A case of pseudomyxoma peritonei: visualization of septa using diffusion-weighted images with low b values

Pseudomyxoma peritonei (PMP) is a rare disease with neoplastic growth of mucin-secreting cells in the peritoneal cavity, resulting in mucinous ascites. The septum of intra-abdominal fluid collection is a key imaging finding characteristic to PMP. In magnetic resonance imaging (MRI), multi-b value diffusion-weighted imaging (DWI) is a method used to obtain an accurate apparent diffusion coefficient. The clinical utilities of DWI using lower b values as diagnostic imaging are rarely highlighted. This report describes a case of PMP in which DWI using b values of 100 and 500 s/mm² exclusively visualized many thick septa with low signal intensity in peritoneal effusion. The septa could not be recognized in DWIs with b values of zero or 1000 s/mm², as with ultrasonography, computed tomography, and conventional MRI. A discrepancy between DWI using lower b values and other MRI sequences or imaging modalities indicates a specific capability of DWI using low b values: the ability to visualize septa of intra-abdominal fluid collection much thicker than in real cases. Results for this case suggest that DWI using low b values might present clinical potential for the preoperative diagnosis of PMP.