Spleen
SPLEEN
Study notes covering the location, size, position, external features, hilum, angles, peritoneal relations, visceral relations, blood supply, lymphatic drainage, nerve supply, functions, vascular segments, histology, development, congenital anomalies and clinical anatomy.
Location
- The spleen is a wedge-shaped organ lying mainly in the left hypochondrium and partly in the epigastrium.
- It is wedged between:
- Fundus of stomach
- Diaphragm
The spleen is tetrahedral in shape.
Dimensions and Size
General Features
Consistency
Soft
Vascularity
Highly vascular
Colour
Dark purple
Palpability
Normally, it is nonpalpable.
Size
Length
9–14 cm (~5 inches)
Breadth
6–8 cm (~3 inches)
Thickness
3–5 cm (~1 inch)
Weight
7 ounces (150 g)
- The size and weight of the spleen vary with age and sex.
- Its weight increases during puberty and tends to diminish in size and weight in old age.
Relation to Ribs
- The spleen lies opposite the 10th, 11th and 12th ribs.
- It lies behind the midaxillary line, under the diaphragm.
- Its long axis lies along the 11th rib.
Position / Axis of Spleen
The spleen lies obliquely along the long axis of the 10th rib.
It is directed:
- Downwards
- Forwards
- Laterally
It makes an angle of about 45° with the horizontal plane.
External Features
The spleen has:
2 Ends
2 Borders
2 Surfaces
1 Hilum
Two Ends
1. Anterior End / Extremity
- Expanded.
- Directed downwards and forwards.
- Reaches the midaxillary line.
2. Posterior End / Extremity
- Rounded.
- Directed:
- Upwards
- Backwards
- Medially
- Rests on the upper pole of the left kidney.
Two Borders
1. Superior Border
Characteristically notched near the anterior end.
2. Inferior Border
Rounded.
Two Surfaces
1. Diaphragmatic Surface
- Convex
- Smooth
2. Visceral Surface
- Concave
- Irregular
Hilum
- The hilum lies on the visceral surface.
- It is situated in the inferomedial part of the gastric impression, along the long axis of the spleen.
Structures Transmitted
Splenic Vessels
Nerves
Attachments
- Gastrosplenic ligament
- Lienorenal ligament
Angles of Spleen
Anterobasal Angle
Junction of:
- Superior border
- Lateral/anterior end
It is the most forward-projecting part of the spleen.
When the spleen is enlarged, this part is felt first.
Therefore, it is called the clinical angle of spleen.
Posterobasal Angle
Junction of:
- Inferior border
- Lateral/anterior end of spleen
Clinical Note
- The spleen is not essential for life.
- In cases of surgical removal of spleen, death due to sepsis is commonly observed.
Peritoneal Relations
The spleen is surrounded by peritoneum.
It is suspended by the following ligaments:
1. Gastrosplenic Ligament
- Extends from the hilum of spleen to the greater curvature of stomach.
Contains
- Short gastric vessels
- Associated lymphatics
- Sympathetic nerves
2. Lienorenal Ligament
- Extends from the hilum of spleen to the anterior surface of the left kidney.
Contains
- Tail of pancreas
- Splenic vessels
- Associated pancreaticosplenic lymph nodes
- Lymphatics
- Sympathetic nerves
3. Phrenicocolic Ligament
- It is not attached to the spleen, but supports its anterior end.
- It is a horizontal fold of peritoneum extending from the splenic flexure of colon to the diaphragm, opposite the 11th rib in the midaxillary line.
- It limits the upper end of the left paracolic gutter.
- Also called sustentaculum lienis.
Visceral Relations
Visceral Surface
The visceral surface is related to:
1. Fundus of Stomach
2. Anterior Surface of Left Kidney
3. Splenic Flexure of Colon
4. Tail of Pancreas
1. Gastric Impression
- For the fundus of stomach.
- Lies between the superior and intermediate borders.
- It is the largest and most concave impression on the spleen.
2. Renal Impression
- For the left kidney.
- Lies between the inferior and intermediate borders.
3. Colic Impression
- For the splenic flexure of colon.
- Occupies a triangular area adjoining the anterior end of the spleen.
- Its lower part is related to the phrenicocolic ligament.
4. Pancreatic Impression
- For the tail of pancreas.
- Lies between the hilum and colic impression.
Diaphragmatic Surface
Related to the diaphragm.
The diaphragm separates the spleen from:
- Costodiaphragmatic recess of pleura
- Lung
- 10th rib
- 11th rib
- 12th rib of the left side
Arterial Supply
- The spleen is supplied by the splenic artery.
- Splenic artery is the largest branch of the coeliac trunk.
- It is tortuous in its course to allow movements of the spleen.
- It passes through the lienorenal ligament to reach the hilum of the spleen.
- At the hilum, it divides into five or more segmental branches.
Venous Drainage
Formation of Splenic Vein
The splenic vein is formed at the hilum of the spleen.
Tributaries of Splenic Vein
1. Short Gastric Veins
2. Left Gastroepiploic Vein
3. Pancreatic Veins
4. Inferior Mesenteric Vein
Lymphatic Drainage
- Lymphatics begin with the peri-arterial lymphatic sheaths (PALS) in the white pulp.
- Lymphatic vessels run along the trabecular arteries in the trabeculae towards the hilum.
- Lymphatic vessels from the subcapsular plexus also run towards the hilum.
Lymphatic Drainage
Superior Pancreatic Nodes
Inferior Pancreatic Nodes
Pancreaticoduodenal Nodes
There are no lymphatic vessels in the red pulp of the spleen.
Nerve Supply
- Sympathetic fibres are derived from the coeliac plexus.
- They are vasomotor in nature.
- They also supply some of the smooth muscle present in the capsule.
Functions of Spleen
- Removal of worn-out old RBCs by phagocytosis.
- Haematopoiesis during foetal life and lymphopoiesis throughout life.
-
Immune response by:
- Production of lymphocytes under antigen stimulation
- Production of plasma cells which produce antibodies
- Phagocytosis of microorganisms.
- Reservoir of RBCs.
Vascular Segments of Spleen
Splenic Vascular Segments
- Before entering the spleen, the splenic artery gives:
- Superior branch
- Inferior branch
- These branches do not anastomose in the spleen.
- Therefore, an avascular zone exists between their territories.
- Thus, the spleen has:
Superior Segment
Inferior Segment
- These segments are separated by an avascular plane passing perpendicular to the long axis of the spleen.
- This can be used for segmental resection of spleen.
Types Based on Branching of Splenic Artery
Diffuse Type
Terminal branches of splenic artery arise away from the hilum.
Compact Type
Terminal branches arise near the hilum.
Histology of Spleen
- The spleen is covered by a dense connective tissue capsule.
- The capsule sends trabeculae into the parenchyma of the spleen.
1. White Pulp
- Consists of central arterioles surrounded by periarterial lymphatic sheaths of T lymphocytes.
2. Splenic Nodules / Malpighian Corpuscles
- Consist of B cells.
- B cells aggregate with a germinal centre around eccentric arterioles.
3. Red Pulp
Consists of cords of Billroth.
Cords are made up of:
RBCs
Lymphocytes
Macrophages
Plasma Cells
4. Red Pulp Sinusoids
Red pulp has sinusoids lined by elongated stave cells (endothelial cells).
5. Marginal Zone
- Lies between red and white pulp.
- Contains numerous antigen-presenting cells.
Development of Spleen
- The spleen develops in the dorsal mesogastrium from mesoderm.
- In the 5th week of IUL, mesenchymal cells condense to form small masses called spleniculi.
- Spleniculi fuse to form a single mass of spleen.
- Lobulated development of spleen in an adult is indicated by splenic notches.
- The spleen acts as a haematopoietic organ in foetal life until birth.
Congenital Anomalies
1. Accessory Spleen
Failure of fusion of spleniculi with the main splenic tissue gives rise to an accessory spleen.
Sites
Hilus of Spleen
Gastrosplenic Ligament
Lienorenal Ligament
Tail of Pancreas along the Splenic Artery
Left Spermatic Cord
2. Lobulated Spleen
Incomplete fusion of spleniculi (persistent foetal spleen) produces a lobulated spleen.
3. Right-Sided Bilaterality / Isomerism
Characterized by:
- Asplenia
- Hypoplastic spleen
Left-Sided Bilaterality
Characterized by polysplenia.
Clinical Anatomy
Movements of Spleen
- The spleen is an intraperitoneal structure and is related to the diaphragm.
- Hence, the spleen moves with respiration.