Subcutaneous Splenosis of the Abdominal Wall: Report of a Case and Review of the Literature

Splenosis is a common benign condition that occurs after splenic rupture via trauma or surgery. The mechanism behind splenic cell autotransplantation begins with the splenic rupture, either from trauma or surgical removal. Splenosis is usually found incidentally and, unless symptomatic, surgical therapy is not indicated. Subcutaneous splenosis is an extremely rare form of splenosis, mostly observed in abdominal surgical scars. We report a case of subcutaneous splenosis, as well as a comprehensive review of the literature. In our case, a 43-year-old woman who had splenectomy after traumatic splenic rupture at the age of 7 years old presented for plastic reconstruction of her postoperative scar. Upon surgery, two asymptomatic subcutaneous nodules were incidentally discovered. The presence of splenic tissue was confirmed by the histological study. The nodules were not excised, as the patient was not symptomatic.


Introduction
Splenosis is a term initially used by Buchbinder and Lipkoff in 1939 in order to describe the heterotopic transplantation of splenic tissue within the abdominal cavity [1]. Splenosis usually occurs aer traumatic or surgical rupture of the spleen with autotransplantation of splenic tissue into ectopic sites.
e pathogenesis of splenosis is not well understood and therefore it is not possible to predict when splenic implants will develop. e mechanism behind autotransplantation begins with the splenic rupture, either from trauma or surgical removal. It is presumed that spillage of the damaged splenic pulp into the adjacent cavities begins the seeding process [1][2][3], while a second mechanism is the hematogenous spread of splenic pulp as suggested by case reports of intrahepatic splenosis [4,5].
e present report describes a rare case of subcutaneous splenosis in a patient with history of splenectomy, along with a comprehensive review of the literature.

Case Presentation
A 43-year-old woman, with a history of splenectomy aer traumatic rupture at the age of 7, was referred to our surgical department for plastic reconstruction of a postoperational scar at the le abdominal wall. Preoperative laboratory values were within normal limits. At surgery, we accidentally discovered two subcutaneous nodules that appeared to be immobile and �rmly embedded in the subcutaneous fat tissue, whereas the underlying abdominal fascia and muscles appeared intact. e two dark red lesions measured 2.7 cm and 1.7 cm, respectively, and had a hard consistency, resembling with splenic tissue. Biopsy specimens were acquired from both lesions and the histological examination con-�rmed the presence of splenic tissue with white and red pulp, and no evidence of malignancy ( Figure 1). e connective tissue also appeared to contain blood vessels adjacent to splenic red pulp ( Figure 2). e red pulp consisted of a complex network of venous sinuses and cords of Billroth, which contain most of the splenic macrophages. e sinuses F 1: Splenic tissue (H&E). e splenic capsule is thick and trabeculae connective tissue vaguely subdivides the organ. F 2: ick connective tissue containing blood vessels next to red pulp of the spleen.
were lined by a particular type of endothelial cells (known as littoral cells) and had a discontinuous wall, which allows traffic of blood cells between cords and sinuses ( Figure 3). e above histological assay reveals that the splenic tissue performed normal splenic function, with absence of Howell-Jolly and Heinz bodies, siderocytes or other abnormal red blood cells. e architecture of the splenic tissue was well developed with nodules of splenic tissue separated by the connective tissue of the capsule ( Figure 4). e location of the ectopic splenic tissue strongly favored of the diagnosis of splenosis rather than accessory spleen, a signi�cant clinical dilemma.
It is known that the diagnostic method of choice, before surgery and histological con�rmation, is nuclear scintigraphy, a heat-damaged red blood cell scan [20]. As we incidentally discovered the nodules, we did not have the opportunity to perform such an examination, so, we only performed a postoperative ultrasound examination, to examine for more nodules in other regions of the abdominal or thoracic cavity. e ultrasound revealed no other mass. e nodules were not further excised, as no further work up is necessary, once splenosis is con�rmed, unless the patient is symptomatic.

Discussion
Splenosis usually occurs aer traumatic or surgical rupture of the spleen with autotransplantation of splenic tissue to  ectopic sites. e �rst known reference to the condition of autotransplantation of splenic tissue following rupture of the spleen was made by Garamella and Hay in 1910 [21]. Albrecht, in 1896 [22], and Schilling [23], in 1907, reported cases of splenic foci, dispersed throughout the peritoneal cavity. Buchbinder and Lipkoff later proposed the term splenosis to describe the presence of multiple peritoneal implants with a widespread location unusual for accessory spleens and with a previous history of trauma to the spleen [1].
e traumatic etiology of splenosis was �rst demonstrated by Kreuter in 1920, who reported that controlled, clean, total splenectomy in monkeys was not followed by the appearance of any nodules, while splenic pulp seeded in the peritoneal cavity produced hundreds of implants [24]. Certain studies estimate that splenosis may occur in up to 67% of individuals who suffer traumatic rupture of the spleen and undergo splenectomy [25]. us, Most cases of splenosis present as intraperitoneal nodules, especially on the serosa surfaces of the small and large bowel, in the parietal peritoneum, the mesentery, and the diaphragm, which are found either incidentally or aer symptomatic complications. Extraperitoneal locations are very rare and mainly include the thoracic cavity aer thoracoabdominal trauma with simultaneous splenic rupture and diaphragmatic laceration. Other uncommon locations have also reported, for example, the female genital organs and the brain [26]. Subcutaneous splenosis is also an extremely rare condition, mostly observed in abdominal surgical scars [26]. It presumes a splenic rupture and a path for escape of the splenic tissue from the peritoneum, for example through a laparotomy incision. e splenic cells may successfully implant subcutaneously and produce nodules of splenic tissue that present as a subcutaneous tumor [27].
e functional capacity of splenic autoimplants is a subject of controversy. ere is some suggestion that splenic autoimplants are in fact functional. Speci�c studies in animals indicate the functional ability of splenic transplants. Rats which developed Bartonella muris anemia following splenectomy are protected in 50% of instances if subcutaneous splenic transplants are performed seven weeks prior to splenectomy [28]. Such transplants also reduce the severity of Trypanosoma lewisi infection in splenectomized rats [28]. ere are cases that reported recurrence of hematological diseases in human patients with splenosis following splenectomy, such as congenital hemolytic anemia, idiopathic thrombocytopenic purpura, and Felty syndrome [15]. In addition, the frequency of postsplenectomy infections appears higher aer elective splenectomy than aer splenectomy following splenic rapture (where splenosis should be more common), implying a protective rate of splenic implants [15]. e degree of function may relate to the total bulk of splenic tissue present, and studies report that roughly 20-30 cm 3 of splenic tissue is required to ensure satisfactory immune response against bacteremia [25]. Other experiments concluded that in adult humans the ectopic splenic tissue does not normalize the altered antibody responses observed following splenectomy [29]. Autograed patients, however, had signi�cantly better splenic function than did asplenic patients. is suggests that autotransplantation can restore at least partial reticuloendothelial function. Whether this is sufficient to reduce overwhelming postsplenectomy sepsis rates compared with those in asplenic patients is unknown. us, it can be suggested that the small volume of functioning splenic tissue resulting from autotransplantation may provide some degree of immunoprotection [30].
Subcutaneous splenosis is extremely rare. Our research revealed 16 published cases, including the present, that have been reported in the English medical literature [2,[6][7][8][9][10][11][12][13][14][15][16][17][18][19]. e clinical features of those cases are summarized in Table 1. Except for two female patients, all the others were male. All the patients had a history of splenic rupture. Ten cases were younger than 30 years old at the time of splenic injury, which is consistent with the fact that splenosis occurs commonly in young men. e time interval between splenic injury and discovery splenosis ranged from 2 to 54 years with a median of 21 years. e long interval seems to re�ect very slow growth of the splenic tissue. In 10 cases, autoimplants of splenic tissue were found in old abdominal surgical scars, whereas 6 cases presented at the site of an exit gunshot wound scar. e majority of cases presented as an asymptomatic subcutaneous mass with a reddish blue macroscopic appearance. None of the patients experienced local hemorrhage or pain. All laboratory data in all patients were within normal limits.
Almost half of the patients had a single nodule, whereas the other half presented with multiple nodules. e size of the nodules ranged from 0,7 to 8 cm, with a subcutaneous splenic mass of 8 × 5 × 7 cm representing the largest nodule reported to date. However, it is evident that the size of the lesions is usually restricted by limited blood supply, most frequently resulting to nodules less than 3 cm in diameter.
Microscopically, subcutaneous splenosis presents as nodular lesions rich in vascular channels. e tissue in splenosis usually reveals distorted architecture with no hilum, a poorly formed capsule and tissue of any shape and size. Most reports describe the tissue as lacking trabecular structures, having less elastic tissue than a normal spleen, and poorly formed or de�cient white pulp with normal appearing red pulp and thus present a diagnostic challenge, as the microscopic picture may simulate lymphoproliferative disorder, nodular Kaposi sarcoma, or vascular malformation. Extensive sampling and thorough examination for a typical organoid arrangement of splenic structures of white and red pulp is recommended in such cases. e red pulp usually consists of a complex network of venous sinuses lined by littoral cells and the cords of Billroth form together a pattern not found in vascular tumors and malformations. In other instances, a full complement of red pulp with cords of Billroth and slightly congested venous sinuses, and white pulp showing central arteries with periarteriolar lymphoid sheaths, follicles, and marginal zones are readily recognizable resulting in the appearance similar to that of accessory spleen. e latter would be the main differential diagnosis on solely microscopic grounds. e localization in the subcutis excludes the possibility of an accessory spleen, which occurs in the tail of the pancreas or within the gastrosplenic ligament, re�ecting the prenatal development of the abdominal viscera. Furthermore, the presence of a �brous capsule, sinusoidal vascular channels, and focal lymphoid aggregates is reminiscent of an accessory spleen.
e patient's history should be taken under serious consideration when traumatic spleen rupture or splenectomy is noted. Apart from the history, the diagnosis of splenosis can be determined with the aid of laboratory �ndings, such as the presence of Howell-Jolly bodies in peripheral blood, absence of spherocytosis and with imaging techniques. e diagnosis is difficult using conventional imaging studies such as ultrasound (U/S) and computed tomography (CT), with frequent false positive imaging �ndings which refer to neoplastic lesions. In most of the cases the diagnosis was made at the operating room. A technetium-99 m sulfur colloid (TC-99 m SC) scintigraphy is the gold standard technique for the diagnosis of splenosis, and it is currently used to monitor splenosis progression (20r). However, technetium-99 m labeled heat-damaged erythrocyte studies have also been shown to provide important information on the existence of ectopic splenic tissue with accuracy [20]. Information on the activity of splenic tissue can be extracted by measuring serum tusin levels [3]. us, splenosis can be suspected by conventional imaging and con�rmed noninvasively by scintigraphy regardless of its ultimate point of implantation [11]. Current clinical practice suggests the preservation of asymptomatic splenosis to preserve immunologic functions and host defenses [14]. Management of splenosis depends on the patient's symptoms. In general it is accepted that asymptomatic implants should not be removed because splenic tissue may be functional and thus useful for the patient. Furthermore, unnecessary excisions of the implants may lead to serious bleeding and damage to the surrounding organs. For symptomatic patients, resection of the implants either by laparoscopy or laparotomy is the treatment of choice [14,15].
In conclusion, subcutaneous splenosis is a rare condition that can occur aer splenic rupture. It represents a diagnostic challenge that may oen lead to confusion and cause the patient to be subjected to needless surgical operations. In all patients with a history of a splenic rupture or splenectomy, subcutaneous splenosis should be considered in the differential diagnosis of a subcutaneous nodule, especially when it occurs in a surgical or gunshot wound scar. Immunohistochemistry is useful in order to con�rm the diagnosis.

Consent
Written informed consent was obtained from the patient for publication of this paper and accompanying images. A copy of the written consent is available for review by the Editor-in-Chief of this journal.

Con���t o� �nte�ests
�e authors declare that they have no con�ict of interests.