The Spleen's Role in a Dog's Body
The spleen is a large, elongated organ located on the left side of the abdomen, nestled close to the stomach. It acts as a reservoir for red blood cells, filters abnormal or aged blood cells from circulation, and plays a role in immune function. Despite being vital, the spleen is not essential for survival — dogs can and do live full lives following its surgical removal.
Unfortunately, the spleen is also a common site for serious disease in dogs, particularly in large and giant breeds. Splenic masses — abnormal growths on or within the spleen — represent one of the most urgent presentations in veterinary emergency medicine.
Splenic Masses in Dogs: How Common Are They?
Splenic masses are among the most frequently encountered abdominal tumours in dogs. When a splenic mass is identified, particularly in a large or giant breed dog, the stakes are high. Approximately 50% of splenic masses in large and giant breed dogs are haemangiosarcoma, a highly aggressive malignant tumour arising from blood vessel lining cells. The remaining cases include benign conditions such as nodular hyperplasia, haematomas, and other, less common tumour types.
The breeds most commonly affected by haemangiosarcoma of the spleen include German Shepherds, Golden Retrievers, and Labradors, though any large breed can be affected. Golden Retrievers appear to be disproportionately represented, likely due to a genetic predisposition. The condition typically presents in middle-aged to older dogs, most commonly between eight and thirteen years of age.
Haemangiosarcoma: What Makes It So Dangerous
Haemangiosarcoma grows within the blood-filled spaces of the spleen, forming fragile, blood-filled nodules that can rupture without warning. When rupture occurs, blood pours rapidly into the abdominal cavity — a condition known as haemoabdomen. This can happen gradually over time with minor bleeds, or catastrophically and acutely.
Haemangiosarcoma is particularly treacherous because the tumour itself rarely causes obvious symptoms until it ruptures. Dogs may appear entirely well right up to the point of collapse. By the time clinical signs are evident, the situation is often critical.
Recognising Acute Haemoabdomen
Acute haemoabdomen is a surgical emergency. The classic signs include:
- Pale or white gums — a sign of significant blood loss and shock.
- Visibly distended or swollen abdomen — caused by accumulating blood.
- Sudden collapse or extreme weakness.
- Rapid, shallow breathing.
- Rapid, weak pulse.
- Restlessness or apparent abdominal discomfort.
Some dogs experience episodic haemoabdomen, where they collapse, appear critically ill, and then seem to recover as their body temporarily clots the bleed. These episodes are often described by owners as the dog having a "funny turn" or being "off" for a period before seeming fine again. This pattern should never be dismissed — it typically signals an imminent major bleed and requires urgent investigation.
Emergency Splenectomy: What Happens in Surgery
If acute haemoabdomen is suspected, the dog will typically be stabilised with intravenous fluids and possibly a blood transfusion before being taken to surgery. In some cases, where the dog is deteriorating rapidly, surgery begins almost immediately.
Splenectomy — surgical removal of the spleen — is the treatment for splenic rupture and for splenic masses where surgery is elected. The procedure involves ligating the blood supply to the spleen and removing the organ in its entirety. In skilled hands, splenectomy is a well-established operation with reasonable perioperative outcomes in otherwise healthy patients.
Survival through surgery is achievable for many dogs, but the prognosis beyond the immediate recovery period depends heavily on the underlying diagnosis — which is why histopathology after removal is essential.
Why Histopathology After Splenectomy is Non-Negotiable
Following splenectomy, the removed spleen should always be submitted for histopathological examination — analysis of the tissue under a microscope by a veterinary pathologist. This is not optional. Without histopathology, it is impossible to know whether the mass was malignant or benign, and therefore impossible to give an accurate prognosis or guide post-operative care.
If the mass proves to be haemangiosarcoma, the median survival time following splenectomy alone is approximately one to two months. With the addition of doxorubicin-based chemotherapy, this can extend to four to six months in some patients, though individual responses vary. Owners who understand this from the outset are better placed to make decisions about quality of life and further treatment.
If the mass proves to be a haematoma or nodular hyperplasia, the prognosis following surgery is excellent, and the dog is effectively cured. Knowing this makes a dramatic difference to how owners plan their dog's future.
Nodular Hyperplasia: The Benign Possibility
Not all splenic masses are malignant. Nodular hyperplasia is a common benign condition in which normal splenic tissue develops into discrete nodules. It is age-related and extremely common in older dogs, found incidentally on ultrasound in many patients being scanned for other reasons.
Nodular hyperplasia is not dangerous in itself, but a large nodule can still bleed and cause haemoabdomen if it ruptures. The difficulty is that nodular hyperplasia and haemangiosarcoma can look similar — or even co-exist — on ultrasound, and cannot be reliably distinguished without histopathology. Approximately 50% of surgically removed splenic masses in large breed dogs are benign, which provides some hope, but this figure cannot be used to avoid surgery when bleeding has occurred.
Other Causes of Splenic Enlargement
Splenomegaly — generalised enlargement of the spleen — can occur for reasons other than a discrete mass. These include:
- Immune-mediated haemolytic anaemia, in which the body destroys its own red blood cells and the spleen enlarges as it removes the damaged cells.
- Extramedullary haematopoiesis, in which the spleen compensates for bone marrow failure by producing blood cells.
- Splenic mast cell tumours, particularly in certain breeds.
- Lymphoma involving the spleen.
- Infectious causes including leishmaniosis in dogs that have travelled to endemic areas.
A thorough diagnostic workup including ultrasound, fine needle aspirate cytology, and blood tests is needed to investigate the underlying cause.
Monitoring and Prevention
There is currently no reliable way to prevent splenic tumours. However, owners of large and giant breed dogs — particularly those in at-risk breeds such as Golden Retrievers and German Shepherds — should be aware of the warning signs described above.
Routine abdominal ultrasound as part of a senior health screen can sometimes detect splenic masses before they rupture, allowing for planned rather than emergency surgery. Discuss senior screening options with your vet if your dog is a large breed aged seven or older.