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1 Introduction to Pathology
Pathology is the branch of medicine that is involved with the
study of injury and disease, and forensic pathology deals with
the application of this to the law. As part of the standard medical
school curriculum, all physicians study pathology. For this rea-
son, pathology is regarded as one of the basic sciences of med-
icine along with other disciplines such as anatomy, microscopic
anatomy
The second of the two major branches within the medical
specialty of pathology is anatomic pathology. The term ‘‘ana-
tomic’’ refers to the structure (or ‘‘morphology’’) of tissues and
organs. The job of the anatomic pathologist is to recognize and
diagnose abnormal or diseased anatomy from tissue specimens
that have been taken from living patients either at surgery or
during a minor biopsy procedure. Pathologists use the gross and
microscopic appearance of diseased tissues, as well as various
laboratory tests, to render their diagnoses. There are three basic
areas within anatomic pathology: surgical pathology, cytology
(also called cytopathology), and autopsy pathology.
Surgical pathology involves the gross and microscopic eval-
uation of tissues or organs that have been removed during
surgery. The tissues are taken directly to the laboratory from
the operating room where the pathologist or resident examines
and dissects the specimen and dictates a careful description of
the normal and abnormal features. Such a report includes the
name of the patient, the unique hospital and laboratory coding
numbers, the date and nature of the procedure, and the exact
nature of the specimen. Routine details also include the overall
size and weight, and the dimensions and characteristics of any
abnormal areas such as tumors. Any significant areas may also be
documented photographically. After the tissues are dissected,
selected small amounts are chosen for further processing. These
will include the edges of the surgical specimen to check for
adequacy of removal, and any abnormal areas that may represent
tumors or infection. Further processing includes dehydrating
and embedding in paraffin wax (to enable cutting into thin
sections), and placing the sections onto glass slides and staining
(to show the different constituents of the tissues being exam-
ined). The pathologist will then view the tissue sections on glass
slides (the histology) under a microscope and render
a diagnosis. Typical questions that physicians and surgeons will
want the pathologist to answer include: Is it an infection? Is it
a tumor? Is it benign (noncancerous) or is it malignant (cancer)?
What kind of cancer is it? Is it low grade (slow growing) or high
grade (rapidly growing)? Did the surgeon remove all of the
cancer? Has there been spread through the tissues and into the
blood stream? And are the lymph nodes involved? The answers
to these questions are vitally important in determining the type
of treatment that the patient will undergo and how the disease
may respond to therapy.
Cytology, or cytopathology, is similar to surgical pathology
in that diagnoses are made by pathologists looking at glass slides
under a microscope to answer similar questions. In contrast to
histology slides, cytology slides are composed of cells that have
been scraped off a tissue surface or aspirated (sucked) out of
a solid or fluid-filled tissue using a needle and syringe. The cells
are then smeared onto a glass slide and stained so that different
cell types can be identified.
(‘‘histology’’),
physiology,
biochemistry,
and
pharmacology.
In the United States, there are two types of medical degrees,
the MD or doctor of medicine, and the DO or doctor of osteop-
athy. Physicians with either of these degrees must pass board
examinations in order to be licensed to practice medicine and/
or if they want to pursue specialist training. In countries outside
North America that follow the British system more closely, med-
ical students graduate with degrees of Bachelor of Medicine and
Bachelor of Surgery (MB, BS or MB, ChB). In these countries, an
MD is a higher degree (a doctorate) akin to a medical PhD.
After graduating from medical school, a physician may
undertake additional postgraduate specialty training, which in
the United States is referred to as the residency years. In British-
based systems, physicians in such training programs are referred
to as ‘‘registrars.’’ Although pathology is an essential basic sci-
ence within the traditional medical school curriculum, it is also
a medical specialty along with others such as internal medicine,
surgery, pediatrics, cardiology, and radiology. Generally,
a specialty falls into one of three general types: (1) medical
(meaning nonsurgical); (2) surgical; and (3) miscellaneous.
Pathology fits into the latter category as it deals with the scien-
tific study of injuries and illnesses usually without involving
direct patient contact or management.
The standard pathology residency training program in the
United States entails 4 years of additional study and involves two
basic branches of pathology: clinical and anatomic pathology.
Clinical pathology refers to ‘‘laboratory medicine’’; pathologists
who train in this field direct and supervise laboratories where the
day-to-day work is performed by laboratory technologists and
technicians. Laboratories cover a wide range of subspecialties
including the chemistry laboratory (where electrolytes, choles-
terol and lipids, and other substances are measured in the blood
or other body fluids such as urine); the hematology laboratory
(where ‘‘blood counts’’ are performed), the blood bank (where
blood typing and matching ensures that blood transfusions
occur safely); and the microbiology laboratory (where various
tests are performed to identify infectious organisms such as
bacteria, fungi, and viruses, and to work out which antibiotics
are the most appropriate to use). Another example is the molec-
ular genetics laboratory, where the identification of genes
(DNA) and their products assists with the diagnosing of certain
diseases, prediction of the prognosis (the expected outcome),
and treatment.
J.A. Prahlow, R.W. Byard,
Atlas of Forensic Pathology
, DOI 10.1007/978-1-61779-058-4_1,
#
Springer Science+Business Media, LLC 2012
1
2
Introduction to Pathology
.
Fig. 1.1
‘‘Medical’’ specialties include family practice, internal medicine, pediatrics, and other nonsurgical specialties and involve
clinical examinations (Photo courtesy of Department of pathology, Wake Forest University and North Carolina Baptist Hospital,
Winston-Salem, NC)
Fig. 1.2
‘‘Surgical’’ specialties include any specialty that involves the performance of operations (Photo courtesy of Department of pathology,
Wake Forest University and North Carolina Baptist Hospital, Winston-Salem, NC)
.
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Introduction to Pathology
.
Fig. 1.3
An automated chemistry machine in a clinical pathology laboratory
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Introduction to Pathology
Fig. 1.4
A blood smear on a microscope slide. The round cells with no nuclei are red blood cells. The slightly larger cells with dark purple nuclei
are white blood cells, including a neutrophil on the left and a lymphocyte on the right. The small granular bodies are platelets
.
Fig. 1.5
Gross examination and dissection of a surgical pathology specimen, in this case a portion of lung
.
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