What is Histopathology
It is a branch of pathology or clinical pathology which deals with the study of diseases in a tissue section.These tissues undergoes series of steps before reaching the histopathologist desk for microscopic examination.
To achieve this,it is always important that the tissue must be prepared in such a manner that it is sufficiently thick or thin to be examined microscopically (light or electron microscope) so as to enable easy differentiation of all the structures or cell component of the tissue.
Common definition in Histopathology
- Histochemistry : The study of chemical natures of the tissue components by histological methods.
- immunohistochemistry : Immunohistochemistry involves the selective imaging of antigens in tissue cells by taking advantage of the principle of antibodies specifically binding to antigens in biological tissues.
- immunocytochemistry : Immunocytochemistry is a common laboratory technique used to visualize anatomically the location of a specific protein or antigen in cells using a specific primary antibody that binds to it.
- mesothelioma :Mesothelioma is an aggressive and rare cancer.A cell : It is the single structural unit of all tissues.The study of cells is known as Cytology
- A Tissue : It is a group of cells specialized and differentiated to perform a specialized function.Collection of different type of cells from an Organ.
- Fixation : It is a complex series of chemical events which brings about changes in the various chemical constituents of cell like hardening,however the cell morphology and structural details is preserved.
- Decalcification : A process of complete removal of calcium salt from calcified tissues like bones and teeth following fixation.
- Tissue processing : This refers to the treatment of tissues necessary to impregnate it into a solid medium so that the tissue is rendered sufficiently firm yet elastic for the tissue sections of desirable thickness to be cut on microtome.
- Clearing : This means appearance of tissue after it has been treated by the fluid chosen to remove the dehydrating agent.
- Impregnation : It is the complete removal of clearing reagents by substitution of paraffin or any such similar media
- Embedding : It is the orientation of tissue in melted paraffin which when solidified provides a firm medium for keeping intact all parts of the tissue when sections are cut.
Types of speciment obtained in a Histopathology Laboratory
The human tissue comes from the surgery and autopsy room from surgery.Mostly two types of tissue are obtained :
- Biopsy : A small piece of lesions or tumor which is sent for diagnosis before final removal of the lesion or the tumor (Incisional biopsis)
- If the whole of the tumor or lesion is sent for examtion and diagnosis by the pathologist,this is called an Excisional biopsy
Tissues from these autopsy are sent for the study of disease and its course for the advancement of medicine.
Types of Histological Preparation
We have Three types of Histological preparation which are Smear,Whole mount and tissue section.
- Smear : They are mostly made from blood,bone marrow or any fluid such as Pleural fluid or Ascitic fluid.These are immediately fixed in alcohol to preserve the cellular structures and are then stained.Smears are also made by crushing soft tissue between two slides or an impression smear is made by pressing a clean slide in contact with the moist surface of a tissue.By doing this,the cells are imprinted on the slide and these may be stained for cytological examination
- Whole Mount : These preparation is derived from an entire animal eg. Fungus parasite.These preparation should be no more than 0.2-0.5 mm in thickness.
- Sections : The majority of the preparations in histology are sections.The tissue is cut about 3-5 mm thick pieces processed and 5 microns thick sections are cut on a microtome. These are then stained and permanently mounted (histology stains). Microtomes are special instruments which have automatic mechanism for cutting very thin sections.To cut the sections on the microtome;the tissue must be made hard enough to not get crushed.There are two methods of hardening the tissue which are by Freezing them and the other is by embedding them in a hard material such as Paraffin wax or Gelatin.
Responsabilities of a Laboratory technician in Histopathology
The following are responsibilities of a Laboratory technician in handling histopathological specimen in order to achieve a reliable result.
- To preserve the specimen as soon as it is received in the laboratory
- To label,register and provide identification to the specimen
- Preparation of the specimen in order to facilitate their gross and microscopy
- finally the laboratory technician is responsible to keep record of each specimen.
The above responsibilities are achieved by considering the following points
- Check if the specimen is properly labeled with the name,age,hospital registration number and the nature of the tissue to be examined and the requisition form is also duly filled as soon as the specimen is received in the laboratory.
- Checking if the specimen is in a proper fixative.Note that fixative should be at most fifteen to twenty times the volume of the specimen.If not, add fixative in sufficient amount.
- Checking if the financial matters has been taken care off
- Make the entries in biopsy register and give the specimen a pathology number called accession number. It is advisable to carefully note this number on the requisition form as well as the container because this number will accompany the specimen every where.
- If the specimen is large,always inform the pathologist who will make cut in the specimen so that proper fixation is done.Container should also be appropriate to hold the specimen without distorting it.
- Blocks of tissues taken for processing should be left in 10% formalin at 60°C till processing. These would be fixed in 2 hours
- histopathology slides should be released for recording after consultation with the pathologist
- Specimens should be kept in their marked container and discarded after checking with pathologist.
- Block must be stored at their proper number the same day.Note the blocks have to be kept preserved for life long.Slides should be stored in their proper number after 3 days.It gives time for the slides to be properly dried.