Color Atlas of Pathology (eBook)

Pathology

Pathology is the branch of medicine that analyzes the causes, mechanisms of development, and morphologic manifestations of a disease using the methods of natural science. Nearly every disease is associated with dysfunction at the level of the organ, cell, or organelle. This allows the pathologist to identify functional damage and the cascade of disease processes on the basis of abnormal structural changes.

  Methods

General methods: The pathologist is able to identify the various forms of for example inflammation of an organ by analyzing biopsy material, whether in the form of needle aspiration or a specimen obtained endoscopically (by incision, forceps, or wedge biopsy). Analysis of 4 µm paraffin-embedded stained tissue sections ( B) determines whether a tumor is malignant or benign. These examinations require that an adequate amount of biopsy material has been obtained and sent to the pathologist (usually fixed in a 4% formaldehyde solution).

Examination of frozen sections: Biopsy material is sent to the pathologist as a fresh specimen during the surgical procedure. The pathologist then prepares frozen sections ( A) and within 5–10 minutes can verify or disprove clinical suspicion of malignancy. However, this quick fixation technique, with its greater slice thickness, produces less accurate results than conventional fixation.

Examination of crush preparation: Cerebral masses whose malignancy status is unknown are located and aspirated under stereotactic guidance. The needle biopsy obtained is flattened between two slides. Once the proper stain is applied, the cells contained in the specimen can be evaluated within a few minutes ( C, D).

Aspiration cytology: This technique permits quick morphologic diagnostic evaluation of a tumor. The affected organ, such as the prostate, or fluid-filled space is punctured with a fine needle, and the cells drawn out with a syringe are smeared on a slide ( E). The accuracy of this technique is quite high.

Exfoliative cytology: Here, cells obtained from the surfaces of tissues such as the cervix of the uterus ( F), or by centrifuging body fluids, are smeared on a slide.

A

Mucinous carcinoma (frozen section)
          × 250

B

Mucinous carcinoma (paraffin-embedded)
          × 250

C

Pilocytic astrocytoma
          × 350 crush preparation toluidine blue

D

Anaplastic astrocytoma
          × 350 crush preparation toluidine blue

E

Mesothelioma cells (MGG)
          × 600

F

Cervical epithelial cells (Papanicolaou smear)
          × 600

Disease

Disease is defined as a dysfunction of life processes that changes the entire body or its parts in such a manner that the affected person requires help for subjective, clinical, or social reasons.

  Etiology

This involves the study of pathogens that cause disease and of developmental anomalies.

  Causal Pathogenesis

This answers the question of why a certain pathogen causes disease in a certain individual. It describes the conditions under which disorders occur or, in other words, the interplay between the causes of disease and the body's susceptibility to disease. This involves several factors:

Environmental factors, which might include such factors as the causing size of quartz dust particles silicosis.

Disposition is the body's susceptibility to disease, without regard to its adaptability (see Chapter 7), and the affected individual's constitution.

Resistance is the body's ability to withstand the influence of disease-causing factors. It represents the interplay between unspecific immune mechanisms without the involvement of specific immune mechanisms (immunity; see Chapter 12).

  Formal Pathogenesis

This describes the structural change observed during the clinical course of the disorder, which leads to the structural or functional damage specific to the disorder.

  Clinical Course

Peracute disorders are fulminant and usually lead to death within several days.

Acute disorders are usually intense and last for a few days or weeks. Recuperation (recovery of normal health and function) is possible.

Subacute disorders are characterized by an insidious onset and a clinical course that lasts for weeks. Recuperation is often doubtful.

Chronic disorders are usually mild and progress in stages over a period of months:

–  Primary chronic disorders begin without a manifest acute phase. The clinical course is episodic. Recuperation is not possible.

–  Secondary chronic disorders occur subsequent to an acute inflammation that fails to heal because of complicating factors.

–  Recuperation in these cases is characterized by structural damage and functional deficits that remain after the disease subsides. This results in restricted functional and social adaptability.

Recurrence is the resurgence of what is usually a chronic disorder after a period of time (see p. 350).

Remission is the temporary disappearance of the symptoms of the disorder (see p. 350).

Death (exitus letalis = lethal end).

Signs of Death

The cessation of all vital processes can be clinically diagnosed by the following signs.

  Equivocal Signs of Death

These signs include cardiac arrest, lack of pulse, cessation of breathing, areflexia, and decreasing body temperature. This is referred to as clinical death.

  Brain Death

A patient is regarded as biologically dead where brain death has been diagnosed according to the following criteria:

–  An isoelectric or ‘flat’ electroencephalogram for 24 hours.

–  Two angiographic studies performed at an interval of 30 minutes demonstrating the absence of cerebral circulation.

–  Irreversible absence of spontaneous respiration.

–  Irreversible areflexia (lack of corneal and pupillary reflexes).

  Unequivocal Signs of Death

Livores: After cardiac arrest, gravity causes the blood in the venous system to collect in the lowest parts of the body. This produces reddish violet skin spots that can be mobilized by applying local pressure.

Rigor mortis or postmortem rigidity begins 3–6 hours after death. According to Nysten's law, rigor mortis begins at the head and spreads toward the feet, later subsiding in the same manner. It occurs due to lack of ATP and the subsequent coagulation of actin and myosin filaments.

Autolysis or decomposition (p. 132): The failure of tissue respiration activates the intrinsic protease from lysosomes (p. 26) and extrinsic pro-tease from intestinal bacteria, which digest the organic components of the body in the process of decomposition.

Statistics

Average life expectancy is the time period in which 50% of a certain population group, such as women, have...