Page 161 - Textbook of Pathology, 6th Edition

3. SUPPURATION (ABSCESS FORMATION). When bacilli of plague etc. Septicaemia is generally accompanied 145
acute bacterial infection is accompanied by intense by systemic effects like toxaemia, multiple small
neutrophilic infiltrate in the inflamed tissue, it results in tissue haemorrhages, neutrophilic leucocytosis and disseminated
necrosis. A cavity is formed which is called an abscess and intravascular coagulation (DIC).
contains purulent exudate or pus and the process of abscess iii) Pyaemia is the dissemination of small septic thrombi in
formation is known as suppuration. The bacteria which cause the blood which cause their effects at the site where they are
suppuration are called pyogenic. CHAPTER 6
lodged. This can result in pyaemic abscesses or septic infarcts.
Microscopically, pus is creamy or opaque in appearance a) Pyaemic abscesses are multiple small abscesses in various
and is composed of numerous dead as well as living organs such as in cerebral cortex, myocardium, lungs and
neutrophils, some red cells, fragments of tissue debris and renal cortex, resulting from very small emboli fragmented
fibrin. In old pus, macrophages and cholesterol crystals from septic thrombus. Microscopy of pyaemic abscess
are also present (Fig. 6.15). shows a central zone of necrosis containing numerous
bacteria, surrounded by a zone of suppuration and an
An abscess may be discharged to the surface due to outer zone of acute inflammatory cells (Fig. 6.16,A).
increased pressure inside or may require drainage by the b) Septic infarcts result from lodgement of larger fragments
surgeon. Due to tissue destruction, resolution does not occur of septic thrombi in the arteries with relatively larger foci
but instead healing by fibrous scarring takes place. of necrosis, suppuration and acute inflammation e.g. Inflammation and Healing
Some of the common examples of abscess formation are
as under: septic infarcts of the lungs, liver, brain, and kidneys from
septic thrombi of leg veins or from acute bacterial
i) Boil or furruncle which is an acute inflammation via hair endocarditis (Fig. 6.16,B).
follicles in the dermal tissues.
ii) Carbuncle is seen in untreated diabetics and occurs as a SYSTEMIC EFFECTS OF ACUTE INFLAMMATION
loculated abscess in the dermis and soft tissues of the neck.
The account of acute inflammation given up to now above is
4. CELLULITIS. It is a diffuse inflammation of soft tissues based on local tissue responses. However, acute
resulting from spreading effects of substances like inflammation is associated with systemic effects as well.
hyaluronidase released by some bacteria. These include fever, leucocytosis and lymphangitis-
5. BACTERIAL INFECTION OF THE BLOOD. This lymphadenitis.
includes the following 3 conditions: 1. Fever occurs due to bacteraemia. It is thought to be
i) Bacteraemia is defined as presence of small number of mediated through release of factors like prostaglandins,
bacteria in the blood which do not multiply significantly. interleukin-1 and TNF-α in response to infection.
They are commonly not detected by direct microscopy. Blood 2. Leucocytosis commonly accompanies the acute
culture is done for their detection e.g. infection with inflammatory reactions, usually in the range of 15,000-
Salmonella typhi, Escherichia coli, Streptococcus viridans. 20,000/μl. When the counts are higher than this with ‘shift
ii) Septicaemia means presence of rapidly multiplying, to left’ of myeloid cells, the blood picture is described as
highly pathogenic bacteria in the blood e.g. pyogenic cocci, leukaemoid reaction. Usually, in bacterial infections there is

Figure 6.15 An abscess in the skin. It contains pus composed of necrotic tissue, debris, fibrin, RBCs and dead and living neutrophils. Some
macrophages are seen at the periphery.