A splenule is a small nodule of normal splenic tissue that exists separately from the main spleen, and in the vast majority of cases it is completely harmless. Also called an accessory spleen, a splenule is a congenital leftover from fetal development, when the spleen forms from several small tissue buds that normally fuse into one organ. Sometimes a bud fails to merge, leaving behind a pea- to walnut-sized extra piece of spleen tucked somewhere in the abdomen. Most people never know they have one unless it shows up incidentally on a CT scan or ultrasound ordered for something else entirely.
How Common Are Splenules
Splenules are far more common than most people realize. A large systematic review pooling data from over 22,000 subjects across 81 studies found an overall prevalence of about 14.5 percent.1PubMed. The prevalence and morphometry of an accessory spleen: A meta-analysis and systematic review of 22,487 patients Individual imaging studies report similar numbers. One CT-based study found accessory spleens in about 16 percent of patients undergoing contrast-enhanced abdominal scans,2PubMed. CT features of the accessory spleen while another using multidetector CT detected them in roughly 19 percent of the patients studied.3PubMed Central. Accessory Spleen: Prevalence and Multidetector CT Appearance Autopsy studies, which can catch smaller nodules that imaging misses, have reported prevalence figures as high as 30 to 40 percent. In other words, somewhere between one in seven and one in three people walk around with at least one splenule, and many have more than one.
There is no strong evidence that splenules favor one sex over the other, and they occur across all age groups. They are simply a normal anatomical variant, much like an extra kidney lobulation or a small accessory lobe of the liver. If your radiology report mentions one, the finding alone is not a red flag.
Where Splenules Turn Up
Splenules can appear in a surprisingly wide range of locations, though most cluster near the spleen itself. The two most common sites are the splenic hilum, the area where blood vessels enter and leave the spleen, and the tail of the pancreas.4PubMed Central. An unusual presentation of accessory spleen mimicking a pancreatic neoplastic lesion in a splenectomized patient: A case report After those, the greater omentum (the fatty apron that drapes over the intestines) and the tissue around the stomach are the next most frequent spots. Less commonly, splenules have been found along the small bowel mesentery, in the pelvis, and even in the chest wall.
One especially rare variant is splenogonadal fusion, where splenic tissue ends up attached to or near a gonad during fetal development. This can produce a mass near the testicle that is sometimes mistaken for a tumor, leading to unnecessary worry or surgery.5PubMed Central. Splenogonadal fusion: A rare paratesticular lesion and how to recognise it on ultrasound The location of a splenule matters most when it sits inside the pancreas, because that is where it causes the most diagnostic headaches.
Accessory Spleen Versus Splenosis
Not all extra splenic tissue is the same. A splenule is congenital, meaning you were born with it. Under a microscope, its internal architecture looks identical to a normal spleen, with the same organized structure of red pulp and white pulp. Splenosis is a different phenomenon altogether. It occurs when the spleen is damaged, usually by abdominal trauma or surgery, and fragments of splenic tissue seed themselves onto surfaces throughout the abdomen or even the chest. Those implanted bits grow into small nodules, but they lack the organized internal structure of a normal spleen.6PubMed Central. Splenic anomalies of shape, size, and location: pictorial essay
The distinction matters clinically. A splenule found in a person who has never had abdominal surgery or trauma is almost certainly congenital and benign. A nodule of splenic tissue found scattered in unusual locations after a past spleen injury or splenectomy is more likely splenosis. Both are generally harmless, but distinguishing them from other types of tissue (especially tumors) requires different diagnostic thinking depending on the patient’s history.
Why Splenules Get Mistaken for Tumors
The location that causes the most diagnostic anxiety is inside the pancreas. An intrapancreatic accessory spleen sits embedded in the tail of the pancreas, and on a CT scan or MRI it can look almost identical to a hypervascular pancreatic tumor, such as a neuroendocrine tumor or acinar cell carcinoma.7PubMed Central. Intrapancreatic Accessory Spleen Misdiagnosed as a Nonsecreting Endocrine Tumor: Case Report and Review of the Literature Both enhance brightly with contrast dye, both are small and round, and both sit in the same anatomical neighborhood. The resemblance has led to documented cases of patients undergoing unnecessary pancreatic surgery for what turned out to be harmless splenic tissue.
Radiologists have developed strategies to tell them apart. On MRI, splenic tissue tends to behave exactly like the main spleen at every phase of contrast enhancement, so comparing the suspicious nodule’s signal to the spleen itself can be revealing. A stepwise approach using multiple imaging techniques, starting with CT, then MRI, and sometimes adding nuclear medicine scans, can usually reach a confident diagnosis without the need for a biopsy or surgery.8International Surgery Journal. Incidental intrapancreatic accessory spleen on computed tomography: the value of a stepwise imaging approach
Needle biopsy of a suspected intrapancreatic splenule is generally considered a last resort. Sticking a needle into the pancreas carries real risks, including bleeding and pancreatic fistula (a leak of pancreatic fluid), and the tissue sample may not even be representative enough to give a definitive answer.9HPB. Diagnosis and management of intrapancreatic accessory spleen: a systematic review and ethics of literature For that reason, imaging confirmation is strongly preferred over tissue sampling when the clinical picture and scan features point toward benign splenic tissue.
Nuclear Medicine Scans for Tricky Cases
When standard imaging leaves doubt, nuclear medicine offers a highly specific tool. A scan using red blood cells that have been heat-damaged and then labeled with a radioactive tracer exploits the spleen’s unique function: the spleen is the organ that filters and removes damaged red blood cells from circulation. Inject labeled, denatured red blood cells into the bloodstream, and they concentrate wherever functional splenic tissue exists. If the suspicious nodule lights up, it is splenic tissue. If it does not, it is something else.10PubMed Central. SPECT/CT with 99mTc labelled heat-denatured erythrocyte to detect thoracic and abdominal splenosis
This technique works for both accessory spleens and splenosis. One study analyzing the uptake ratios of these scans found that splenic tissue showed dramatically higher tracer uptake compared to non-splenic lesions, with essentially no overlap between the two groups.11PubMed Central. Detection of Splenic Tissue Using 99mTc-Labelled Denatured Red Blood Cells Scintigraphy—A Quantitative Single Center Analysis The scan also sometimes discovers additional splenic nodules that were not visible on CT or MRI. It is not a routine first-line test, but for ambiguous cases, especially in patients with a history of splenectomy and new nodules, it can be the test that ends the diagnostic uncertainty.
Rare Complications That Can Cause Symptoms
The overwhelming majority of splenules never cause a single symptom. But in rare cases, a splenule can develop its own problems. The most dramatic is torsion: if a splenule is attached to the surrounding tissue by a narrow stalk (or pedicle), that stalk can twist. When this happens, blood flow gets cut off. Initially the venous drainage is blocked, causing the splenule to swell and become congested. If the twist tightens further, the arterial supply is also compromised, leading to ischemia and eventually infarction, where the tissue dies.12PubMed Central. Accessory spleen torsion: a hidden etiology of acute abdominal emergency
Torsion of an accessory spleen presents as sudden, severe abdominal pain, often in the left upper quadrant, and can mimic appendicitis, a ruptured ovarian cyst, or other surgical emergencies. It is rarely diagnosed before surgery because it is so uncommon. Accessory splenic infarction without torsion has also been reported, presenting with more vague symptoms like abdominal pain, nausea, and vomiting.13PubMed Central. Accessory splenic infarction presenting as acute abdominal pain: A case report These events make for interesting case reports precisely because they are so unusual. If you have a known splenule and develop acute abdominal pain, mention it to your doctor so it can be considered in the differential diagnosis, but the odds of this happening are vanishingly small.
The One Situation Where Splenules Truly Matter
There is one clinical scenario where a splenule can be genuinely consequential: when a person has had their spleen removed to treat an autoimmune blood disorder. In conditions like immune thrombocytopenic purpura (ITP, where the immune system destroys platelets) and autoimmune hemolytic anemia (AIHA, where the immune system destroys red blood cells), the spleen is often the organ responsible for carrying out that destruction. Removing the spleen frequently improves blood counts.
But if a splenule was present and was missed during surgery, it may grow larger over time, essentially taking over some of the main spleen’s function, including the unwanted function of destroying blood cells. This can lead to disease relapse months or years after the initial splenectomy. The accessory spleen, previously too small to notice, hypertrophies and becomes the new site of cell destruction. Case reports have documented this pattern, including patients with multiple relapses traced back to retained accessory splenic tissue that was not apparent at the time of surgery.14PubMed. Recurrence of immune thrombocytopenic purpura after splenectomy
The prevalence of accessory spleens in ITP patients specifically is around 17 percent according to the same large meta-analysis that estimated the general population rate at about 14.5 percent.1PubMed. The prevalence and morphometry of an accessory spleen: A meta-analysis and systematic review of 22,487 patients When disease recurs after splenectomy and a hypertrophied accessory spleen is identified, surgical removal of that residual tissue is the standard treatment. Laparoscopic removal of the accessory spleen has been shown to be an effective approach in these recurrence scenarios, for both ITP and AIHA.15PubMed Central. Laparoscopic excision of accessory spleen for recurrent autoimmune hemolytic anemia after splenectomy: a case report
Intrapancreatic accessory spleens are particularly problematic in this context. Because they sit within the pancreatic tissue, they are easy to miss during splenectomy and harder to remove when found later. Case reports describe intrapancreatic accessory spleens causing recurrent ITP, with removal of the tissue restoring acceptable platelet counts and reducing the need for medications.16PubMed Central. Intrapancreatic accessory spleen: a rare cause of recurrence of immune thrombocytopenic purpura
What to Do If Your Scan Finds One
If a radiologist reports a splenule on your CT or ultrasound, the most likely correct response is nothing at all. For the vast majority of people, an accessory spleen is a benign anatomical variant that requires no treatment, no follow-up imaging, and no lifestyle changes. Radiology guidelines for incidental splenic findings are designed to reduce unnecessary anxiety and testing by helping clinicians distinguish genuinely concerning findings from harmless variants.17PubMed. CAR Recommendations for the Management of Incidental Findings of the Spleen and Nodes in Adults
Situations that might prompt further investigation include:
- Unclear imaging: If the nodule’s appearance on CT is ambiguous and could represent either splenic tissue or a tumor, additional imaging with MRI or a nuclear medicine scan may be recommended.
- History of splenectomy for blood disorders: If you have had your spleen removed for ITP, AIHA, or a similar condition, the presence of an accessory spleen is clinically relevant and your hematologist should be aware of it.
- Intrapancreatic location: A nodule within the pancreas warrants careful characterization to exclude a pancreatic tumor, even when the probability of a splenule is high.
- Symptoms: Acute abdominal pain in the presence of a known accessory spleen should raise the possibility of torsion or infarction.
Outside these specific scenarios, a splenule is truly one of those findings where the most important thing a doctor can say is “this is normal.”
Splenules in Animals
Humans are not the only species with accessory spleens. The phenomenon has been well documented in dogs, where ectopic splenic tissue appears as dark, reddish-brown nodules most commonly in the omentum and mesentery. A review of 46 canine surgical biopsy specimens found that the omentum was by far the most frequent site, accounting for 39 of the 46 cases.18PubMed Central. Ectopic splenic tissue in 46 dogs, 2000-2024 As in humans, the distinction between a congenital accessory spleen and post-traumatic splenosis applies in dogs as well, with congenital splenules showing normal splenic architecture and splenosis lacking it. For pet owners, the practical relevance is similar: a dark nodule found incidentally in a dog’s abdomen during surgery may look alarming but could simply be a harmless splenule. Veterinarians use the same histological criteria to tell them apart from more concerning growths like hemangiosarcoma, a common and aggressive splenic tumor in dogs. Knowing that accessory spleens exist in companion animals can spare owners unnecessary panic when a surgeon mentions finding “an extra piece of spleen” during an abdominal procedure.