The spleen and adrenal glands

Introduction

The spleen is a little understood organ largely mystifying early physicians since antiquity. It was not until the latter half of the 20th century that the spleen’s four main functions are better understood: antibody presentation and production, foetal haematopoiesis, sequestration of formed blood elements, and phagocytosis for recycling of blood cells, iron and particulate matter. Though splenic primary and secondary malignancies are rare, the differential diagnosis and indications for surgical splenectomy remain broad. Indications include traumatic rupture, autoimmune disorders, red blood cell dyscrasias, vascular abnormalities, lymphomas or myeloproliferative disorders, adjacent organ resection, hypersplenism/cytopenias or abscesses/cysts. Given the immunological consequences of asplenism—notably overwhelming post-splenectomy infection syndrome (OPSI)—the indications for complete surgical resection have evolved, giving rise to splenic conservation in trauma and left upper quadrant operations.

Anatomy and embryology

The spleen is the largest reticuloendothelial organ, defined by monocyte progenitors participating in phagocytosis and antigen presentation, approximately the size of a clenched fist measuring 10 to 12 cm in length and normally weighting 150–250 g. The spleen has two surfaces, the diaphragmatic surface that is smooth and convex and is in contact with the diaphragm, and the visceral surface that is irregular and concave and has impressions contacting the fundus of the stomach, left kidney, splenic flexure of the colon and tail of the pancreas. The spleen is invested by two fibrous capsules, the outer tunica serosa that is derived contiguous with the peritoneum and invests the organ except at the hilum, where the peritoneum reflects into the phrenicocolic and gastrosplenic ligaments, and the tunica albuginea that invests the entire organ and at the hilum is reflected inward along the vessels to form sheaths from which the trabecular framework of the spleen emanates. The spleen is an intraperitoneal organ that is suspended by multiple ligamentous folds of peritoneum, namely, the gastrosplenic connecting the hilum of the spleen with the greater curvature of the stomach, the splenorenal connecting the hilum of the spleen to the left kidney and containing the splenic vessels and tail of the pancreas, and the phrenicocolic connecting the left colic flexure and diaphragm to the diaphragmatic surface of the spleen. The spleen forms from the cephalic aspect of the lateral plate mesoderm during the 5th week of gestation. Multiple aggregations of mesodermal cells condense to form a single organ. In up to 11% of individuals, one or more of these aggregates of splenic tissue fails to condense, and instead forms an accessory spleen, or splenules.

The spleen derives its major blood supply from the splenic artery, which emanates from the abdominal aorta as a branch of the coeliac trunk, traverses a tortuous course along the superior border of the pancreas, giving rise to the left gastroepiploic artery and short gastric arteries before dividing into multiple branches that enter the hilum of spleen. The arteries ramify throughout the organ radially into splenic arterioles that branch into penicillar arterioles that ultimately terminate in splenic cords. Here, the reticuloendothelial cells and splenic macrophages come in intimate contact with blood and its contents as it percolates through the splenic cords and across walls of the splenic sinuses. Owing to the large amount of infiltrating blood, the red pulp is a principal site of blood filtration, where ageing blood cells are destroyed via programmed cell removal. Scattered throughout the red pulp are local expansions of lymphocytes that appear as white pulp ( Fig. 11.1 ). White pulp is closely associated with central arterioles that are surrounded by periarterial lymphatic sheaths containing T lymphocytes. Surrounding the T lymphocytes are follicles that contain B lymphocytes. In response to antigen presentation, these B lymphocytes become activated and produce antibodies that play a significant role in opsonisation of extracellular organisms including encapsulated bacteria. Between the red and white pulps is a marginal zone that contains antigen-presenting cells crucial for initiating lymphocyte activation. The association of lymphoid and myeloid cells in the red and white pulp makes the spleen a principal site of intersection between the innate and adaptive immune systems. The major vascular outflow from the spleen occurs via coalescence of the open sinuses via reticular trabeculae into the splenic vein, which exits via the hilum of the spleen and courses medially to converge with the superior and inferior mesenteric veins to form the portal vein.

Management of surgical asplenia

Splenectomy decreases innate and adaptive immune responses which can manifest in OPSI. OPSI is the development of a fulminant, rapidly fatal bacterial infection following splenectomy. OPSI is the most feared complication after removal of the spleen. All patients undergoing splenectomy or at high risk for splenectomy should receive vaccinations for the encapsulated bacteria Streptococcus pneumoniae , Haemophilus influenzae type b and Neisseria meningitidis . Administration is recommended 14 days after emergent splenectomy or prior to discharge from the hospital if patient follow-up is tenuous. For elective splenectomy, vaccinations should be given at least 14 days prior but ideally 10 to 12 weeks in advance; however, early vaccination is difficult to realise in practice.

Depending on the country of practice and vaccinations available, providers should anticipate multiple temporally spaced doses for optimal response against meningococcal and pneumococcal serotypes. All other recommended vaccinations, such as seasonal influenza, should be administered. In high-risk patients, daily penicillin-based prophylactic regimens may be preferred with clarithromycin being an acceptable alternative in highly allergic patients unable to be desensitised. High risk applies to children withing the first year of splenectomy or younger then 5 years of age. Additionally, any patient, regardless of age, with a concurrent immunocompromising condition is considered high risk. The risk of OPSI does depend on the indication behind the resection. When trauma is the indication, OPSI is nearly five times less likely to occur when compared with haematological malignancies. Left upper quadrant solid tumour resections with simultaneous splenectomy also appear to have a lower incidence of OPSI and are generally not prescribed daily prophylactic antibiotics.

Indications for splenectomy

Traumatic splenic injury was previously the most common indication for splenectomy and routinely performed through celiotomy during exploratory surgery; however, medical indications are overtaking indications for splenectomies performed worldwide. Haematologic diseases, like immune thrombocytopenia (ITP), are now among the most common indications. Elective splenectomy allows for preoperative planning, appropriate vaccinations and use of minimally invasive approaches.

Trauma

The spleen’s juxtaposition in the left upper abdomen to the 9th, 10th and 11th ribs renders some protection posteriorly, though the spleen remains at risk of injury during blunt or penetrating trauma. Haemodynamically unstable patients should undergo emergency celiotomy and splenectomy without delay. The use of focused assessment with sonography for trauma (FAST) is particularly useful in cases of patient instability where an abdominal source of extravasation is not certain. FAST allows rapid diagnosis and preparation for abdominal exploration if free fluid or a large perisplenic anechoic band is seen. Patients who are haemodynamically stable should undergo abdominal computed tomography (CT) with intravenous contrast and delayed phases to evaluate the extent of splenic injury. The most widely used grading criteria for traumatic splenic injuries is shown in Table 11.1 . Non-operative management (NOM) has become the standard of care for haemodynamically stable patients with low to moderate-grade injuries (grade I–III) in the absence of peritonitis or active extravasation on initial contrast-enhanced CT. Contrast blush on CT imaging by itself is not an indication for selective angioembolisation (SAE) or operative intervention and may not be seen on subsequent angiography, especially in paediatrics. ^, Failure of NOM, defined as hypotension or evidence of ongoing haemorrhage requiring operative intervention, is associated with hypotension on presentation, grade III injury with contrast blush, or grade IV/V injuries. Furthermore, 95% of NOM failures occur within 72 hours of injury. Increasingly, spleen-preserving SAE is performed as an adjunct to prevent NOM failure in patients with grade IV or V injuries or following failure of NOM. Angiography is reasonable in patients with evidence of ongoing bleeding or contrast blush as well as moderate haemoperitoneum. Success rates vary widely depending on the institution and protocols used, but centres that perform angioembolisation frequently have reduced splenectomy rates. ^,

Selective angioembolisation should be considered in grade IV and V splenic injuries. There is evidence of retained splenic function following SAE, although significant complications including pain, fever, hyposplenism, splenic abscess, splenic infarction, contrast-induced renal insufficiency or pancreatitis do occur ( Fig. 11.2 ). ^,

Table 11.1

Spleen organ injury scale (2018 revision)

From Kozar RA, Crandall M, Shanmuganathan K, et al. Organ injury scaling 2018 update: Spleen, liver, and kidney. J Trauma Acute Care Surg 2018;85(6):1119–1122.

AAST grade	AIS severity	Imaging criteria (CT findings)	Operative/Pathologic criteria
I	2	- Subcapsular haematoma < 10% surface area - Parenchymal laceration < 1 cm depth - Capsular tear	Identical to CT findings
II	2	- Subcapsular haematoma 10–50% surface area; intraparenchymal haematoma < 5 cm - Parenchymal laceration 1–3 cm	Identical to CT findings
III	3	- Subcapsular haematoma > 50% surface area; ruptured subcapsular or intraparenchymal haematoma > 5 cm Parenchymal laceration > 3 cm depth	Identical to CT findings
IV	4	- Any injury in the presence of splenic vascular injury or active bleeding confined within splenic capsule - Parenchymal laceration involving segmental or hilar vessels producing > 25% devascularisation	- Parenchymal laceration involving segmental or hilar vessels producing > 25% devascularisation
V	5	- Any injury in the presence of splenic vascular injury with active bleeding extending beyond the spleen into the peritoneum. - Shattered spleen	- Hilar vascular injury which devascularises the spleen - Shattered spleen

Vascular injury is defined as a pseudoaneurysm or arteriovenous fistula and appears as a focal collection of vascular contrast that decreases in attenuation with delayed imaging. Active bleeding from a vascular injury presents as vascular contrast, focal or diffuse, that increases in size or attenuation in delayed phase. Vascular thrombosis can lead to organ infarction. Grade based on highest grade assessment made on imaging, at operation or on pathologic specimen. More than one grade of splenic injury may be present and should be classified by the higher grade of injury. Advance one grade for multiple injuries up to a grade III.

Haematological

Thrombocytopenic disorders

Immune thrombocytopenia and thrombotic thrombocytopenic purpura

The most common indication for splenectomy is in patients with ITP. ITP, previously known as idiopathic thrombocytopenic purpura, is an autoimmune disorder characterised by both antibody-induced platelet destruction and decreased antibody production while clinically absent splenomegaly. ITP has an incidence rate of 3.3 per 100,000 adults and 1.9–6.4 per 100,000 children per year. Children are more likely to achieve remission, whereas adults are at higher risk of developing chronic ITP defined by greater than 12 months of ongoing disease. ITP is nearly always initially treated with glucocorticoids. Splenectomy was previously indicated for steroid refractory ITP. Now, rituximab and thrombopoietin-receptor agonists (TPO-RA), such as romiplostim, are mainstays of the traditional armamentarium and recommended prior to undergoing splenectomy. Splenectomy is superior to TPO-RA and rituximab in achieving durable responses (86.7%, 65.7%, and 62.1%, respectively); however, splenectomy is generally postponed until after at least a year of diagnosis due to the higher chance of spontaneous remission or medical cure. ^, Laparoscopic approach achieved equal remission rates as open splenectomy.

Laparoscopic splenectomy should be performed in refractory ITP following failure of steroid and TPO-RA therapy ( Fig. 11.3 ).

Thrombotic thrombocytopenic purpura

Once uniformly fatal, thrombotic thrombocytopenic purpura (TTP) is an autoimmune disorder caused by antibodies to ADAMTS13 that results in altered von Willebrand factor homeostasis leading to thrombotic microangiopathy. TTP classically has been defined as the pentad of fever, thrombocytopenia, microangiopathic haemolytic anaemia, renal dysfunction and neurologic symptoms, although presentation of these symptoms is highly variable. Acutely, TTP is treated with plasmapheresis, which results in remission in more than 80% of cases. Patients who are refractory to plasmapheresis or who develop recurrence of disease require splenectomy. The majority of patients undergoing splenectomy experience complete disease remission.