could speculate that the presence of a retrovesical mass might indicate an advanced stage of disease, we could not find any correlation between a retrovesical mass and survival rate (Table 1).
Previous descriptions of initial chest CT findings in DSRCT at the time of diagnosis are limited [4]. Most chest CT findings have been described on follow-up studies [7, 8]. Unlike reports by Tateishi et al. [4], pleural dissemination was a relatively uncommon finding (25%) in our series. Four (50%) of the eight patients displayed chest lymph node involvement, usually internal mammary or paracardiac. Paracardiac lymph node involvement has also been known to occur from dissemination of other abdominal tumors, such as colon and ovary carcinomas. Contrary to previous reports, no pulmonary parenchymal nodules were seen in our patients. Hematogenic dissemination in DSRCT thus seems to occur less often within the chest than within the abdomen. Lack of pathologic confirmation of findings on chest CT limits the study; however, recognizing the aggressiveness of the abdominopelvic tumor, we presume that those findings in the chest likely represent metastatic disease. Metastases to bones, adrenal glands, kidneys, and spleen did not occur.
The differential diagnosis for DSRCT includes tumors, often malignant, that produce bulky mesenteric masses, such as rhabdomyosarcoma, lymphoma, neuroblastoma, PNET, mesothelioma, peritoneal leiomyosarcomatosis, and intraabdominal desmoid tumor. A diagnosis of DSRCT usually can be favored by a combination of factors, including adolescent age at presentation; frequent tumor calcification; extensive peritoneal involvement at the time of diagnosis; absence of an organ of origin; and, from our experience, a proclivity to involve the retrovesical region. Rhabdomyosarcoma usually affects younger children (70% are younger than 10 years old), and although intraperitoneal involvement can be seen (in approximately 10%), mesenteric nodules and intraperitoneal masses are typically smaller than those seen in DSRCT; tumor calcification is uncommon [10]. Burkitt's lymphoma, unlike DSRCT, shows a predilection to the ileocecal region; omental or serosal nodules and calcification are not common features [11]. Neuroblastoma can present as a pelvic mass but typically affects younger children (mean age at time of diagnosis is 22 months, with 79% of diagnoses occurring before the age of 4 years). PNET can appear like DSRCT if it arises in the pelvis, retroperitoneum, or abdomen. Like DSCRT, PNET is an aggressive tumor with a predilection for adolescents and young adults. The imaging findings of PNET are similar to those of DSRCT, although fine tumor calcification is rarely seen. Malignant mesothelioma rarely occurs during the first two decades of life, and only approximately 15% of cases originate in the peritoneum [12]. Peritoneal leiomyosarcomatosis tends to occur in patients older than 24 years, with multiple well-defined peritoneal nodules or mesenteric masses. Because a known primary gastrointestinal leiomyosarcoma is not always apparent, differentiation from DSRCT might be difficult. Intraabdominal desmoid tumors are a rare, benign proliferation of musculoaponeurotic fibrous tissue that can present in isolation or in association with Gardner's syndrome. The usual presentation is isolated or multiple masses with attenuation less than or similar to that of muscle tissue in the mesentery, abdominal wall, retroperitoneum, and pelvis. The absence of metastases and association with Gardner's syndrome should assist in this differential diagnosis.
Despite aggressive treatment, including surgical debulking, radiation therapy, and multiagent chemotherapy, the prognosis in DSRCT is poor. The mean survival is 17 months [7]. In our series, eight patients died between 12 and 48 months after the initial diagnosis (mean survival, 23 months).
In conclusion, DSRCT is a rare tumor, most commonly presenting in adolescence, with significant radiologic features that can allow the radiologist to suggest the diagnosis and differentiate it from other intraperitoneal tumors. In particular, the presence of a dominant, heterogeneous solid mass in the retrovesical space, along with omental, mesenteric, or peritoneal surface masses, is a striking characteristic feature of DSRCT. Unfortunately, most patients come to clinical attention when the disease is at an advanced stage and has disseminated, especially to the liver and to the retroperitoneal and mediastinal lymph nodes.
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