Transplantation of splenic tissue is caused by splenic trauma, including splenectomy and bodily injury, leading to partial rupture of the spleen and the fragments embedding in other parts of the body (1). Splenic hyperplasia may occur in implanted spleen tissue (2). Transplantation of splenic tissue is occasionally detected on imaging. Most cases have no clinical symptoms or signs, but certain cases of gastrointestinal splenomegaly may result in bleeding (3). The typical clinical manifestations of an implanted ectopic spleen are single or multiple, round or oval masses, that are sometimes misdiagnosed as malignant tumors, such as gastrointestinal stromal tumors (4), lymphomas (5), peritoneal mesotheliomas (6), renal cancer (7) or liver cancer (8).

It is generally thought that the best treatment may be planned only once a sample is obtained and the nature of the nodule is determined preoperatively. However, when the nature of the nodule cannot be determined preoperatively, the nodule size, the possible diagnosis, patient characteristics and clinical symptoms should be assessed prior to surgery (9).

The present study reported on a case of intraperitoneal transplantation of splenic tissue that was only able to be characterized after surgery.

A 38-year-old Asian male with a familial hemolytic disease had undergone laparoscopic splenectomy due to traumatic rupture of the spleen one year previously at our hospital (The Second Affiliated Hospital of Soochow University, Souzhou, China). At seven months previously, the patient developed middle-upper abdominal pain without any obvious cause that radiated to the chest and back. The condition improved with conservative treatment at our hospital, but the patient experienced recurrent episodes. The mass was discovered incidentally on a CT scan (May 2021; The Second Affiliated Hospital of Soochow University, Souzhou, China) performed to check for the cause of pain in the upper abdomen.

The patient had a white blood cell count of 12.6x10⁹/l (normal range, 4-10x10⁹/l) and a platelet count of 458x10⁹/l (normal range, 100-300x10⁹/l). Furthermore, the patient's blood test results indicated a slight increase in total bilirubin. However, the levels of other markers, including those of several serum tumor markers (carbohydrate antigen199, fetal protein, neuron-specific enolase, gastrin-releasing polypeptide and soluble interleukin-2 receptor) were normal.

Abdominal CT suggested multiple gallstones in the gallbladder, which changed after splenectomy, and multiple nodules in the original splenic area, suggesting transplantation of splenic tissue (Fig. 1). MRI revealed round T1-weighted imaging (T1WI)/T2WI/T2W hyposignal foci in the splenic area (the larger foci were ~39 mm in length). No retroperitoneal lymph nodes were observed. The gall bladder bile was thick. Multiple stones and cholecystitis were present. The spleen was not visualized (the patient underwent laparoscopic splenectomy at our hospital one year previously due to traumatic splenic rupture) and there were multiple abnormal signal foci in the splenic area, so the possibility of ectopic spleen implantation was considered. Due to the patient's history of a hereditary hemolytic disease, laparoscopic cholecystectomy and accessory splenectomy were performed simultaneously (Fig. 2). The results of abdominal ultrasonography indicated a stable strong echo sound group in the gallbladder cavity, suggesting that the patient had cholecystolithiasis and cholecystitis (Fig. 3).

The patient was subjected to laparoscopic cholecystectomy and a laparoscopic exploration of the abdomen was performed to remove the mass under laparoscopic guidance. Intraoperative exploration revealed that the gallbladder exhibited chronic inflammatory changes and it was resected successfully. A subphrenic broad-based protuberant lesion of ~40 mm in size was found and completely removed using an ultrasonic scalpel. The excised mass was ~40 mm in diameter and contained splenic parenchyma (Fig. 4).

The final pathological report (routine hematoxylin-eosin staining) revealed chronic cholecystitis, mixed calculi, red pulp dilation, hyperemia and bleeding in round tissue with blood clot formation and acute and chronic inflammatory cell infiltration (Fig. 5). Combined with the gross findings, the symptoms were consistent with the diagnosis of transplantation of splenic tissue.

Transplantation of splenic tissue refers to the regeneration of splenic tissue in other parts of the body through various means due to trauma or splenectomy (7). The regenerated tissue is composed only of undifferentiated reticular cells, which further differentiate into endothelial sinuses, capillaries and lymphocytes after forming a scaffold with fibrous tissue, and finally form splenic tissue (10). Splenic implanted nodules have no splenic hilum and only several small vessels from the penetrating nodular capsule maintain the blood supply to the ectopic splenic tissue. The splenic-implanted nodule's blood supply is derived from the arteries of the surrounding tissues rather than from the splenic artery (1).

Since most patients have a history of splenic trauma, a large amount of scar tissue remains after abdominal surgery (11). Asymptomatic spleen implantation is not a malignant disease and certain patients with clinical symptoms may survive for a long time without treatment (12). With the enlargement of the implanted spleen, abdominal pain, abdominal distension and other relevant clinical manifestations occur from occupation or compression. Intestinal obstruction or gastrointestinal bleeding are clear indications for surgery (13). The patient described in the present study was treated surgically due to symptoms of hypersplenism, the patient's medical history being suggestive of hypersplenism and the patient having a strong desire for surgical treatment.

The diagnosis of an implanted spleen may be challenging. An implanted spleen may resemble several abdominal malignancies. Several studies have reported cases of splenic masses mimicking pancreatic masses (14), lymphomas (5), neuroendocrine tumors (1), intramural colonic masses (15), liver masses (16) and gastrointestinal stromal tumors (17,18).

The imaging findings of the implanted spleen were also atypical. CT images indicated a slightly lower density, which was similar to that of normal splenic tissue and slightly higher than that of liver parenchyma. However, there were no signs of mosaic enhancement of normal spleen tissue in the arterial enhancement phase. Uniform enhancement was observed in the arterial enhancement phase and portal vein phase, with high density in the arterial phase and slightly high density in the portal vein and delayed phase, without any characteristic appearance (19). Most MR images revealed a slightly low signal on T1WI and a medium-high signal on T2WI, similar to signals from normal splenic tissue (20). It has been reported that ^99mTc-DRBC has high specificity in spleen imaging and the concentration of radioactivity in the spleen is 2-4 times higher than that in the liver, which is of great significance when diagnosing an ectopic spleen (9). If the patient has no clinical symptoms, the mass may be diagnosed through needle biopsy and a pathological examination; however, the tissues may be difficult to distinguish from lymph nodes, so the puncture results must be scrutinized (21). However, it must be emphasized that the real key to diagnosing splenopathy is to consider it in the context of a pertinent past medical history.