Objective To investigate the magnetic resonance imaging (MRI) features of desmoplastic small round cell tumor (DSRCT) of the abdomen and pelvis.

Method The retrospec-tive and descriptive study was conducted. The clinicopathological data of 8 patients with DSRCT of the abdomen and pelvis, including 3 cases admitted in Yueqing People's Hospital and 5 cases admitted in Wenzhou People's Hospital, from January 2008 to June 2022 were collected. There were 5 males and 3 females, aged (43±5)years. All patients underwent MRI plain and enhanced scanning. Observa-tion indicators: (1) imaging features of DSRCT of the abdomen and pelvis; (2) treatment and pathological examination characteristics of DSRCT of the abdomen and pelvis; (3) follow-up. Measurement data with normal distribution were represented as Mean±SD, and measurement data with skewed distri-bution were represented as M(range). Count data were described as absolute numbers.

Results (1) Imaging features of DSRCT of the abdomen and pelvis. ① Tumor location. Of the 8 patients, there were 6 cases with tumors located respectively at the lower edge of the liver in the right quarter costal region, the medial side of the ileocecal region in the right iliac region, the medial side of the caecum in the right iliac region, the gastro-pancreatic space in the left quarter costal region, the mesenteric space in the left iliac region and the right side of pelvic bladder, and 2 cases with tumors located at retroperitoneal space of left quarter rib region. ② Tumor size. There were 13 lesions in the 8 patients, and the maximum diameter of tumor was 9.1 (range, 3.5‒20.0)cm. Of the 8 patients, there were 5 cases with single tumor and 3 cases with multiple tumors. ③ Tumor shape and boundary. Of the 8 patients, there were 4 cases with tumor in expansive growth and 4 cases with tumor in invasive growth. There were 5 cases with tumor of intratumoral necrosis and cystic degene-ration, 4 cases with tumor of intratumoral hemorrhage, 4 cases with tumor of intratumoral spot calcification, 3 cases with tumor of peritumoral tissue exudation. One patient may combined with multiple imaging manifestations. ④ Imaging characteristics of MRI plain scanning. Of the 8 patients, there were 4 cases with tumor of homogeneous hypointensity signal and 4 cases with tumor of hypointensity mixed with speckled hyperintensity (with hemorrhage) in T1 weighted imaging of MRI plain scanning. There were 3 cases with tumor of homogeneous hyperintensity and 5 cases with tumor of high signal at the edge, patchy and spot-shaped in the center in T2 weighted imaging of MRI plain scanning. There were 5 cases with tumor of high, equal and low confounding signals and 3 cases with tumor of high and low signals in T2 weighted imaging fat suppression sequence of MRI plain scanning. There were 3 cases with tumor of uniform high signals and 5 cases with tumor of high, equal and low mixed signals in diffusion weighted imaging of MRI plain scanning. ⑤ Imaging characteristics of MRI enhanced scanning. All 8 patients had tumor of heterogeneous enhancement in MRI enhanced scanning, including 2 cases with significant enhancement in arterial phase, continuous enhancement in portal phase, slightly reduced enhancement in delayed phase, 4 cases with moderate enhancement in arterial phase, continuous enhancement in portal phase, slowly exited enhancement in delayed phase, 2 cases with mild enhancement in arterial phase, continuous enhancement in portal phase, slowly exited enhancement in delayed phase. Of the 8 patients, there were 3 cases with tumor of annular enhancement with intratumoral strip or grid signals and 3 cases with tumor of peritumoral blood vessels increased and thickened signals. ⑥ Tumor invasion and metastasis. Of the 8 patients, there were 4 cases with tumor invaded bowel, 2 cases with tumor invaded surrounding tissues, 1 case with tumor invaded left kidney, spleen and pancreatic tail, 1 case with tumor invaded distal of left ureter. There were 5 cases with abdominal, retroperitoneal and inguinal lymph nodes enlargement, 4 cases with multiple nodular thickening of peritoneum and ascites, 2 cases with tumor liver and lung metastasis and 1 case with tumor rib, femur and sacrum metastasis. One patient may combined with multiple tumor metastasis. (2) Treatment and patholo-gical examination characteristics of DSRCT of the abdomen and pelvis. Of the 8 patients, 3 patients underwent complete resection as clear tumor boundary, 3 patients underwent tumor partial resection as tight adhesion between tumor and surrounding blood vessels, 2 cases underwent tumor tissue pathological examination as extensive metastasis of peritoneum, omentum, mesentery and surrounding intestine. All 8 patients were diagnosed as DSRCT by microscopic examination, electron microscopic examination, immunohistochemical staining and cytogenetic examination. (3) Follow-up. All 8 patients underwent postoperative follow-up and died during the follow-up.

Conclusion MRI features of abdominal and pelvic DSRCT include single or multiple lobulated masses with unclear boundaries, invading the omentum, mesentery, peritoneum and adjacent tissues in most cases, mixed signals and heterogeneous mild to moderate enhancement in enhanced scanning.