Hemangiosarcoma

What Is Hemangiosarcoma?

Hemangiosarcoma (HSA) is a type of soft tissue sarcoma that originates from vascular endothelial cells, the specialized cells that form the inner lining of blood vessels. These tumors tend to form fragile, irregular vascular channels and grow rapidly. Their location in the vascular system makes them highly prone to spontaneous rupture and bleeding, which can lead to sudden collapse or death.

There are three primary forms of hemangiosarcoma in dogs:

• Visceral hemangiosarcoma (most common): affects internal organs, particularly the spleen, liver, and heart.
• Cutaneous hemangiosarcoma: affects the skin or subcutaneous tissue, typically less aggressive but can be invasive.
• Musculoskeletal or other locations: rare, but possible.

The internal form, especially when located in the spleen or heart, is often not detected until it causes acute symptoms due to internal bleeding.

Prevalence and Risk Factors

• Species affected: Occurs almost exclusively in dogs, with rare cases in other species.
• Age: Most commonly diagnosed in middle-aged to older dogs (typically over 6 years of age).
• Breed predisposition:
  • Golden Retrievers
  • German Shepherds
  • Labrador Retrievers
  • Boxers
  • Portuguese Water Dogs
  • Flat-Coated Retrievers

The genetic component is not fully understood, but certain breeds appear to have a heritable predisposition.

Clinical Presentation and Symptoms

Hemangiosarcoma is known as a “silent killer” because it typically does not produce symptoms until it has already caused internal bleeding. Symptoms can vary based on tumor location and whether rupture has occurred.

Common signs include:

• Sudden collapse or episodes of weakness
• Distended abdomen (due to internal bleeding)
• Pale gums
• Increased heart rate
• Labored or rapid breathing
• Lethargy
• Intermittent weakness followed by apparent recovery (micro-bleeding events)
• Seizures (if bleeding occurs in the brain)
• In cutaneous forms: red, black, or ulcerated masses on the skin

In some cases, there may be no outward signs until a crisis occurs.

How and When Veterinarians Diagnose Hemangiosarcoma

Diagnosis typically occurs after acute symptoms prompt emergency evaluation. In many cases, a ruptured splenic mass is identified incidentally during emergency abdominal surgery or imaging.

Diagnostic Tools Include:

• Abdominal ultrasound: Can detect masses in organs (e.g., spleen, liver).
• X-rays: Help assess heart involvement or metastasis to lungs.
• Echocardiogram: For evaluating heart-based tumors (especially right atrial masses).
• Abdominocentesis: Fluid sample from abdomen to confirm presence of blood.
• Bloodwork:
  • Low red blood cell count (anemia)
  • Elevated white blood cells (inflammation)
  • Evidence of coagulation issues
• Histopathology: Required for definitive diagnosis, typically after surgical removal of a mass.
• Fine needle aspirate: Sometimes attempted but may be inconclusive or contraindicated due to bleeding risk.

Why Hemangiosarcoma Is So Dangerous

• Vascular origin: Tumors are blood-filled and fragile, prone to rupture and hemorrhage.
• Rapid progression: Even small tumors can metastasize early.
• Asymptomatic early course: Often undetectable without imaging until catastrophic bleeding occurs.
• Commonly spreads (metastasizes) to the lungs, liver, omentum, brain, or other organs.

Prognosis and Disease Course

Hemangiosarcoma is considered high-grade and aggressive.

Without treatment:

• Survival time after rupture and diagnosis is often 1 to 3 months.

With surgery (e.g., splenectomy):

• Median survival is 2 to 3 months if no additional treatment is pursued.

With surgery + chemotherapy:

• Median survival may extend to 4 to 6 months, with some dogs living 9–12 months or longer.

Cutaneous hemangiosarcoma generally carries a better prognosis than visceral forms if caught early and fully excised.