Splenic imaging is done using Tc-99m in vitro labeled heat damaged red cells for diagnosis of residual splenic tissue or splenosis

There are two distinct forms: accessory spleens and splenosis.

Accessory spleens 

1. Congenital and arise from the left side of the dorsal mesogastrium during the embryological period of development.

2. They are usually few in number, totaling six or less.

3. Normal splenic histology with its blood supply uniformly arising from a branch of the splenic artery.

Splenosis 

1. Acquired condition defined as autotransplantation of viable splenic tissue throughout different anatomic compartments of the body. It occurs after traumatic or iatrogenic rupture of the spleen

2. 100 or more individual splenic nodules are commonly found in splenosis and greater than 400 have been reported.

3. Blood supply  is derived from the surrounding tissues and vessels.The architecture is distorted with no hilum, a poorly formed capsule and tissue of any shape or size. The histology is varied as well.

Abdominal and pelvic splenosis are often mistaken for abdominal lymphoma, metastatic disease, carcinomatosis, primary renal or hepatic malignancy, adenomas, endometriosis or simple adenopathy

The differential diagnosis of pleural-based nodules includes primary and metastatic cancers such as lung, breast, pancreas, gastrointestinal tract, kidney, lymphoma, melanoma, mesothelioma, invasive thymoma, and neurogenic tumors, as well as benign conditions including fibrous tumors, extramedullary intrathoracic hematopoiesis, infections and asbestos-related pleural plaques.

The differential diagnosis of cutaneous splenosis includes differentiated cutaneous lymphoma, lymphocytoma, nodular Kaposi sarcoma, and subcutaneous vascular malformations.

X-rays- The low density of splenic tissue makes it difficult to visualize.

CT scanning reveals the number, shape and size, but not the identity of the nodules.

Standard magnetic resonance imaging (MRI) is not useful in narrowing the differential diagnosis.

Nuclear scintigraphy using Technetium-99m heat-damaged erythrocytes (RBC) is the current diagnostic modality of choice for splenosis.

Splenosis should be included in the differential diagnosis in all patients with abdominal, pelvic, thoracic or subcutaneous nodules with a history of splenic trauma or spleen removal. Some patients may not know the reason for their splenectomy, but this history is paramount and should immediately broaden a clinician's differential. Once considered, the diagnostic workup for this mostly benign condition is simple, inexpensive, noninvasive, and may prevent future stress and procedures.