The Anatomy of the Spleen

Sitting in the upper left abdomen where it’s protected by the rib cage, the spleen is the largest organ of the lymphatic system. Located just below the diaphragm and to the side of the lower portion of the stomach, this organ recycles old red blood cells (RBCs) and is a repository for platelets and white blood cells (WBCs).

Clinically, the spleen can become enlarged (a condition called splenomegaly) due to a range of conditions, including cancer, pressure from the veins, and bacterial or viral infections. Furthermore, this organ can be injured due to significant abdominal trauma; in serious situations, splenectomy surgery, which is the removal of the spleen, may be required.

Anatomy

In adults, the spleen is a purple organ that is about the size of a clenched fist.

Structure

The visceral peritoneum, a smooth membrane that’s composed of two layers of cells, covers the spleen. The membrane secretes fluid and serves a protective function. An opening in this membrane, called the hilum of the spleen, allows the splenic artery and vein to circulate blood to the organ. 

This organ is held in place by three major ligaments, connected to major structures and organs around the spleen. Two of these connect the stomach to the hilum—the gastrosplenic ligament, which arises from the curvature of the stomach, and the splenorenal ligament which attaches to the left kidney. The phrenicocolic ligament runs from the colon to the diaphragm.

The spleen is composed of two types of tissues:

• White pulp is associated with WBC production and is made up of structures called periarteriolar lymphoid sheaths (PALS) and lymphatic nodules.
• Red pulp, composed of wide blood vessels called splenic sinusoids, works to filter blood and store elements that help repair injuries.

These tissues are separated by a marginal zone, a membrane border that also serves a filtering function.

Location

The spleen resides in the upper left portion of the abdomen or “hypochondriac” region, just behind the stomach, with the left kidney to its immediate right, and the diaphragm just above it.

The spleen’s forward- and rear-facing surfaces are defined by what they face:

• The lateral diaphragmatic surface fits into the space as it abuts the diaphragm.
• The medial surface, which is perforated by the hilum, includes a colic area (adjacent to the bend of the intestines), a gastric area next to the stomach, and a renal area alongside the left kidney.     

Anatomical Variations     

While relatively rare, there are several prominent anatomical variations of the spleen. These include:

• Alterations of shape: These are usually present at birth. In some cases, the spleen may have extra features or variations in shape, Lobulation is a variation in which lobules that usually disappear prior to birth persist. These can vary in size and location. The spleen may display clefts or notches, some of which can be so sizable as to make the organ look like it has a band around it. 
• Wandering spleen: This rare situation, occurring in 0.13% of people, is characterized by the spleen migrating from its usual location in the upper quadrant of the abdomen. This can be a congenital condition due to the absence or malformation of the ligaments that anchor it in position. It may also occur with other conditions, including pregnancy or muscular dystrophy.  
• Accessory spleen: This occurs when the two buds that usually unite to form the spleen during gestation fail to do so, leading to a small portion (called a nodule) remaining separate from the rest of the organ. This occurs in about 10% of the population.
• Polysplenia (Heterotaxy syndrome): In this relatively rare condition, also referred to as isomerism of the atrial appendages, there are multiple small spleens rather than one fixed organ. This developmental failure occurs more commonly in women. It is caused by disruption of left-right axis orientation during early embryonic development. Cardiac malformations are a major component of heterotaxy syndrome and can be associated with considerable morbidity and mortality.

Function

As part of the lymphatic system, the spleen serves multiple major and inter-related functions involving the body’s blood supply. It plays an important role in immune function and in recycling RBCs.

Red pulp: This part of the organ filters blood, removing foreign bodies, microbes, and faulty RBCs. These are filtered in specialized WBCs called lymphocytes located in the lymph nodules of the spleen.

The RBCs are recycled in the spleen, which also stores WBCs and platelets (cells that help with clotting). These cells are released to aid in healing when there is an infection or injury.

White pulp: The spleen produces WBCs and synthesizes antibodies. This tissue is the site of lymphocyte production.    

Associated Conditions

The spleen is involved in a number of health issues, including some potentially life-threatening disorders or diseases. Medication and other treatments can resolve some of these problems. Sometimes splenectomy—the removal of the spleen—is required as treatment for these conditions,

The most common conditions involving the spleen include:

• Rupture: Given its location, the spleen is the most frequently injured abdominal organ. This can occur due to blunt trauma, puncture wound, or rib fracture . When it’s ripped, the capsule around it is torn, and blood can leak into the surrounding cavity (internal bleeding). A leak can be life-threatening, so it is a medical emergency.
• Splenomegaly: Enlargement of the spleen—splenomegaly—can occur due to a variety of reasons, including viral or bacterial infection, disruption of blood circulation, cancer, or other issues. This increases the risk of rupture, and surgery may be necessary.
• Idiopathic thrombocytopenic purpura: This is a rare blood disorder, characterized by a low platelet count due to overactivity of antibodies. Though often asymptomatic, it can lead to bruising and excessive internal bleeding.  
  
• Sickle-cell anemia: Spleen function can become hampered by sickle-cell anemia, a disease in which the shape of RBCs is affected.
  

After a splenectomy the immune system is partially compromised, leading to a susceptibility to certain bacterial infections, including Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae. Vaccination against these organisms is strongly recommended.

Post operatively, antibiotics may be prescribed for an extended period of time. And when you don't have a spleen. preventative antibiotics might be needed when there's a risk of infection.

Tests

Assessment of spleen function involves several different kinds of tests and will vary based on symptoms.

These are:

• Physical examination: In some cases, doctors can detect splenomegaly or signs of inflammation by abdominal palpation (careful touch to feel the edges and size of the spleen).
• Blood testing: Blood tests can assess the amount and characteristics of red and white blood cells, and sometimes can detect the presence of antibodies.
• Imaging: Ultrasound, computerized tomography (CT), magnetic resonance imaging (MRI), or X-ray can help doctors visually assess the shape and health of the spleen.
• Bone marrow biopsy: A biopsy is a procedure that's done to obtain a sample of tissue to check for the presence of cancer or other issues. While a biopsy of the spleen is not recommended, a bone marrow biopsy might shed light on certain disorders that involve the spleen.