The spleen

Published on 11/04/2015 by admin

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The spleen

Chee-Chee H. Stucky and Richard T. Schlinkert

Introduction

The history of the spleen, including surgery, anatomy and physiology, has been nicely detailed by McClusky et al. and will not be reviewed here.¹^,² The spleen lies in the posterior left upper quadrant superior to the level of the costal margin. It is attached to adjacent structures via a series of ligaments including the splenophrenic, splenorenal, splenocolic and gastrosplenic ligaments.

The splenic artery arises from the coeliac trunk. Aberrant anatomy may include direct origination from the aorta, the superior mesenteric, middle colic or left gastric arteries. The splenic artery gives off pancreatic branches (the largest of which is the pancreatic magna) as well as the left gastroepiploic artery before branching and entering the spleen. The hilum may consist of a single, long splenic artery that branches late into the spleen, or an artery branching much earlier after its origin. Each artery ends in the sinusoids of a segment of the spleen. The spleen also receives blood flow from the short gastric vessels.

The splenic vein leaves the hilum and runs along the posterior aspect of the pancreas, providing venous drainage of the pancreas as well. It is joined by the inferior mesenteric vein before merging with the superior mesenteric vein to form the portal vein.

The spleen is composed of two or three lobes and two to ten segments with unique arterial supplies. Accessory spleens occur in approximately 10–15% of patients and are most commonly located near the splenic hilum, but may also be located at distant sites.

The spleen plays a significant role in fighting infections, particularly of encapsulated organisms. It also serves to filter aged blood cellular elements and removes intracellular inclusions, a process known as pitting. There are extensive T-cell and dendritic cell populations located primarily in the periarterial lymphatic sheaths. B cells are located in the lymphoid nodules while macrophages are distributed widely.

While the spleen provides important immune and housekeeping functions, it may also be a source of massive blood loss from trauma, excessive cellular destruction or sequestration, certain lymphomatous or myeloid diseases, symptomatic splenomegaly, or tumours. Splenic preservation is always preferred due to its many functions, but splenectomy may be necessary in these instances.

Postsplenectomy sepsis

Asplenic patients are at increased risk of developing overwhelming sepsis throughout their lives. This lifetime risk of postsplenectomy sepsis is approximately 0.02% for adults.³ In a recent large population-based study from Scotland, Kyaw et al.⁴ showed severe infection, defined as need for hospitalisation, occurred with an incidence of 7 per 100 person-years. The risk of overwhelming infection, defined as septicaemia or meningitis, was 0.89 per 100 person-years.

A high mortality is associated with overwhelming postsplenectomy infection and therefore prevention is of utmost importance. Davies et al.⁵ in 2002 revised the guidelines of the British Committee for Standards in Haematology published in 1996.⁶ Ideally, vaccinations should be administered a minimum of 2 weeks prior to splenectomy. Vaccinations should include polyvalent pneumococcal, haemophilus influenza type B and meningococcal C vaccines (Box 9.1). Pneumococcal vaccines should be repeated after 3–5 years.⁷ Shatz et al.⁸ prospectively studied 59 patients in a randomised fashion to determine the ideal timing of postoperative immunisation in patients who did not receive preoperative vaccines. Improved functional antibody responses to certain serotypes and serogroups were identified if immunisations were delayed for 14 days. Surgeons globally must be fastidious regarding compliance with vaccination guidelines.⁷^,⁹

Box 9.1 Immunisation recommendations

Vaccine recommendations:

• Polyvalent pneumococcus

• Haemophilus influenza B

• Meningococcus

Timing:

• Ideal: > 2 weeks preoperative

• If postoperative:

• delay 2 weeks if possible

• better to give sooner than 2 weeks if follow-up is unlikely

Repeat pneumococcus vaccine once at 5 years

Trauma

The most common cause of splenic injury is blunt trauma.¹⁰ Rupture may also occur from penetrating trauma, iatrogenic injury or, rarely, diseases such as mononucleosis or typhoid. Management of splenic trauma has evolved significantly over the last several years. Non-operative management is used in 60–80% of blunt injury cases, with success rates of 95%.¹¹ Initial management of all traumas should begin with primary and secondary surveys completed according to the Advanced Trauma Life Support guidelines.¹² Diagnostic evaluation for splenic injury follows and is based on the haemodynamic status of the patient. Haemodynamically unstable patients should undergo rapid focused assessment by sonography for trauma (FAST).¹¹^,¹³ If FAST is not available or inconclusive, diagnostic peritoneal lavage may be used. Scant fluid on the FAST exam should prompt a search for other causes of shock. A large amount of intraperitoneal blood on FAST is an indication for emergent laparotomy. Currently, exploration for traumatic splenic injury is performed in an open fashion.

Haemodynamically stable patients with physical findings of abdominal trauma should undergo abdominal computed tomography (CT) to assess all potential injuries. A grading system for splenic injury based on CT findings has been developed by the American Association for the Surgery of Trauma (AAST)¹⁴ and is presented in Table 9.1. The decision to proceed to operative exploration, however, is not based solely upon these grades. All grades of injury have undergone successful non-operative management. Patients with higher grade injuries or age > 55 years, however, are at increased risk for failure of non-operative management and warrant a low threshold to proceed with operative intervention.^15–17

Table 9.1

American Association for the Study of Trauma (AAST) splenic injury scale based on CT criteria

Grade		Injury description
I	Haematoma	Subcapsular, < 10% surface area
	Laceration	Capsular tear, < 1 cm parenchymal depth
II	Haematoma	Subcapsular, 10–50% surface area. Intraparenchymal, < 5 cm in diameter
	Laceration	1–3 cm parenchymal depth, which does not involve a trabecular vessel
III	Haematoma	Subcapsular, > 50% surface area or expanding; ruptured subcapsular or parenchymal haematoma; intraparenchymal haematoma ≥ 5 cm or expanding
	Laceration	> 3 cm parenchymal depth, or involving trabecular vessels
IV	Laceration	Laceration involving segmental or hilar vessels producing major devascularisation (> 25% of spleen)
V	Laceration	Completely shattered spleen
	Vascular	Hilar vascular injury that devascularises spleen

Advance one grade for multiple injuries, up to grade III.

Indications for operative intervention in splenic trauma from the Society for Surgery of the Alimentary Tract (SSAT) Patient Care Guidelines ¹⁸ are shown in Box 9.2. The group also suggests an aggressive non-operative approach for children < 14 years of age.

Box 9.2 Accepted indications for operative intervention in trauma of the spleen based on Society for Surgery of the Alimentary Tract (SSAT) Patient Care Guidelines

• Haemodynamic instability

• Bleeding > 1000 mL

• Transfusion of more than 2 units of blood

• Other evidence of ongoing blood loss

More aggressive non-operative approach in children < 14 years of age

The use of selective arterial embolisation in the management of splenic trauma was initially described by Sclafani et al.¹⁹ but remains somewhat controversial. Protocol-driven strategies utilising both conservative and aggressive indications for implementing embolisation have yielded excellent results.²⁰^,²¹ Other groups, however, have highlighted difficulties in using CT grading systems and selective arterial embolisation, hence the conflict preventing widespread use.²²^,²³

The decisions implicit in non-operative management are difficult and protocols will be useful to aid this process.¹⁴ Ultimately, decisions will be determined by clinical acumen and resources available at the centre treating the patient. The risk of postsplenectomy-related sepsis of 0.02% in adults³ will need to be weighed against the risks of transfusions, ongoing haemorrhage and late re-bleeding.

As many as 40% of splenectomies are performed as a result of iatrogenic splenic injury.²⁴^,²⁵ Such injuries usually result from excess traction against either the splenic ligaments or adhesions to the spleen. The standard use of laparoscopic procedures may lower the risk of splenic injury by providing better visualisation, application of less traction, improved instrumentation for perisplenic dissection, and better control of capsular haemorrhage by the pressure of the pneumoperitoneum.²⁶

Haemostatic control of splenic injuries begins with direct pressure. Haemostatic agents such as microfibrillar collagen, microporous polysaccharide hemispheres or injectable haemostatic matrices may be applied to aid haemostasis.²⁷ Haemostatic instruments such as argon-beam coagulators may also be helpful. Ligation of selected arteries in the hilum may help control bleeding but potentially lead to a need for partial splenectomy. Splenorrhaphy and partial splenectomy have been described for splenic trauma; however, Holubar et al.²⁸ showed the most important factor in preventing adverse outcome after iatrogenic splenic injury is prompt cessation of bleeding by whatever means. Splenectomy, while not desirable, is preferable to significant blood loss and should be performed when bleeding is excessive, if the patient cannot tolerate prolonged procedures, or if there are other factors that would make re-bleeding a greater risk than splenectomy.

Elective indications for splenectomy

Most recommendations for elective splenic surgery are based on level III or IV evidence. This is likely due to the relative rarity of diseases requiring splenectomy and the length of follow-up required to assess results. Recent literature reviews are referenced in this chapter when the supporting literature is composed largely of smaller non-prospective studies regarding a particular disease.

Immune thrombocytopenic purpura

The most common non-traumatic indication for splenectomy is immune thrombocytopenic purpura (ITP). This disease is characterised by low platelet count, normal bone marrow (increased megakaryocytes) and absence of other causes of thrombocytopenia. The destruction of platelets in this condition is mediated by platelet antibodies and the spleen is typically the site of destruction of the platelets. ITP remains a diagnosis of exclusion as tests for antiplatelet antibodies are not reliable indicators of the disease. The spleen is usually normal in size. Platelet function is also normal and while spontaneous bruising is common, severe haemorrhage is less likely unless platelet levels drop below 10 000.

Corticosteroid therapy is frequently instituted with platelet counts of 20 000–30 000.29–31 Most patients will respond to medical therapy, at least initially. If counts respond and are sustained, the treatment is stopped and patients are observed. Intravenous immunoglobulin may be used to increase platelet counts temporarily, but the response lasts days to weeks only. Patients who require prolonged treatment or do not respond to medical therapy should be considered for splenectomy.

Approximately 80% of patients respond to splenectomy and 65–85% of patients sustain response long term.³¹ There is no widely accepted factor to predict response to splenectomy. If platelet counts drop after splenectomy, peripheral blood smears may show absence of nuclear inclusions (e.g. Howell–Jolley bodies) indicating residual splenic tissue. Nuclear medicine scans, magnetic resonance imaging or CT may help localise such remnants for re-exploration or embolisation. Mild to moderate degrees of thrombocytopenia without symptoms of purpura or bleeding postsplenectomy may be observed without resuming medical therapy.³¹