| What is the spleen? | • The spleen is the largest secondary immune organ in the body.
• It’s a filter for the blood and a site of immune responses to blood-borne antigens.
• Accessory spleens occur in about 10 % of individuals
• Following traumatic rupture, small nodules of splenic tissue may grow on the peritoneal surface as implants (splenosis) |
| How is gross anatomy of spleen? | • Normally in the adult it weighs about 150 gm.
• It is enclosed within a thin, glistening, slate-gray connective tissue capsule.
• Its cut surface reveals extensive red pulp dotted with gray specks, which are the white pulp follicles.
• Hilus, where it is penetrated by vessels and nerves which follow the extensive branching network of fibrous trabeculae. (! Hilar lymph nodes). |
| How is spleen white pulp | • 25% of the spleen, the white pulp is responsible for the
immunological function of the spleen. It comprises the
lymphoid compartment of the spleen, and contains:
• Periarteriolar lymphatic sheaths (PALS): tightly packed T cells arranged in cylindrical sheaths around central arterioles (may expand to form nodule of B cells developing into germinal centers)
• Lymphoid follicles: spherical aggregations of B cells scattered throughout the PALS |
| How are primary and secondary B cell follicules? | • Primary (unstimulated) follicles contain resting (inactive) B cells
• Secondary (stimulated) follicles contain activated B cells in a central region (germinal center)
Marginal Zone:
• Surrounds the primary follicle and the mantle zone of secondary follicles
• Consists of a corona of mediumsized lymphoid cells with prominent pale cytoplasm |
| How is spleen red pulp? | • Constituting 75% of the spleen, the red pulp is
responsible for the hematological function of the spleen.
• The red pulp contains :
Splenic sinusoids: blood-filled spaces located
throughout the red pulp. The endothelial lining of the
sinusoid is discontinuous, providing a passage for blood
cells between the sinusoids and cords.
Splenic cords (Billroth’s cords): consist of all cells
between the sinusoids in the red pulp (reticular cells,
macrophages, plasma cells, lymphocytes, RBCs, platelets,
other leukocytes) |
| How are spleen sinusoids? | • The sinus-lining cells, also called littoral cells (specialized endothelial cells), have overlapping cytoplasmic processes without tight junctions.
• Sinusoids are surrounded by distinctive ring fibers.
• The littoral cells, which literally means “shoreline” or “tidal”, comprise 30% of the red pulp and are phenotypically distinct from endothelial cells in other tissues, including those with sinusoidal compartments. |
| How are compartments of red pulp? | • The cords contain a labyrinth of macrophages loosely connected through long dendritic processes to create both a physical and a functional filter. As it traverses the red pulp, the blood takes two routes to reach the splenic veins.
1. Open circulation or slow compartment: Some flows through capillaries into the cords, from which blood cells squeeze through gaps in the discontinuous basement of the endothelial lining to reach the sinusoids.
2. In the other “closed circuit,” blood passes rapidly and directly from the capillaries to the splenic veins.
Although only a small fraction of the blood pursues the “open” route, during the course of a day the entire blood volume passes through the cords, where it is closely examined by macrophages |
| What are functions of spleen? | 1. Phagocytosis of blood cells and particulate matter.
2. Antibody production against microbial
polysaccharides, as well as autoantibodies against a
variety of self antigens.
3. Hematopoiesis. the spleen can become a major
site of compensatory extramedullary hematopoiesis
in the setting of severe chronic anemia and in
patients with myeloproliferative disorders.
4. Sequestration of formed blood elements. |
| What is splenomegaly? Splenic insufficiency? | Splenomegaly:
• Systemic inflammations, generalized hematopoietic disorders, and many metabolic disturbances, can cause spleen enlargement
• It is rarely the primary site of disease.
Insufficiency:
• Insufficiency due to splenectomy or autoinfarction (sickle-cell disease) has a major clinical manifestation: increased susceptibility to sepsis.
• The decrease in phagocyticcapacity and antibody production contribute to the increased risk of sepsis, caused by encapsulated bacteria (pneumococci, meningococci, Haemophilus influenzae)
• Asplenic individuals should be vaccinated against these agents. |
| What are types of splenomegaly? | . |
| What is hypersplenism? | • A chronically enlarged spleen often removes excessive numbers of one or more of the formed elements of blood, resulting in anemia, leukopenia, or thrombocytopenia. This is referred to as hypersplenism.
• Platelets are particularly susceptible to sequestration in the interstices of the red pulp; as a result, thrombocytopenia is more prevalent and severe in persons with splenomegaly than is anemia or neutropenia. |
| What are lesions of spleen? | . |
| What are epithelial cysts of spleen? | • Splenic cysts are usually solitary, seen in children and young adults.
• Histogenesis in unknown.
• Most epithelial cysts of spleen are large, often symptomatic, and require splenectomy. Unilocular cyst filled with serous fluid.
• There are rare cases of mucinous epithelial cysts with associated pseudomyxoma peritonei.
• The cyst lining may consist of columnar, cuboidal or squamous epithelium.
• The lining cells may be positive for CEA and CA19-9. |
| What are spleen pseudocysts? | They make up about 75% of non-parasitic cysts of spleen.
• Most are solitary and asymptomatic and usually the result of trauma.
• By definition, they lack epithelial lining. Some of them might be true epithelial cysts in which the lining has been destroyed over time.
• The cyst wall is composed of fibrous tissue which may undergo calcification.
• They are usually filled with blood and necrotic debris. |
| What are splenic lymphomas? | • Wide and heterogeneous array of diseases.
• Clinical behavior spans from indolent to highly aggressive.
• Spleen rarely represents the exclusive site of the lymphomatous burden.
• Distinguish pathologic conditions primarily involving the spleen v/s those in which splenomegaly presents as an epiphenomenon of
hepatic or systemic diseases.
• Diagnostic workup: PB, BM, Splenectomy
PB evaluation
• PB examination is therefore a mandatory step
in the diagnostic workup of SLs.
• Almost invariably show the presence of
neoplastic cells in the PB
+/- Flow for peculiar cell types |
| How is BM evaluation in splenic lymphomas? | • BM is almost constantly involved, even when the leukemic component is inconspicuous.
• BM represents the most easily accessible tissue for the histopathologic analysis.
• Also, it is an invaluable source of fresh cells for immunophenotypic, biomolecular & cytogenetic characterization of the neoplastic clone |
| How is splenectomy in dx? | • Diagnostic workup integrating clinical and imaging data, and data from PB and BM investigations, can help recognizing most cases of lymphomas presenting as unexplained splenomegaly as specific B- or T-cell lymphoma histotypes.
• However, in a minority of cases:
– generic diagnosis of B-cell chronic lymphoproliferative
disorder,
– or it can even leave the nature of the splenomegaly
unsolved |
| What is indication for splenectomy? | • Diagnostic splenectomy when neither PB examination nor BM assessment highlights the presence of a lymphoid neoplastic clone.
• Patients receiving a generic diagnosis of B-cell chronic lymphoproliferative disorder after PB and BM assessment: Avoid splenectomy as a mere diagnostic refinement.
• Given the indolent pace of the SLs commonly falling in this “basket diagnosis,” (SMZL, SL-u, and LPL), allowing the adoption of a watchful waiting policy, we consider splenectomy only when it fully matches the need of a
therapeutic intervention. |
| What is splenic hamartoma? | • A tumor-like mass of disorganized but mature tissue indigenous to the spleen.
• Splenic hamartoma is composed exclusively of red pulp elements.
• It lacks follicles or fibrous trabeculae. |
| What are vascular splenic neoplasms? | • The most common non-lymphoid primary
tumour of the spleen.
1. The benign vascular tumours are:
haemangioma, lymphangioma, and peliosis.
2. Splenic lesions with intermediate biological
behaviour include littoral cell angioma,
Kaposi sarcoma and hemangioendothelioma.
3. The main primary malignant splenic vascular
lesion is angiosarcoma. |
| What is hemangioma? | • It is the most common primary tumor of spleen.
• Usually cavernous subtype.
• Most are small and discovered incidentally. Occasionally, they involve whole organ.
• They may rupture spontaneously and present with hemoperitoneum.
• The vascular channels , variably sized , are lined by plump endothelial cells.
• If the channels involved the entire spleen:angiomatosis |
| What is littoral cell angioma? | • Rare tumor
• Arises from littoral cells: These cells have features intermediate between those of endothelial cells and macrophages.
• Anastomosing vascular channels which may anastomose with normal splenic sinuses at the periphery. The vascular channels may have a pseudopapillary aspect
• The vascular spaces are lined by tall plump cells which express both endothelial and histiocytic markers.
• IHC: CD68+, CD31+, ERG + |
| What is lymphangioma? | • Mostly in children.
• Location usually tends to be subcapsular.
• Capillary, cavernous, and cystic
• Variably sized cysts filled with proteinaceous fluid and lined by flattened endothelial cells.
• Cystic spaces are lined by attenuated endothelium resembling that seen in normal lymphatics.
• The cysts are separated by a delicate vascular stroma.
• IHC: CD31 + |
| What is hemangioendothelioma? | • Young adults
• Intermediate between hemangioma and angiosarcoma.
• May recur locally and some have ability to metastasize, although less frequently than angiosarcomas.
• Relatively uniform population of spindle cells lacking atypia or mitotic activity.
• Spindle cells are positive for CD31 and CD34 and negative for S-100 and Desmin. |
| What is angiosarcoma? | • Angiosarcoma is the most common primary malignancy (non-lymphoid) of the spleen.
• Older patients
• Prognosis is poor and most patients die within 1 yr of diagnosis
• The tumor shows anastomosing vascular channels lined by atypical endothelial cells.
• It may also exhibit solid or papillary growth patterns.
• Highly atypical cells lining the vascular spaces.
• IHC: CD31, CD34 positive |
| What is myelofibrosis? | • Extra-medullary hematopoiesis consisting of clusters of megakaryocytes and myeloid precursors. |
