New intra-abdominal mass after operation for colorectal cancer: desmoid tumor versus peritoneal seeding

Desmoid-type fibromatosis: imaging features and course

Desmoid-type fibromatosis (DF) is a soft tissue tumor characterized by infiltrative growth and a tendency toward local recurrence, while it exhibits self-limiting behavior and shows spontaneous regression. With its unpredictable behavior, a change in treatment strategies from initial surgery to nonsurgical management has been proposed, and active surveillance is currently widely chosen as the initial treatment strategy for DF. We reviewed the imaging features of DF regarding its clinical course, focusing on regression cases, postoperative cases, and imaging changes after systemic treatment.

Differentiation of intra-abdominal desmoid tumor from peritoneal seeding based on CT and/or 18F-FDG PET-CT in patients with history of cancer surgery

PURPOSE

To investigate differential imaging features of intra-abdominal desmoid tumors and peritoneal seeding in patients with history of cancer surgery.

METHODS

Thirty-two patients who had a single pathologically proven intra-peritoneal lesion that developed after cancer surgery were enrolled between January 2000 and June 2019. There were 16 desmoid tumors and 16 peritoneal seeding lesions. Portal phase CT and/or ¹⁸F-FDG PET findings were analyzed by two radiologists in consensus for the following items: location, size, shape, margin, contour, homogeneity, necrosis, adjacent organ invasion, calcification, intra-lesional fat, peritoneal infiltration, mass effect, and degree of enhancement. Hounsfield units (HU) and maximum standardized uptake values (SUV_max) of the lesions were measured. Imaging findings were compared using the Chi square test, Fisher's exact test, and student t test.

RESULTS

Desmoid tumors frequently showed well-defined margins (9/16) and smooth contours (12/16), whereas peritoneal seeding had ill-defined margins (13/16) and lobulated contours (11/16) (P = 0.028 and 0.013, respectively). Intra-lesional fat was found more frequently in desmoid tumors (7/16) than peritoneal seeding (1/16) (P = 0.014). Desmoid tumors showed iso-attenuation (13/16) compared to psoas muscle in portal phase, while peritoneal seeding depicted high attenuation (12/16) (P = 0.002). Mean HU was significantly lower in desmoid tumors (64.3) than peritoneal seeding lesions (95.1) (P = 0.001). However, the mean SUV_max of desmoid tumors (4.1) did not significantly differ from peritoneal seeding lesions (5.2) (P = 0.519).

CONCLUSION

Several CT features including iso-attenuation in portal phase and presence of intra-lesional fat can be helpful in differentiating desmoid tumors from peritoneal seeding in patients with history of intra-abdominal cancer surgery.