Spleen

Introduction

The spleen is suspended in a portion of the greater omentum (the gastrosplenic ligament) that extends from the diaphragm, fundus, and greater curvature of the stomach to the spleen.¹ The splenic artery arises from the celiac artery and supplies branches to the left lobe of the pancreas as it courses to the splenic hilus (Figure 44-1). The splenic artery divides into a dorsal and a ventral branch several centimeters from the spleen. The dorsal branch continues to the dorsal portion of the spleen, where it gives off the short gastric arteries. The left gastroepiploic artery arises from the ventral branch of the splenic artery before it contacts the spleen. Venous drainage from the spleen is through the portal vein.

The spleen contains smooth muscle and is innervated by both sympathetic (from the celiac plexus) and parasympathetic (from the vagus) nerve fibers. The spleen also has a considerable population of adrenergic receptors that control contraction and relaxation.²
 

Multiple spleens are uncommon in dogs, but trauma may result in the widespread dissemination of splenic tissue throughout the abdomen. Such fragments of splenic tissue become revascularized, and the resultant condition (splenosis) may be confused with neoplasia. Intentional splenic reimplantation during surgery has been recommended as a means of salvaging splenic function,³ but the mere presence of tissue of splenic origin does not ensure that normal splenic function will be maintained.^4,5

The spleen may have white fibrin deposits or siderotic plaque on its surface. Siderotic plaque consists of iron and calcium deposits and is brown or rust colored. This appearance should not be considered abnormal. Similarly, splenic nodules (areas of benign hyperplasia) may be confused with neoplasia. Distinguishing splenic nodular hyperplasia from neoplasia may be difficult without a biopsy. The size of the spleen is variable, and the spleen may appear abnormally large during barbiturate anesthesia or when it is relaxed during minimal adrenergic stimulation. Anemia, blood loss and stress all cause the spleen to contract.

The spleen has several functions: blood storage, blood filtration and phagocytosis of particles, parasites, bacteria, and damaged or aged red blood cells; contributions to the body’s immune defenses; hematopoiesis; and iron metabolism. The spleen may retain as much as 10% of the total red blood cell mass^6,7 that can be discharged into the general circulation in response to adrenergic stimulation during stress or blood loss. The structure of the spleen places red blood cells in close contact with macrophages; therefore, red cells that are damaged, contain parasites, or have immunoglobulins attached to the surface are removed from circulation in the spleen. The spleen also appears to remove blood-borne bacteria efficiently.⁸ It produces immunoglobulins (particularly I gM) and opsonins, as well.⁹ Although not reported in animals, overwhelming sepsis after splenectomy has occurred in human patients.¹⁰ Hematopoiesis is not a significant function of the spleen in adult animals, unless it is necessitated by decreased function of the bone marrow. Iron is extracted from hemoglobin as red blood cells are broken down and is stored in the spleen for future transport to the bone marrow for production of more hemoglobin.

Indications

Indications for removal of the spleen include neoplasia, torsion of the splenic pedicle (isolated or in conjunction with gastric dilatation volvulus), and severe traumatic injuries. Splenectomy has been recommended as adjunctive treatment for immune mediated thrombocytopenia and hemolytic anemia unresponsive to medical therapy.¹¹ The spleen is often removed in dogs used as blood donors to prevent undetected infection with Haemobartonella canis or Babesia canis. Because the spleen has several functions, partial splenectomy should be considered (when feasible) to retain functional splenic tissue.

Hemangiosarcoma is the most common primary tumor of the spleen. Other tumors of the spleen include hemangioma, leiomyosarcoma, fibrosarcoma, lymphosarcoma, plasma cell sarcoma, mast cell sarcoma, and reticular cell sarcoma. Euthanasia of an animal should not be recommended to an owner solely because of the presence of a splenic tumor. Splenectomy prevents intra abdominal bleeding subsequent to rupture of the tumor, and mean survival times of at least 4 to 6 months in the dog^12,13 and longer in the cat¹⁴ may be expected after splenectomy for hemangiosarcoma. Removal of the spleen for treatment of splenic leiomyosarcoma in dogs resulted in a median survival of 10 months.¹⁵ The spleen may also be enlarged because of infiltration with mast cells in association with feline systemic mastocytosis. Splenectomy appears to improve the duration of survival in affected cats.¹⁶

Determining when irreversible splenic injury has occurred after torsion of the splenic pedicle is difficult. The onset of clinical signs may be insidious or peracute, necessitating emergency surgery.¹⁷ Occlusion of the splenic vein causes vascular stasis, and the vessels ultimately become thrombosed. If the spleen is engorged and blue black, or if thrombi are observed within the vasculature, the spleen should probably be removed. Untwisting the splenic pedicle to restore circulation may release toxic byproducts of anaerobic metabolism.

Preoperative Considerations

Intravenous fluid administration should begin before, and should continue during and after, splenectomy. The rate of administration and total volume given depend on the animal’s condition. If the hematocrit is low (less than 18 to 20%), a transfusion of whole blood or packed red blood cells before surgery should be considered. Although a certain percentage of the red cell mass is removed with the spleen, this volume of cells does not contribute to the peripheral hematocrit at the time of the surgical procedure. Removal of the spleen, however, has a negative effect on the body’s ability to compensate for subsequent blood loss. The presence of a splenic tumor is an indication that the patient should be evaluated thoroughly to detect primary tumors or other sites of metastasis that would diminish the animal’s ability to tolerate anesthesia and surgery or would decrease its life span after surgery.

Surgical Techniques

Splenorrhaphy

Superficial lacerations of the capsule of the spleen may be closed with sutures. If hemorrhage from the splenic wound is brisk, the injured tissue can be devascularized by ligation of the arteries supplying the wounded area near their junction with the spleen (Figure 44-2A and B.). This tissue does not remain ischemic, and collateral circulation develops within 3 weeks.¹⁸ Large isolated arteries within the splenic parenchyma that have been injured can be individually ligated. The splenic capsule is closed with 3-0 or 4-0 absorbable suture swaged onto an atraumatic needle in an interrupted or continuous pattern (Figure 44-2C). It may be necessary to close the defect in the spleen with an interrupted or continuous horizontal mattress suture pattern placed in the splenic parenchyma to control hemorrhage. Pressure may be applied to the surface of the spleen to control continued hemorrhage, or the omentum may be wrapped around the spleen. If complete hemostasis cannot be achieved, a partial or total splenectomy should be performed.
 

Partial Splenectomy

A portion of the spleen can be removed for biopsy purposes or to treat localized splenic trauma or abscessation. A partial splenectomy can be performed with sutures or a mechanical stapling device. The vascular supply of the area to be removed is isolated, ligated, and divided. The tissue to be removed soon assumes an ischemic appearance. The parenchyma is compressed between the fingers along the proposed line of excision. Two pairs of forceps are applied to the spleen approximately 1 to 2 cm apart (Figure 44-3A). Atraumatic forceps (large, straight vascular forceps or Doyen intestinal forceps) should be applied to the splenic remnant to be retained; crushing forceps may be applied to the portion to be excised. The spleen is completely incised between the two forceps approximately 3 to 5 mm from the atraumatic forceps. The capsule is closed with 3 0 or 4 0 absorbable suture in a simple continuous pattern, and the forceps are removed (Figure 44-3B). A second suture line is placed proximal to the first suture material in a continuous horizontal mattress pattern to ensure hemostasis. Partial splenectomy can be performed easily with stapling devices. Staples of a length sufficient to incorporate all tissue must be used. In most animals, staples at least 3.5 mm in length are adequate; if splenic tissue cannot be compressed to a width less than 2 mm, staples 4.8 mm in length should be used.¹⁹ If hemorrhage is observed after application of staples and excision of a portion of the spleen, individual vessels can be ligated.
 

Splenectomy

Splenectomy is usually performed though a midline celiotomy. The incision should be of sufficient length to allow the spleen to be easily delivered from the abdomen. If an essentially normal spleen is being removed (e.g., to prevent hidden parasitemia or to treat an autoimmune disorder), 1 to 2 mL of 1:100,000 epinephrine can be applied to the surface to cause the spleen to contract. Use of larger volumes or higher concentrations of epinephrine may predispose the animal to cardiac arrhythmias, especially if anesthesia is maintained with halothane.

Vessels should be ligated as close to the hilus of the spleen as possible to minimize the potential for damage to the left gastroepiploic and short gastric vessels that supply the greater curvature of the stomach or the vessels passing to the left lobe of the pancreas. Ligation of vessels during splenectomy can be achieved with suture, metal clips, a mechanical stapling device or vessel sealing device. Although absorbable suture may be used for ligation of vessels, I prefer 2-0 or 3-0 silk. The vasculature of the spleen is usually isolated, ligated, and then divided. Alternatively, two rows of hemostatic forceps may be applied to the vasculature. The vasculature is divided, and vessels are ligated after the spleen has been removed. This technique often results in placement of ligatures some distance from the spleen, thereby increasing the potential for inadvertent ligation of vessels supplying the stomach and pancreas. As mentioned previously, when splenectomy is performed to treat splenic torsion, the splenic pedicle should not be untwisted. The vessels are usually adequately accessible to allow individual ligation near the spleen. If this is not possible, forceps can be applied, and the vessels can be ligated individually after the spleen has been removed.

The abdomen should be explored thoroughly after removal of the spleen. When the spleen has been removed to treat neoplastic disease, particular attention should be paid to the liver and lymph nodes, and biopsies should be obtained if these structures appear abnormal. The pancreas and stomach should be examined to be sure that these structures and their vasculature have not been damaged during surgery.

The splenic bed should be examined for hemorrhage before closure of the abdomen. Lavaging the abdomen with sterile saline or another balanced salt solution helps to remove blood clots and improves the surgeon’s view of the splenic pedicle.

Postoperative Complications

Hemorrhage as a result of displacement of a ligature is the most common complication of splenectomy. Intraabdominal hemorrhage causes a progressive decline in the packed cell volume and plasma protein concentration when these values are measured repeatedly. Abdominal paracentesis and diagnostic peritoneal lavage also are useful for detecting hemorrhage after splenectomy. If tests support a diagnosis of intra abdominal hemorrhage after splenectomy, the abdominal incision should be reopened, and the splenic bed should be examined directly. A transfusion of whole blood may be required to compensate for blood loss. If a donor is not available, blood may be retrieved from the patient’s abdomen, mixed with an appropriate volume of anticoagulant, and given back to the patient (autotransfusion). This blood should be filtered as it is administered to remove microemboli and other debris. Blood should be removed from the abdomen using suction or sponges, and clots should be removed from the splenic bed to allow direct observation of the splenic vessels.

In the absence of continued hemorrhage, anemia after splenectomy is of limited duration if the bone marrow is functioning satisfactorily. Splenectomy does impair the capacity of the animal to maintain the circulating red blood cell volume during hemorrhage. Removal of the spleen 2 to 3 weeks before experimentation impaired the ability of anesthetized dogs to respond to hypoxemia.²⁰ Although this phenomenon may be transient, it does suggest that animals that have undergone splenectomy may be less able to maintain cardiovascular homeostasis during surgery, anesthesia, or other stressful situations.

Damage to the vasculature of the stomach or pancreas can cause ischemic necrosis of these organs. Pancreatitis may result from traumatic handling of the pancreas during surgery. These complications occur infrequently.

Ventricular arrhythmias have been reported to occur in as many as 44% of dogs after splenectomy, and it has been observed that these may not be detected in the absence of continuous electrocardiographic monitoring.²¹ Not all dogs that develop ventricular arrhythmias after splenectomy require treatment, and treatment of arrhythmias often prolongs hospitalization. Treatment should be reserved for ventricular arrhythmias that result in significant pulse deficits or ventricular rates that exceed established standards.²²

As mentioned previously, overwhelming septicemia (occasionally observed in humans after splenectomy) has not been reported after splenectomy in dogs and cats. However, splenectomy may render animals more susceptible to infection by blood borne organisms (Haemobartonella, Babesia). Other, as yet undetected immunologic abnormalities may also result from splenectomy in dogs and cats.

Editors Note: Reported survival times in dogs following splenectomy for malignent neoplasia vary considerably. Consultation with an oncologist regarding chemotherapy following surgery is recommended.

References

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