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CHAPTER 3 Surgical pathology
142
Cellular injury
Causative agents
Cellular injury is caused by:
• Trauma.
• Thermal injury.
• Chemicals, including drugs.
• Infectious organisms.
• Ionizing radiation.
Mechanisms of injury
These causative agents cause cell damage via a number of mechanisms.
• Mechanical disruption. Trauma, freezing, osmotic imbalance.
• Failure of membrane integrity. Failure of ion pumps, cytolysis, trauma.
• Blockage of metabolic pathways. Cellular respiration (e.g. cyanide),
protein synthesis (e.g. streptomycin), DNA damage or loss (e.g.
X-rays).
• Defi ciency of essential metabolites. Oxygen (ischaemia), glucose
(diabetic ketoacidosis), hormones (d trophic hormones results in
apoptosis).
• Free radicals. Toxins (e.g. carbon tetrachloride), ischaemia-reperfusion
injury, intracellular killing of bacteria.
Necrosis
Necrosis is death of tissue or cells.
Coagulative necrosis
This is the most common form of necrosis and occurs in all organs.
Cells retain their shape as cell proteins coagulate and metabolic activity stops. Digestion by macrophages may cause the tissue to become
soft. Histologically, there is progressive loss of staining. The presence of
necrotic material normally provokes an infl ammatory response.
Colliquative necrosis
This occurs in the brain because of the lack of tissue architecture provided
by substantial surrounding stroma.
Caseous necrosis
Dead tissue lacks any structure and is characterized by a white, soft, or
liquid ‘cheesy’ appearance. This is common in TB.
Gangrene
Necrosis with dessication or putrefaction (see b p. 158).
Fibrinoid necrosis
In malignant hypertension, necrosis of smooth muscle vessel walls allows
seepage of plasma into the media and deposition of fi brin.
Fat necrosis
• Direct trauma. Release of extracellular fat produces an infl ammatory
response, fi brosis and eventually, in some cases, a palpable mass.
• Acute pancreatitis. Fat is digested by pancreatic lipase to produce fatty
acids which precipitate with calcium in the process of saponifi cation.
CELLULAR INJURY
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Apoptosis (programmed cell death) is the cell-mediated, controlled
elimination of individual cells.
Apoptosis
Apoptosis is a physiological process requiring energy. It is the normal
means of maintaining the size of an organ in the face of continuing cell
turnover or a reduction in size during atrophy. It is mediated by endogenous endonucleases. The cell shrinks and fragments into apoptotic bodies. Examples include:
• Physiological. Epithelium of GI tract, bone marrow, clonal selection in
immune system, targets of cytotoxic T cells.
• Pathological. After exposure to ionizing radiation, chemotherapy,
smooth muscle cells around atherosclerotic plaque, viral hepatitis.
143
CHAPTER 3 Surgical pathology
144
Infl ammation
Infl ammation is the local physiological response to tissue injury. It can
be acute or chronic.
Acute infl ammation
This is the initial tissue reaction to a wide range of agents: accumulation of
neutrophil polymorphs in the extracellular space is diagnostic. It lasts hours
to days and is usually described with the suffi x ‘-itis’.
Causes
• Physical and chemical, e.g. mechanical trauma, X-rays, acid, alkali.
• Infection: bacteria, viruses, parasites, fungi, or protozoa.
• Ischaemia.
• Hypersensitivity.
Macroscopic appearance
Calor, rubor, tumor, dolor, and functio laesa (heat, redness, swelling, pain,
and impaired function). Special macroscopic appearances include:
• Serous. Infl ammation + abundant fl uid-rich exudates, e.g. peritonitis.
• Catarrhal. Infl ammation + mucus hypersecretion, e.g. common cold.
• Haemorrhagic. Infl ammation + vascular injury, e.g. pancreatitis.
• Suppurative. Infl ammation + pus produced to form abscess or
empyema.
• Fibrinous. Exudates contain fi brin which forms coating, e.g. pericarditis.
• Membranous. Coating of fi brin and epithelial cells, e.g. laryngitis.
• Pseudomembranous. Superfi cial mucosal ulceration with slough, e.g.
pseudomembranous colitis secondary to C. diffi cile (see b p. 396).
• Necrotizing (gangrenous). Infl ammation + tissue necrosis (see b
p. 158).
Microscopic changes
Mediated by endogenous chemicals released by cells (histamine, prostaglandins, leukotrienes, serotonin, and lymphokines) and plasma factors (complement, kinin, coagulation, and fi brinolytic cascades). Changes are:
• Changes in vessel calibre and fl ow.
Immediate and transient smooth muscle vasoconstriction.•
Vasodilation (active hyperaemia) lasting 15min to hours.•
Capillaries, then arterioles dilate to increase blood fl ow.•
• Increased vascular permeability and fl uid exudates.
Capillary hydrostatic pressure is increased.•
Endothelial cells contract, creating gaps.•
Plasma proteins escape into extracellular space.•
Increase in colloid osmotic pressure draws more fl uid.•
• Formation of cellular exudates.
Accumulation of neutrophil polymorphs in extracellular space.•
Begins with margination of neutrophils (fl ow next to vessel walls).•
Neutrophils then adhere to vessel walls: mechanism unknown.•
Migrate by amoeboid movement through gaps between cells.•
INFLAMMATION
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Neutrophil polymorphs phagocytose debris and kill microbes •
intracellularly using oxygen-dependent (hydrogen peroxide and
hydroxyl radicals) and -independent (lysosymes) means.
Sequelae of acute infl ammation
• Resolution. Restoration of tissue to normal; likely if minimal tissue
damage, rapid destruction of causal agent, rapid removal of exudates
by good vascular drainage, and organ with restorative capacity, e.g.
liver.
• Suppuration. Formation of pus (see b p. 144).
• Organization. Replacement by granulation tissue.
• Chronic infl ammation.
Chronic infl ammation
This is an infl ammation where lymphocytes, plasma cells, and macrophages
predominate, granulation tissue often accompanies.
Causes
• Resistance of infective agent to phagocytosis (TB, viral infections).
• Foreign body (endogenous, e.g. urate or exogenous, e.g. asbestos).
• Autoimmune (e.g. contact hypersensitivity, RA, organ-specifi c).
• Primary granulomatous disease (e.g. Crohn’s, sarcoidosis).
• Unkown aetiology (e.g. ulcerative colitis).
Macroscopic appearances
The commonest appearances are:
• Chronic ulcer, e.g. peptic ulcer;
• Chronic abscess cavity, e.g. empyema;
• Thickening of wall of hollow viscus, e.g. Crohn’s disease;
• Granulomatous infl ammation, e.g. TB;
• Fibrosis, e.g. chronic cholecystitis.
Microscopic changes
Lymphocytes, plasma cells, and macrophages (see b p. 145) predominate;
neutrophil polymorphs are scarce, eosinophil polymorphs are present.
Fluid exudate is not prominent.
Granuloma
This is different to granulation tissue (see b p. 147).
A granuloma is an aggregate of epithelioid histiocytes.
Causes
• Specifi c infections.
Endogenous. necrotic bone or fat, keratin, urate.•
Exogenous. Talc, silicone, asbestos, sutures.•
• Drugs. Sulphonamides, allopurinol.
• Unknown. Crohn’s, sarcoidosis, Wegener’s granulomatosis.
145
CHAPTER 3 Surgical pathology
146
Wound healing
Classifi cation of wounds
• Clean. Non-traumatic wounds with no break in surgical technique,
no septic focus, and no viscus opened (e.g. hernia repair).
• Clean contaminated. Non-traumatic wounds with contaminated
entry into a viscus, but with minimal spillage (e.g. elective
cholecystectomy).
• Contaminated. Clean, traumatic wounds or signifi cant spillage from
a viscus or acute infl ammation (e.g. emergency appendectomy).
• Dirty. Includes traumatic wounds from a dirty source or when
signifi cant bacterial contamination or release of pus is encountered.
General principles of healing
Tissue healing in any organ follows some basic principles:
• Cells may be labile (good capacity to regenerate, e.g. surface epithelial
cells), stable (capacity to regenerate slowly, e.g. hepatocytes), or
permanent (no capacity to regenerate, e.g. nerve and striated muscle
cells).
• Tissue architecture is important: complex arrangements cannot be
reconstructed if destroyed, e.g. renal glomeruli.
• Complete restitution occurs when part of a labile population of cells is
damaged, e.g. a minor skin abrasion.
Key revision points—the four stages of wound healing
When specialized tissue is destroyed, it cannot be replaced and a stereotyped response called repair then follows in four stages:
• Haemostasis (immediate). In response to exposed collagen, platelets
aggregate at the wound and degranulate, releasing infl ammatory
mediators. Clotting and complement cascades activated. Thrombus
formation and reactive vasospasm achieve haemostasis.
• Infl ammation (0–3 days). Vasodilation and increased capillary
permeability allow infl ammatory cells to enter wound and cause
swelling. Neutrophils amplify infl ammatory response by release of
cytokines, reduce infection by bacterial killing, and debride damaged
tissue. Macrophages follow and secrete cytokines, growth factors,
and collagenases. They phagocytose bacteria and dead tissue
and orchestrate fi broblast migration, proliferation, and collagen
production.
• Proliferation (3 days–3 weeks). Fibroblasts migrate into the wound
and synthesize collagen. Specialized myofi broblasts containing actin
cause wound contraction. Angiogenesis is stimulated by hypoxia and
cytokines and granulation tissue forms.
• Remodelling (3 weeks–1y). Reorientation and maturation of collagen
fi bres increases wound strength.
WOUND HEALING
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• Granulation tissue is the combination of capillary loops and
myofi broblasts. This is unrelated to a granuloma (see b p. 145).
• Organization is the process where specialized tissues are repaired by
formation of mature connective tissue, e.g. pneumonia or infarcts.
• Wound contraction mediated by myofi broblasts; can reduce the tissue
defect by up to 80%, but can lead to problems, e.g. burns contractures.
• Collagen is secreted at the same time to form a scar.
Factors affecting wound healing
• Impaired arterial supply or venous drainage (global or local).
• Excessive movement, local distension, or distal obstruction.
• Infection, malignancy, foreign body, necrotic tissue, smoking.
• Malnutrition. Obesity, recent weight loss, nutrient defi ciency.
• Immunosuppressive. Cancer, steroids, immunosuppressants, HIV.
• Anticancer therapies. Radiotherapy and chemotherapy.
• Metabolic. Diabetes, jaundice, uraemia, musculoskeletal diseases, age.
Wound healing in specifi c tissues
Skin: fi rst intention healing
This takes place where there is close apposition of clean wound edges.
• Thrombosis in cut blood vessels prevents haematoma formation.
• Coagulated blood forms a surface scab which keeps the wound clean.
• Fibrin precipitates to form a weak framework between the two edges.
• Capillaries proliferate to bridge the gap.
• Fibroblasts secrete collagen into the fi brin network.
• Basal epidermal cells bridge the gap and are eventually resorbed.
• The elastic network in the dermis cannot be replaced.
Skin: second intention healing
This takes place in wounds where skin edges cannot be cleanly apposed.
• There is phagocytosis to remove debris.
• Granulation tissue to fi ll in defects.
• Epithelial regeneration covers the surface.
Gastrointestinal tract
• Erosion is loss of part of the thickness of the mucosa.
Adjacent epithelial cells proliferate to regenerate the mucosa.•
Healing may take place this way in a matter of hours.•
• Ulceration is loss of the full thickness of the mucosa.
Mucosa is replaced from the margins.•
The muscularis propria cannot be regenerated: it is replaced by scar.•
Damaged blood vessels bleed, fi brin covers the raw surfaces.•
Macrophages migrate in and phagocytose dead tissue.•
Granulation tissue is produced in the base.•
If the cause persists, the ulcer becomes chronic.•
Fibrous scar tissue may result in contractions.•
147
CHAPTER 3 Surgical pathology
148
Ulcers
An ulcer is a breach in an epithelial surface.
Classifi cation
Venous, arterial, diabetic, neuropathic, malignant, traumatic.
Features to note on examination
• Site. Neck, groin, and axilla (TB); legs and feet (vascular); anywhere
(malignant).
• Surface. Usually depressed. Elevated in malignancy, vascular
granulations.
• Size. Measure the ulcer. Is it large by comparison to the length of
history?
• Shape. Oval, circular, serpiginous, straight edges.
• Edge. Eroded (actively spreading), shelved (healing), punched out
(syphilitic), rolled or everted (malignant).
• Base. Fixed to underlying structures? Mobile? Indurated? Penetrating?
• Discharge. Purulent (infection), watery (TB), bleeding (granulation or
malignancy).
• Pain. Usually occurs during the extension phase of non-specifi c ulcers.
In diabetic patients, ulcers are relatively painless.
• Number. Widespread locally (local infection such as cellulitis),
widespread generally (constitutional upset).
• Progress. Short history (pyogenic), chronic (vascular or trophic, e.g.
post-phlebitic syndrome, decubitus ulceration of paraplegia).
• Lymph nodes. In the region of an ulcer may indicate secondary infection
or malignant change.
Natural history
• Extension. There is discharge, thickened base, infl amed margin. Slough
and exudates cover the surface.
• Transition. Slough separates and the base becomes clean. The discharge
becomes scanty, the margins less infl amed.
• Repair. Granulation becomes fi brous tissue and forms a scar after
re-epithelialization.
Investigations
History, biopsy and histology, serology, as indicated by presentation.
Chronic leg ulcers
Their aetiology is diverse, but can usually be diagnosed clinically.
Venous ulcers
Part of post-phlebitic limb syndrome where there may be a history of past
DVT. The ulcer is associated with oedema, lipodermatosclerosis (woody
thickening of soft tissues around the calf), and venous congestion with
secondary calf perforators and varicose veins. The ulcer is usually over
the medial malleolus, but can be large, involving the whole of the gaiter
region.
ULCERS
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• If pulses are absent in the foot, there may be an arterial element which
can be excluded by measurement of the ankle to brachial pressure
index (ABPI).
• If any doubt persists, a vascular referral for arterial reconstruction
should be considered, but four-layer bandaging must be avoided when
there is arterial insuffi ciency.
Arterial ulcers
These are often multiple and occur distally over and between the toes or
at pressure points such as heels or malleoli. They may occur elsewhere on
the leg, usually when there is an associated diabetic or venous element.
There is usually a history of arterial disease, particularly peripheral vascular
disease with claudication.
• Unlike venous ulcers where bacterial colonization is common, the
presence of organisms suggests infection, particularly when there is
moisture around the ulcers: wet gangrene (caused by staphylococci
and streptococci, not clostridia, see later) may ensue with cellulitis.
• If the leg is kept dry, infection is minimized and a line of demarcation
may aid in decision-making for the level of amputation.
• Arterial reconstruction should be considered before this stage.
Diabetic ulcers
These commonly occur in conjunction with arterial disease. They represent large- and small-vessel disease with an impaired ability to heal and
increased susceptibility to infection. Ulcers may occur in the arterial distribution, particularly at pressure points, and involve deep tissue infections
(such as plantar abscesses) and osteomyelitis. The associated diabetic neuropathy with Charcot’s joints presents with deformed feet and joints, which
are susceptible to ulceration.
• Management involves good diabetic and ulcer care, which includes
orthotist help with shoes and gait.
• Surgery aims to avoid major amputation, but requires debridement
of necrotic tissue, drainage of abscesses, and excision of dead tissue,
often involving bone as ‘ray’ excisions of toes.
Other causes
Include pressure, vasculitic, lymphatic, infective, and artefactual causes. Leg
ulcer clinics have emphasized the value of a team approach.
149
CHAPTER 3 Surgical pathology
150
Cysts, sinuses, and fi stulas
Cysts
A cyst is a collection of fl uid in a sac lined by endothelium or epithelium
which usually secretes the fl uid.
• True cysts are lined by endo- or epithelium.
• False cysts are the result of exudation or degeneration, e.g.
pseudocyst of pancreas, cystic degeneration in a tumour.
Classifi cation
Congenital
• Sequestration dermoid. Due to displacement of epithelium along
embryonic fi ssures during closure, e.g. skin. Sites include outer and
inner borders of orbit, midline of the body, anterior triangle of neck
(brachial cyst), (cf. implantation dermoid due to skin implantation from
injury).
• Tubulo-dermoid/tubulo-embryonic. Abnormal budding of tubular
structures, e.g. enteric cysts, post-anal dermoid, thyroglossal cyst.
• Dilatation of vestigial remnants. For example, urachal, vitellointestinal,
paradental and branchial cleft cysts, hydatid of Morgagni, Rathke’s
pouch.
Acquired
• Retention cysts. Due to the blocking of a glandular or excretory duct,
e.g. sebaceous cyst (sweat gland); ranula (salivary gland); and cysts
of the pancreas, gall bladder, parotid, breast, epididymis, Bartholin’s
glands, hydronephrosis, hydrosalpinx.
• Distension cysts. Due to the distension of closed cavities as a result
of exudation or secretion, e.g. thyroid or ovarian cysts; hygroma
(lymphatic cysts), hydrocoele, ganglia, bursas (false cysts).
• Cystic tumours. For example, cystadenoma, cystadenocarcinoma of
ovary.
• Parasitic cysts. For example, hydatid cysts (Taenia echinococcus).
• Pseudocysts. Due to necrosis of haemorrhage with liquefaction and
encapsulation, e.g. necrotic tumours, cerebral softening, or coalescence
of infl ammatory fl uid collections, e.g. pseudocyst of pancreas.
Clinical features
Subcutaneous/superfi cial
Smooth, spherical, soft, and fl uctuant when palpated in two planes with
the fi ngers at right angles to each other. If tense contents, may produce
pain in the cyst or surrounding tissue. If the fl uid is clear, the swelling
will transilluminate. Ultrasound and aspiration of contents are methods
of determining whether a given swelling is cystic and may differentiate a
cyst from a lipoma. May compress surrounding tissues. May produce pain
if complications supervene. They are also subject to infection, torsion if on
a pedicle, haemorrhage, and calcifi cation.
CYSTS, SINUSES, AND FISTULAS
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Treatment
• Excision. Only if symptomatic, cosmetic, or concern over diagnosis.
• Marsupialization (deroofi ng and suture of the lining to skin). If chronic
or infected.
• Drainage (deep site). If symptomatic or complicated. Not if concern
over malignancy.
Sinuses/fi stulas
• A sinus is a blind epithelial track, lined by granulation tissue which
extends from a free surface into the tissues, e.g. pilonidal sinus.
• A fi stula is an abnormal communication between two epithelial
surfaces. It is lined by granulation tissue and colonized by bacteria,
e.g. fi stula-in-ano, pancreaticocutaneous, colovesical, vesicovaginal.
Causes
• Specifi c disease, e.g. Crohn’s.
• Abscess formation and spontaneous drainage, e.g. diverticular abscess
discharging into vagina with fi stula formation.
• Penetrating wounds.
• Iatrogenic (e.g. anastomotic leak discharging via wound).
• Neoplastic.
Persistence of a fi stula is due to the following
• Presence of foreign material, e.g. suture/bone in a sinus.
• Distal obstruction of the viscus of origin.
• Continuing active sepsis, e.g. TB, actinomycosis.
• Epithelialization of the track.
• Chronic infl ammation, e.g. Crohn’s.
• Malignancy in the track.
Investigation
Establish the extent by sinography/fi stulogram. MRI scan is often helpful.
Treatment
Principles of sinus treatment:
• Ensure adequate drainage, laying it open and remove granulations.
• Remove septic material, foreign bodies.
• Biopsy sinus wall if concern over underlying diagnosis.
• Loose packs may be used to help drainage.
Principles of fi stula treatment:
• Treat any sepsis, fl uid imbalances, and poor nutrition if associated.
• Ensure good drainage to prevent fi stula extension.
• Identify the anatomy, use examination under anaesthetic (EUA) or
imaging if required.
• Biopsy the fi stula if concern over underlying diagnosis.
• Defi nitive treatment requires:
Excision of the organ of origin or closure of the site of origin.•
Removal of chronic fi stula track and surrounding infl amed tissue.•
Closure of ‘recipient’ organ if internal or drainage of external site •
if to skin.
151
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