The Role of the Spleen
The spleen is an organ tucked under the stomach on the left side of the abdomen. It serves several important functions: filtering the blood, removing ageing or abnormal red blood cells, storing a reserve of blood cells and platelets, and contributing to immune responses. Despite being a vital organ, dogs can survive and live well following surgical removal of the spleen, which is an important consideration given the frequency with which splenic disease occurs in the species.
Splenic masses are among the most common abdominal findings in older, large-breed dogs. They may be discovered incidentally during a routine health check or ultrasound, or they may present acutely when a mass ruptures and causes life-threatening internal haemorrhage. Understanding the range of conditions that affect the spleen — and how they differ in severity — helps owners navigate what can be an emotionally and practically overwhelming situation.
Types of Splenic Masses
Not all splenic masses are malignant. Broadly, they fall into two main categories: haematomas and malignant tumours. Research consistently shows that roughly half of splenic masses in dogs are benign, most commonly haematomas (blood-filled cysts or nodules) or nodular hyperplasia (overgrowth of normal tissue). The other half are malignant, with haemangiosarcoma being the most common and most feared.
Other less common splenic tumours include lymphoma, mast cell tumours, fibrosarcoma, and leiomyosarcoma. Each carries its own prognosis and treatment implications, which is why tissue diagnosis following surgical removal is so important.
Haemangiosarcoma: The Aggressive Exception
Haemangiosarcoma is a malignant tumour arising from the cells that line blood vessels. In dogs, the spleen is the most common primary site, though it can also affect the heart, skin, and liver. German Shepherd Dogs, Golden Retrievers, and Labrador Retrievers are disproportionately represented, and the condition is most commonly diagnosed in dogs over eight years of age.
The tumour is biologically aggressive. It grows rapidly, is highly vascular, and carries a strong tendency to metastasise early — most commonly to the liver, lungs, and omentum. In many cases, microscopic spread has already occurred by the time the primary tumour is detected, which significantly affects prognosis even with surgery and chemotherapy.
The most acutely dangerous feature of splenic haemangiosarcoma is its propensity to rupture. When a blood-filled tumour tears, rapid haemorrhage into the abdominal cavity follows. Dogs may collapse suddenly, have pale or white gums, a rapid weak pulse, and a distended abdomen. This constitutes an immediate veterinary emergency requiring stabilisation and usually emergency surgery.
Signs of Splenic Disease
Splenic masses often cause no symptoms until they rupture or grow large enough to be palpated. When signs are present, they tend to be non-specific and easily mistaken for less serious conditions. Watch for:
- Intermittent lethargy or episodes of weakness that resolve on their own — these may represent small, self-limiting bleeds
- Reduced appetite or subtle changes in behaviour
- Abdominal distension or a palpable mass on examination
- Pale gums, rapid breathing, or sudden collapse — indicating significant haemorrhage
- Weight loss over weeks to months
The episodic weakness that some owners describe — where a dog briefly seems very unwell and then recovers — is a recognised pattern associated with small haemorrhages from a splenic mass that temporarily self-seal. These episodes should never be dismissed or attributed to overexertion, particularly in at-risk breeds.
Diagnosis and Imaging
Abdominal ultrasound is the most useful diagnostic tool for evaluating the spleen. It can detect masses, assess their size and internal characteristics, and identify free fluid in the abdomen indicative of bleeding. However, ultrasound cannot reliably distinguish between benign and malignant splenic masses — the appearance overlaps considerably. The widely cited "two-thirds rule" (that roughly two-thirds of splenic masses with free fluid are malignant) provides some probabilistic guidance but is not definitive.
Chest radiographs are performed to assess for visible pulmonary metastases, though early spread may not be detectable on plain films. Blood tests including a full count and coagulation profile help assess the dog's overall condition and fitness for surgery. Definitive diagnosis requires histopathological examination of the removed spleen.
Treatment: Surgery and Beyond
Splenectomy — surgical removal of the entire spleen — is the primary treatment for splenic masses, both for diagnosis and for immediate management of the bleeding risk. In emergency situations involving haemorrhage, stabilisation with intravenous fluids and sometimes blood transfusions precedes surgery. Elective surgery carries a lower risk when the dog is stable.
Following splenectomy, the tissue is sent for histopathology to determine whether the mass is benign or malignant. For benign conditions, splenectomy is curative and the prognosis is excellent. For haemangiosarcoma, surgery alone extends median survival to approximately two months. The addition of doxorubicin-based chemotherapy typically extends median survival to four to six months, with a small percentage of dogs surviving beyond one year.
These are median figures, meaning half of dogs do worse and half do better, and they should be interpreted in the context of each individual animal's health and quality of life. Honest conversations with a veterinary oncologist about realistic expectations — and what monitoring for metastatic spread looks like — are an important part of navigating this diagnosis alongside your vet.