Histopathology is the study of tissues (histology) and cells (cytology) and usually includes morbid anatomy (autopsies).
Histopathologists do not work in a lab in isolation, but work closely with other doctors in the hospital. For cancers they are part of the team that meet and discuss every patient. Histopathologists examine biopsies and larger pieces of tissue to aid in the diagnosis and treatment of patients. The tissue has to be processed to enable thin enough slices of the tissue to be cut to examine under a microscope. With cytology a thin layer of cells is put on a glass slide and can be examined directly without any complicated processing. Autopsies are performed either at the request of the doctor who looked after the patient during life or after an autopsy has been requested by a coroner.
Histopathology, or cellular pathology, is very important as the final diagnosis of a patient is often made by the histopathologist.
After surgery, biopsy or autopsy, the tissue is removed, and placed immediately in a fixative (a stabilizing or preservative agent), to preserve cells and components. Most specimens need to be fixated for a minimum of 24 hours. Small biopsies need to be fixated for at least 12 hours.
The specimen is described, weighed and measured and will normally be ‘processed’ overnight. This involves removing all water and replacing it with wax. This takes approximately 15 hours. Tissue is manually embedded into rectangular wax blocks for support and very thin sections of tissue are cut manually and stained with different dyes to show nuclei and cytoplasm.
They are then labelled, quality checked and given to a pathologist for diagnosis.
The pathologist will either:
- Diagnose specimen, dictate report and authorise the case
- Order more diagnostic tests. Diagnosis, dictation and authorisation will follow.
- Discuss the case in more detail with colleagues or send the case to reference centres.
Paper reports leave the department after being authorised.
Biopsies are usually obtained either during an investigation or as an arranged procedure.
- An endoscopy (eg, looking at the oesophagus and stomach)
- Colposcopy (examination of the cervix with a magnifying instrument)
- A kidney biopsy when a core of tissue is obtained by passing a needle through the skin and into the kidney.
Many biopsies are reassuring as they have been taken, by a doctor, to rule out cancer and the biopsy does not show cancer, but may, for instance, show inflammation which explains the symptoms and signs. Other biopsies may show cancer and the pathologist is able to look for features that can tell what sort of cancer is present, how aggressive it is and whether it may respond to certain types of treatment.
Larger pieces of tissue may come from surgical operations, such as:
- Operation for bowel cancer
- Hysterectomy (eg, for fibroids)
- A breast lump removed for cancer
Cytology is used to look at fluids that have collected in the body during illnesses for example pleural (chest) fluid. Fine needles are often used to aspirate cells from suspicious lumps for example in the neck. Most cytology in the UK is performed by histopathologists who devote part of their time to cytology and part to histology.
Autopsies performed at the request of the doctors who looked after the patient and with the permission of the next of kin are requested to help confirm the illness the patient was suffering from, to see if the treatment given had any effect on the disease and the effect of the disease on various organs and whether the patient was suffering from any other disease.