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Accessory Spleen – Causes, Diagnosis and Treatment

An accessory spleen is a small nodule of splenic tissue found separately from the main spleen. It is usually a harmless incidental finding with no symptoms.

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Things worth knowing about "Accessory Spleen"

An accessory spleen is a small nodule of splenic tissue found separately from the main spleen. It is usually a harmless incidental finding with no symptoms.

What Is an Accessory Spleen?

An accessory spleen (also called a splenunculus or supernumerary spleen) is a small, separate mass of splenic tissue located apart from the main spleen. It arises during embryonic development when parts of the developing splenic tissue fail to fuse completely, remaining as an independent structure. The medical Latin terms Splen accessorius and Lien accessorius are also used.

Accessory spleens are relatively common, occurring in an estimated 10 to 30 percent of the general population. In most cases, they represent a harmless anatomical variant that causes no symptoms and requires no treatment.

Location and Appearance

Accessory spleens are typically small, round nodules ranging from a few millimeters to approximately 2–3 centimeters in diameter. They consist of the same tissue as the main spleen and are therefore functionally active. The most common locations include:

The splenic hilum (where blood vessels enter and exit the spleen) – by far the most frequent site
The gastrosplenic or splenorenal ligaments
The tail of the pancreas
The mesentery of the small bowel
Rarely: the pelvis or the gonadal region

Causes and Development

An accessory spleen is a congenital anatomical variant resulting from incomplete fusion of embryonic splenic tissue. During fetal development, the spleen originates from the mesoderm. If the individual splenic buds do not merge fully, isolated pockets of splenic tissue persist as accessory spleens. This is not a disease in the traditional sense but rather a variation of normal anatomy.

Clinical Significance

In the vast majority of cases, an accessory spleen is clinically insignificant and is discovered as an incidental finding during abdominal imaging (e.g., ultrasound, CT scan, or MRI). However, there are specific clinical scenarios in which it becomes relevant:

Relevance After Splenectomy

When the spleen is surgically removed – for example, in conditions such as immune thrombocytopenic purpura (ITP) or hereditary spherocytosis – an undetected accessory spleen may sustain the disease, as it can take over part of the function of the removed spleen. In these situations, removal of the accessory spleen is medically necessary.

Differential Diagnostic Importance

On imaging, an accessory spleen can resemble other lesions such as enlarged lymph nodes, pancreatic tumors, or adrenal masses. Correct identification is therefore important to avoid unnecessary diagnostic procedures or surgery.

Complications (Rare)

In very rare cases, an accessory spleen may cause complications, including:

Torsion (twisting) with subsequent infarction – can cause acute abdominal pain
Spontaneous rupture following trauma
Extremely rare: malignant transformation

Diagnosis

An accessory spleen is most often diagnosed incidentally during abdominal imaging studies:

Ultrasound (sonography): The most common method of initial detection; the accessory spleen appears as a round, echogenic structure near the main spleen.
Computed tomography (CT): Allows precise localization and differentiation from other abdominal masses.
Magnetic resonance imaging (MRI): Particularly useful for characterizing tissue and distinguishing from other structures.
Scintigraphy: Using radiolabeled red blood cells, splenic tissue can be specifically identified – helpful in ambiguous cases.

Treatment

A healthy accessory spleen generally requires no treatment. Intervention is considered only in the following situations:

Detection of an accessory spleen after splenectomy in a condition requiring complete removal of all splenic tissue
Complications such as torsion or rupture
Uncertain diagnosis where malignancy cannot be reliably excluded

When removal is necessary, it can usually be performed minimally invasively (laparoscopically).

References

Cotran R.S., Kumar V., Collins T.: Robbins Pathologic Basis of Disease. 9th edition. Saunders Elsevier, Philadelphia, 2015.
Dodds W.J. et al.: The accessory spleen. Radiographics, 1997; 17(4): 869–882. (PubMed PMID: 9225387)
Moore K.L., Persaud T.V.N., Torchia M.G.: The Developing Human – Clinically Oriented Embryology. 10th edition. Elsevier, Philadelphia, 2016.

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