Splenic neoplasia: the surgeon's approach

The spleen is composed of a variety of tissues, and splenic neoplasia may arise from blood vessels, lymphoid tissue, smooth muscle, or the connective tissue that makes up the fibrous stroma. In a recent study of 249 dogs with splenic masses nearly half were found to have non-malignant disease. The most common splenic tumor in dogs is hemangiosarcoma (HAS); this tumor is more commonly diagnosed in large dogs (>27.8 kg) than small dogs. Other malignant tumors of the spleen in dogs include liposarcoma, fibrohistiocytic nodules, lymphoma, blastoma, and adenocarcinoma. Non-malignant masses include nodular hyperplasia, hemangioma, hematoma, and splenitis. Dogs with hemoperitoneum have a higher frequency of splenic neoplasia; similarly cats with hemoperitoneum commonly have abdominal neoplasms and HSA is the most common malignant splenic tumor in cats.

Canine splenic HSA may be seen in more than a third of dogs presenting with acute nontraumatic hemoabdomen. Because HSAs arise from blood vessels, they may form in several different sites in the body (e.g., spleen, right atrium, subcutaneous tissue, liver). The incidence of concurrent splenic and right atrial HSA is unknown, but was recently reported to be as low as 8.7%. Splenic HSAs are aggressive tumors that frequently metastasize to the liver, omentum, mesentery, and brain. Most dogs with HSA have gross evidence of metastatic disease on initial presentation.

Splenic hematomas vary in size and are encapsulated, blood- and fibrin-filled masses that often are grossly and ultrasonographically indistinguishable from HSAs. Histologically, the cavities are surrounded by congestion, fibrosis, and areas of necrosis. They may result from trauma, may occur spontaneously, or may develop secondary to other diseases (e.g., nodular hyperplasia). Hemangiomas and HSAs may be difficult to distinguish histologically, but because the prognosis for these lesions is very different, it is important that they be accurately differentiated. Splenic masses with evidence of malignant neoplastic endothelial cell proliferation can be easily identified as HSAs. However, multiple sections of a malignant mass may be studied without finding malignant cells. More importantly, a proliferation of plump endothelial cells that resemble neoplastic endothelium, but do not have evidence of mitotic activity, may be misdiagnosed as HSA. Hyperplastic nodules are also a common finding at necropsy.

Medical management

Surgical resection is the mainstay of therapy in dogs with splenic HSA; however, postoperative chemotherapy or immunotherapy may prolong survival. Readers are referred to an oncology text for discussion of protocols and treatment regimens used in dogs with HSA.

Surgical treatment

Splenectomy is the treatment of choice for animals with splenic hematoma and hemangioma. It is also the treatment of choice for animals with HSA in which evidence of extensive metastasis or other organ failure does not preclude the short-term benefits of removing the enlarged or ruptured spleen. Laparoscopy is a more sensitive method of detecting visceral HSA metastasis than imaging and can be done before surgery to decide whether surgery is appropriate for a given patient. Splenectomy may not be warranted in dogs with concurrent right atrial tumor; therefore careful preoperative examination (e.g., echocardiogram) of patients is necessary. Dogs with splenic lymphoma and clinical signs associated with massive splenomegaly, splenic rupture, and hemoperitoneum may also benefit from splenectomy. Gastropexy may be performed concurrently (see previous discussion on splenectomy).

Preoperative management

Anemic animals may require blood transfusions before surgery, and they should be preoxygenated. An electrocardiogram should be performed to determine whether ventricular arrhythmias requiring preoperative or intraoperative therapy are present. Ventricular arrhythmias are present in some dogs with splenic masses, and anemia and hemoabdomen may be strongly associated with arrhythmia development. Hydration, electrolyte, and acid-base abnormalities should be corrected before induction of anesthesia, but it must be remembered that fluid therapy may result in worsening of previously mild anemia; the hematocrit must be re-examined shortly before anesthesia. Perioperative antibiotics (e.g., cefazolin 22 mg/kg IV) may be indicated in some animals undergoing splenectomy.

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