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Gastrointestinal Imaging |
1 Mallinckrodt Institute of Radiology (P.J.P., A.J.F., D.M.B.)
2 Lauren V. Ackerman Laboratory of Surgical Pathology (L.P.D., P.C.H.), Washington University School of Medicine, 510 S Kingshighway Blvd, St Louis, MO 63110.
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Abstract |
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 TOP Abstract IntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: Eleven of 14 patients with desmoplastic small round cell tumor had primary abdominal involvement. In nine of these patients (mean age, 20 years), results of imaging studies (computed tomography in nine patients, ultrasonography [US] in three) and histopathologic specimens were retrospectively analyzed.
RESULTS: The hallmark imaging feature was lobulated peritoneal masses (mean number, 4.4; range, 1–17) with a mean diameter of 5.0 cm (range, 2–12 cm). Omental and paravesical tumors were each present in six patients. Retroperitoneal masses were present in three patients. The tumors were well defined and hypoechoic at US. Heterogeneity due to tumor hemorrhage or necrosis was seen in seven patients. Ascites was present in five patients. Parenchymal and/or serosal hepatic metastases, punctate calcifications, nodular peritoneal thickening, lymphadenopathy, hydronephrosis, and bowel obstruction were less common associated findings.
CONCLUSION: Bulky peritoneal soft-tissue masses without an apparent organ-based primary site are characteristic of intraabdominal desmoplastic small round cell tumor. Although the findings are nonspecific, this diagnosis can be considered in adolescents and young adults with characteristic imaging findings.
Index terms: Abdomen, neoplasms, 791.329 • Omentum, neoplasms, 792.329 • Peritoneum, neoplasms, 791.329 • Retroperitoneal space, neoplasms, 87.329 • Soft tissues, neoplasms, 791.329
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The purpose of our study was to further characterize the imaging features of desmoplastic small round cell tumor with the typical intraabdominal manifestations and correlate the radiologic and histopathologic findings. In addition, the differential diagnosis was considered.
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MATERIALS AND METHODS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The radiologic studies performed in these nine patients included abdominal computed tomography (CT) in all nine patients and ultrasonography (US) in three patients. At least one CT scan in each of the nine patients and all of the sonograms were obtained before diagnosis and treatment. Serial CT scans obtained after treatment were reviewed in five patients. The CT technique varied somewhat due to the retrospective nature of the study; however, orally administered contrast material was used in all nine patients and intravenously administered iodinated contrast material was used in seven patients (78%). CT was performed with a conventional or spiral technique, 5–10-mm collimation, and 5–10-mm scanning or reconstruction intervals. Abdominal US was performed with 3.5–5.0-MHz curvilinear phased-array transducers. Endovaginal US was performed in one patient.
Two reviewers (P.J.P., D.M.B.) analyzed the images together, a process that resulted in a consensus interpretation. In each case, the diagnosis of desmoplastic small round cell tumor was established before the imaging review. The images of each patient were systematically reviewed, and the following parameters were entered into a data set: Intraabdominal soft-tissue tumors were characterized according to size, shape, number, distribution, degree of enhancement, and internal architecture (eg, heterogeneity, calcification). The presence or absence of solid organ involvement, ascites, lymph node enlargement (>1.5 cm), bowel obstruction, peritoneal thickening, and hydronephrosis was also noted. The radiologic findings were correlated with the histopathologic findings whenever possible. The methods of diagnosis and treatment, the results of follow-up imaging, and the posttreatment clinical course were recorded.
For histopathologic review, a mean of three slides of hematoxylin-eosin–stained specimens were analyzed for each case (range, two to seven slides). In addition, results of immunohistochemical staining were reviewed in all cases. Immunohistochemical stains included antibodies to cytokeratin, epithelial membrane antigen, desmin, vimentin, CD99, neuron-specific enolase, and muscle-specific actin. A complete panel of these antibodies was not applied in each case.
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RESULTS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Radiologic Findings
The abdominal CT findings are summarized in Table 1. The most characteristic imaging finding in desmoplastic small round cell tumor was multiple peritoneal soft-tissue masses without an apparent organ-based primary site. The mean diameter of the masses was 5.0 cm (range, 2–12 cm), and there was a mean of 4.4 masses per case (range, 1–17). The tumors were predominantly intraperitoneal (Table 2), with paravesical and omental sites each involved in six of nine patients (67%) (Figs 1, 2). Solitary peritoneal tumors in two patients were located in the omentum and paravesical region (Fig 3). Progression of the tumor with diffuse, nodular thickening of the peritoneum occurred in one patient despite therapy (Fig 3).
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Histopathologic Findings
Gross descriptions of tumors were available in eight cases. In three cases, biopsy specimens from multiple peritoneal and hepatic masses up to 2.5 cm in diameter were described as firm to rubbery and tan, white, or yellow. Large tumors (up to 12 cm in diameter) were excised in five cases and were described as firm to rubbery with some variation in color from yellow-gray to tan-white (Fig 1). Focal hemorrhage in the absence of gross necrosis was noted in two cases.
At microscopic analysis, the tumors were characterized by sharply demarcated, angulated, cohesive nests of uniform tumor cells with round to oval nuclei, inconspicuous nucleoli, and scant cytoplasm; the nests were surrounded by abundant fibrous stroma (Fig 1). In three cases, populations of larger cells with rhabdoid features were also present. Rosettelike structures were present diffusely in one case and focally in two others. One case exhibited prominent calcification at microscopic examination. The results of the immunohistochemical studies are summarized in Table 3. In general, the tumors coexpressed epithelial and mesenchymal markers.
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Because of the often nonspecific manifestations of desmoplastic small round cell tumor, patients are often referred for cross-sectional imaging. Indeed, even though not all patients underwent the same imaging evaluation in our retrospective study, abdominal CT was performed before diagnosis in all patients. The most characteristic feature of desmoplastic small round cell tumor at cross-sectional imaging is single or multiple peritoneal soft-tissue masses without an apparent organ of origin that are located within the omentum, within the mesentery, or adjacent to the bladder. Areas of central low attenuation on CT scans appear to correspond to focal hemorrhage within the tumor at gross pathologic analysis. Ascites and hepatic metastases are other associated features. Both hematogenous and intraperitoneal serosal spread to the liver were observed in our study. Intraabdominal lymphadenopathy, punctate foci of tumor calcification, diffuse nodular peritoneal thickening, and hydronephrosis due to an obstructing tumor were less common findings, but all have been documented in earlier studies (2,6,7).
The radiologic differential diagnosis for multiple solid peritoneal masses is broad and includes various neoplastic, inflammatory, and miscellaneous processes. Peritoneal carcinomatosis from a variety of primary malignancies, including ovarian, gastrointestinal, and lymphomatous sources, may manifest as solid masses or infiltration of the intraabdominal fat (8,9). Malignant mesothelioma of the peritoneum is usually infiltrative but may also manifest as discrete tumors, which are usually accompanied by a variable amount of ascites (10). Gastrointestinal carcinoid, malignant melanoma, and soft-tissue sarcomas such as malignant fibrous histiocytoma may also have a similar radiologic appearance (11). Desmoid fibromatosis, peritoneal tuberculosis, fibrosing mesenteritis, splenosis, and amyloidosis are other disorders whose infiltrative and/or tumefactive manifestations overlap with the appearance of desmoplastic small round cell tumor (12–14). The omental and mesenteric masses of desmoplastic small round cell tumor may resemble conditions with marked lymphadenopathy, such as malignant lymphoma, Castleman disease, Whipple disease, mycobacteriosis, actinomycosis, and other conditions with bulky intraabdominal disease (15,16). Retroperitoneal lymphadenopathy appears to be less extensive in desmoplastic small round cell tumor than in lymphoma. When soft-tissue masses are confined to the pelvis in female patients, a neoplastic or inflammatory disorder of the reproductive tract is a reasonable initial consideration. Leiomyomatosis peritonealis disseminata, a rare condition affecting premenopausal women, can appear similar to desmoplastic small round cell tumor at imaging (17). Likewise, with a scrotal mass in a young male patient, diagnostic considerations include germ cell and other testicular neoplasms, paratesticular sarcoma, and tumefactive inflammatory processes. The paratesticular location of desmoplastic small round cell tumor allows exclusion of the much more common testicular neoplasms.
In practice, the presence of a presumed organ-based primary site strongly favors the diagnosis of carcinomatosis, whereas an associated pleural rind likely represents mesothelioma. In the absence of an apparent primary tumor in an adolescent or young adult, desmoplastic small round cell tumor should be considered. Tumor hemorrhage or necrosis and ascites can be seen with most of the aforementioned entities but are more common with malignancies, tuberculous peritonitis, and desmoplastic small round cell tumor. A patient age of less than 25 years might favor the diagnosis of desmoplastic small round cell tumor or inflammatory diseases. However, given the large overlap in the radiologic appearances of peritoneal diseases, biopsy is generally warranted.
The peritoneal cavity is clearly the most common site of desmoplastic small round cell tumor; however, since the initial report, it has become apparent that this tumor can occur elsewhere in a minority of cases. Desmoplastic small round cell tumor arising from the retroperitoneum occurred in five of 19 patients in the original series by Gerald et al (1), in 15 of 101 patients in the review by Kretschmar et al (2), and in three patients in our series. Paratesticular involvement with desmoplastic small round cell tumor has been reported, with tumor arising from the tunica vaginalis of the testis (18). One of the five male patients in our study had a scrotal mass due to desmoplastic small round cell tumor in addition to abdominal disease. Finally, desmoplastic small round cell tumor of the pleura has also been reported (19), and the pleura was the site of origin in two of the cases without intraabdominal disease that were excluded from our series. It was initially postulated that desmoplastic small round cell tumor is a primitive neoplasm of mesothelial derivation because of the immunophenotypic similarity and geographic proximity to mesothelium (3). However, the histogenesis of desmoplastic small round cell tumor remains as speculative as it does for a possibly related entity, Ewing sarcoma–primitive neuroectodermal tumor. Both desmoplastic small round cell tumor and Ewing sarcoma–primitive neuroectodermal tumor are characterized by reciprocal translocations of the Ewing sarcoma gene (EWS) on chromosome 22 with specific but separate loci on chromosome 11 (20).
The pathologic differential diagnosis for desmoplastic small round cell tumor is influenced to some extent by the age of the patient at presentation. The differential diagnosis for an abdominal malignant small cell tumor in a child or adolescent includes rhabdomyosarcoma, non-Hodgkin lymphoma, Ewing sarcoma–primitive neuroectodermal tumor, Wilms tumor, neuroblastoma, and desmoplastic small round cell tumor. Immunohistochemical, electron microscopic, and molecular genetic studies in selected cases allow reliable discrimination of these small cell neoplasms (21). The coexpression of epithelial and mesenchymal antigens in desmoplastic small round cell tumor allows it to be distinguished from the other small, blue, round cell tumors (3). In a young to middle-aged patient with a malignant small cell tumor of the abdomen, neuroendocrine carcinoma, including carcinoid and islet cell carcinoma, and the small cell variant of mesothelioma are additional considerations.
Although an initial response to chemotherapy has been reported in many cases of desmoplastic small round cell tumor, the vast majority of cases eventually follow a course toward lethal progression, with a median survival of approximately 17 months (1,2). Aggressive multimodality therapy consisting of high-dose chemotherapy, surgical resection, and radiation therapy may prolong survival (22).
In summary, as desmoplastic small round cell tumor continues to gain more widespread recognition, radiologists should familiarize themselves with this rare entity because the diagnosis may be first suggested by the imaging findings.
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Footnotes |
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Author contributions: Guarantor of integrity of entire study, P.J.P.; study concepts, P.J.P.; study design, P.J.P., P.C.H.; definition of intellectual content, P.J.P., D.M.B., L.P.D.; literature research, P.J.P., A.J.F.; clinical studies, P.J.P.; experimental studies, P.C.H., L.P.D.; data acquisition, P.J.P., P.C.H.; data analysis, P.J.P.; statistical analysis, P.J.P.; manuscript preparation, P.J.P., P.C.H., A.J.F.; manuscript editing and review, D.M.B., L.P.D.
Received May 28, 1998;
revision requested July 16, 1998; revision received July 29, 1998;
accepted October 19, 1998.
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References |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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