Essential Basic Pathological Processes
Start from a single first principle: the body has only a small repertoire of ways to respond to injury, and every disease you will meet in O&G is one of those responses, or a combination of them, expressed in a particular tissue. A cell can adapt, recover or die. A tissue can inflame, repair or grow abnormally. Blood can clot in the wrong place. A cavity can fill with fluid. That is almost the whole alphabet. Once you can name the response, you can predict the symptoms, the signs, the morphology and the danger — without memorising each disease separately.
Pathology, then, is not a list of definitions to recite. It is the discipline of explaining why a patient with fever, pelvic pain, vaginal bleeding, a wound breakdown, an ovarian cyst, a thromboembolus or a cervical cancer looks the way she does. The same limited set of tissue responses appears again and again: cell adaptation, cell injury and death, acute inflammation, chronic inflammation, infection, sepsis, repair, thrombosis, embolism, cyst formation and neoplasia. This chapter builds them in that order — each one resting on the one before — because that is the order in which they unfold in a real patient: an insult injures cells, injured cells provoke inflammation, inflammation either resolves into repair or persists into chronic disease, and a stem-cell compartment that is repeatedly pushed can eventually grow without restraint.
The useful mental sequence to carry into the exam is:
| Step | Question | O&G example |
|---|---|---|
| Insult | What is stressing or damaging the tissue? | Hypoxia in placental malperfusion, HPV in the cervix, bacteria after caesarean section |
| Cellular response | Can the cell adapt, recover or die? | Endometrial hyperplasia, infarcting fibroid, apoptotic endometrium |
| Tissue response | Is the dominant pattern inflammation, repair, thrombosis or growth? | PID, caesarean scar healing, puerperal VTE, CIN |
| Morphology | What would be seen grossly or microscopically? | Pus, necrosis, granulation tissue, dysplasia, invasion |
| Clinical expression | How does the structural change create symptoms and signs? | Pain, fever, discharge, bleeding, mass, organ dysfunction |
Cell Adaptation, Injury and Death
Begin one level below the tissue, at the cell. A cell stays alive by doing five jobs continuously: maintaining its membranes, generating energy (ATP, mostly mitochondrial), synthesising protein, protecting its DNA, and holding its ionic gradients (low intracellular sodium and calcium, high potassium). Every form of cell injury can be traced back to the failure of one or more of these. When a stress is mild or slow, the cell adapts — it changes size, number or phenotype to cope. When the stress exceeds what adaptation can absorb, the cell is injured, and if the injury is severe or sustained, it dies. The usual stresses are hypoxia/ischaemia, toxins, infection, immune injury, nutritional imbalance, physical trauma, radiation, genetic defects and ageing.
The adaptations come first because they are reversible and physiological as often as they are pathological — the pregnant uterus and the postmenopausal vagina are both adaptations, not diseases.
| Cellular event | Core mechanism | Morphology | O&G application |
|---|---|---|---|
| Hypertrophy | Increased cell size from greater workload or trophic stimulation | Enlarged cells and organ | Myometrial enlargement in pregnancy; hypertrophied bladder wall with bladder-outlet obstruction |
| Hyperplasia | Increased cell number from hormonal or growth-factor stimulation | Thickened tissue, more glands or stroma | Endometrial hyperplasia from unopposed oestrogen; lactational breast lobular hyperplasia |
| Hypoplasia / aplasia | Failure of a tissue or organ to reach (or develop) its normal cell number | Small or absent organ | Müllerian agenesis or hypoplasia; ovarian dysgenesis in Turner syndrome |
| Atrophy | Reduced cell size and function from reduced stimulation, blood supply or nutrition | Small, thin, pale tissue | Postmenopausal vulvovaginal and endometrial atrophy causing dryness, dyspareunia or spotting |
| Metaplasia | Replacement of one mature cell type by another better suited to stress | Mature but changed epithelium | Squamous metaplasia in the cervical transformation zone; the vulnerable field for HPV-related dysplasia |
| Dysplasia | Disordered epithelial maturation with atypia (a step beyond adaptation, towards neoplasia) | Nuclear enlargement, hyperchromasia, loss of polarity, mitoses | CIN; vulval and vaginal intraepithelial lesions |
| Necrosis | Uncontrolled death with membrane rupture and inflammation | Cell swelling, eosinophilia, nuclear breakdown, tissue architecture loss | Infarcted fibroid, placental infarct, pressure necrosis, severe infection |
| Apoptosis | Programmed cell death with membrane integrity preserved | Cell shrinkage, apoptotic bodies, little inflammation | Endometrial shedding, follicular atresia, tumour-cell death after therapy |
Reversible injury is dominated by ATP depletion, sodium/potassium-pump failure and cell swelling, with detachment of ribosomes and clumping of chromatin; if perfusion or the stress is relieved quickly, the cell recovers. Irreversible injury follows sustained mitochondrial failure, a sharp rise in cytosolic calcium that activates destructive enzymes, membrane rupture, and leakage of intracellular contents into the surrounding tissue. The biochemical "point of no return" is the combination of severe membrane damage and inability to reverse mitochondrial dysfunction. Once the cell is dead, necrosis provokes inflammation because those spilled contents are read by the host as danger signals.
Free Radicals as a Final Common Pathway
A recurring mechanism that links hypoxia, reperfusion, toxins, radiation and inflammation is oxidative injury by free radicals (reactive oxygen species such as superoxide, hydroxyl radical and hydrogen peroxide). These unstable molecules attack three targets: they peroxidise membrane lipids (breaking the membrane), cross-link and fragment proteins (disabling enzymes and pumps), and damage DNA (a mutagenic step relevant to carcinogenesis). The cell defends itself with antioxidant systems — superoxide dismutase, catalase, glutathione and vitamins such as ascorbate and tocopherol — and disease results when free-radical production overwhelms these defences. This single idea explains why ischaemia-reperfusion is so destructive, why the syncytiotrophoblast in pre-eclampsia shows oxidative stress, and why antioxidant capacity matters in placental disease.
The Morphological Patterns of Necrosis
"Necrosis" is one process but several appearances, and the pattern often points to the cause — useful at the bedside and on the slide.
| Necrosis pattern | What it looks like | Typical setting | O&G relevance |
|---|---|---|---|
| Coagulative | Firm, pale tissue; cell outlines preserved at first | Ischaemic infarction of a solid organ | Placental infarct, infarcted (red-degenerating) fibroid, ovarian infarction after torsion |
| Liquefactive | Tissue dissolves into pus or a soft cavity | Bacterial abscess; brain infarction | Tubo-ovarian abscess, Bartholin abscess, pelvic abscess |
| Caseous | Cheesy, amorphous debris within a granuloma | Tuberculosis | Genital and tubal TB — important in the South African setting |
| Fat | Chalky saponified fat with calcium | Trauma or enzymatic injury to fat | Traumatic fat necrosis of the breast (a benign mimic of carcinoma) |
| Fibrinoid | Bright pink protein deposited in vessel walls | Immune-complex and severe hypertensive vascular injury | Decidual vasculopathy and the vascular lesions of severe pre-eclampsia |
| Gangrenous | Coagulative necrosis of a limb/viscus ± superadded infection | Critical ischaemia, sometimes with anaerobes | A late, ominous sign in neglected bowel or limb ischaemia complicating obstetric catastrophe |
Distinguishing these is not academic. Liquefactive necrosis means pus that may need drainage; caseous necrosis should prompt thoughts of TB; fibrinoid necrosis is a fingerprint of severe vascular/immune injury; and a chalky breast lump that turns out to be fat necrosis spares a woman an unnecessary cancer scare once histology is in.
Hypoxia and ischaemia are not identical. Hypoxia is low oxygen delivery or use. Ischaemia is reduced blood flow, so oxygen and substrate delivery fall and waste removal fails. Ischaemia therefore injures faster than hypoxaemia alone. In O&G, ischaemia explains the pain of ovarian torsion, placental infarction in maternal vascular malperfusion, infarcting fibroid pain, and shock-related organ dysfunction.