The lymphatic system comprises of a network of conduits called lymphatic vessels that carry a clear fluid called Lymph unidirectionally toward the heart. It was first described by Olaus Rudbeck and Thomas Bartholin. Itincludes all the structures dedicated to the circulation and production of lymphocytes i.e. spleen, thymus, bone marrow and the lymphoid tissue associated with the digestive system.
The lymphatic system has multiple interrelated functions: 1. Responsible for the removal of interstitial fluid from tissues. 2. Absorbs and transports fatty acids and fats as chyle from the digestive system. 3. Transports WBCs to and from the lymph nodes. 4. The lymph transports antigen-presenting cells (APCs), such as dendritic cells, to the lymph nodes where an immune response is stimulated.
Thestudy of lymphatic drainage of various organs is important in diagnosis, prognosis, and treatment of cancer. The lymphatic system → responsible for carrying cancerous cells b/w various body parts in a process called metastasis. Theintervening lymph nodes can trap the cancer cells →if not successful in destroying the cancer cells → become sites of secondary tumors.
Divisions of the lymphatic system: 1. the conducting system and 2. the lymphoid tissue. The conducting system carries the lymph consists of tubular vessels i.e. the lymph capillaries, the lymph vessels, and the right and left thoracic ducts. The lymphoid tissue primarily involved in immune responses consists of lymphocytes and other white blood cells
1. Lymphedema is the swelling caused by the accumulation of lymph fluid, Cause→lymphatic system damage or malformations. It usually affects the limbs, though face, neck and abdomen may also be affected. ◦ Some common causes of swollen lymph nodes include: infections, infectious mononucleosis, and cancer→ Hodgkins & non-Hodgkin lymphoma metastasis of cancerous cells via the lymphatic system.
1. Lymphangiomatosis is a disease involving multiple cysts or lesions formed from lymphatic vessels.2. Elephantiasis, infection of the lymphatic vessels cause a thickening of the skin and enlargement of underlying tissues, especially in the legs and genitals. It is most commonly caused by a parasitic disease known as lymphatic filariasis.3. Lymphangiosarcoma is a malignant soft tissue tumor.4. Lymphangioma is a benign tumor occurring frequently in association with Turner syndrome.5. Lymphangioleiomyomatosis is a benign tumor of the smooth muscles of the lymphatics that occurs in the lungs.
The spleen has important roles in regard to RBCs and the immune system. Functions: 1. It removes old red blood cells and holds a reserve of blood in hemorrhagic shock while also recycling iron. 2. As a part of the mononuclear phagocyte system → metabolizes hemoglobin removed from erythrocytes. 3. It is one of the centers of activity of the reticuloendothelial system → analogous to a large lymph node → absence leads to a predisposition toward certain infections. Red Pulp involved in the filtration of RBCs White Pulp involved in active immunity via hormonal & cell-mediated pathways (antibodies) Composed of Malpighian corpuscles : o "lymphoid follicles" → B-lymphocytes o "periarteriolar lymphoid sheaths" (PALS) → T-lymphocytes
It is secondarily involved in wide variety of systemic diseases & its response causes its enlargement (Splenomegaly). The disorders are classified on the basis of the degree of the Splenomegaly characteristically produced & is given in the next slides:
Hypersplenism → a state associated with many diseases affecting spleen Characteristics → removal of excessive numbers of one or more of the formed elements (blood) resulting into → Anemia, Leukemia, or Thrombocytopenia. Thrombocytopenia is more prevalent & severe.
The thymus is a central lymphoid organ of the immune system. Functions 1. T cells that attack the bodys own proteins are eliminated in the thymus through programmed cell death (apoptosis). 2. Provides an inductive environment for development of T- lymphocytes from hematopoietic progenitor cells(T-cell differentiation ).
Thymus is involved in Lymphomas (particularly those of T-cell lineage). The most frequent thymic disorders are: 1. Thymic hyperplasia 2. Thymoma
Associated with the appearance of Lymphoid follicles/germinal centers(containing reactive B-cells) within the medulla. Thymic follicular hyperplasia is present in those with Myasthenia gravis, SLE, RA. Hyperplastic thymus removal is often beneficial early in the disease.
Tumors in which the epithelial cells constitute the neoplastic elements. Characteristics → Presence of abundant precursor T- cells(thyrocytes).
1. Benign or Encapsulated thymoma which is cytologically & biologically benign.2. Malignant thymoma Type-I: cytologically benign but biologically aggressive & capable of local invasion. Type-II (Thymic Carcinoma): cytologically malignant with all of the features of cancer & comparable behavior.
Malignant more than the benign Occur at any age but typically in Middle adult life 30% Asymptomatic 15-20 % with Myasthenia gravis have a thymoma Tumor removal often leads to the improvement in Neuromuscular disorder 30-40% produce Local manifestations Mass demonstrable on CT Scan in the Anterosuperior mediastenum associated with Cough, Dyspnea, & Superior Vana Caval Syndrome. The remainder were associated with some systemic disease (Myasthenia gravis). Associations with thymoma are: ◦ Hypogammaglobulinemia, SLE, Pure red cell aplasia, & nonthymic cancers
CT scan of the chest revealing a large necrotic mass in the left anteriormediastinum (indicated by the red line).
Usually fleshy, obviously invasive masses sometimes accompanied by metastases to sites as the lungs. Most resmeble poorly/well-differentiated SCCs. Next most common malignant pattern → Lymphoepithelium-like carcinoma Composed of anaplastic cortical-type epithelial cells mixed with large numbers of benign lymphocytes. Most common in Asian populations Sometimes contain EBV genome(member of Herpes virus family) →B-cell polyclonal activation & proliferation
Thymomas → lobulated, firm, gray white masses, 15-20cm longest in dimension Most appear Encapsulated 20-25% with apparent penetration of the capsule & infiltration of perithymic tissues & structures All thymomas made up of a mixture of epithelial cells & a variable infiltrate of non- neoplastic thymocyte
Benign thymomas (medullary thymomas): spindled or elongated epithelial cells resemble those that normally populate the medulla Mixed thymoma an admixture of the plumper, rounded, cortical-type epithelial cells Medullary & Mixed patterns → 60-70% of all thymomas. Malignant thymoma type-II (Thymic Carcinoma) Cytologically malignant accounting for 5% thymomas
Malignant thymoma type-I Cytologically bland but locally invasive tumor(Ocassionally metastasize) 20-25% of all thymomas Critical distinguishing feature → penetration of the capsule & the invasion of sorrounding structures Neoplastic epithelial cells often from palisades around blood vessels → spindled epithelial cells present sometimes Composed of varying proportions of the Epithelial cells & Reactive thymocytes Epithelial cells resemble those found in the Cortex & are with abundant cytoplasm & rounded Vesicular nuclei.