Extramedullary hematopoiesis in the spleen

Extramedullary haematopoiesis in the spleen represents a physiologic compensatory event that may be seen in many haematologic diseases leading to chronic anaemia. The liver and the spleen are the most common site of extramedullary haematopoiesis, both usually manifesting on imaging as organomegaly and, rarely, with focal masslike lesions. 

For a general discussion on this subject, please refer to the main article on extramedullary haematopoiesis.

Radiographic features

The splenic involvement is commonly diffuse and characterised 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 masslike 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 haematological 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 haematopoietic 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
  • T2: low signal intensity
  • IP-OOP: reduced in-phase signal due to iron  
  • T1 C+ (Gd): no enhancement