MR imaging appearance of intraperitoneal gelatin sponge in mice

Intraperitoneal gelatin sponge can mimic a mass lesion on magnetic resonance (MR) images. To determine the MR imaging characteristics of gelatin sponge over time, a 15 × 10 × 4‐mm piece of gelatin sponge soaked in saline was surgically implanted in the peritoneal cavity of 14 mice. Two mice underwent a sham operation. Contiguous axial spin‐echo images of the abdomen were obtained with T1‐weighted, spin‐density, and T2‐weighted sequences preoperatively and over a 6‐week period postoperatively. Gelatin sponge initially appears as a heterogeneous mass of low signal intensity on T1‐weighted images and increasing intensity on spin‐density and T2‐weighted images, containing multiple round foci of very low signal intensity, attributable to air, at all sequences. Over time, signal intensity further increases and becomes more homogeneous on spin‐density and T2‐weighted images, although foci of air persist to 3 weeks. By 2‐4 weeks, the mass is no longer discrete. Foci of air should help differentiate gelatin sponge from tumor and add gelatin sponge to the differential diagnosis of abscess.