Anatomy of Spleen : Comprehensive Guide

The spleen, at 7–13 cm in length and 250 g in weight, is the biggest lymphoid organ. During the fifth week of development, the spleen emerges from the mesogastrium's cephalic region.

The greater curvature of the stomach and the splenic flexure of the colon are related to the visceral surface of the spleen.

• Left kidney's apex
• The pancreatic tail.

The spleen's long axis is connected to the 10th rib and it is associated with the 9th, 10th, and 11th ribs. In adulthood, the spleen is not perceptible until it enlarges to a size greater than 2.5 times its original size. The spleen is palpable in babies below the costal edge in the mid-axillary line; the splenophrenic ligament suspends the spleen's diaphragmatic surface.

Splenic Ligaments

• Gastro splenic ligament
• Spleno-phrenic ligament
• Spleno-renal ligament
• Spleno-colic ligament

The spleno-colic and spleno-phrenic ligaments are comparatively avascular. The splenic artery, vein, and tail of the pancreas are located in the splenorenal ligament; the short gastric artery and vein is located in the superior aspect, and the gastroepiploic artery and vein is located inferiorly.

The Tail Of Pancreas

 In 30% of instances, the pancreatic tail abuts the splenic hilum, and in 70% of cases, it is found within 1 cm of the hilum.
Splenic arteries are ligated within 1 cm of the splenic hilum to prevent damage to the pancreatic tail.

Arterial Supply Of Spleen : The splenic artery and the short gastric arteries supply the spleen. There are two variations in the splenic artery branching:
Thirty percent of the cases have the mistral form of branching, whereas seventy percent have the dispersed type.

The splenic artery divides into terminal and polar arteries close to the spleen's hilum in the Magistral form of branching.
The splenic artery branches into terminal arteries at a distance from the splenic Hilum in the distributed type of branching.
The left gastro-epiploic vein, the inferior mesenteric vein, the short gastric vein, and the posterior pancreatic veins are the tributaries of the splenic vein. The splenic vein is composed of several smaller splenic veins.

The splenic vein and the superior mesenteric vein unite to produce the portal vein, which is located beneath the pancreas' neck. Splenic vessels split into smaller branches within the organ and merge with the trabeculae; ultimately, arterioles leave the trabeculae and merge with the splenic pulp; the adventitia of the splenic arterioles is replaced by the covering of lymphatic tissues, and these lymphatic sheets form the white pulp.

The spleen is encased within a fibroelastic capsule, from which trabeculae extend and compartmentalize the spleen.The marginal zone is where the white and red pulps meet. It is also where the arterioles lose their lymphatic tissues and develop into splenic sinusoids, which empty into venules and veins that follow the trabeculae to become splenic veins.

Also Read: Hemobilia & Bilhemia: Understanding The Conditions

Functions Of Spleen

Haematopoietic Function

The spleen is the primary organ involved in extramedullary erythropoiesis in myelodysplastic syndrome. • It aids in the synthesis of red and white blood cells from the third to fifth week of fetal development.

Reserve function

Because the spleen stores 2% of all blood, it is referred to as the body's blood bank. Within the spleen, one-third of all platelets are gathered.  Up to 80% of the platelets with pathological splenomegaly are contained in the spleen. Therefore, the typical finding is thrombocytopenia.
Patients who have splenectomy experience an increased risk of thrombo-embolic events as well as thrombocytosis.

Filtration Function

 Both closed and open systems are involved in the splenic filtering process.
• Closed system: Blood moves from arteries to veins in this system.
• Open system: Blood passes via the arterioles, passes through the reticuloendothelial cell-rich parenchyma that resembles a sieve, passes through the splenic sinus, and then enters the venous system. 

The cellular cleansing process includes:

• Removal of senescent cells
• Removal of Cellular inclusions like RBC nucleoli
•  Removal of Parasites
• Sequestration of RBCs for maturation
• Storage of platelets as the spleen acts as a reservoir of platelets.

Numerous soluble antigens found in plasma can trigger an immunogenic response in lymphoid tissue, which results in the development of antibodies directed against the antigens.RBC shape and function are preserved after splenic filtration.

RBCs with poor morphology, such as those with inclusion bodies, are unable to pass through the splenic sinusoids and are subsequently destroyed by reticuloendothelial cells.

Also Read: Image Based Question On Intestinal Obstruction

Imperfect RBCs with Inclusions

• Howell-jolly bodies -basophilic inclusion bodies. These are mainly due to nuclear remnants.
• Heinz bodies- denatured hemoglobin.
• Pappenheimer bodies- Iron granules.
• Acanthocytes also known as spur cells
• Codocytes are known as target cells.
• The presence of Howell jolly bodies in a peripheral smear is a characteristic feature of asplenia. 
• Causes of asplenia include surgical removal of the spleen or autosplenectomy as in the case of sickle cell anemia.
• Abnormal erythrocytes lack elasticity and cannot pass through splenic sinusoids and are therefore destroyed in the spleen leading to anemia. This causes splenomegaly.

Conditions in which abnormal erythrocytes are seen:      

Abnormal erythrocytes are seen in

• Sickle cell anemia
• Hereditary spherocytosis
• Thalassemia, 
• Pyruvate kinase deficiency.

 Anemia worsens under these circumstances because red blood cells are stuck in the spleen. Early on, splenomegaly is observed. Later on, auto-splenectomy is observed as a result of auto-infarction of the spleen.

Immunity

The spleen plays a role in phagocytosis and antibody creation. Immune response components include the development of IgM. Properdin/factor P aids in the elimination of bacteria and abnormal cells; The spleen aids in the cleavage of Tuftsin from the heavy chain of IgG; Tuftsin (increases the phagocytic activity of mononuclear phagocytes and neutrophils cells); Patients with asplenia have abnormally low levels of Tuftsin in the blood.

Also Read: High-Yield Image Based Questions On Liver

Splenectomy And Indications Of Splenectomy

Trauma is the most frequent reason for splenectomy. Immunothrombocytopenic purpura is the most frequent reason for elective splenectomy.

ITP / Immune Thrombocytopenia            

 Usually observed in women under 40 years of age;  Typical features include:  Low platelet count;  Normal bone marrow; Absence of other causes of thrombocytopenia.
 In children, immunological thrombocytopenia manifests as severe thrombocytopenia with a quick onset in both boys and girls. Up to 80% of cases show evidence of spontaneous remission.  Girls who are older than ten years old still have immune thrombocytopenia.

ITP Types

The cause of primary immune thrombocytopenia is unclear.
It is known what causes secondary immune thrombocytopenia.

Primary Immune Thrombocytopenia

 When Ig G autoantibodies are produced against platelet membranes, macrophages and cytotoxic T cells destroy the platelets.  Megakaryocyte dysfunction with decreased thrombopoietin levels is present.

Primary Immune Thrombocytopenia Subtypes

Recently diagnosed: seen within a three-month period
Chronic type: lasting longer than 12 months;  Persistent type: lasting three to twelve months

Secondary Immune Thrombocytopenia

Causes include drug-induced, autoimmune disorders, viral or bacterial infections.

Clinical Features

The symptoms of immune thrombocytopenia include purpura, epistasis, and gingival bleeding.  Haematuria and gastrointestinal bleeding are less frequent.  Although uncommon, intracerebral bleeding is deadly.

Diagnosis

Primary immune thrombocytopenia is diagnosed by ruling out other thrombocytopenia-related conditions.Immune thrombocytopenia is characterized by a typically normal spleen size. Thus in these circumstances a laparoscopic splenectomy can be performed.

Management

In asymptomatic patients

Platelet counts less than 50,000/ mm3 and symptoms like:

Mucous membrane hemorrhage, high-risk ailments such as hypertension, peptic ulcer disease, and an active lifestyle.
. Glucocorticoids, such as prednisone, are started at a daily dosage of 1 mg/KG.

Platelet counts less than 20,000 to 30,000/mm3 even without symptoms:

 The use of glucocorticoids should begin.  In two-thirds of the patients, the platelet counts rise to more than 50,000/mm3 within one to three weeks of starting glucocorticoids.  Of the patients, 25% had complete responses.

In conditions like

• Acute bleeding
• Pregnancy
• Platelet transfusion being prepared
• For operation splenectomy cases

 IV Ig boosts the platelet count within three days and increases the effectiveness of platelet transfusion. IV1 g per KG is administered daily for two days.

Also Read: Image Based Questions On Gall Bladder And Bile Duct

Medical Options for refractory ITP

• Oral Prednisone
• Oral dexamethasone
• Rituximab
• Thrombopoietin receptor antagonist: Eltrombopag

Splenectomy Is The Treatment Of Choice In Conditions Like

• Platelet count less than 10,000 per mm3 for six weeks or longer
• Thrombocytopenia refractory to glucocorticoid treatment
• Requiring toxic doses of steroids to achieve remission.
• Incomplete response to Glucocorticoids
• In pregnant patients in the second trimester of pregnancy who failed to respond to steroid treatment or IV Ig treatment with the platelet count less than 10,000 per mm3 without symptoms or less than 30,000 per mm3 with bleeding problems.

Also Read: Biliary Tree Pathophysiology & Investigations

Durable Platelet Responses Are Seen In Patients Who Have

• Platelet counts of 1,50,000 per mm3 by Day 3 POD.
• More than five lakhs per mm3 by day 10 POD.
• 15% of patients have accessory spleen.
• Radio nucleotide imaging helps to detect the presence of accessory spleen and its exact location.
• In cases of chronic ITP with accessory spleen, the treatment is excision of the accessory spleen.

Also read: High-Yield GIT, Hepatobiliary and Pancreatic Surgery Questions

Hope you found this blog helpful for your GIT, Hepatobiliary and Pancreatic Surgery preparation. For more informative and interesting posts like these, keep reading PrepLadder’s blogs.