Asplenia

Excerpt

Asplenia means the absence of a spleen. Asplenia can occur in a variety of clinical settings, and it can refer to an anatomic absence of the spleen or functional asplenia secondary to a variety of disease states. The spleen is one of the primary extramedullary lymphoid organs. It is located in the left upper quadrant of the abdomen. Normally, the spleen is not palpable on physical exam and measures on average 10.65 by 5.16 cm. Normal spleen size can vary by gender and race. For example, men on average have larger spleens than females, and whites, on average, tend to have larger spleens compared to African American individuals. When palpable or notably enlarged on imaging, the clinician must consider a variety of underlying disease states (whether acquired or inherited) contributing to the enlargement.

Functionally, the spleen’s primary physiologic role is the filtration and processing of senescent blood cells (predominantly red blood cells or RBCs) and immunologically helps protect against encapsulated microorganisms and respond to infectious pathogens. It contains both hematopoietic and lymphopoietic elements, providing a basis for extramedullary hematopoiesis when necessary. The spleen has two functionally and histologically distinct tissues where these processes take place: the white pulp and the red pulp. The white pulp has a large mass of lymphoid tissue that produces antibodies against recognized antigens, whereas the red pulp has a tight network of sinusoids called the cord of Billroth which helps in blood filtration. As the body's largest filter of blood, it helps to remove old RBCs from the circulation aiding in the removal of blood-borne microorganisms. Beyond the spleen, the lymphatic system of the body consists of a complex myriad of lymphatic vessels, lymph nodes, and other specific extramedullary lymphoid organs including the thymus, tonsils, and appendix, which collectively play a very important role in immune defenses.

Asplenia can be caused by damage to the white pulp, the red pulp, or both. The spleen is a direct and indirect site of potential toxicity that can secondarily arise from underlying disease processes or infection. One must understand and appreciate the various etiologies and potential complications of asplenia, such as being a great risk factor for encapsulated microorganisms. Bacterial infections with Neisseria meningitides or Streptococcal pneumoniae, among many others, can become life-threatening if untreated in patients with anatomic or functional asplenia. Patients without a spleen have a 200-fold greater risk of death from septicemia compared to those with an adequate functioning spleen. There are many case reports in the medical literature reporting of asplenic patients, unfortunately, succumbing to infectious disease leading to death. One notable example reported by Heubner ML et al. (2015) described the rare case of a patient who had required splenectomy due to refractory immune thrombocytopenia (ITP). He subsequently developed a pneumococcal meningitis infection and died despite best supportive efforts. The rate of invasive bacterial infection and mortality in asplenic patients is significantly higher compared to normal controls – 69% in meningitis, 64% in septicemia, and 7% in Purpura fulminans.