Vivian Hayashi MD and Robert Smith MD, Mystery Quiz Section Editors
The answer to the mystery quiz is thoracic splenosis. The key to the solution is the past medical history of a gunshot wound. Shrapnel is seen on the plain CXR (Image 1) as well as in the soft tissue of the back (Image 5). The CXR also shows a lateral diaphragmatic abnormality (Image 1, arrow) likely due to adhesions. The left upper quadrant is notable for colonic gas where one might expect a soft tissue density due to the spleen. The lateral film (Image 2) shows abdominal wall sutures. Presumably, the patient’s gunshot wound resulted in trauma to the upper abdomen and diaphragm necessitating a splenectomy (the left upper quadrant on Image 5 is noteworthy for the absence of a spleen).
Thoracic splenosis (Images 3 and 4, arrows) is a condition that can follow traumatic injury to the spleen. During rupture, the splenic tissue disperses to distant sites including the peritoneal cavity, and possibly the thorax if the diaphragm is injured and tears. The splenic implants are often multiple. One study collected data over a twenty year period and identified five cases of splenosis: two were intraperitoneal and one each in intrahepatic, intrathoracic, and subcutaneous sites. In these five cases, there was an average interval of 29 years between the splenic injury and diagnosis, and most were incidental findings (Khosravi MR. Am Surg 2004 Nov; 70(11):967-70). The implants may mimic neoplasm or thoracic endometriosis.
Consideration of the diagnosis of thoracic splenosis may obviate surgical exploration. Radioisotope scanning, using either Tc99m sulfur colloid or labeled, heat-denatured red cells may confirm the diagnosis non-invasively as splenic tissue will take up these radioisotopes . Importantly, the splenic implants are functional and will keep the peripheral blood smear free of cells ordinarily observed in asplenic individuals (eg, Howell-Jolly bodies, Heinz bodies, and nucleated red cells).