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Histology is the study of tissues and organs through the examination of the microscopical architecture of tissues and the relationship between the different types of cells and tissue types found within tissues and organs.
The histopathology department receives tissue specimens from patients, taken at either surgical operations, out patient or GP clinics, or at post-mortem examination. Specific pieces of tissue or biopsies are taken that are associated with the condition under investigation and sent to the laboratory, usually in a fixative solution to prevent degradation of the tissue, so that when the microscopical examination of the tissue is made, it resembles the state of the tissue as close as possible to what it was when still within the patient.
Diseases such as inflammatory diseases, benign abnormal growth, infections and cancer are diagnosed by this method.
Once received, the specimens are processed into paraffin wax blocks and thin slices or sections are cut and stained for microscopical examination to determine the underlying disease process. Further staining techniques may be required to identify a specific tissue component not readily seen in the first stained section, by using a more specific staining technique, one example would be for the detection of the presence of a micro-organism such as TB. Other specialised techniques such as immunocytochemistry can be used to identify a tumour or variant of a tumour.
Very rapid results (within minutes) can be obtained by freezing the tissue in liquid nitrogen and cutting sections in a refrigerated cabinet called a cryostat. This technique is often used when the patient is still in the operating theatre and enables a surgeon to determine the progress or course of a particular operation, especially when they are removing tumours. This can give broad answers to specific questions, such as whether the tissue is benign or malignant but still usually requires processing into a paraffin block for a more definitive diagnosis.
There are four groups of staff within histology
The first are medically qualified histopathologists who carry out the microscopical examination and diagnosis of the tissue samples. They are also involved in the work of mortuaries and provide a post-mortem service for HM Coroner and their Health Authority. They often have advanced roles involving management, medical research, consultancy, media and education.
The second group of staff are biomedical scientists. This group of staff carry out the scientific processes and techniques to produce the material that the histopathologist examines when making the diagnosis. This involves preparing tissue for processing into paraffin embedded blocks and then cutting the sections for staining. The recent development of advanced roles in specimen dissection has seen many biomedical scientists taking on some of the roles traditionally carried out by the histopathologist within the specimen dissection room.
This staff group also carry out the staining techniques to demonstrate the tissue components, infective agents etc and also carry out Immunological staining of tumours and tissues to identify specific proteins within the tissues which once identified can aid in the diagnosis of the disease condition.
In more recent times, with the advent of molecular biology techniques, biomedical scientists also carry out molecular techniques to identify specific proteins, hormone receptors, viruses and enzymes in tissues, which enhance both the diagnosis and the treatment of the patient. The demonstration of the Her2 receptor site is especially important in determining which breast cancer patients are suitable for Herceptin therapy.
The third group of staff are associate practitioners and medical laboratory assistants. This group of staff provide a variety of support activities to both the histopathologists and biomedical scientists and in some cases perform advanced roles in some areas traditionally covered by biomedical scientists.
The fourth group are mortuary or anatomical pathology technicians. This group of staff is responsible for providing support to histopathologists during post mortems and organise the mortuary services. They also liase with the Coroner’s Officers and undertakers with regard to burials and cremations of the deceased, ensuring that the deceased and the relatives of deceased receive a respectful bereavement service.
Together with cytology, histology forms the pathology discipline of cellular pathology.
Name: Rebecca Wise
Works at: Cellular pathology department, St Peters and Ashford Hospital
Career: graduated with a BSc degree in Biomedical Science from the University of Bradford completed a MSc course in biomedical science provided by the University of Hull (both courses accredited by the IBMS). Plans to complete the IBMS Higher Specialist Diploma and then specialise in advanced histology dissection.
My work usually begins at 9 am but today I am on the early schedule so I start at 8 a.m., which is not too bad since I go home early.
All’s quiet at this time of the day. When you start work early in histology, your main job is to embed the tissue blocks that were processed following dissection yesterday. I check the processor to make sure the program was completed successfully, then I check the embedding centre to make sure that the thermal consol is hot and the cold plate is working. I make a record of the temperature of all the fridges, freezers and the cryostat. Monitoring the laboratory equipment is part of the regular maintenance procedures.
Finally, I start embedding. Dissected tissues that were fixed, dehydrated, cleared, and impregnated with paraffin wax, are now carefully orientated in tissue moulds and filled with molten paraffin wax. Then we make them very cold so the wax solidifies quickly to produce our tissue blocks. We call this process 'tissue embedding' and the hard wax blocks allow us to cut sections of the tissue only 3 microns thick.
At quarter to nine, other staff start to come in and the blocks are allocated to all the staff that are assigned to microtomy. Today I am assigned to immunohistochemistry - one of the most important sections in histology. A patient can have a biopsy that contains some tumour cells that cannot be recognised but it's important for their treatment to find out where the cancer cells came from. This is where immunohistochemistry comes in - we use lots of antibodies against different cell types and the type of tumour cell is worked out by the antibodies that attaches to the celI.
I receive a call from a doctor who has a patient with an appointment to see him tomorrow morning and he’s asking if it would be possible to have a diagnosis by the end of the day. We have to make sure that the requests are attended to as soon as possible. Any urgent requests have to be done promptly and we make sure that the pathologist concerned receives the results quickly. It means an early diagnosis and therefore early treatment for the patient.
I start with immuno by sorting out the slides. Some slides would need pre-treatment before staining because the antigens that the antibody will attach to is hidden - an example is oestrogen and progesterone receptors. The number of positive cells in a breast tumour will help indicate which drugs to use in the patients treatment. These cells would have to be microwaved for about 20 minutes so that the antigens would be 'available' for the reaction. Other antibodies might need enzyme pre-treatment or even the use of a pressure cooker! While the slides are being treated I can take my break. There’s nothing else to do except wait.
So now its time to load up the slides and the antibodies onto the Immunostainer. There's a program of course that we have set up and it usually takes around 2 hours to finish all the staining. In the meantime, there are some large blocks to cut. I have just started learning this and I’m lucky I get to use the new microtome, which is a joy to use as it’s so hi-tech.
Usually, when I get back from lunch, the immunostaining has ended and all I have to do next is manual counterstaining of these slides. Of course, we have to check that all the tests have worked perfectly, hence the use of controls. The sections have to be perfect as well - even staining with no patches. Negative controls are negative. All this done, with the proper label of course, means it’s time to hand it to the pathologist.
Time for home although not before I sign up to attend a journal discussion group tomorrow. No matter how experienced you become you always need to keep up with scientific and professional trends, but that's what makes a career in histology so interesting.
Our thanks to the pathology department at Ashford's and St Peter's Hospitals and Nick Kirk, IBMS Council member and cellular pathologist at Papworth NHS Trust.