Hidden Spleen Tissue Masquerades as Cancer Until Scans Reveal the Truth

Two patients whose scans pointed ominously toward cancer turned out to have something far stranger: fragments of their own spleens, seeded into their chests and abdomens decades earlier, quietly growing into working splenic tissue.

The condition, known as splenosis, occurs when splenic tissue breaks free after the spleen ruptures and reimplants elsewhere in the body. Writing in the journal, the authors define it as the heterotopic implantation of functional splenic tissue in extra-splenic compartments, usually secondary to traumatic or iatrogenic splenic rupture. Although implants most commonly take root in the abdominal and pelvic cavities, they have been reported in less common sites such as the thorax, the liver, and even subcutaneous tissue.

The report, published on 27 July 2026, presents two cases diagnosed with nuclear medicine techniques. The first involves a 65-year-old woman with a history of a gunshot wound that required laparotomy, splenectomy, and removal of her left kidney. She arrived with infectious symptoms, including cough, fever, and desaturation, and underwent a chest CT scan. The scan diagnosed pneumonia but also revealed nodular thickening of the left basal pleura along with solid nodules in the peritoneum and the lower left rib cage. Given the suspicion of neoplastic involvement, her medical team ordered an 18F-FDG PET/CT scan.

That PET/CT revealed pleural lesions with very low metabolism, suggesting a benign process rather than an aggressive cancer. Because of the patient’s history of trauma, clinicians considered a possible diagnosis of splenosis, which was then confirmed by scintigraphy using 99mTc-labeled heat-damaged red blood cells, abbreviated 99mTc-HDRBC. The scan showed high-intensity hyperactive foci in the left hemithorax and other smaller foci with uptake in the left hypochondrium, the flanks, and the iliac fossae. SPECT/CT images confirmed focal hyperactive lesions in the left chest wall involving the pleura and soft tissues at the ninth intercostal space, along with additional deposits in perihepatic and supraumbilical locations. The scintigraphic signs were consistent with thoracoabdominal splenosis.

The second case involves a 58-year-old man who suffered blunt chest trauma at age 25 that required splenectomy. During staging for prostate cancer, he underwent an 18F-PSMA PET/CT scan. That scan documented a primary lesion in the right peripheral zone of the prostate associated with lymph node metastases in the right external iliac chain and multiple blast lesions in the costal arches and pubic symphysis related to secondary involvement. But it also documented multiple foci with an abnormal increase in radiotracer uptake in the peritoneum, the periumbilical region, the epigastrium, the left renal fossa, and the right parietocolic gutter. These foci showed lower maximum standardized uptake values than the secondary lesions, and, combined with his traumatic history, were considered possible foci of splenosis.

A 99mTc-HDRBC scan settled the question. It showed multiple soft tissue density lesions distributed throughout the abdomen, with radiopharmaceutical uptake, confirming the presence of splenosis. Static images captured a high-intensity hyperactive focus in the splenic bed and another in the mesogastrium, while SPECT/CT confirmed hyperactive foci with soft tissue density in the splenic bed and a lesion immediately posterior to the paraumbilical abdominal wall with a smaller adjacent lesion further lateral.

According to the authors, splenosis is a benign acquired condition characterized by heterotopic autotransplantation of functional splenic tissue following splenic rupture, usually of traumatic or surgical origin. The main causes are blunt abdominal trauma and splenectomy, which allow viable splenic tissue to be seeded in ectopic sites. Dissemination occurs when splenic fragments spill into the peritoneal cavity or, less frequently, into extra-abdominal locations such as the thorax, especially when there is concomitant diaphragmatic injury. Because most cases are asymptomatic and discovered incidentally, the true incidence is unknown, though the authors cite an estimate that up to 67 percent of patients with a history of splenic trauma may develop splenosis.

Thoracic splenosis, the form that most concerns the report, was first described in 1896 during an autopsy and represents a rare variant, with an approximate prevalence of 18 percent among patients with splenic rupture associated with diaphragmatic injury. Its pathogenesis involves the spread of viable splenic tissue to the left hemithorax through diaphragmatic defects, where it most often implants on the parietal or visceral pleura, develops a vascular supply from adjacent tissues, and slowly evolves into mature functional splenic tissue. Clinically it is usually silent. In a review of 38 reported cases cited by the authors, only four patients presented respiratory symptoms, such as recurrent hemoptysis, productive cough, or pleuritic chest pain, and all of them shared a history of thoracoabdominal trauma with splenectomy and exclusive involvement of the left hemithorax. The average interval between trauma and diagnosis has been estimated at approximately 21 years, with a wide range between 3 and 45 years, and incidental findings are the most frequent scenario.

Thoracic splenosis can present as a solitary pulmonary nodule with pleural involvement in approximately 25 percent of cases, while the remaining 75 percent show multiple pulmonary or pleural nodules. These findings may mimic primary tumors, metastatic disease, or infectious processes, particularly when a detailed medical history is not available or the abdominal region is not evaluated to confirm the absence of the spleen. Intra-abdominal splenosis can likewise be confused with liver neoplasms, gastrointestinal tract tumors, or mesothelioma. Historically, biopsy with histopathological confirmation was considered the gold standard for diagnosis, but as an invasive procedure with a potential risk of complications, its use is limited.

Scintigraphy with 99mTc-heat-damaged red blood cells has established itself as the diagnostic tool of choice, thanks to its high sensitivity and specificity, derived from the high uptake of heat-damaged erythrocytes by ectopic splenic tissue and minimal physiological hepatic uptake compared with other nuclear imaging techniques. In complex cases, SPECT/CT may be necessary for better anatomical localization. In the two cases presented, PET/CT with 18F-FDG and 18F-PSMA allowed initial metabolic characterization of the lesions, revealing uptake patterns atypical for malignant disease, and the 99mTc-HDRBC scintigraphy then definitively confirmed the splenic nature of the implants. Proper recognition of splenosis has important clinical implications: it avoids unnecessary invasive procedures such as biopsies or surgical resections and prevents erroneous treatments targeting lesions suspected of malignancy. Management is conservative in most cases, given the benign nature of the entity and its possible partial contribution to splenic immune function, with surgical resection reserved exclusively for symptomatic patients or those with complications, limited to the implants responsible for the clinical presentation. The authors’ key teaching points are straightforward: thoracic splenosis should be suspected in patients with pleural nodules and prior splenic trauma, 99mTc-HDRBC scintigraphy is the gold standard for non-invasive diagnosis, and functional imaging prevents unnecessary invasive procedures.

Subject of Research: Diagnosis of thoracic and abdominal splenosis using nuclear medicine imaging in patients with prior splenic trauma

Article Title: Thoracic splenosis: a great mimic diagnosed by functional imaging

Article References: Sandoval, T. L., Arroyave, S. P., Yepes, J. C. R., Cadavid, T., & Zamudio, C. C. (2026). Thoracic splenosis: a great mimic diagnosed by functional imaging. EJNMMI Reports, 10(1), Article 28. https://doi.org/10.1186/s41824-026-00308-5

Image Credits: AI Generated

DOI: 10.1186/s41824-026-00308-5

Keywords: splenosis, thoracic splenosis, nuclear medicine, 99mTc-HDRBC scintigraphy, PET/CT, SPECT/CT, splenectomy, splenic trauma, 18F-FDG PET/CT, 18F-PSMA PET/CT, pleural nodules, case report