Splenosis is a rare condition that results from autotransplantation of splenic tissue into abnormal sites, such as the peritoneal cavity, thoracic cavity, subcutaneous tissue, and pericardium. This ectopic spleen tissue usually occurs after traumatic rupture of the spleen and is generally asymptomatic. However, the ectopic spleen tissue may occasionally cause pain or gastrointestinal obstruction, or mimic primary and metastatic malignancy. Therefore, splenosis is usually found incidentally on imaging studies, and is rarely diagnosed without invasive biopsy including surgical methods. However, radionuclide scanning can provide an alternative to these invasive procedures.

Previously reported cases of splenosis in South Korea involved single compartments of the body, either intraperitoneal or intrathoracic^1-9. Moreover, most were diagnosed through surgical pathological confirmation. We describe a 54-year-old Korean male who presented with intrathoracic and intraperitoneal splenosis diagnosed by radionuclide imaging.

A 54-year-old male was referred to Severance Hospital for evaluation of incidental left diaphragmatic mass and right upper lobe consolidation on chest X-ray (Figure 1A). Pleural core needle biopsy done at the previous hospital showed acute and chronic inflammation with mixed inflammatory cell infiltration. He had no unusual medical conditions and worked as a miner for 10 years in his twenties. He had smoked half a pack of cigarettes per day for 40 years, and quit 3 months before.

On admission, he did not have any symptoms, physical examination was unremarkable, and laboratory tests were normal. Chest computed tomography (CT) revealed multiple lobulated masses and nodules along diaphragm, lower mediastinum, and costal pleura of left side. Moreover, multiple calcified granulomas with fibrosis were seen in the right upper lobe (Figure 1B-E). Considering the previous history of smoking and mining, malignant tumors such as mesothelioma or pleural metastasis had to be differentiated and we proceeded ¹⁸F-fluoro-2-deoxygluocose (¹⁸F-FDG) positron emission tomography-CT (PET-CT). FDG PET-CT showed previously detected multiple masses and nodules along left diaphragm and multiple small nodular lesions in the left perigastric area and omentum with faint FDG uptake. Acute and chronic inflammation with fibrosis and calcified granulomas were observed in right upper lobe with intense FDG uptake (Figure 2A). However, his spleen was not visualized on PET-CT and review of chest CT. From further medical history obtained, he had undergone splenectomy following splenic trauma from a dynamite explosion while working in the mine 30 years ago.

With this history, splenosis was suspected, and a technetium (Tc)-99m-labeled heat-damaged red blood cell (RBC) scan was performed. The RBC scan showed multiple foci of increased uptake in the left thorax and left upper quadrant of the abdomen, consistent with thoracic and abdominal splenosis (Figure 2B). This patient has been followed up at our outpatient clinic without further invasive evaluation or treatment for the splenosis. He was diagnosed with pulmonary tuberculosis based on positive sputum culture and is on anti-tuberculous medications.

Ectopic splenic tissue usually manifests in the body in two forms, accessory spleens and splenosis. Accessory spleens are congenital and found in approximately 20% of the population. They result from failure of spleen tissue union during embryogenesis and arise from the left side of the dorsal mesogastrium. Accessory spleen usually has normal splenic histology with its blood supply from a branch of the splenic artery. On the other hand, splenosis is an acquired condition, which is rare compared to accessory spleen. It is autotransplantation of viable splenic tissue to any anatomic compartments of the body and usually exhibits distorted architecture.

Von Kuttner¹⁰ first reported splenosis in the peritoneal cavity after splenectomy during autopsy in 1910. The first intrathoracic splenosis was reported by Shaw and Shafi¹¹. There are two possible pathogeneses of splenosis One is through mechanical implantation of splenic tissue after splenectomy or splenic rupture. It is assumed that the damaged splenic pulp is released into the adjacent cavity, which begins the seeding process. The other mechanism is hematogenous spread of splenic pulp resulting in intrahepatic and cerebral splenosis¹². Therefore, splenosis can occur in any part of the body, but is most frequently observed in the peritoneal cavity. Among the extraperitoneal splenosis, thoracic splenosis is the most common form and few cases have been reported in the pericardium, subcutaneous tissue, and occipital pole of the brain¹³.

The reason thoracic splenosis is most common among the extraperitoneal sites is probably due to the anatomic boundaries of the abdominal and thoracic cavities. Most of the patients with thoracic splenosis had history of thoracoabdominal trauma including diaphragm injury and splenic rupture¹³. This accounts for all the thoracic splenosis observed being on the left side. Thoracic splenosis is usually asymptomatic and results in no significant morbidity or mortality. However, one case of thoracic splenosis reported several milliliters of hemoptysis¹⁴. The differential diagnosis for thoracic splenosis includes pleural metastasis or malignant mesothelioma.

Previously, many cases of thoracic splenosis were diagnosed through percutaneous biopsy or intraoperative resection of masses when the splenosis was not considered at first. However, fine-needle aspiration cytology of subpleural splenosis can lead to misdiagnosis if the cytologist is not informed of the patient's history of splenic injury. Moreover, pleural adhesions in patients with previous surgery make thoracotomy surgical biopsy difficult. Therefore, preoperative diagnosis of splenosis by radionuclide imaging study can avoid unnecessary biopsy or surgical procedures. Tc-99m sulfur colloid is sequestered in the reticuloendothelial system of ectopic splenic tissue and therefore can be used to detect it. Indium-111-labeled platelets and Tc-99m-labeled heat-damaged RBC are very sensitive and specific for splenic sequestration and phagocytosis¹⁵.

In Korea, nine cases of splenosis were previously reported. Seven cases were located in the abdominal cavity, one case in the pelvis, and one in the thoracic cavity (Table 1). Seven patients were diagnosed through surgical pathological confirmation and only two patients were diagnosed through Tc-99m-labeled heat-damaged RBC scan.

In conclusion, splenosis can develop in multiple sites depending on the extent of injury. Therefore, thoracic splenosis should be considered in asymptomatic patients with multiple left-side pleural masses and previous thoracoabdominal trauma and splenic injury. Tc-99m-labeled heat-damaged RBC scan is the diagnostic method of choice for noninvasive evaluation of splenosis instead of invasive pathological confirmation.