Pamela Schwartz Schwarzman Animal Medical Center, New York, NY, USA Knowledge of the splenic and regional anatomy is paramount prior to performing splenectomy. The spleen is a dynamic organ typically residing in the left cranial quadrant of the abdomen. The dorsal extremity (head) is less mobile, as it is tethered to the greater curvature of the stomach by the gastrosplenic ligament, in which the short gastric vessels are located. The larger ventral extremity (tail) is more mobile and generally resides across the ventral midline caudal to the ribs. The concave visceral surface of the spleen gives way to the attachments of nerves, vessels, and omentum.1–3 The surgical approach to the spleen is simplified due to its peripheral location within the abdomen, moderately long vascular pedicle, and mostly loose mesenteric attachment.4 The main blood supply to the spleen is from the splenic branch of the celiac artery. The splenic artery generally gives off three to five primary branches as it courses in the greater omentum toward the spleen. The first branch is to the pancreas and is the main supply to the left limb of the pancreas. The two remaining branches run toward the spleen where they spread into several vessels supplying the splenic parenchyma. The dorsal branch continues toward the head of the spleen supplying the cranial parenchyma before coursing through the gastrosplenic ligament to supply the short gastric vessels, which provide blood to the fundus of the stomach. The caudal branch of the splenic artery is the left gastroepiploic artery, which supplies several branches to the caudal portion of the spleen, including the main splenic arteries (usually 2) and omental branch of the splenic artery, before turning back to the supply greater curvature of the stomach (Figure 23.1). The splenic vein drains the many hilar veins into the gastrosplenic vein prior to entering the portal vein.1–3 Splenectomy is indicated in cases of torsion, trauma, diffuse infiltrative disease, splenomegaly, and solitary or multiple splenic masses caused by both neoplastic and non‐neoplastic causes (hematoma, nodular hyperplasia). Less frequently, splenectomy is performed as a treatment for immune‐mediated disorders or splenic abscessation.1,2,4 Splenic disorders are common in middle‐aged to older dogs with clinical signs ranging from absent (incidentally found on palpation or with imaging) or vague signs to life‐threatening (hemoperitoneum).5 Figure 23.1 Diagram showing the splenic arterial supply. (a) Splenic artery and vein, (b) left gastroepiploic vessels, (c) short gastric vessels, and (d) branches to the greater omentum. Original artwork by Taylor Bergrud. The most common causes of splenic disease in dogs are hemangiosarcoma (HSA), extramedullary hematopoiesis, multicentric lymphoma, hematoma or nodular hyperplasia, and congestion.4–7 The most common reasons for splenectomy in cats are mast cell tumors (53%) followed by HSA (21%) and lymphoma (11%).8 HSA is the most common malignant splenic mass neoplasia in dogs.7,9 Historically, the double two‐thirds rule regarding HSA was relied on for all splenic masses (approximately two‐thirds of dogs with splenic masses will have a malignant tumor, with two‐thirds of those malignancies being HSA), although this appears to apply more closely to dogs with hemoperitoneum. A systematic review questioning the validity of the double two‐thirds rule with non‐traumatic hemoperitoneum found an even higher percentage of malignancy at 73%, with 87.3% of the malignant masses being HSA.10 Another recent study documents a higher number of benign splenic tumors (37.5%) in dogs with hemoperitoneum associated with splenic rupture than previously reported.11 Dogs that have splenic masses or nodules without associated hemoperitoneum more commonly have benign (70.5–72.7%) than malignant (27–29.5%) lesions.12,13 Preoperative coagulation profiles should be performed, especially in cases of non‐traumatic hemoperitoneum.3 Discrepancies in the literature make it difficult to interpret possible outcomes, and decisions should not be made based solely on the clinical presentation. Because the decision to proceed with surgery or not can be difficult, especially in the face of hemoperitoneum requiring emergent treatment, clinical decision tools based on initial assessments have been developed to help predict the risk of HSA. An online decision support calculator was developed to aid in the preoperative discrimination of benign from malignant splenic tumors on the basis of preoperative variables. The clinical variables used to estimate the probability of malignancy include serum total protein concentration, presence of (versus absence of) ≥2 nucleated red blood cells/100 white blood cells and ultrasound assessment of the following: splenic mass size, number of liver nodules, presence of multiple splenic masses/nodules, moderate to marked splenic mass inhomogeneity, marked to moderate abdominal effusion, and mesenteric, omental, or peritoneal nodules. Although this model has an accurate level to assist in clinical decision‐making, the calculator should always be considered supplementary to the full clinical presentation.7 A hemangiosarcoma likelihood prediction (HeLP) score was also developed for dogs with hemoperitoneum, which can facilitate identification of dogs at low (≤40%) or high (>55%) risk for HSA based on body weight, total plasma protein, platelet count, and thoracic radiographs. This score may help owners move forward with surgical treatment in dogs with lower risk; however, the decision to euthanize should not be made solely on a higher HeLP score. It is also important to note that a lower risk (non‐HSA diagnosis) does not signify diagnosis of a benign disease, as alternate neoplasms (hepatocellular carcinoma, hepatoma, histiocytic sarcoma) were also included.14 Abdominal masses are often initially diagnosed radiographically; however, there are many factors that can make definitive location of a mass within the spleen difficult (Figure 23.2). Either thoracic radiographs or thoracic CT should be performed in animals with splenic masses to screen for pulmonary or thoracic neoplasia or metastatic spread, especially to the right auricle or right atrium.1 Brief echocardiogram may also be performed to evaluate for cardiac metastasis. Ultrasonography is recommended to provide information regarding the location of a primary mass, evidence of metastasis if present, and surgical planning. Abdominal ultrasound (AUS) has a high sensitivity for detection of splenic masses (87.4%); however, benign and malignant lesions can be indistinguishable prior to pathologic evaluation.10,15 Ultrasound is an excellent screening tool, but there are differences recognized between AUS and gross findings. In one study evaluating dogs with nontraumatic hemoperitoneum, differences were identified between AUS and gross findings in 54% of dogs.15 It is important for clients to know that although obvious metastasis is not noted on AUS, it can still be present at the time of surgery. AUS does not accurately detect diffuse peritoneal or omental nodular metastasis in dogs in which it is identified grossly.11,15 However, when diffuse omental or peritoneal nodular metastasis is evident on AUS, a neoplastic process is most likely supported. The correlation between the sizes of splenic masses detected on ultrasound in relationship to malignant or benign disease is also variable.13,16 Ultrasound is often performed initially due to its wide availability and noninvasive nature. Computed tomography (CT) is becoming more commonplace in veterinary medicine and has greatly improved the accuracy of imaging diagnosis.13 One study evaluating the presurgical assessment of CT in dogs with splenic masses showed that precontrast lesion attenuation was significantly different between malignant and benign tumors. The mean precontrast lesion attenuation of malignant tumors was 40.3 Hounsfield units (HU) compared to 52.8 HU for benign tumors, with most malignant tumors having attenuation lower than 50 HU.13 A previous study noted significantly lower attenuation values on both pre‐ and post‐contrast images; however, a postcontrast threshold value of 55 HU was the best at determining malignant from benign masses (<55 HU being malignant).17 Another study evaluating dual‐phase CT exhibited variable CT features, which do not corroborate with the previous studies.18 A more recent study classifies focal splenic lesions based on their CT features, with a very high accuracy for sarcomas and a moderate accuracy for benign lesions and nodular hyperplasia, while round cell tumors could not be classified.19 Investigation of triple‐phase helical CT in dogs with solid splenic masses found that the enhanced volumetric ratio of HSA was significantly lower than that of hematoma and nodular hyperplasia in all phases; however, it was not possible to differentiate undifferentiated sarcomas with nodular hyperplasia or hematoma.20 Figure 23.2 Left lateral radiograph of a dog with a suspected splenic tumor. The origin of the tumor was confirmed via ultrasound prior to splenectomy. While initial examination of CT to detect differences between malignant and benign disease is promising, disadvantages of utilizing CT for surgical decision‐making are that it is limited to non‐emergent cases, and cost may be preventive for some. Although CT shows significant promise to aid in identification of tumor features, it should not be the sole modality when considering splenectomy (Figure 23.3). Magnetic resonance imaging (MRI) provides soft tissue contrast superior to that of ultrasound or CT; however, there has been very little investigation regarding the use of MRI for focal splenic lesions.21,22 In a study of MRI results for focal splenic and hepatic lesions in dogs, the overall accuracy in differentiating malignant from benign tumors was 94.3%, although only eight of the cases included were of splenic origin.21 While MRI is more readily available than previously, it is likely restricted to specialty facilities and limited by cost and duration of time required under anesthesia. The decision for clients to move forward with surgery can be difficult since the prognosis varies significantly depending on the histopathologic diagnosis, which is usually not known prior to surgery. Owners should be counseled on all possible prognoses, cost, and aftercare to allow them to make the most informed decision given the work‐up provided. Complete splenectomy is the most performed and recommended surgical treatment of suspected neoplasia, diffuse infiltrative disease, torsion, and most focal and/or generalized splenic enlargement. The spleen can be approached as an open abdominal procedure or with laparoscopic assistance. Prior to surgery, patients with shock and coagulative dysfunction should be stabilized using appropriate supportive treatment and blood products. Figure 23.3 Axial CT image of a large (11.4 × 9.0 × 9.1 cm) heterogeneously contrast‐enhancing mass expanding from the tail of the spleen. Histopathology was consistent with splenic nodular lymphoid hyperplasia and extramedullary hematopoiesis with infarction and hematoma formation. Performing splenectomy as close to the hilus of the spleen as possible avoids ligating the splenic vessels proximal to the pancreatic branches, which could damage the pancreatic blood supply. The vessels are ligated as they terminate into the spleen. Conventional techniques for splenectomy include suture ligation or stapling devices. These have largely been replaced with the use of a bipolar vessel sealing device (BVSD), which is an electrosurgical instrument that can be utilized in both open and laparoscopic procedures. The BVSD applies direct pressure and bipolar energy to the tissue, causing vessel sealing by fusing the collagen and elastic fibers within the blood vessel walls. BVSDs have been shown to achieve sufficient and safe hemostasis during hilar splenectomy as well as shorten the surgical and anesthetic time.23–26 There are several different commercial BVSDs available for veterinary use, such as the LigaSure™,i the EnSeal®,ii and the Harmonic device system.iii,,27 Each BVSD device will be slightly different depending on the system, but noted advantages include monopolar, bipolar, and vessel sealing capabilities within a single system (LigaSure™), variable handpieces, the ability to seal vessels of ≤7 mm diameter (LigaSure™ and EnSeal®), and the ability to reuse the handpieces for a limited number of times28,29 (Figure 23.4a,b). Additional benefits include the ease of use and the lack of suture material needed. Figure 23.4 (a) LigaSure™ handpieces for laparoscopic use (top) and open laparotomy (bottom), although either can be used in both open and MIS cases. There are also a variety of other LigaSure™ handpieces not pictured. (b) The Maryland and Impact handpieces with jaws opened and closed. The seal length is 20 mm for the Maryland handpiece (top) versus 36 mm for the Impact (bottom). Open laparotomy is often required due to the large size of a splenic mass in relation to the size of the patient and in cases of hemoperitoneum or splenic torsion. The presence of adhesions associated with larger masses may also limit minimally invasive procedures (Figure 23.5). Historically, individual suture ligation of all short terminal branches at the hilus of the spleen was performed, preserving the left gastroepiploic artery and short gastric arteries. If the integrity of the blood supply to the stomach is not compromised (e.g., during gastric dilatation and volvulus if the short gastric arteries are torn), these vessels are not required to be preserved. Since the individual ligation technique is not necessary and is time‐consuming, a modified en masse ligation technique has been described that only involves four ligatures of the short gastric arteries, dorsal branch of the splenic artery, main splenic artery, and omental branch of the splenic artery.30 Complete splenectomy can be performed using sutures, staplers, or BVSDs. The Ligate and Divide stapler (LDS) places two U‐shaped staples around a vessel and divides between the two (Figure 23.6). The LDSs can save a considerable amount of time for procedures that require multiple vessel ligation, such as the hilar ligation technique for splenectomy.31 Figure 23.5 Note that large size of the splenic mass (>15 cm), which makes an open laparotomy approach to complete splenectomy more feasible than laparoscopic splenectomy. Source: © Pamela Schwartz. Figure 23.6 The Ligate and Divide Stapler handpiece, which can save time compared to hand sutures during hilar splenectomy. A disposable cartridge of staples is attached to the handpiece, which can be re‐sterilized for multiple uses. There are single‐use handles and cartridges available as well as power LDS staplers. This technique is reported as described by Fox‐Alvarez and Case.2 The patient is placed in dorsal recumbency, and the entire abdomen aseptically prepped. A ventral midline abdominal laparotomy is made starting caudal to the level of the xiphoid and extending as far caudally as necessary for full abdominal exploration and complete splenectomy. Removal of the falciform fat, using electrocautery or suture, and placement of the Balfour retractor improve visualization (Figure 23.7
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Splenectomy
Anatomy
Pathology
Diagnostic Imaging Techniques
Surgical Techniques
Open Laparotomy with Suture Hilar Ligation Technique
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