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Splenosis

Splenosis is one type of ectopic splenic tissue (the other being accessory spleen). It is an acquired condition and is defined as autoimplantation one or more focal deposits of splenic tissue in various compartments of the body.

Abdominal splenosis is seen after abdominal trauma or surgery (e.g. splenectomy). They result from seeding of the peritoneal cavity with splenic tissue which recruits local blood supply. They are typically small, sessile (as they grow on serosal / peritoneal surfaces) and multiple. They may grow overtime to become quite sizeable. If located isolated intrahepatically, they can cause serious diagnostic problems.

Similar process occurring in the thorax is called thoracic splenosis. It is rare and presents as multiple pleural based nodules in the left hemithorax. It typically occurs following blunt trauma causing a combination of splenic injury and left diaphragmatic rupture4.

They are benign, their greatest importance being the need to distinguish them from more sinister pathology.

Radiographic features

CT

They typically rounded or sessile nodules, and have density and enhancing characteristics similar to the rest of the spleen or expected density of the spleen if there has been a splenectomy.

MRI

Signal characteristics are similar to normal spleen 2 : i.e.

  • T1 - hypo intense
  • T2 - hyper intense
  • C+ (Gd) - heterogenous enhancment
Scintigraphy
Tc 99m sulphur colloid scan

The diagnosis can be confirmed with Tc99m sulphur colloid scan which will demontrate increased uptake as long as the splenunculus is at least 2cm in diameter, although hybrid imaging with SPECT/CT could reach beyond this limit 7.

When Tc99m sulphur colloid fails to prove splenic tissue, Tc99m-tagged heat-damaged RBC scan (Tc-99m-DRBC) with autologous erythrocytes remains gold-standard of imaging, being capable of specifically proving splenic tissue 6,8

Differential diagnosis

They should not be confused with polysplenia or accessory spleens (splenunculi) which are congenital in origin and retain arterial supply from the splenic artery. They are also composed of normal splenic tissue

  • peritoneal metastases
  • enlarged lymph nodes (abdominal lymphadenopathy)
  • endometriosis
  • depending on their location they may appear to be arising from various organs, and thus mimic malignancy

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