Areas that are hypoechoic in relation to the remaining splenic parenchyma include as possible causes all focal lymphomatous infiltrations. In non-Hodgkin lymphoma, these lymphomatous infiltrations can be localized as well as diffuse throughout the spleen giving it a heterogeneous appearance. Congenital (dysontogenetic) splenic cysts are rather uncommon and do not differ sonographically from hepatic cysts (64) (Fig. 29.1), thus they are not illustrated again here. Acquired splenic cysts frequently develop after trauma or infarcts. As is true for hepatic cysts, internal septations suggest a parasitic origin (compare Fig. 30.3).
Recognizing a splenic hematoma (Fig. 49.2) might be difficult since a fresh hemorrhage can be iso-echoic with the surrounding splenic parenchyma (37). In general, the echogenicity of the extravasated blood decreases within a few days, and subacute or old hematomas (50) are usually well visualized as hypoechoic space-occupying lesions. A parenchymal laceration without a capsular tear can produce an initially unrecognized subcapsular hematoma. The risk of such a hematoma is a delayed tear of the splenic capsule, which releases the tamponaded hematoma and causes free bleeding into the abdominal cavity. More than 50% of these so-called "delayed" splenic ruptures occur within 1 week after the trauma, and it is advisable during this interval at least to perform serial follow-up studies.
Finally, the spleen can exhibit echogenic foci. They could represent splenic hemangiomas, which are rare, or calcified granulomas, which are rather common and usually found with tuberculosis or histoplasmosis. Splenic calcifications can also accompany cirrhosis. A spleen harboring multiple echogenic foci (53) has been called the „star-sky spleen" (Fig. 49.3). Splenic abscesses and splenic metastases, which are rare, can have a rather varied sonomorphology, in part depending on their duration and underlying cause. There are no simple reliable differential diagnostic criteria, and consultation of reference textbooks is recommended. Splenic infarcts (71) can be observed in splenomegaly with compromised vascular supply (Fig. 49.1).
Suggestion: Patients with acute abdominal and thoracic trauma should be searched for free fluid in the cul-de-sac and below the diaphragm (13) as well as around the spleen and liver. Carefully scrutinize the spleen for a double contour along its capsule (subcapsular hematoma?) and for a heterogeneous echo pattern of its parenchyma, to avoid overlooking a possible splenic rupture.
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