CONDITION
Splenic Mass
A splenic mass is a lump or growth that develops in the spleen, an organ tucked beneath the ribcage on the left side of the abdomen. These masses can be discovered during routine imaging, after a period of vague unwellness, or sometimes when a dog collapses unexpectedly. They range from benign blood-filled nodules to more serious tumours, and the spleen's rich blood supply means that larger masses can occasionally rupture and bleed into the abdomen. Many owners arrive at this page after an ultrasound or X-ray has shown something unusual, or because their dog has had an episode of weakness or pale gums that prompted investigation. The mass itself often causes no outward signs until it reaches a certain size or changes in some way. Because the spleen sits out of sight and performs quiet background work in filtering blood and storing red cells, changes within it tend to go unnoticed until imaging brings them to light. This page explores what signs may appear, what is happening inside the spleen when a mass forms, how these growths are investigated and characterised, and what approaches exist depending on the type and behaviour of the mass. The goal is to provide a framework for understanding what has been found and what questions may be worth exploring as the picture becomes clearer.
Why this matters now
Splenic masses are encountered most often in middle-aged and older dogs, typically from seven years onward, though younger animals can occasionally develop them. Certain larger breeds—including Golden Retrievers, German Shepherds, and Labrador Retrievers—appear in clinical reports more frequently than smaller breeds, though the reasons for this pattern are not fully understood. The spleen's role in filtering aged blood cells and managing immune responses means that nodules and growths can arise as part of normal wear, benign change, or as true tumours.
The timeline for a splenic mass varies widely depending on its nature. Some masses remain stable for months or years, detected only incidentally during imaging for an unrelated concern. Others grow steadily, and a portion may change suddenly if the mass ruptures and bleeds into the abdomen, which can happen with little warning. Because the spleen sits quietly in the background, progression is often silent until the mass reaches a size or behaviour that produces symptoms or is caught on a scan.
Signals & patterns
Early signals
Reduced stamina or quiet behaviour
A dog may seem less enthusiastic about walks or play, or may choose to rest more than usual. This can reflect anaemia if the mass is slowly bleeding internally, or simply a vague sense of not feeling quite right that owners notice over weeks.
Intermittent pale gums
The gums may look lighter than normal, or the colour may seem to come and go. This pattern can occur if the mass is leaking small amounts of blood into the abdomen, reducing the number of circulating red cells temporarily before the body compensates.
Subtle abdominal distension
The belly may look slightly rounder or fuller, particularly on the left side, though this is often difficult to spot in deep-chested or well-covered dogs. It may be noticed during grooming or when the dog stretches.
Unexplained weight loss
A gradual decline in weight can occur without an obvious change in appetite. This may reflect the metabolic cost of the mass itself, or changes in how the spleen is managing blood and immune cells.
Occasional vomiting or reduced appetite
Some dogs show mild digestive upset or become pickier about food. This is non-specific and can arise if the mass is large enough to press on nearby organs or if there is low-grade internal discomfort.
Later signals
Sudden collapse or weakness
A dog may become wobbly, lie down abruptly, or seem disoriented without warning. This often signals that the mass has ruptured and blood is pooling in the abdomen, causing a rapid drop in circulating volume and blood pressure.
Markedly pale or white gums
The gums become very pale or almost white, and the dog may breathe rapidly or seem anxious. This reflects significant blood loss, either from a ruptured mass or ongoing internal bleeding that has outpaced the body's ability to replace red cells.
Distended, tense abdomen
The belly becomes visibly swollen and may feel firm to the touch. This occurs when a substantial volume of blood or fluid has accumulated inside the abdominal cavity, often following rupture of the mass.
Persistent lethargy and reluctance to move
The dog may remain lying down, resist standing, and show little interest in food or surroundings. This advanced weakness reflects significant anaemia, discomfort from abdominal pressure, or systemic effects if the mass is malignant and spreading.
Click to read about the biological mechanisms
How this is usually investigated
Investigation of a splenic mass typically begins with a review of the history and a physical examination, though the spleen itself is rarely palpable unless enlarged. Imaging forms the next layer, allowing the size, shape, and position of the mass to be characterised, and often prompting further tests to understand what the mass is made of and whether changes have occurred elsewhere in the body. Blood tests provide information about how the spleen and other organs are functioning, and sometimes a sample of the mass or the fluid around it is taken to examine the cells directly.
Abdominal ultrasound
Abdominal radiography
Haematology and biochemistry
Fine-needle aspiration or fluid analysis
Thoracic radiography or staging imaging
Options & trade-offs
Management of a splenic mass depends on its size, behaviour, the dog's overall health, and the goals of the household. Some masses are monitored over time if they appear stable and cause no symptoms, while others prompt surgical removal to prevent rupture or to obtain a diagnosis. Treatment plans often combine several approaches, and what works for one animal may not suit another.
Monitoring with serial imaging
Small, incidental masses that cause no symptoms can be tracked with repeat ultrasound examinations at intervals agreed with the veterinary team. This allows changes in size or structure to be noted over weeks or months, and decisions about intervention can be revisited as the picture evolves. Some masses remain stable for extended periods, while others show gradual or sudden growth.
Trade-offs: Monitoring avoids surgery and its attendant risks, but it does not provide tissue diagnosis or prevent rupture if the mass continues to grow. It suits dogs with smaller, stable masses and owners comfortable with periodic reassessment rather than definitive action.
Splenectomy
Surgical removal of the spleen (splenectomy) eliminates the mass and allows the entire organ to be examined by a pathologist, providing a definitive tissue diagnosis. The procedure is performed under general anaesthesia and involves opening the abdomen, ligating the blood vessels supplying the spleen, and removing the organ intact. Dogs can live without a spleen, though they may be slightly more vulnerable to certain blood-borne infections.
Trade-offs: Splenectomy carries the risks associated with any major abdominal surgery, including anaesthetic complications, bleeding, and delayed healing, and it does not prevent spread if the mass has already seeded elsewhere. It is typically considered when the mass is large, growing, or has ruptured, or when a diagnosis is needed to guide further treatment.
Medical management of anaemia or bleeding
When a mass has ruptured or is causing ongoing low-level bleeding, supportive care may include intravenous fluids, blood transfusions, or medications to stabilise blood pressure and maintain oxygen delivery to tissues. This approach is often used to stabilise a dog before surgery or when surgery is not pursued.
Trade-offs: Medical support can improve comfort and buy time for decision-making, but it does not address the underlying mass or prevent further rupture. It is a bridging measure rather than a standalone solution and is sometimes chosen when anaesthetic risk is high or when the household is weighing options.
Chemotherapy following splenectomy
If the removed spleen is found to contain a malignant tumour such as haemangiosarcoma, chemotherapy with drugs such as doxorubicin may be offered to slow the spread of microscopic disease to other organs. Treatment typically involves several intravenous infusions given at intervals over a number of weeks. The goal is to extend the period before visible metastases develop, rather than to cure.
Trade-offs: Chemotherapy adds cost, requires repeated clinic visits, and can cause side effects including nausea, low white cell counts, and fatigue, though many dogs tolerate it reasonably well. It may prolong survival in some cases but does not prevent progression entirely, and response varies between individuals.
Common misconceptions
"A splenic mass that has ruptured must be malignant."
Both benign and malignant masses can rupture and bleed into the abdomen. Haematomas, haemangiosarcomas, and haemangiomas can all cause sudden internal bleeding, and the only reliable way to distinguish them is to examine the tissue after removal. The act of rupture alone does not confirm the nature of the growth.
"Removing the spleen will cure the problem regardless of the type of mass."
Splenectomy removes the visible mass and allows tissue diagnosis, but if the mass is a malignant tumour that has already spread microscopically to the liver, lungs, or heart, removing the spleen does not eliminate disease elsewhere. Surgery is one part of the picture, and the pathology report provides information about what may happen next.
"A dog with a splenic mass will always show clear symptoms before anything serious happens."
Many splenic masses produce no outward signs until they rupture or grow large enough to press on neighbouring structures. Some dogs remain active and appear well until a sudden episode of weakness or collapse prompts investigation. The quiet nature of splenic disease is one reason imaging sometimes reveals unexpected findings.
Related conditions
Hemangiosarcoma
Haemangiosarcoma is the most common malignant tumour found in the spleen of dogs, and when a splenic mass ruptures and bleeds into the abdomen, this tumour is often the underlying cause. Many dogs with splenic haemangiosarcoma present in the same way as those with other splenic masses—an incidental finding on imaging, or sudden collapse from internal bleeding.
Splenic Lymphoma
Splenic lymphoma can appear as a diffuse enlargement of the spleen or as discrete masses within it, and it shares many of the same clinical presentations as other splenic growths. The distinction typically requires tissue sampling, as imaging alone often cannot reliably differentiate lymphoma from other mass lesions in the spleen.
Cardiac Tamponade
Cardiac tamponade can develop in dogs with haemangiosarcoma affecting the heart base, and dogs with splenic masses—particularly haemangiosarcoma—may also have tumours in the heart or pericardium that bleed and compress the heart chambers. Both conditions can present with sudden weakness, pale gums, and circulatory collapse, though the source of bleeding differs.
Congestive Heart Failure in Dogs
Congestive heart failure and splenic masses can occasionally be discovered together in older dogs, and the decision-making around anaesthesia and surgery for a splenic mass may be influenced by the presence and severity of concurrent heart disease. In some cases, a dog with a bleeding splenic mass may present with signs that overlap with those of heart failure, such as weakness and difficulty breathing.
Adrenal Tumours
Adrenal tumours and splenic masses can both present as abdominal masses found incidentally on imaging, and in some cases dogs may have growths in both locations, particularly when screening for metastatic disease. The distinction is usually clear on ultrasound, but both share the context of tumour evaluation in older dogs and may raise similar questions about surgical intervention and prognosis.
Once imaging or surgery has clarified the nature of the mass, it may be useful to explore how the spleen fits into the broader picture of immune function and ageing, particularly in breeds where vascular tumours appear more frequently. Questions about what signs to observe at home, how often to revisit imaging if monitoring is chosen, or what the pathology report means in practical terms can be part of ongoing conversations as the situation unfolds. Understanding the range of outcomes and the variation between individual dogs can help shape expectations and decisions as more information becomes available.