Accessory spleen
Encyclopedia
An accessory spleen is a small nodule of splenic tissue found apart from the main body of the spleen
. Accessory spleens are found in approximately 10 percent of the population and are typically around 1 centimeter in diameter. They form either by the result of developmental anomalies or trauma. They are medically significant in that they may result in interpretation errors in diagnostic imaging or continued symptoms after therapeutic splenectomy.
when some of the cells from the developing spleen are deposited along the path from the midline, where the spleen forms, over to its final location on the left side of the abdomen by the 9th–11th ribs. The most common locations for accessory spleens are the hilum of the spleen and adjacent to the tail of the pancreas. They may be found anywhere along the splenic vessels, in the gastrosplenic ligament
, the splenorenal ligament
, the walls of the stomach
or intestine
s, the pancreatic tail
, the greater omentum
, the mesentery
or the gonad
s and their path of descent
. The typical size is approximately 1 centimeter, but sizes ranging from a few millimeters up to 2–3 centimeters are not uncommon.
Splenogonadal fusion
can result in one or more accessory spleens along a path from the abdomen into the pelvis
or scrotum
. The developing spleen forms near the urogenital ridge from which the gonads develop. The gonads may pick up some tissue from the spleen, and as they descend through the abdomen during development, they can produce either a continuous or a broken line of deposited splenic tissue.
Splenosis is a condition where foci of splenic tissue undergo autotransplantation
, most often following physical trauma
or splenectomy
. Displaced tissue fragments can implant on well vascularized surfaces in the abdominal cavity, or, if the diaphragmatic
barrier is broken, the thorax
.
, accessory spleens may be confused for a enlarged lymph nodes or neoplastic growth in the tail of the pancreas, gastrointestinal tract, adrenal gland
s or gonads.
Spleen
The spleen is an organ found in virtually all vertebrate animals with important roles in regard to red blood cells and the immune system. In humans, it is located in the left upper quadrant of the abdomen. It removes old red blood cells and holds a reserve of blood in case of hemorrhagic shock...
. Accessory spleens are found in approximately 10 percent of the population and are typically around 1 centimeter in diameter. They form either by the result of developmental anomalies or trauma. They are medically significant in that they may result in interpretation errors in diagnostic imaging or continued symptoms after therapeutic splenectomy.
Causes and locations
Accessory spleens may be formed during embryonic developmentEmbryogenesis
Embryogenesis is the process by which the embryo is formed and develops, until it develops into a fetus.Embryogenesis starts with the fertilization of the ovum by sperm. The fertilized ovum is referred to as a zygote...
when some of the cells from the developing spleen are deposited along the path from the midline, where the spleen forms, over to its final location on the left side of the abdomen by the 9th–11th ribs. The most common locations for accessory spleens are the hilum of the spleen and adjacent to the tail of the pancreas. They may be found anywhere along the splenic vessels, in the gastrosplenic ligament
Gastrosplenic ligament
The gastrosplenic ligament is part of the greater omentum.Embryonically the gastrosplenic ligament is derived from the dorsal mesogastrium....
, the splenorenal ligament
Splenorenal ligament
The splenorenal ligament , is derived from the peritoneum, where the wall of the general peritoneal cavity comes into contact with the omental bursa between the left kidney and the spleen; the lienal vessels pass between its two layers...
, the walls of the stomach
Stomach
The stomach is a muscular, hollow, dilated part of the alimentary canal which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects , and molluscs. It is involved in the second phase of digestion, following mastication .The stomach is...
or intestine
Intestine
In human anatomy, the intestine is the segment of the alimentary canal extending from the pyloric sphincter of the stomach to the anus and, in humans and other mammals, consists of two segments, the small intestine and the large intestine...
s, the pancreatic tail
Tail of pancreas
The tail of the pancreas, located anatomically left near the hilum of the spleen, is not simply an anatomical distinction. The tail is the only part of the pancreas which contains Pancreatic Polypeptide cells, which are responsible for secreting pancreatic polypeptide to coordinate exocrine and...
, the greater omentum
Greater omentum
The greater omentum is a large fold of parietal peritoneum that hangs down from the stomach...
, the mesentery
Mesentery
In anatomy, the mesentery is the double layer of peritoneum that suspends the jejunum and ileum from the posterior wall of the abdomen. Its meaning, however, is frequently extended to include double layers of peritoneum connecting various components of the abdominal cavity.-Mesentery :The...
or the gonad
Gonad
The gonad is the organ that makes gametes. The gonads in males are the testes and the gonads in females are the ovaries. The product, gametes, are haploid germ cells. For example, spermatozoon and egg cells are gametes...
s and their path of descent
Development of the gonads
The prenatal development of the gonads is a part of the development of reproductive system and ultimately forms the testes in males and ovaries in females. They initially develop from the mesothelial layer of the peritoneum....
. The typical size is approximately 1 centimeter, but sizes ranging from a few millimeters up to 2–3 centimeters are not uncommon.
Splenogonadal fusion
Splenogonadal fusion
Splenogonadal fusion is a rare congenital malformation that involves an abnormal connection between the spleen and the gonad. It manifests itself as a mass consisting of splenic and testicular or ovarian tissue...
can result in one or more accessory spleens along a path from the abdomen into the pelvis
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
or scrotum
Scrotum
In some male mammals the scrotum is a dual-chambered protuberance of skin and muscle containing the testicles and divided by a septum. It is an extension of the perineum, and is located between the penis and anus. In humans and some other mammals, the base of the scrotum becomes covered with curly...
. The developing spleen forms near the urogenital ridge from which the gonads develop. The gonads may pick up some tissue from the spleen, and as they descend through the abdomen during development, they can produce either a continuous or a broken line of deposited splenic tissue.
Splenosis is a condition where foci of splenic tissue undergo autotransplantation
Autotransplantation
Autotransplantation is the transplantation of organs, tissues or even proteins from one part of the body to another in the same individual. Tissue transplanted by such "autologous" procedure is referred to as an autograft or autotransplant. It is contrasted with xenotransplantation and...
, most often following physical trauma
Physical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...
or splenectomy
Splenectomy
A splenectomy is a surgical procedure that partially or completely removes the spleen.-Indications:The spleen, similar in structure to a large lymph node, acts as a blood filter. Current knowledge of its purpose includes the removal of old red blood cells and platelets, and the detection and fight...
. Displaced tissue fragments can implant on well vascularized surfaces in the abdominal cavity, or, if the diaphragmatic
Thoracic diaphragm
In the anatomy of mammals, the thoracic diaphragm, or simply the diaphragm , is a sheet of internal skeletal muscle that extends across the bottom of the rib cage. The diaphragm separates the thoracic cavity from the abdominal cavity and performs an important function in respiration...
barrier is broken, the thorax
Chest
The chest is a part of the anatomy of humans and various other animals. It is sometimes referred to as the thorax or the bosom.-Chest anatomy - Humans and other hominids:...
.
Significance
If splenectomy is performed for conditions in which blood cells are sequestered in the spleen, failure to remove accessory spleens may result in the failure of the condition to resolve. During medical imagingMedical imaging
Medical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...
, accessory spleens may be confused for a enlarged lymph nodes or neoplastic growth in the tail of the pancreas, gastrointestinal tract, adrenal gland
Adrenal gland
In mammals, the adrenal glands are endocrine glands that sit atop the kidneys; in humans, the right suprarenal gland is triangular shaped, while the left suprarenal gland is semilunar shaped...
s or gonads.