+ Biologic Behavior

  • 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


+ 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


+ 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


+ Hemorrhage

  • 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)



T0 No evidence of neoplasia
T1 Tumor less than 5 cm in diameter and confined to primary site - Primary Tumor
T2 Tumor ≥ 5 cm in diameter, ruptured, or invading subcutaneous tissue
T3 Tumor invading adjacent structures including muscle
M0 No evidence of metastasis
M1 Evidence of distant metastasis with site specified - Metastasis
N0 No evidence of regional lymph node involvement
N1 Regional lymph node involvement - Node
N2 Distant lymph node involvement

Clinical Stage

I II III T T1 T0-1 T1-2 T2-3 N N0 N0-1 N0-2 M M0 M0 M2