Table of Contents
Location of the Spleen
The spleen, with a size of about 4 x 7 x 11 cm (‘4711-rule’) and a weight of 150—200 g, is an organ shaped like a shoe that lies relative to the 9th and 11th ribs and is located in the left hypochondrium and partly in the epigastrium.
Thus, the spleen is situated between the fundus of the stomach and the diaphragm. The spleen is very vascular and reddish-purple; its size and weight vary. The healthy spleen is not palpable. It can be palpated when it is enlarged (splenomegaly). The causes of splenomegaly include infections (mononucleosis), metabolic disorders (Gaucher’s disease), or tumors (see below).
External Shape of the Spleen
The splenic tissue itself is very soft and filled with blood that trickles through the parenchyma and clears off its old and deformed RBCs and WBCs. However, the spleen is surrounded by a fibrous capsule (tunica fibrosa) made out of tough connective tissue, resulting in its relatively constant ‘coffee bean shape’. From the capsule, so-called trabeculae run through the inside of the spleen; they form a supporting framework and divide the spleen into segments.
The spleen’s 3 borders are the superior, inferior, and intermediate. The superior border of the spleen is notched by the anterior end. The inferior border is rounded. The intermediate border is directed toward the right. The 2 surfaces of the spleen are the convex diaphragmatic surface, which abuts the diaphragm and rests on the upper pole of the left kidney and the concave visceral surface, which overlays the bowel and contains the splenic hilum where vessels enter and leave the spleen.
Peritoneal Relationships of the Spleen
The spleen is an intraperitoneal organ. Various ligament structures run to and from it:
- The gastrosplenic ligament extends from the hilum of the spleen to the greater curvature of the stomach. It contains short gastric vessels and associated lymphatics and sympathetic nerves.
- The splenorenal ligament extends from the hilum of the spleen to the anterior surface of the left kidney. It contains the tail of the pancreas and splenic vessels.
- The phrenicocolic ligament is a horizontal fold of peritoneum that extends from the splenic flexure of the colon to the diaphragm along the midaxillary line. It forms the upper end of the left paracolic gutter.
Relation of the Spleen to Adjacent Organs
With its visceral surface, the spleen borders on various other visceral organs.
- Stomach (gastric surface): When the stomach is very full, the spleen moves into a more vertical position. An important radiological feature in a plain film of the abdomen is the moving of the gastric bubble away from the spleen and toward the midline. This may signify a subcapsular hematoma of the spleen or perisplenic hemorrhage such as mononucleosis-induced splenic rupture.
- Colon with left colic flexure (colic surface): When experiencing strong flatulence, the spleen moves into a more horizontal position. Because of its close relationship with the spleen, the left colic flexure is also called the splenic flexure.
- Pancreas: The tail of the pancreas joins the splenic artery and vein and they abut on the splenic hilum.
- Diaphragm (diaphragmatic surface): The spleen sits very close to the diaphragm and therefore follows the respiratory movements.
- The anterior surface of the left kidney (renal surface): Between the left kidney and the spleen lays the splenorenal recess. This is an anatomical space where sonography can quickly detect any free fluid or blood accumulated in the recess from trauma or other pathological events.
Blood Circulation of the Spleen
The spleen is made up of the following 4 components:
- Supporting tissue
- White pulp
- Red pulp
- Vascular system
Supporting tissue is fibroelastic and forms the capsule, coarse trabeculae, and a fine reticulum.
The white pulp consists of lymphatic nodules, which are arranged around an eccentric arteriole called the Malpighian (or splenic) corpuscle.
The red pulp is formed by a collection of cells in the interstices of its reticulum, in between the red pulp sinusoids. The cell population includes all types of lymphocytes, blood cells, and fixed and free macrophages. The lymphocytes are freely transformed into plasma cells, which can produce large amounts of antibodies and immunoglobulins.
The terminal vessels of the spleen’s arterial tree are the sheathed capillaries, which either enter directly into splenic sinusoids or empty openly into the spleen’s connective tissue. This open circulation is unique in the human circulatory system which is normally a closed circuit. The sinusoids form the beginning of the venous system. From the sinuses, blood is collected in short pulpar veins, and emptied into the trabecular veins which finally join together as the splenic vein. The splenic vein then collects the inferior mesenteric vein and other branches from the pancreas and the stomach and joins the superior mesenteric vein to ultimately form the hepatic portal vein.
Accessory Spleen as an Anatomical Variation
In around 20% of people, incidental findings reveal a solitary or multiple accessory spleens. Usually, it is found near the hilum of the main spleen, but also further in the abdomen, or even in the pelvic or scrotal area.
The histological structure corresponds to that of the main spleen. In principle, the presence of an accessory spleen does not represent any health risks. If, however, the main spleen has to be removed in a splenectomy, the accessory spleen is too small and too remote from the splenic artery to take over its functions—which would mean that the desired treatment effect (e.g., trapping of old RBCs and WBCs) cannot be achieved.
Functions of the Spleen
The spleen is one of the secondary lymphatic organs and can be described as the central organ of the immune system. Furthermore, it filters the blood and removes old or damaged red blood cells (RBCs).
In the macroscopic view of a transected spleen, a division of the parenchyma into white and red areas, the white and red pulp, becomes apparent. The different coloring is due to the different tissue composition: In the white pulp, there are mainly splenic corpuscles and lymphoid sheaths, while the red pulp consists of numerous erythrocytes located in the splenic sinusoids.
White Pulp and the Immune System
The white pulp contains lymphocytes, which is why it belongs to the lymphatic tissue. T cells surround the central arteries like a cuff, forming the peri-arteriolar lymphoid sheath (PALS). PALS is an important histological characteristic of the spleen that distinguishes it from other lymphatic organs— and which makes it a frequently tested exam topic. B cells are mostly found in the splenic (Malpighian) corpuscles.
In the marginal zone, the junction between the white and red pulp, there are mostly B but also T cells, macrophages, and dendritic cells.
After leaving the bloodstream, the lymphocytes move to their ‘place of destination’: the T cells to PALS and the B cells to the splenic (Malpighian) corpuscles.
Red Pulp and Blood Filtration
Cellular elements of the blood are destroyed when they become obsolete. This occurs in the red pulp of the spleen. Here, the erythrocytes have to ‘wedge’ through a close-meshed network of splenic cords. They can only achieve this when they are still young and flexible. Obsolete or deformed erythrocytes are not flexible enough and get caught in the meshes, where they eventually become phagocytized by macrophages.
If the spleen is depleting too much blood, it can cause hemolytic jaundice. Because of the increased breakdown of hemoglobin (red pigment of the erythrocytes), more bilirubin is produced from the heme, which gives the skin a yellowish color.
During prenatal development, the spleen contributes to the development of RBCs (erythropoiesis). Since the liver also participates in this process of hematopoiesis, which takes place between the 2nd and 7th month, this is called the hepatolienal phase.
Diseases of the Spleen
Splenomegaly is massive enlargement of the spleen, which makes the spleen palpable under the left costal arch. Ultrasounds show a bulging shape and rounding of the normally pointy poles. Any ectopic tissue such as accessory spleens would also be hypertrophied.
Diseases associated with splenomegaly include:
- Infectious mononucleosis (glandular fever): triggered by the Epstein-Barr virus. Mild splenomegaly without clinical significance can persist throughout the entire life.
- Congestion in the portal vein: caused by portal hypertension, right heart insufficiency, or splenic vein thrombosis.
- Hematological systemic diseases: acute or chronic lymphatic leukemia, hemolytic anemia, and polycythemia vera.
- Malaria: extreme enlargement of the spleen can occur in chronic forms of malaria tropica.
- Echinococcosis: splenic cysts caused by Echinococcus granulosus (dog tapeworm).
Asplenia: Life without a Spleen
Asplenia describes the absence of a spleen. The most common anatomical reason for this is surgical removal; only rarely is asplenia congenital. If this is the case, it is often associated with a malformation of the big thoracic vessels. In functional asplenia, the spleen is existent but not functioning. The causes can include autoimmune diseases like systemic lupus erythematosus or sickle-cell anemia.
The absence of a spleen implies the lack of a filtration function for bacteria, especially for encapsulated bacteria (pneumococci, meningococci, and Hemophilus influenzae type B). The result is a lifelong increased risk of sepsis. Physicians dread the OPSI syndrome (overwhelming post-splenectomy infection) which can, within a few hours, lead to septicemia, caused by pathogenic bacteria getting into the bloodstream, which can result in severe general symptoms and eventually lead to death.
Prophylactic vaccination against the mentioned bacteria is therefore advisable for asplenic patients and should be repeated every 5 years. Also, annual vaccination against influenza is important for prophylaxis. If fever or chills should suddenly set in, early use of antibiotics is indicated. Asplenic patients must receive an emergency card from their doctor so that 1st responders or other doctors may be informed about the immune disorder.
Rupture of the Spleen
The most common reason for a rupture of the spleen is a blunt abdominal trauma; for individuals with splenomegaly, a minimal trauma is already enough to cause a rupture of the capsule. The distinction is made between an early or delayed rupture. In an early rupture, the splenic capsule and parenchyma are both ruptured at the same time, which leads to immediate bleeding into the abdominal cavity.
In a delayed rupture, the parenchyma is injured 1st, but it may take hours or even weeks until the capsule ruptures, causing bleeding into the abdominal cavity.
Please note: In case of blunt abdominal trauma, the possibility of a splenic rupture should always be considered and ruled out, as covert bleeding can be life-threatening!
Sonography or computed tomography (CT) scans are the appropriate tools since they can show, among other things, any accumulations of fluid in the splenorenal recess. Furthermore, patients may feel referred pain in their left shoulder.
Because of the possible severe consequences, a splenectomy can have, the goal of surgery should be the preservation of the spleen (especially in children) or at least the (difficult) partial resection.
Removal of the Spleen (Splenectomy)
It is difficult to only partially resect the spleen since it is not as distinctly divided into lobes as, for instance, the lungs or the liver. Also suturing the thin capsule is a challenging procedure.
Total splenectomy, in turn, is relatively easy because it only requires the dissection of the splenic artery and vein at the hilum of the spleen. Accesses to the spleen are: laparoscopic, left subcostal incision, or laparotomy with the upper midline incision.
The spleen is an important but not a vital organ as its functions can be compensated by other organs. For instance, immune responses by other lymphatic organs or RBC breakdown by the liver.
Removal of the spleen (e.g., after a spleen rupture) could lead to severe sepsis. Splenectomized patients should receive a prophylactic vaccination against pathogens that frequently cause sepsis, such as Streptococcus pneumoniae, H. influenza, and Meningococci.
Examination of the Spleen
Please note: In healthy individuals, the spleen is not palpable!
|Palpation||Healthy spleen: not palpable. Splenomegaly: palpable below left costal arch. Cave: if the pressure is too hard, the capsule can burst. Start: always in the lower abdomen in order not to overlook a splenic tumor.|
|Percussion||Spleen: dull percussion note. Cranial: resonant percussion note of the lung. Ventral: tympanitic percussion note of the stomach and colon. Caudal: no distinction to the dull note of the kidney. BUT: difficult because the location of the spleen does not admit definite distinctions.|
|Sonography||Right lateral decubitus or supine position (preferably supine position). Expiration (no attenuation through acoustic shadowing of the lung). ‘Kissing phenomenon’: displacement of the stomach caused by splenomegaly so that the spleen touches the left hepatic lobe. Ultrasonographic visualization of clear splenorenal space is helpful to exclude splenic rupture. Incidental finding: accessory spleen. BUT: parts of the spleen that are directly caudal of the diaphragm are often difficult to visualize.|
|Scintigraphy||Evaluation of the exact dimensions of the spleen can be achieved by using radioactively marked and thermally damaged erythrocytes.|