Ectopic spleen presenting with anemia and an abdominal mass in a dog

Abstract

An 11.5-year-old, neutered male, golden retriever dog that had previously had a splenectomy for benign disease 2 years prior to presentation was diagnosed with anemia and a large abdominal mass. Necropsy and histopathology identified the abdominal mass as ectopic splenic tissue.

An 11.5-year-old, neutered male, golden retriever dog was presented to the Internal Medicine Service of the Mississauga-Oakville Veterinary Emergency Hospital & Referral Group (MOVEH) in February, 2012 for investigation of a mid-abdominal mass diagnosed on referral abdominal radiographs. The patient was reported to have had intermittently pale mucous membranes and periods of lethargy in the 2 wk prior to presentation. Referral serum biochemical profile and complete blood (cell) count (CBC), performed 1 d prior to presentation, demonstrated a moderate, normocytic, normochromic, poorly responsive anemia [hematocrit 0.28 L/L; reference interval (RI): 0.39 to 0.60 L/L], mild lymphopenia (0.9 × 10⁹/L; RI: 1.0 to 4.8 × 10⁹/L), hyperglobulinemia (40 g/L; RI: 18 to 39 g/L), and hypochloridemia (105 mmol/L; RI: 107 to 123 mmol/L). Peripheral blood smear evaluation demonstrated few Howell-Jolly bodies, mild poikilocytosis, rare polychromasia, and shift platelets. Thoracic radiographs were normal. The patient lived in southern Ontario and no travel history was reported. The patient had been presented to the Internal Medicine Service at the MOVEH, on March 7, 2010, for evaluation of a cranial abdominal mass found incidentally on physical examination by the referring veterinarian. Ultrasound examination at that time revealed a splenic mass of mixed echogenicity that measured 6.6 cm × 4.6 cm. Although no free abdominal fluid was noted, the mesentery surrounding the mass was hyperechoic suggesting possible previous rupture. Thoracic radiographs were normal. Based on the size of the mass, the possibility of previous rupture, and potential for future hemorrhage, splenectomy was performed 8 d after initial presentation. Histopathology of the mass and adjacent splenic tissue was consistent with splenic red pulp nodular hyperplasia with congestion and hematopoiesis; no evidence of neoplasia was reported.

Case description

At the time of the more recent presentation, the patient was bright and alert, and abdominal palpation revealed a large mid-abdominal mass on physical examination. Abdominal ultrasound demonstrated a mixed echogenicity mass, measuring 11.28 cm × 9.09 cm, located in the mid-abdomen caudal to the stomach and liver (Figure 1). An organ of origin could not be determined on abdominal ultrasound. Sedation with hydromorphone (Hydromorphone hydrochloride; Sandoz, Boucherville, Quebec), 0.05 mg/kg body weight (BW), IV, was administered to facilitate ultrasound-guided fine-needle aspiration of the abdominal mass. Cytologic evaluation of the aspirates was consistent with cells of splenic origin, with evidence of mild plasma cell hyperplasia, mild stromal hyperplasia, and mild extramedullary hematopoiesis (Figure 2). Further investigation via exploratory laparotomy was declined.

Figure 1.

Ultrasonographic sagittal image demonstrating echogenic appearance and size of the mid-abdominal mass.

Figure 2.

Photomicrograph of a fine-needle aspirate of the mid-abdominal mass demonstrating a background of red blood cells, mixed lymphocyte population (arrowhead), uniform fusiform stromal cells (asterisk), and mild plasma cell hyperplasia (arrow), consistent with splenic origin. Wright’s stain; bar = 50 μm.

Reassessment CBC, performed May 13, 2012, demonstrated a marked, normocytic, normochromic, non-responsive anemia (hematocrit 0.22 L/L; RI: 0.39 to 0.60 L/L) and moderate lymphopenia (0.4 × 10⁹/L). The patient was subsequently presented to the referring veterinarian May 15, 2012 for lethargy; repeat blood work demonstrated a progressive, normocytic, normochromic, non-responsive anemia (hematocrit 0.18 L/L), moderate lymphopenia (0.4 × 10⁹/L), hypoalbuminemia (28 g/L; RI: 31 to 43 g/L), hyperglobulinemia (43 g/L), hypochloridemia (105 mmol/L), and hypermagnesemia (1.07 mmol/L; RI: 0.70 to 1.00 mmol/L). The owners elected humane euthanasia and permitted a postmortem examination. Gross postmortem examination revealed a large, well-encapsulated red mass in the mid-abdomen. The mass was located within the mesentery and did not originate from any organ. When incised, the mass contained a viscous, dark red fluid-filled center. No other gross abnormalities were noted. Postmortem samples of renal, hepatic, pancreatic, gastrointestinal, and pulmonary tissues, and the mid-abdominal mass were submitted for histopathology. Bone marrow sampling was not performed. The mass was identified as splenic tissue with evidence of parenchymal congestion and siderotic plaques; no evidence of neoplasia was identified (Figures 3a, b). The remaining tissue samples were reported to be within normal limits.

Figure 3.

a — Photomicrograph of the mid-abdominal mass demonstrating normal splenic tissue, including: red pulp (arrowhead), siderotic plaque (asterisk), and fibromuscular capsule (arrow). Hematoxylin and eosin stain; bar = 200 μm. b — Photomicrograph of the mid-abdominal mass demonstrating normal splenic tissue, including: white pulp (asterisk), red pulp (arrowhead), and plasmacytosis (black arrow). Hematoxylin and eosin stain; bar = 100 μm.

Discussion

Ectopic spleen is a rarely reported clinical condition in companion animal literature and has a reported incidence of < 0.5% in human literature (1). To date, cases of ectopic spleen have been reported in 3 dogs in association with the liver, mesentery, diaphragm, omentum, and peritoneal wall and in 1 cat in association with the pancreas (2–5). Ectopic spleen is defined as histologically normal splenic tissue in an abnormal location. This can result from a congenital defect due to incomplete fusion of the dorsal mesogastrium, termed an accessory spleen (6). Ectopic spleen can also occur secondary to splenosis, an acquired condition due to autotransplantation of viable splenic tissue, which results from splenic trauma or elective splenectomy (6,7). Abdominal or pelvic splenosis is reported to occur in up to 65% of human splenic rupture cases (7). Due to the patient’s history of splenectomy 2 years prior to presentation, and lack of an accessory spleen noted at that time, it is hypothesized that the etiology of the ectopic splenic tissue was splenosis. However, the presence of an accessory spleen not visualized during exploratory laparotomy cannot be ruled out. Regardless of whether the origin is accessory spleen or splenosis, ectopic splenic tissue has been reported to undergo hypertrophy secondary to splenectomy, which is suspected to have occurred in this patient (3,8).

Autotransplantation of splenic tissue occurs as nodules predominantly within the abdominal cavity and, generally, represents a benign, incidental discovery during investigation of an unrelated condition. An abdominal mass was identified during the diagnostic evaluation of all canine patients reported in the literature, including the patient reported here. Currently, technetium-99m (Tc-99) heat-damaged erythrocyte scintigraphy is the non-invasive diagnostic modality of choice in human patients suspected of having ectopic spleen, regardless of location (6,7). This diagnostic modality prevents invasive abdominal surgery for investigation of a potentially benign etiology. If ectopic spleen is confirmed in an asymptomatic patient, no further investigation or intervention is recommended. To date, all reported cases of canine ectopic spleen, including the case reported here, were diagnosed via histopathology of tissue samples collected at either exploratory laparotomy or postmortem examination (2–4). The 3 other reported cases of canine ectopic spleen identified multiple nodules affecting a single organ (hepatic) or disseminated throughout the peritoneal cavity (2–4). This patient’s manifestation of ectopic splenic tissue was unusual as it was present as a single, large mass within the mesentery with no evidence of additional ectopic splenic tissue identified during gross postmortem examination. As ectopic spleen is typically a benign, incidental finding, there are no true incidence data in the dog. A review of 1372 non-neoplastic canine splenic lesions reported the incidence of accessory spleen to be 3% (41/1372) (9). The low incidence of ectopic spleen suggested by the current paucity of case reports is suspected to be falsely low. If ectopic spleen is suspected in the dog, then Tc-99 heat-damaged erythrocyte scintigraphy could be considered as a non-invasive way to obtain a diagnosis. Tc-99 was employed to monitor reimplated spleens in canine patients in a 1994 study; however, this modality has not been validated in canine patients (10).

Although the majority of human patients are asymptomatic, atypical presentations of ectopic spleen, including abdominal mass, hemoptysis, pleurisy, clinical signs mimicking myocardial infarction, pyrexia of unknown origin, abdominal pain, spontaneous mass rupture with hemorrhage into body cavities, and splenosis within the thorax, subcutaneous tissue, and cranium, have been reported (1,6,7). One of the 3 previously reported cases of canine ectopic spleen was discovered incidentally, presenting as a cranial abdominal mass on radiographs, during monitoring of a clinically normal patient 4 y after splenectomy (2). Serial physical and radiographic examinations over a period of 8 mo demonstrated progressive hepatic increase and abdominal distension; the patient was subsequently euthanized when anorexia and jaundice developed (2). Rapid hypertrophy of intrahepatic splenosis nodules was considered to be the cause of clinical signs, which resulted in euthanasia of the patient (2). The other 2 reported cases of ectopic splenic tissue were identified during investigation of dogs, whose clinical presentations included lethargy, pain, and weakness after abdominal trauma jumping into an automobile and acute abdominal pain and distension, anorexia, tachycardia, tachypnea, hypothermia, and hemoperitoneum (3,4). The clinical presentation of both dogs was attributed to hepatic cyst rupture, with cyst formation secondary to cystic dilation of lymphatic and bile ducts resulting from compression of hepatic parenchyma by hypertrophic intrahepatic splenic tissue (3,4). The patient reported here was presented for investigation of intermittently pale mucous membranes and periods of lethargy, which was suspected to be secondary to progressive anemia; an etiology for the clinical presentation was not definitively determined. Although the lethargy, pallor, and anemia may have been secondary to the presence of the abdominal mass, concurrent pathology resulting in the clinical presentation cannot be excluded.

Ectopic splenic tissue is reported to perform normal splenic functions in splenectomized patients (6–8,10). Howell-Jolly bodies, which were reported in the peripheral blood of splenectomized dogs, were absent months after surgical splenic reimplantation (8). This phenomenon could account for the lack of abnormal red blood cells, such as Howell-Jolly bodies and schistocytes that are typically removed from circulation by the spleen, in the reassessment peripheral blood smears and the presence of EMH identified on cytology of this patient.

There are several potential causes for the progressive, poorly responsive anemia noted on referral CBC. Anemia of chronic disease (ACD), secondary to the hypertrophic ectopic splenic tissue, would explain the poor response characterizing the anemia; however, the anemia was more profound than typically found with ACD. Alternatively, the anemia could have been due to hemorrhage within the ectopic spleen, which is supported by the fluid-filled center of the mass, suspected to represent hemorrhage and necrosis, identified during postmortem examination. However, unless acute, this would typically present as a regenerative anemia. Rupture of the ectopic spleen and subsequent hemoabdomen was not supported at postmortem examination, although historical hemoabdomen with resorption cannot be excluded. An alternative explanation for the progressive, non-regenerative anemia is the presence of bone marrow disease (i.e., dyserythropoeisis, pure red cell aplasia, myelofibrosis, immune-mediated hemolytic anemia). If bone marrow disease was present, it may have induced hypertrophy of the ectopic splenic tissue. Although the patient’s clinical presentation of lethargy and anemia could have been secondary to the ectopic splenic mass, another etiology cannot be excluded at this time and investigation with bone marrow biopsy obtained at postmortem would have been required to further evaluate the anemia.

Bone marrow evaluation would have also enabled further investigation of persistent hyperglobulinemia. Although hyperglobulinemia has not previously been reported in cases of canine ectopic spleen, this patient’s atypical presentation of a single, large, necrotic, and fluid-filled mass could induce chronic inflammation and subsequent hyperglobulinemia. Alternatively, the presence of plasmacytosis within the splenic tissue, which is supported by plasma cell hyperplasia identified on cytology, could result in hyperglobulinemia. Due to a lack of bone marrow evaluation, concurrent neoplasia (i.e., malignant lymphoma, multiple myeloma) cannot be ruled out. In most cases, concurrent neoplasia would have been discovered on postmortem examination; however, primary bone marrow neoplasia can exist without systemic evidence. As this case was assessed over a 3-month period, it would be atypical for primary bone marrow disease to have no peripheral atypical cells, changes in multiple cell lines, or more dramatic progression of clinical signs in this timeframe.

This case illustrates the rare circumstance when ectopic spleen can result in a solitary abdominal mass. Ectopic splenic tissue should be considered as a possible cause of an abdominal mass in dogs, including dogs that have undergone splenectomy. CVJ