CTICasesThymoma with Thoracic Splenosis Proven by Ferumoxytol MRI
[...]. Thymoma with Thoracic Splenosis Proven by Ferumoxytol MRI. CTICases. Published September 11, 2026. https://cticases.com/c/5zkjt
Imaging findings
A 59-year-old was referred to thoracic surgery with a lobulated mediastinal mass, most likely a thymoma given the age. The difficulty was numerous small nodular implants along the diaphragmatic and costal pleura, which could equally represent pleural spread of thymoma or splenosis, since the spleen was absent following splenectomy for remote trauma and a splenule was visible. The mediastinal mass sat within mediastinal fat with a small tail and a preserved extrapleural fat plane, confirming an extrapleural mediastinal origin. MRI showed the implants dark on T2 with no fat on fat-suppressed sequences. After ferumoxytol the pleural and subphrenic nodules took up the agent while the thymoma did not. At surgery the thymoma was resected and the implants were confirmed to be splenules.
Key takeaways
Ferumoxytol is an iron-based agent taken up by the reticuloendothelial system, and it outperforms sulfur colloid for confirming ectopic splenic tissue; it is infused slowly and the patient can be imaged for roughly 24 to 48 hours afterwards. Separating pleural splenosis from thymoma drop metastases changes management completely, here permitting a straightforward R0 thymectomy instead of an extended resection. An absent spleen with a remote splenectomy history is the clue that should prompt the question. The agent is expensive and delivers an iron load, so it is unsuitable in iron overload states, but it can be given in pregnancy when gadolinium cannot and supports MR angiography as a blood pool agent. Note also that a mediastinal tail and an intact extrapleural fat plane are what identified the dominant mass as mediastinal rather than pleural.
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