The Anatomy of the Spleen

The spleen sits in the upper left abdomen just below the diaphragm

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

Clinically, the spleen can become enlarged (a condition called splenomegaly) due to a range of conditions, including cancer, pressure from the veins, as well as bacterial or viral infections. Furthermore, this organ has a relatively high incidence of injury; depending on the scope of the issue, removal surgery called splenectomy may be required.

Anatomy

Structure

In adults, the spleen is a purple organ that is about the size of a clenched fist. It’s covered in visceral peritoneum, a smooth membrane that’s composed of two layers of cells, which secrete fluid and serve a protective function. There is, however, an opening in this membrane called the hilum of the spleen, which 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. Finally, the phrenicocolic ligament runs from the colon to the spleen.

Notably, the spleen is composed of two types of tissues: white pulp and red pulp. The former of these is associated with white blood cell production and is made up of structures called periarteriolar lymphoid sheaths (PALS) and lymphatic nodules. In turn, the 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, which places it just behind the stomach, with the left kidney to its immediate right, and the diaphragm just above it. As such, the spleen’s forward- and rear-facing surfaces are defined by what they face, with the lateral of diaphragmatic surface fitting into the space as it abuts the diaphragm. The other side, 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, as well as 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: Present at birth, in some cases the spleen may have extra features or variations in shape, including lobulation, in which lobules that usually disappear prior to birth persist. These can vary in size and location. In addition, some spleens 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 case, 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 occur congenitally due to the absence or malformation of the ligaments that anchor it in position. It may also occur due to pregnancy or muscular dystrophy (a condition characterized by deterioration of the muscles) and is associated with a range of other conditions, including Hodgkin lymphoma (a cancer of parts of the immune system).  
  • 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 (Chaudhry’s disease): In this relatively rare condition, there are multiple small spleens rather than one fixed organ. This developmental failure occurs more commonly in women.

Function

As part of the lymphatic system, the spleen serves multiple major and inter-related functions involving the body’s blood supply; however, despite the significance of what it does, the body can survive without it. If removed or damaged, the liver, bone marrow, lymph nodes, and other surrounding organs can take up some of what it does. However, medical supplementation is often needed in such cases.

One major function is that this organ filters blood, removing foreign bodies, microbes, and faulty red blood cells (RBCs) in its red pulp. This it does by filtering such bodies to specialized white blood cells called lymphocytes located in the lymph nodules. In turn, RBCs are recycled in this tissue, and it stores white blood cells (WBCs) as well as platelets (cells that help with clotting), which are released to aid in healing when there is infection or injury.

In its white pulp, the spleen produces white blood cells (WBCs), and synthesizes antibodies, making it essential to immune function. In particular, this tissue is the site of lymphocyte production (white blood cells that are deeply involved in immune function) that make up the antibodies.    

Associated Conditions

As noted above, while the spleen is not a completely essential organ, it can be implicated in a number of health issues, with some disorders or diseases becoming life-threatening. Oftentimes, splenectomy—the removal of the spleen—is required as treatment for these conditions, though sometimes more conservative measures can work. The most prominent of these conditions include:

  • Rupture: Given its location, the spleen is the most frequently injured abdominal organ, something which 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). Sometimes the leak is catastrophic, resulting in 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. Since risk of rupture is raised, surgery may be required.
  • Idiopathic thrombocytopenic purpura: This is a rare blood disorder, characterized by there being a low platelet count due to overactivity of antibodies. Though often asymptomatic, it can lead to bruising and excessive internal bleeding.  
  • Infections: Following splenectomy, patients have partially compromised immune systems. They are prone to certain bacterial infections, including Streptococcus pneumoniae, Neisseria meningitidis, and Haemophilus influenzae, and vaccination against these organisms is needed. After splenectomy, the person is often placed on antibiotics for an extended period and afterward may require preventative antibiotics when at risk of infection.
  • Sickle-cell anemia: Spleen function can become hampered by sickle-cell anemia, a disease in which the shape of RBCs is affected.

Tests

Assessment of spleen function involves several different kinds of tests and will vary based on symptoms that are reported. These are:

  • Physical examination: In some cases of splenomegaly, doctors can actually detect inflammation by touch.
  • Blood testing: Since splenic activity is intimately connected to red and white blood cell levels—as well as the presence of antibodies—blood tests are an early line assessment of spleen activity.
  • Imaging: Once initial examinations have turned up an issue, ultrasound, computerized tomography (CT), magnetic resonance imaging (MRI), or X-ray is used to allow doctors to get a closer look at the shape and health of the spleen.
  • Bone marrow biopsy: Biopsy is when doctors remove a piece of tissue to check for the presence of cancer or other issues. While it’s not advised to use parts of the spleen for this, bone marrow—a closely related sight of blood cell development—can be assessed.
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