Category Archives: General Pathology For Dentistry

RADIOSENSITIVITY OF TUMORS

Posted by on February 3, 2012 No comments

RADIOSENSITIVITY OF TUMORS

 

Tumors, like their cell of origin, differ in their susceptibility to radiation injury. In general, a poorly differentiated tumor is more radiosensitive than a well differentiated one of the same type.

1-    Radio-sensitive tumours:

Destructive dose of radiation_causes no significant damage in adjacent normal tissues.

Examples

  • Malignant lymphoma – Seminoma of testis
  • Lymphoepithelioma -Dysgerminoma of ovary
  • Ewings tumour of bone.

     

    2-    Radio-responsive tumors:

    Destructive dose of radiation could do some damage to adjacent normal tissues.

    Examples

  • Squamous and basal cell carcinoma.
  • Breast carcinoma.
  • Adenocarcinoma.

     

    Radio-resistant tumors:

    Destructive dose of radiation is equally destructive_to adjacent normal tissues.

    Examples:

  • Sarcomas
  • Malignant melanoma N.B.

    1 – Metastatic tumors are more radiosensitive.

    2- Poorly differentiated tumors are more radiosensitive than well-differentiated.

     

    Recurrence of tumours after irradiation

    Recurrent tumors after irradiation are usually radioresistant because the few resistant cells which survive transmit the property of resistance to their descendants.

RADIATION EFFECTS ON DIFFERENT TISSUES

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RADIATION EFFECTS ON DIFFERENT TISSUES

 

 

Following a substantial dose of radiation, there is a latent interval of hours or days before histological evidence of tissue injury is seen. As already explained, the damage depends on:

a- The dose

b- Type of radiation

c- The interval following exposure

d- The tissue exposed.

Skin

A) Early changes in the skin include:

  1. Dilatation of blood vessels, congestion of dermal vessels and other signs of acute inflammation and these reflect acute tissue injury.
  2. With a single dose, the mitotic activity of the basal cells is arrested with subsequent loss of the epidermis and epilation (loss of hair).
  1. The walls of the dermal vessels are infiltrated with fibrin.

    B- Late changes: The dermal vessels show the picture of endarteritis obliterans followed by replacement with hyaline collagen and this will hinder regeneration of epidermis.

    2- With repreated exposure to radiation; large bizarre fibrocytes are present in the dermal connective tissue, the dermal collagen becomes very dense and there is a tendency to become necrotic even years after exposure.

    3- Persistent melanin pigmentation is noted.

    Lymphoid and hemopoeitic tissue (are very sensitive to radiation).

    Necrosis of lymphoid and hemopoeitic tissue is manifested by changes in the peripheral blood cells which appear at different times depending on the length of life of different cells.

    1. The lymphocytes: are easily degenerated and necrosed with marked decrease in their number in the peripheral blood.
    2. The granulocytes: many show an initial rise followed by marked drop by the end of the second to the fourth weeks. This leads to diminished resistance with subsequent infection.
    3. The platelets: show an initial rise followed within few days by marked drop leading to haemorrhagic tendency.
    4. The red blood cells: are lately dcreased and anemia shows up after several weeks (6 weeks) due to their relative long life span.
    5. Leukemia may develop after many years from exposure to ionizing radiation due to mutation in lymphoid tissue.

    Intestinal Epithelium

    Degeneration and necrosis occur after two days and are accompanied by severe diarrhea. Disturbances in fluid and elecholyte balance may cause death.

    Healing of intestinal lesions may be followed by stensosis.

    Ovary

    Grauulosa cells are affected than the ovum so Graffian follicles appear small, and anovular.

    Testis

    1-    Destruction of spermatogonia prevents further
    production of spermatorytes and spermatozoa.

    2-    Interstitial cells are not affected.
    Blood vessels

    1. Degeneration and necrosis of endothelium followed by acute inflammation of the wall and thrombosis.
  2. Healing is followed by vascular occlusion.

IONISING RADIATIONS

Posted by on February 3, 2012 No comments

IONISING RADIATIONS

 

 

Types of ionizing radiation:

  1. Electromagnetic radiation: X-rays and Gamma rays.
  1. Particulate radiation:

    alpha particles – beta particles – protons – electrons and neutrons.

    - All of these radiations can be administered to animals and human beings: Externally or Internally.

    1. External sources include X-ray machines, electron accelerators.
    2. Internal irradiation arises from the ingestion of any of the hundreds of known radionucleotides (radioactive isotopes) many of which are used for medical diagnostic or therapeutic purposes.

    Mode of action of ionizing radiation

    A) Direct action:

    Radiation causes its effects by transferring energy to the substance through which it passes.

    This energy can produce two changes:

  2. Ionization: Loss or gain of an electron.
    1. Excitation: Movement of an electron into an outer orbit. Occurs in some DNA molecules (genes) and this results in a change in their chemical structure (mutation).

    (B) In direct action:

    Diffuse ionization of water in the cell leads to the formation of oxidizing agents such as H202 which inactivate cellular enzymes.

    Forms of Radiation injury of cells:

  3. Cloudy swelling, hydropic degeneration or necrosis.
  4. Temporary or permanent arrest of mitosis results from: a) Interference with synthesis of DNA.

    b) Injury of mitotic spindle.

    1. Fragmentation of chromosomes with failure of correct reconstruction results in necrosis of daughter cells.
    2. Mutation: Mutation may be lead to neoplastic transformation as follows:

     

  • If mutations are in the germ cells, the children of irradiated parents can be affected.
  • If the mutations are in somatic cells malignant tumors can be induced by radiation. The commonest radiation-induced tumors are leukemia and tumors of thyroid, breast, bone and lung.

Radiosensitivty of cells or tissues:

Two general rules govern the variable susceptibility of different tissues to the effects of ionizing radiations:

1- Embryonic and undifferentiated cells are more susceptible to radiation injury than differentiated cells.

2- Rapidly proliferating cells are more easily damaged by ionizing radiation during interphase or early phase of mitosis.

Human tissues are classified into three groups:

1-    Radio-sensitive Tissues:

a- Lymphoid tissue b- Hemopoietic tissue
c- Germ cells    d- Intestinal epithelium.

2-    Radio-responsive tissues (intermediate):

a- Skin    b- Vascular endothelium

c- Conjunctiva, cornea and lens.

3-    Radio-resistant tissues

a- Bones    b- lungs    c- Nerve cells

d- Skeletal muscles e- kidneys, f- Endocrine glands.

Pictures Of Disturbance of growth and neoplasia

Posted by on February 3, 2012 No comments

Pictures Of Disturbance of growth and neoplasia

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Fibroadenoma

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Squamous cell carcinoma

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Adenocarcinoma

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Chondroma Lipoma

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Leiomyoma

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Osteosarcoma

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Intradermal nevus

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Malignant melanoma

DIAGNOSIS OF TUMORS

Posted by on February 3, 2012 No comments

DIAGNOSIS OF TUMORS

 

The final diagnosis of any tumor is usually based on the histological examination using the following ways:

  1. Frozen section.
  2. Paraffin section.
    1. Exfoliative cytology (based on the fact that the tumor cells are shed off and appear in exudates and secretions.

    4. Tumor markers: These are markers present in blood or tissues in case of tumor and are used for diagnosis and follow up.


     

ETIOLOGY OF TUMORS

Posted by on February 3, 2012 No comments

ETIOLOGY OF TUMORS

 

The actual cause of tumors remains obscure up till now. However many pre-disposing factors known as carcinogenic agents, appear to play a certain role in the development of certain tumor.

These factors are:

1) Chemical carcinogens:

  1. The hydrocarbons: the development of carcinoma of the scrotum in chimney sweepers was observed very early. Experimentally carcinoma of the skin of the ear of the rabbit can be induced by painting tar daily for 6 months.
  2. The aromatic amines: as aniline, benzidine. Carcinoma of urinary bladder is observed in laborers working with aniline dyes.
  3. Heavy cigarette smoking has direct relation with development of carcinoma of lung and urinary bladder.
  4. High incidence of mesothelioma (a malignant tumor of pleura) is found in laborers working in contact with asbestos.

 

2- Physical agents:

a) Ionizing radiation: usually leads to the development of carcinoma of the skin, leukemia, and osteogenic sarcoma.

 

  1. The continuous exposure of the skin to the ultraviolet rays of sunshine may lead to basal cell carcinoma and squamou cell carcinoma.
  2. Heat: it was shown that an increased incidence of carcinoma of the lip occurs in pipe smokers, but the action of tobacco may be added to the effect of heat.

 

3-    Hormones: THE sex hormones are considered as
carcinogenic agents and carcinoma of the breast in
mice can be produced by administration of large
doses of estrogen. There are some tumors which
depend in their growth on hormones and are known
as hormone dependant tumors such as:

b- Carcinoma of the prostate: is stimulated by androgen and its growth can be arrested by administration of estrogen.

c- Carcinoma of the breast: depends on its growth estrogen and prolactin. Removal of both ovaries may lead to arrest of growth of this tumor.

 

  1. Benign tumors: may be followed by malignant transformation such as villous papilloma of the urinary bladder and duct papilloma of the breast.

 

  1. Chronic inflammation:

    d- Urinary bilharziasis: usually predisposes to carcinoma of the urinary bladder (squamous metaplasia).

    e- Squamous cell carcinoma may develop in the edge of a chronic ulcer of the skin.

    f- Chronic gastric ulcers are precancers lesions.

     

     

     

    6- Viruses and tumors: virus infection as an etiological factor in tumor formation is now becoming more and more popular. (It may induce certain changes in the genetic material of the affected cells rendering them capable of division and proliferation). Recently a true virus (the plyoma virus) was isolated from leukaemic mice, which in turn produced leukemia when injected into healthy mice.

    Three classes of genes are target for genetic change which result in the formation of tumors:

    1. Growth promoting genes (proto-oncogenes) which when change to oncogenes become tumorogenic.
  2. Cancer suppressor genes
  3. Genes regulating apoptosis.

    Any disturbance in the balance between these genes may result in tumorogenesis.

HAMARTOMA

Posted by on February 3, 2012 No comments

HAMARTOMA

 

 

Hamartion: fault in development.

It is a tumor like mass which is formed due to developmental error and consists of the normal tissues of the part from which it arises but is irregularly arranged.

EMBRYONIC TUMORS

Posted by on February 2, 2012 No comments

EMBRYONIC TUMORS

 

 

These are usually malignant tumors which arise in children and are formed of malignant cells that resemble the embryonic cells which are initially present in the particular part of the body from which the tumor arises.

These tumors are:

  • Nephroblastoma (Wilm’s tumor) in kidney.
  • Neuroblastoma in adrenal medulla.
  • Medulloblastoma in cerebellum.
  • Retinoblastoma in Retina.

TERATOMA

Posted by on February 2, 2012 No comments

TERATOMA

 

Is a tumor which contains multiple types of tissue related to the three germinal layers i.e. ectoderm, mesoderm, endoderm, and are usually foreign to the part in which it arises.

Sites: the commonest site is the ovary. Types:

1-    Benign teratoma: More common and may be:

a- Solid.

b- Cystic (dermoid cyst): It contains hair, bone, cartilage etc..

2-    Malignant teratoma: (rare) It usually shows a mixture
tissues one of which shows malignant change of
squamous cell carcinoma or adenocarcinoma, or may
contain immature tissues.

Origin of teratoma:

Many theories were put to explain the origin of teratoma. The most accepted one is that it arises from foci of totipotent embryonic cells which are capable of division into many types of cells related to the three germinal layers.

TUMORS OF PIGMENTED CELLS

Posted by on February 2, 2012 No comments

TUMORS OF PIGMENTED CELLS

 

Nevus or pigmented mole:

It is a benign tumor of melanocytes of the skin of the face, neck and chest. It is present in nearly everyone and usually dates since birth and so now it is considered as hamartomatous malformation.

Types:

  1. Junctional nevus: appears as a flat brown lesion in which the pigmented cells are present deep in the epidermis and in upper dermis. It is the only type which may rarely turn malignant.
  2. Intradermal nevus: This appears as papillomatous or pedunculated deep brown lesion, in which pigmented cells are in the upper dermis only.
  3. Compound nevus: appears as elevated deep brown lesion having the microscopic picture of both types described above.

 

Malignant melanoma:

It is a highly malignant tumor which arises from the following sites:

1 – Skin either in a pre-existing nevus or more commonly arising directly from the melanocytes.

  1. Pigmented cells of the eye especially the choroid.
  2. Mucous membrane of the rectum, mouth cavity.

Gross appearance: It forms a rapidly growing ulcerated deep brown tumor, which infiltrates the surrounding tissues.

Microscopically: There is infiltration by masses of cuboidal or fusiform malignant cells, having darkly stained nuclei and many mitotic figures. Intra and extra cellular deep brown granules of melanin pigment are usually seen.