Extramedullary hematopoiesis in the spleen represents a physiologic compensatory event that may be seen in many hematologic diseases leading to chronic anemia. The liver and the spleen are the most common site of extramedullary hematopoiesis, both usually manifesting on imaging as organomegaly and, rarely, with focal mass-like lesions.
For a general discussion on this subject, please refer to the main article on extramedullary hematopoiesis.
Radiographic features
The splenic involvement is commonly diffuse and characterized on imaging as splenomegaly, which is seen together with hepatomegaly given the usual synchronous involvement of the liver. In some cases though, it will present as a focal mass-like lesion in the splenic parenchyma, which can be single or multiple.
Ultrasound
Splenomegaly with or without well-defined nodules, which may be either hypo or hyperechogenic 2.
CT
Hepatosplenomegaly is the common imaging finding when performing staging CT for the underlying hematological disease. Focal lesions may be single or multiple, are usually hypodense with poor post-contrast enhancement.
MRI
Focal lesions will have their signal intensity relying on the stage of the hematopoietic process 1,2:
- active lesions
- T1: intermediate signal intensity
- T2: high signal intensity
- T1 C+ (Gd): heterogeneous enhancement
- older lesions
- T1: low signal intensity
- T2: low signal intensity
- IP-OOP: reduced in-phase signal due to iron
- T1 C+ (Gd): no enhancement
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