Chapter 21 Pathology



Infection occurs when microorganisms multiply in tissues where they are normally absent or present in only small numbers. Those that cause disease are described as pathogenic (Table 21.1). The types of microorganism involved in infection include bacteria, viruses, yeast, fungi and protozoa.

Table 21.1 Examples of pathogenic microorganism

Disease Organism and type Effect
Tuberculosis (TB) Mycobacterium tuberculosis (bacterial) Pulmonary or other organ infection resulting in chronic inflammation and tissue destruction
Cholera Vibrio cholera (bacterial) Severe diarrhoea
Pneumonia Streptococcus pneumoniae and others (bacterial) Pulmonary inflammation with fever
Osteomyelitis Staphylococcus aureus and others (bacterial) Often chronic bone infection resulting in pain and swelling
Gangrene Clostridium perfringens (bacterial) Severe tissue destruction resulting in tissue death and putrefaction
Acquired immune deficiency syndrome (AIDS) Human immunodeficiency virus (HIV) Destruction of T lymphocytes resulting in increased susceptibility to infection and development of rare tumours; e.g. Kaposi’s sarcoma
Influenza Influenza virus Severe respiratory tract infection. Potentially fatal depending on the strain
Squamous epithelial tumours Human papilloma virus Malignant transformation of infected squamous epithelium, especially in the cervix
Viral hepatitis Hepatitis B virus and others Liver inflammation and potentially fatal
Pneumonia Pneumocystis carinii (fungus) Another cause of pneumonia, particularly in the immunocompromised; e.g. AIDS
Aspergillosis Aspergillus fumigatus (fungus) Chronic lung infection
Thrush Candida albicans (yeast) Mucous membrane lesions
Malaria Plasmodium (protozoa) Fever, anaemia, liver, spleen and lymph node enlargement. Potentially fatal


Inflammation is a physiological process that may occur in response to infection, damage orsome other disruption of the normal tissue structure. Inflammation is beneficial where it assists in the destruction or isolation of invading organisms; however, it is also possible for harmful effects to result from it. Inflamed tissue may be broken down by the release of digestive enzymes from cells of the immune system, such as neutrophils and macrophages. The swelling associated with inflammation may be harmful if it causes compression of the tissue around it. For example, inflammation in the respiratory tract may result in airway obstruction, or in the brain may result in increased intracranial pressure and impaired blood flow.

Inflammation may be of rapid (acute) or slow (chronic) onset.


Tissues that are growing or that have to replace cells lost or damaged as part of their normal function will show rapid cell division; in other tissues cell division will be very slow. In both cases the process is highly coordinated to ensure that the tissue is renewed in a way appropriate to itsfunction. Sometimes this careful coordination is lost and a cell may begin to divide more frequently than normal. As a result a mass of abnormal tissue may form which may be referred to as a neoplasm or tumour. The transformation of normal tissues or benign tumours into cancer is called carcinogenesis. Box 21.1 explains some of the terminology relating to tumours.


Malignant tumours

The grading and staging of malignant tumours

The prognosis of a person’s cancer is determined by both its grade and its stage. Grade refers to how well differentiated the tumour cells are; that is, how much like the tissue of origin they are. Poorly differentiated cells that have lost the particular characteristics of the organ from which they arise tend to form more aggressive tumours. Stage is determined by the size of the primary tumour and the degree of spread to local or remote organs and lymph nodes. Table 21.3 explains the staging scheme used for breast cancer.

Table 21.3 The main staging systems used to assess the extent of spread of breast carcinomas

Stage Extent of spread
International classification
I Lump with slight tethering to skin, but node negative
II Lump with lymph node metastasis or skin tethering
III Tumour which is extensively adherent to skin and/or underlying muscles, or ulcerating or lymph nodes are fixed
IV Distant metastases
T1 Tumour 20 mm or less; no fixation or nipple retraction. Includes Paget’s disease
T2 Tumour 20–50 mm, or less than 20 mm but with tethering
T3 Tumour greater than 50 mm but less than 100 mm; or less than 50 mm but with infiltration, ulceration or fixation
T4 Any tumour with ulceration or infiltration wide of it, or chest wall fixation, or greater than 100 mm in diameter
N0 Node-negative
N1 Axillary nodes mobile
N2 Axillary nodes fixed
N3 Supraclavicular nodes or oedema of arm
M0 No distant metastases
M1 Distant metastases


The skeleton consists of 206 bones connected by mobile and fixed joints. Bone is living tissue and is susceptible to disease like any other.


Arthritis is a disease of the synovial joints. Pain and loss of mobility results from damage to the hyaline cartilage articular surfaces. In the healthy joint, the articular cartilage is smooth, facilitating the sliding of one bone against the other. In arthritis, the cartilage is thinned and loses its smooth surfaces, increasing friction between the articulating bones. Two important forms of arthritis are osteoarthritis and rheumatoid.

Osteoarthritis affects mainly the elderly and is primarily a condition of the weight-bearing joints, though other joints are also affected. Common presentation includes:

As a result of these changes, those with osteoarthritis may experience pain on movement, stiffness and joint instability. If this becomes severe it may be necessary to perform a total joint replacement (Fig. 21.2).

Rheumatoid arthritis may affect the young as well as the old, though it commonly begins between the ages of 30 and 50. It differs from osteoarthritis in that it is fundamentally an inflammatory condition. Common changes are as follows:

Feb 20, 2016 | Posted by in GENERAL RADIOLOGY | Comments Off on Pathology
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