Cytology is the scientific discipline focused on the study of individual cells, the fundamental building blocks of all living organisms. In medicine, its primary application involves diagnosing and screening various diseases. This is achieved by examining cell samples under a microscope to identify deviations from normal cellular appearance or structure.
What is Cytology
Cytology involves the microscopic examination of cells collected from different parts of the body to detect abnormalities. Diseases often lead to changes in the appearance, internal structure, or arrangement of cells. For instance, cancerous cells may exhibit enlarged nuclei, irregular shapes, or an increased rate of division compared to healthy cells. Specialists prepare these collected cells by smearing them onto glass slides and applying various stains, which highlight specific cellular components like the nucleus and cytoplasm. These stained slides are then meticulously reviewed by cytopathologists, who are trained to interpret the subtle cellular changes that can indicate disease.
How Cytology Samples are Collected
The collection of cell samples for cytological analysis employs several techniques, each suited to different parts of the body or types of conditions. One common approach is exfoliative cytology, where naturally shed cells are collected. A well-known example is the Pap test, which involves collecting cells shed from the cervix into the vaginal fluid to screen for cervical cancer. Similarly, urine cytology examines cells shed from the lining of the urinary tract to detect bladder or kidney abnormalities.
Another method is abrasive cytology, which involves gently scraping or brushing cells from a surface. For instance, a cervical brush is used during a Pap test to directly collect cells from the surface of the cervix. Oral brush biopsies follow a similar principle, collecting cells from suspicious lesions inside the mouth to screen for oral cancers. These methods are designed to obtain sufficient cellular material without causing significant discomfort or tissue damage.
Intervention cytology, often called fine-needle aspiration (FNA), involves drawing cells directly from a lump or organ with a thin needle. This technique is frequently used for investigating palpable masses like thyroid nodules, breast lumps, or enlarged lymph nodes. The needle is inserted into the mass, and a small number of cells are aspirated into a syringe. For deeper or non-palpable lesions, imaging guidance like ultrasound or computed tomography (CT) ensures precise needle placement.
Common Applications of Cytology
Cytology plays a significant role in detecting and screening for various medical conditions, particularly cancers. The Pap test is a widely recognized screening tool for cervical cancer, identifying precancerous changes before they develop into invasive cancer. In respiratory health, sputum cytology examines coughed-up mucus, and bronchial washes or brushings collect cells directly from the airways to help diagnose lung cancers. Fine-needle aspiration cytology is routinely used to assess thyroid nodules to determine if they are benign or malignant, and to evaluate breast lumps for cancerous cells.
Beyond cancer, cytology is also employed to identify infections. For example, specific cellular changes in Pap tests can indicate human papillomavirus (HPV) infection, a common cause of cervical abnormalities. Tzanck smears, which examine cells from skin lesions, can reveal multinucleated giant cells indicative of herpes simplex virus. Furthermore, cytological analysis of body fluids can detect bacterial, fungal, or parasitic infections by identifying microorganisms or the cellular response to them. This method can also help diagnose inflammatory conditions by observing inflammatory cells in samples like joint fluid.
Cytology Versus Biopsy
Cytology and biopsy are both diagnostic methods that involve examining cells or tissues, but they differ significantly in their approach and the type of sample obtained. Cytology involves examining individual cells or small clusters of cells, often collected through less invasive means. This includes techniques like scraping surfaces, aspirating fluid, or collecting naturally shed cells. Cytology procedures are quicker to perform, cause minimal discomfort, and are often outpatient without extensive preparation. Processing of cytological samples is also less complex, often leading to faster diagnostic results and lower costs than biopsies.
In contrast, a biopsy involves the removal and examination of a larger piece of tissue from the body. This usually requires a minor surgical procedure, often under local anesthesia, with more discomfort and a longer recovery time. The tissue sample undergoes more extensive processing, including fixation, embedding in paraffin, and sectioning, which allows for the examination of the tissue’s architectural structure. While cytology provides valuable information about cellular changes, it sometimes lacks the full architectural context a biopsy offers. For certain conditions, especially when a definitive diagnosis or precise tumor grading is required, a biopsy may be necessary even if cytology suggests an abnormality, providing a more comprehensive view.