Malignant Splenic Masses
Lymphoma and Other Hematologic Malignancies
Hodgkin’s and non-Hodgkin’s lymphomas often involve the spleen. Lymphomatous deposits in the spleen frequently parallel the signal intensity of splenic parenchyma on T1- and T2-weighted images. Diffuse involvement of lymphoma may appear as large, irregularly enhancing regions of high and low signal intensity, in contrast to the uniform bands that characterize normal arciform enhancement.
Multifocal disease appears as focal low-signal-intensity mass lesions scattered throughout the spleen. Focal involvement appears as spherical lesions in distinction to the wavy tubular pattern of arciform enhancement of uninvolved spleen.
Focal lymphomatous deposits may be low in signal intensity compared to background spleen on T2-weighted images, which is a feature distinguishing lymphomas from metastases. It is critical to acquire gradient-echo images within the first 30 s after contrast administration because foci of lymphoma equilibrate early, becoming isointense with normal splenic tissue within 2 min and frequently earlier.
Superparamagnetic iron-oxide particles also improve the accuracy of diagnosing splenic lymphoma. These particles are selectively taken up by the RES cells, and cause a decrease in signal intensity. By contrast, malignant cells do not take up superparamagnetic iron-oxide particles. Therefore, splenic lymphoma remains hyperintense compared to the normal spleen, improving tumor-spleen contrast.
Chronic lymphocytic leukemia frequently involves the spleen and may result in massive splenomegaly. Focal deposits are more infiltrative and less well defined than lymphoma. Deposits are well shown after gadolinium administration and appear as irregular hypointense masses on early post-contrast images. Lymphadenopathy is frequently present (Hahn et al. 1988; Rabushka et al. 1994).
Although tumors may invade the spleen from contiguous viscera, true tumor metastasis to the spleen is rare, usually occurring only in the setting of disseminated disease in the terminal stage. Breast cancer, lung cancer, and melanoma are the most common primary tumors.
Lesion detection is best performed, by acquiring immediate post-gadolinium SGE images. Metastases are lower in signal intensity than normal splenic tissue on these images. Images must be acquired within the first 30 s after gadolinium administration because metastases rapidly equilibrate with splenic parenchyma.
Image acquisition with superparamagnetic iron oxide particles renders metastases higher in signal intensity than normal spleen. An attractive feature of iron oxide particles is that the imaging window is longer (60 min) than for gadolinium (< 1 min) (Hahn et al. 1988; Rabushka et al. 1994).