C45-14 Thoracic Splenosis Mimicking Infectious and Neoplastic Disease in a Postsplenectomy Patient: A Diagnostic Challenge

Introduction Thoracic splenosis is a rare, benign condition that occurs when splenic tissue autotransplants within the thoracic cavity after splenic trauma, usually in association with diaphragmatic injury. It may appear years later as pleural-based nodules mimicking malignancy or granulomatous disease, often leading to unnecessary invasive procedures. We report a diagnostically challenging case complicated by axillary lymphadenopathy and presumed infection. Case Description A 46-year-old man with prior exploratory laparotomy and splenectomy (1996) and treated pulmonary tuberculosis 15 years earlier presented with five days of left mid-sternal chest pain, right axillary pain with swelling, and a tender nodule between the right thumb and index finger. He reported 15-20 pounds of unintentional weight loss during prior six months but denied fever, night sweats, or appetite loss. Examination revealed mobile, mildly tender right axillary lymph nodes; lungs were clear. Laboratory results, including complete blood count, were normal.Chest radiography showed a left lower-lobe opacity. CT revealed right axillary and paraesophageal lymphadenopathy and a multilobulated pleural-based soft-tissue mass in the left lower lobe, the largest locule measuring 4.7 × 5.7 × 3.4 cm. The axillary lymphadenopathy and web-space swelling were likely related, representing localized infection or inflammation. Differential diagnoses for the thoracic lesion included malignancy, mesothelioma, granulomatous infection, and thoracic splenosis. Technetium-99m sulfur-colloid SPECT/CT showed focal uptake in the pleural lesion and at the left cardiophrenic angle, confirming thoracic splenosis. The spleen was absent in its expected location, consistent with prior splenectomy. The patient received a short course of azithromycin with marked improvement and resolution of right-hand and axillary pain and swelling. With normal inflammatory markers and no systemic illness, thoracic findings were deemed incidental. He was managed conservatively without biopsy or surgery. Discussion This case highlights how concurrent but unrelated conditions can obscure recognition of thoracic splenosis. The presence of right axillary lymphadenopathy and localized hand swelling alongside left-sided chest pain and weight loss initially raised concern for malignancy or disseminated infection, diverting attention from an incidental benign process. Thoracic splenosis can coexist with separate localized infections, creating diagnostic uncertainty even in the absence of systemic inflammation. Functional imaging remains central to diagnosis; while technetium-99m-labeled heat-damaged RBC scintigraphy is the gold standard, sulfur-colloid SPECT/CT offers a widely available, reliable alternative. Awareness of such overlapping presentations broadens understanding of thoracic splenosis and helps prevent unnecessary invasive procedures.