Benign Splenic Masses
Cysts are the most common of the benign splenic lesions. Three types of non-neoplastic cysts exist: posttraumatic or pseudocysts, epidermoid cysts, and hydatid cysts.
Most splenic cysts are posttraumatic in origin. Epidermoid cysts are true cysts discovered in childhood or early adulthood that may have trabeculations or septations in their walls with occasional peripheral calcification. Hydatids, or echinococcal cysts, are rare. They are characterized by extensive wall calcification.
The MRI features of cysts include sharp lesion margination, low signal intensity on T1-weighted images, and very high signal intensity on T2-weighted images. Complicated cysts are high signal intensity on T1-weighted images, regions of mixed signal intensity on T2-weighted images, or both. Cysts do not enhance on post-gadolinium images.
Pseudocysts may be complicated by hemorrhage particularly early in their evolution and thus may contain foci of high signal intensity on pre-contrast T1-weighted images (Urrutia et al. 1996).
Hemangiomas are the most common of the benign splenic neoplasms. Lesions may be single or multiple.
Splenic hemangiomas are mildly low to isointense on T1- weighted images and mildly to moderately hyperintense on T2-weighted images, similar to hepatic hemangiomas.
Three patterns of contrast enhancement are observed:
- immediate homogeneous enhancement with persistent enhancement on delayed images,
- peripheral enhancement with progression to uniform enhancement on delayed images,
- peripheral enhancement with centripetal progression but persistent lack of enhancement of central scar.
Unlike hepatic hemangiomas, splenic hemangiomas generally do not demonstrate welldefined nodules on early post-gadolinium images. Uniform high signal intensity on immediate post-gadolinium SGE images is a common appearance for small (<1.5 cm) hemangiomas, as it is with hepatic hemangiomas. Rarely hemangiomas with a very large central scar can appear hypointense on T2-weighted images, reflecting the lower fluid content of the central scar (Disler and Chew 1991).
Hamartomas are rare and composed of structurally disorganized mature splenic red pulp elements. The lesions tend to be single, spherical, and predominantly solid.
Hamartomas are mildly low to isointense on T1- weighted images and moderately high in signal intensity on T2-weighted images. They frequently are moderately heterogeneous and may have regions of low signal intensity on T2-weighted images. Hamartomas enhance on immediate post-gadolinium SGE images in an intense diffuse heterogeneous fashion.
Enhancement becomes homogeneous on more delayed images with signal intensity slightly greater than in background spleen. The early diffuse heterogeneous enhancement permits distinction from hemangioma (Ramani et al. 1997).