Veterinary Society of
Surgical Oncology


Biologic Behaviour

  • HSA is a highly metastatic tumor with microscopic or macroscopic metastatic disease at diagnosis
  • HSA arises from vascular endothelial cells
  • HSA is the most common splenic tumor in dogs and accounts for 24%-50% dogs with splenic masses
  • splenic hemangioma and hematoma occur in 3%-34% dogs with splenic masses
  • other primary HSA sites include right atrium, liver, integument, urinary bladder, prostate, kidney, muscle, bone, CNS, and oral cavity
  • median age 9.0-10.5 years
  • sex predisposition: males
  • breed predisposition: GSD, Golden Retriever, Labrador Retriever, and Schnauzer
  • cause is unknown although linked with exposure to thorium dioxide, arsenical or vinyl chloride compounds, ultraviolet light, and local radiation therapy in humans
  • 25% of dogs with splenic HSA have concurrent right atrial HSA
  • HSA is highly metastatic: > 50% metastatic rate for splenic HSA
  • lungs are the most common metastatic site (64%-67%), followed by spleen (36%-60%), kidneys (55%), liver (41%-55%), brain (20%), intestines (20%), adrenal glands (20%), skeletal muscle (20%), visceral lymph nodes (15%), skin and subcutaneous tissue (15%), left ventricle (10%), and mesentery and omentum (10%)
  • tumor rupture or erosion through blood vessels is common and results in seeding of peritoneum or omentum with tumor cells
  • splenic tumors other than HSA include LSA (4%), various sarcomas (i.e., undifferentiated sarcoma, FSA, leiomyosarcoma, mesenchymoma, myxosarcoma, histiocytic sarcoma, OSA, and liposarcoma), and metastatic carcinomas

    Clinical Signs

  • non-specific
  • acute presentation: acute dyspnea, pallor, abdominal effusion, and hypovolemic shock secondary to splenic rupture and hemorrhage
  • chronic presentation: lethargy, anorexia, and weight loss
  • Physical Examination

  • palpable abdominal mass with splenomegaly and abdominal fluid wave
  • cardiac abnormalities: arrhythmia, cardiac murmur, and muffled heart sounds
  • Diagnosis

    General Considerations

  • splenic HSA and hemangioma have similar ultrasonographic and gross appearance and are difficult to differentiate
  • HSA is significantly more likely to have increased VEGF levels
  • hemoabdomen is more common in dogs with HSA (76.4%) compared to hemangioma (29.6%)
  • neoplastic disease accounts for 80% of non-traumatic hemoabdomen cases in dogs and HSA for 88% of these cases
  • neoplastic effusion can be differentiated from non-neoplastic as neoplastic effusions have:
  • significantly lower glucose concentrations (72.6 mg/dL v 110.0 mg/dL)
  • significantly higher lactate concentrations (3.81 mmol/L v 1.68 mmol/L)
  • Laboratory Findings

  • hematology: anemia and morphological changes to red blood cells such as nucleated erythrocytes, polychromasia, poikilocytes, anisocytes, shistocytes, and reticulocytes
  • morphologic changes due to iron loss, altered hepatic lipoprotein metabolism, microangiopathic disease, or DIC and sluggish flow through abnormal vascular channels resulting in increased membrane fragility
  • neutrophilic leukocytosis is common due to either stress or tumor rupture and necrosis
  • thrombocytopenia due to DIC, but may form part of Kasabach-Merritt syndrome
  • Kasabach-Merritt syndrome is characterized by an enlarging vascular tumor, thrombocytopenia, anemia, prolonged PT and APTT, decreased FDP, and increased fibrin split products
  • thrombocytopenia (75%-90%), fragmented red blood cells (80%), and DIC (50%) are common findings
  • anemia and DIC associated with blood loss is common in cats with visceral HSA
  • Survey Radiographs

  • 2 metastatic patterns in dogs with HSA:
  • widely disseminated nodular pattern (common)
  • diffuse interstitial pattern (uncommon)
  • false-negative results are high: 22% from splenic HSA and > 50% for right atrial HSA
  • Ultrasonography

  • abdominal ultrasonography is a highly accurate and sensitive tool for splenic evaluation
  • primary HSA: mixed pattern of anechoic and hyperechoic regions
  • metastatic HSA: diffusely anechoic or hypoechoic appearance
  • ultrasound-guided FNA or needle-core biopsy contraindicated due to risk of seeding and low diagnostic yield
  • Electrocardiography

  • ventricular arrhythmias are commonly associated with HSA due to hypoxia, anemia, or hypovolemia
  • Clinical Staging


    Surgical Management

  • total splenectomy recommended
  • total splenectomy is considered a palliative procedure to reduce the risk of hemorrhage
  • Chemotherapy

  • doxorubicin 30 mg/m2 q 2-3 weeks for 5 doses
  • ± cyclophosphamide 100-150 mg/m2
  • complications: neutropenia (common), severe gastroenteritis, cardiotoxicity, and sepsis
  • Immunotherapy

  • immunotherapy aims at altering host-tumor response
  • mixed bacterial vaccination and liposome-encapsulated muramyl tripeptide phosphatidylethanolamine (L-MTPE) have been investigated with mixed results
  • Other Treatments

  • angiogenesis inhibitors and gene therapy
  • Complications


  • hemorrhage is caused by tumor rupture, manipulation of the spleen or liver, and inadequate ligation
  • treatment: intravenous fluids and fresh whole blood (preferred as thrombocytopenia common in HSA)
  • autotransfusion contraindicated due to neoplastic cells and low clotting factors and platelets
  • Coagulopathy

  • fragmentation anemia and thrombocytopenia are common ± DIC
  • treatment: intravenous fluids (to maintain circulating volume) and fresh whole blood transfusions
  • Cardiac Arrhythmias

  • ventricular extrasystole and ventricular tachycardia
  • possible causes of cardiac arrhythmias include release of emboli during splenic manipulation, transient ischemic episodes, and release of toxic factors from abdominal viscera into the splanchnic circulation
  • treatment: correct underlying cause, correct acid-base and electrolyte abnormalities, intravenous fluids ± anti-arrhythmic drugs (lidocaine)
  • continuous ECG monitoring is recommended for 12-36 hours post-splenectomy
  • Prognosis

  • poor prognosis
  • MST 19-86 days with surgery alone, with 12-month survival rate 6.25%
  • MST 172-202 days with surgery and chemotherapy with 12-month survival rate up to 20%
  • MST 257-273 days for stage I HSA
  • MST 156-210 days for stage II HSA
  • MST 107-136 days for stage III HSA
  • prognostic factors include clinical stage and addition of immunotherapy:
  • stage III disease (i.e., metastasis) significantly decreases MST (60-107 days v 172-273 days) and 12-month survival rate (0% v 20%)
  • L-MTPE combined with surgery and chemotherapy significantly improves MST compared to surgery and chemotherapy only (277 days v 143 days)


    No evidence of neoplasia

    Primary Tumor


    Tumor < 5 cm in diameter and confined to primary site


    Tumor ≥ 5 cm in diameter, ruptured, or invading subcutaneous tissue


    No evidence of regional lymph node involvement


    Regional lymph node involvement



    No evidence of metastasis


    Evidence of distant metastasis with site specified



    Tumor invading adjacent structures including muscle


    Distant lymph node involvement

    Clinical Stage
















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