Miscellaneous Splenic Lesions
Splenomegaly may be observed in a number of disease states including venous congestion (portal hypertension), leukemia, lymphoma, metastases, and various infections. On immediate post-gadolinium images demonstration of arciform or uniform high-signal-intensity enhancement is consistent with portal hypertension and excludes the presence of malignant disease.
Viral infection may result in splenomegaly. The three most common viruses to involve the spleen are Epstein- Barr, varicella, and cytomegalovirus. Nonviral infectious agents that involve the spleen in patients with normal immune status include histoplasmosis, tuberculosis, and echinococcosis. These infectious agents are observed in immunocompromised patients with an even greater frequency.
In the immunocompromised patient, the most common hepatosplenic infection is fungal infection with Candida albicans and Cryptococcus. In the acute phase, hepatosplenic candidiasis results in small (<1 cm) welldefined abscesses in the spleen and liver. They are well shown on T2-weighted fat-suppressed images as highsignal- intensity rounded foci. Lesions also may be visible on post-gadolinium images, but they usually are not visualized on pre-contrast gradient-echo images.
Bacterial and fungal abscesses are rare in the spleen. Abscesses appear slightly hypointense to isointense on T1-weighted images and heterogeneous and mildly to moderately hyperintense on T2-weighted images. These lesions show intense mural enhancement on early gadolinium-enhanced images. This pattern persists on later post-gadolinium images, accompanied by the presence of periabscess-increased enhancement of surrounding tissue on immediate post-gadolinium images (Rabushka et al. 1994).
Lesions of sarcoidosis are small (<1 cm) and hypovascular. Due to their hypovascularity, the lesions are low in signal intensity on T1- and T2-weighted images and enhance on gadolinium-enhanced images in a minimal and delayed fashion. Low signal intensity on T2-weighted images is a feature that distinguishes these lesions from acute infective lesions (Warshauer et al. 1994).
Foci of iron deposition occur commonly in patients with cirrhosis and portal hypertension due to micro hemorrhages in the splenic parenchyma. On occasion, such foci are observed in patients receiving blood transfusions. Lesions vary in size but are generally smaller than 1 cm. Lesions demonstrate signal void on all pulse sequences (Rabushka et al. 1994). Susceptibility artifact is demonstrated on gradient-echo images as blooming artifact, and this artifact is pathognomonic for this entity.
The spleen is the most commonly ruptured abdominal organ in the setting of trauma. Injury to the spleen may take several forms: subcapsular hematoma, contusion, laceration, and devascularization/infarct. Subcapsular or intraparenchymal hematoma secondary to contusion or laceration demonstrates a time course of changes in signal intensity due to the paramagnetic properties of the degradation products of hemoglobin.
Subacute hemorrhage is particularly conspicuous because of its distinctive high signal intensity on T1- and T2-weighted images. Traumatic injury of the spleen, especially devascularization, is well shown on immediate post-gadolinium gradient- echo images. Areas of devascularization are nearly signal voids compared to the high signal intensity of vascularized tissue (Rabushka et al. 1994).
Splenic infarcts are a common occurrence in the setting of obstruction of the splenic artery or one of its branches. The most common cause is cardiac emboli, but local thrombosis, vasculitis, and splenic torsion are also described. Infarcts appear as peripheral wedge-shaped, round, or linear defects that are most clearly defined on 1 to 5 min post-gadolinium images as low-signal-intensity wedge-shaped regions. The splenic capsule is commonly observed as a thin peripheral, enhancing linear structure.
Massive splenic infarcts may appear as diffuse low signal intensity on T1-weighted images and inhomogeneous high signal intensity on T2-weighted images. Lack of enhancement on early and late post-gadolinium images of wedge-shaped regions is the most diagnostic feature (Rabushka et al. 1994).