Lipomas

Lipomas are the most common soft-tissue tumor. These slow-growing, benign fatty tumors form soft, lobulated masses enclosed by a thin, fibrous capsule. Although it has been hypothesized that lipomas may rarely undergo sarcomatous change, this event has never been convincingly documented. It is more probable that lipomas are at the benign end of the spectrum of tumors, which, at the malignant end, include liposarcomas . Because more than half of lipomas encountered by clinicians are subcutaneous in location, most of this article will be devoted to that subgroup. Additional information about other locations (eg, intramuscular, retroperitoneal, gastrointestinal) will be included as appropriate

Etiology

Speculation exists regarding a potential link between trauma and subsequent lipoma formation. One theory suggests that trauma-related fat herniation through tissue planes creates so-called pseudolipomas. It has also been suggested that trauma-induced cytokine release triggers pre-adipocyte differentiation and maturation. To date, no definitive link between trauma and lipoma formation has been prospectively demonstrated.

While the exact etiology of lipomas remains uncertain, an association with gene rearrangements of chromosome 12 has been established in cases of solitary lipomas, as has an abnormality in the HMGA2-LPP fusion gene.

Pathophysiology

Lipomas are common benign mesenchymal tumors. They may develop in virtually all organs throughout the body.

In the gastrointestinal tract, lipomas present as submucosal fatty tumors. The most common locations include the esophagus, stomach, and small intestine. Symptoms occur from luminal obstruction or bleeding.

Duodenal lipomas are mostly small but may become pedunculated with obstruction of the lumen. They may cause pain, obstructive jaundice, orintussusception in younger patients.^[5] Mucosal erosion over the lipoma may lead to severe bleeding, as demonstrated in the image below. Small intestinal lipomas occur mainly in elderly patients. They tend to be pedunculated submucosal lesions. They are more common in the ileum than in the duodenum or jejunum. As with duodenal lipomas, severe hemorrhage or intussusception may occur. Colonic lipomas are usually discovered on endoscopy. Gentle palpation with a biopsy forceps reveals the soft nature of the submucosal mass. A biopsy specimen of the mucosa may reveal underlying fat, the so-called naked fat sign. As with lipomas in other locations, colonic lipomas may cause pain with obstruction orintussusception.

Presentation

Symptoms in other sites depend on the location and can include the following:

• Lipomas in the major airways can cause respiratory distress related to bronchial obstruction. Patients may present with either endobronchial or parenchymal lesions.
• Previously undiagnosed lipomas of the oropharynx may also lead to airway difficulty at the time of intubation.
• Patients with esophageal lipomas can present with obstruction, dysphagia, regurgitation, vomiting, and reflux; esophageal lipomas can be associated with aspiration and consecutive respiratory infections.
• Cardiac lipomas are located mainly subendocardially, are rarely found intramurally, and are normally unencapsulated. They appear as a yellow mass projecting into the cardiac chamber.
• Intramediastinal lipomas may impinge on the superior vena cava, thereby leading to superior vena cava syndrome.
• Intestinal lipomas may manifest as classic obstruction, intussusception, volvulization, or hemorrhage.
• Lipomas arising from fat in the intramuscular septa cause a diffuse, palpable swelling, which is more prominent when the related muscle is contracted.
• Lipomas in intra-articular joint spaces or intraosseous sites, such as the calcaneus, may lead to joint dysfunction and pain that preclude normal ambulation.
• Lipomas may also arise in the dural or medullary components of the spinal cord, thereby leading to cord compression and attendant sequelae.^[7]
• Lipomas occur frequently in the breast but not as frequently as expected considering the extent of fat that is present.
• Lipomas may arise from the subcutaneous tissues of the vulva. They usually become pedunculated and dependent.
  
  
  
  
  
  

MAJOR HISTOCOMPATIBILITY COMPLEX

MAJOR HISTOCOMPATIBILTY COMPLEX:

M.H.C. molecules were discovered as products of genes that evoke rejection of transplanted organs.

· The physiologic function of mhc molecule ,is to display peptide fragments of proteins for recognition by antigen specific T-cells.

· M.H.C molecules are clustered on the chromosome 6,the MHC or the H.L.A. complex.

· The hla system is highly polymorphic.

Mainly there are two types of m.h.c. molecules.:-

· CLASS 1 M.H.C. MOLECULE

· CLASS 2 M.H.C. MOLECULE.

Class 1 m.h.c. molecules :-

· Class 1 M.H.C. molecules are expressed on all the nucleated cells and platelets,designated as HLA-A,HLA-B,HLA-C.

· Consists of three alpha subunits (α1,α2,α3) and a β-2.

· Crystal structure revealed that α-1 & α-2 domains form a cleft,or groove where the peptide binds.

Class 1 mhc molecules display peptides that are derived from proteins,such as viral antigens,that are located in the cytoplasm and usually produced in the cells,and class 1 associated proteins are recognized by CD8+ T lymphocytes.

The non-polymorphic α-3 domain of class 1 M.H.C. molecules has a binding site for CD8, and therefore the peptide class 1 complexes are recognized by CD8+ cells.

CLASS 2 M.H.C. MOLECULE:-

1. Class 2 M.H.C. molecules are encoded in a region called HLA-D,which has three sub regions HLA-DP,HLA-DQ,HLA-DR.

CLASS 2 M.H.C. molecules presents antigens that are internalized into vesicles ,and are typically derived from extracellular microbes and soluble proteins.

The class 2 β-2 domain has a binding site for CD4+ and therefore,the class 2 peptide complex is recognized by CD4+ cells which function as helper cells.

Class 2 M.H.C. molecules are mainly expressed on the cells that present ingested antigens and respond to T- cells help,(macrophages,b-lymphocytes,dendritic cells).

ANTIGEN PROSESSING:-

Class 1 M.H.C.:

1. In the class 1 M.H.C. pathway ,peptide are produced from proteins in the cytosol and transported to the endoplasmic reticulum(E.R),where they bind to class 1 mhc molecule.

2. the peptide M.H.C. complexes are transported to the cell surface and displayed for recognition by CD8+ T cells.

Class 2 M.H.C.:

· in the class 2 M.H.C. pathway, proteins are ingested into vescicles and degraded into peptides, which binds to class 2 M.H.C. molecules being transported in the same vescicles.

· The class 2 M.H.C. peptide complexes are expressed on the cell surface and recognized by CD4+ T cells.

Pushpendra singh

(2008-batch)

m.l.b. medical college

Jhansi (u.p.)

TORCH TEST

The TORCH test, which is sometimes called the TORCH panel, belongs to a category of blood tests called infectious-disease antibody titer tests. This type of blood test measures the presence of antibodies (protein molecules produced by the human immune system in response to a specific disease agent) and their level of concentration in the blood. The name of the test comes from the initial letters of the five disease categories. The TORCH test measures the levels of an infant's antibodies against five groups of chronic infections: toxoplasmosis, other infections, rubella, cytomegalovirus (CMV), and herpes simplex virus (HSV). The "other infections" usually includesyphilis, hepatitis B, coxsackie virus, Epstein-Barr virus, varicella-zoster virus, and human parvovirus.

Since the TORCH test is a screening or first-level test, the pediatrician may order tests of other body fluids or tissues to confirm the diagnosis of a specific infection. In the case of toxoplasmosis, rubella, and syphilis, cerebrospinal fluid may be obtained from the infant through a spinal tap in order to confirm the diagnosis. In the case of CMV, the diagnosis is confirmed by culturing the virus in a sample of the infant's urine. In HSV infections, tissue culture is the best method to confirm the diagnosis.

Purpose

The five categories of organisms whose antibodies are measured by the TORCH test are grouped together because they can cause a cluster of symptomatic birth defectsin newborns. This group of defects is sometimes called the TORCH syndrome. A newborn baby with these symptoms will be given a TORCH test to see if any of the five types of infection are involved.

The symptoms of the TORCH syndrome include:

· Small size in proportion to length of the mother's pregnancy at time of delivery. Infants who are smaller than would be expected (below the tenth percentile) are referred to as small-for-gestational-age, or SGA.

· Enlarged liver and spleen

· Low level of platelets in the blood

· Skin rash. The type of skin rash associated with the TORCH syndrome is usually reddish-purple or brown and is caused by the leakage of blood from broken capillaries into the baby's skin.

· Involvement of the central nervous system. These defects can include encephalitis, calcium deposits in the brain tissue, and seizures.

· Jaundice. The yellowish discoloration of the skin and whites of the eyes due to liver disease.

In addition to these symptoms, each of the TORCH infections has its own characteristic symptom cluster in newborns: